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Late Holocene depositional history of western shelf margin, Gulf of California, Mexico

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Late Holocene depositional history of western shelf margin, Gulf of California, Mexico

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Content INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type o f computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. 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LATE HOLOCENE DEPOSITIONAL HISTORY OF WESTERN SHELF MARGIN, GULF OF CALIFORNIA, MEXICO Kristi Anne Rikansrud A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE (Geological Sciences) December 1998 Copyright 1998 Kristi Anne Rikansrud R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. UMI Number: 13 94794 UMI Microform 1394794 Copyright 1999, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. U NIV ERSITY O R S O U T H E R N C A L IFO R N IA T H E G R A D U A T E S C H O O L U N IV E R S IT Y P A R K LO S A N G E L E S . C A L IF O R N IA 8 0 0 0 7 This thesis, w ritten by Kristi Anne Rikansrud under the direction o f kJzJL Thesis Committee, and approved by a ll its members, has been pre sented to and accepted by the Dean of The Graduate School, in p a rtia l fulfillm ent of the requirements fo r the degree of Master of Science September 23, 1998 :sis CO IT T E E R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. ii Dedication I w ant to thank three special people in m y life for always being there for m e by this dedication. My parents, Bettie and Rudy, taught m e by example that perseverance and determination are omnipotent. I w ould not be the person I am today with my present accomplishments if it were not for their unceasing support and unconditional love. Throughout this last year, Brian Darby, m y future husband, has constantly encouraged m e and believed in me. H is agape love and kindness are unparalleled. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. iii Acknowledgem ents From the day of its inception, this project has evolved and changed numerous times during m y period at USC. Without Donn Gorsline, this project would not have been conceived and I would not have had the privilege of working with cores from the Gulf of California. He was instrumental in bringing m e to USC and involving me in his marine sediment research. He taught me how to read X- radiographs, how to understand his tempermental LECO, to marvel at the mysteries occurring in sediment under 400 meters of water and he lent a helping hand with the hydraulic press m any times! Bob Douglas provided valuable advice in both matters of research and job-hunting. Dave Bottjer gladly gave of his time by serving on m y thesis committee. D oug Hammond spent countless hours instructing me in the methods of biogenic silica extraction: leaching, m ixing reagents, and how to pipet to an extraordinary degree of precision. I am grateful to all of these dedicated scientists for their guidance. Adolfo Molina-Cruz, director of the two UNAM cruises that obtained these cores, played an important role in the existence of this project. I am thankful to Enrique Nava-Sanchez and Janette Murillo de Nava for their hospitality while I was in Loreto and La Paz, Baja California Sur, and for sharing their know ledge of m y field area. Dave Drake of the USGS Sediment Dynamics lab gave much needed equipment and assistance. Michelle Kashgarin of Lawrence Livermore Laboratory analyzed AMS C-14 dates. Karl Flessa of the University of Arizona provided a vital sample of Colorado River delta mud. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Without the help of Lana Krtolic, a w illing volunteer, I w ould still be 1V running total carbon analyses! I have had the good fortune to work alongside Teresa D e Diego, whose research closely parallels mine, in the Marine G eology lab at USC. Her assistance with the XRF and our discussions of the carbon system were much appreciated. I owe a special thanks to my parents and m y entire family, for their constant love and encouragement through m y 18 years of schooling, and to Brian Darby, for helping me w ith the Coulter Counter, whose amazing love was the best inspiration, and who could always make m e smile. This project was funded in part by the American Association of Petroleum Geologists Foundation, the John E. Kilkenny Memorial Grant, and the Graduate Student Research Fund of the Earth Sciences Department, USC. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. V Table of Contents Dedication....................................................................................................................ii Acknowledgements..................................................................................................iii List of Figures...........................................................................................................vii List of Tables............................................................................................................. xii Abstract......................................................................................................................xiii Introduction................................................................................................................. 1 Statement of Intent.......................................................................................1 Geologic Setting - Gulf of California...................................................... 2 General Circulation.................................................................................... 12 Previous Work..............................................................................................17 Methods......................................................................................................................22 Cores and Curating.................................................................................... 22 X-Radiograph Description........................................................................ 23 Sampling........................................................................................................ 23 Organic Carbon and Carbonate.............................................................. 24 Grain Size A nalysis....................................................................................25 Biogenic Silica...............................................................................................26 Age M odels................................................................................................... 28 Potential Errors.............................................................................................32 Results and Discussion...........................................................................................34 AM - Santiago...............................................................................................34 BD - San Juan de la Costa.........................................................................44 CP - Alfonso Basin......................................................................................51 DB - Loreto.................................................................................................... 63 EB - La Giganta.............................................................................................71 FF - Santa Rosalia........................................................................................80 Synthesis.....................................................................................................................90 Carbonate............................................................... 91 Organic Carbon and Paleoproductivity................................................97 Biogenic Silica.............................................................................................106 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Conclusions.. References.... Appendix I... Appendix II.. Appendix m . Appendix IV. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. VLL List of Figures Figure 1. Location of the Gulf of California and the six studied shelf margin areas (modified from Nava-Sanchez, 1997)......................................3 Figure 2. General bathymetry of the Gulf of California show ing the location of the shelf margin areas. The floor of the Gulf consists of a series of silled basins increasing with depth southward and of shallower shelf margin basins. From the north to south, the areas of this study are: 1) Santa Rosalia, 2) La Giganta, 3) Loreto, 4) Alfonso, 5) San Juan de la Costa, and 6) Santiago. The three hydrographic portions of the Gulf are: 1) northern, extending north of the San Esteban sill, 2) central and southern, from Guaymas Basin to the mouth of the Gulf, and 3) the island region which separates the northern Gulf from the southern Gulf, topographically and hydrographically (modified from Nava-Sanchez, 1997).................................................................................................4 Figure 3. Tectonic map of the Gulf of California show ing the extension occurring in a rifting transform system (m odified from Nava-Sanchez, 1997)...............................................................................................................................6 Figure 4. Longitudinal profile of the Gulf of California show ing the vertical dissolved oxygen distribution in m l/1 for April-May 1974. The shelf margins' basin floors all fall within the oxygen minimum zone (<0.5 ml/1) between 200-1200 m (from Alvarez-Borrego and Lara-Lara, 1991).......................................................................................................... 8 Figure 5. Schematic of water masses in the Gulf of California, a) Longitudinal profile and the water mass distributions; arrows indicate the hypothesized thermohaline circulation, b) T-S characteristics of the Gulf water masses. Vertical exaggeration=5x (from Bray, 1988a)....13 Figure 6. A) Schematic of upwelling patterns in the Gulf of California. Upwelling areas: a) w ith northwesterly winds, b) with southeasterly w inds, and c) area characterized by intense tidal m ixing (from Roden and Groves, 1959); B) Gyres in the Gulf of California. From north to south: the cyclonic Guaymas gyre, the anticyclonic Carmen gyre, and the cyclonic Farallon gyre (from Molina-Cruz, 1986.................................... 15 Figure 7. Distribution of dissolved oxygen at, or close to, the bottom of the Guaymas and San Pedro Martir Basins. The points represent oxygen determinations within 200 m of the bottom. Locations of Cores FF and EB from this study are shown to fall in the oxygen minimum zone of <0.2 m l/1 designated by slanted lines (modified from Calvert, 1964)............................................................................................................................ 18 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 8. A representative plot of weight percent silica versus time v m from Alfonso Basin, Core CP 14-15. The best-fit line drawn through the linear portion of this plot results in an intercept at the weight percent of amorphous silica originally present in die sam ple................ 29 Figure 9. Exponential correlation of the excess of 210pb determined from samples taken every 2 cm from Alfonso Basin, Core CA. From this correlation a sedimentation rate of 1.9 m m /year was obtained (from Nava-Sanchez, 1997)................................................................31 Figure 10. Bathymetry and profile of Santiago shelf margin area, showing the location of Core AM at a depth of 480 m. Sedimentation is influenced by the head of Las Palmas submarine canyon and by this basin's close proximity to the Pacific Ocean (modified from Nava- Sanchez, 1997).......................................................................................................... 35 Figure 11. A positive x-radiograph print representative of Santigao's turbidite-dominated facies................................................................................... 38 Figure 12. Sand percent, facies, mean size, organic carbon, and carbonate are plotted together against age for easy comparison of the Santiago open-slope record.................................................................................. 40 Figure 13. A. W eight percent frequency distributions of all the 16- channel grain size data per 10 cm sampled intervals from Santiago. The distributions change according to the m ode of deposition. B. Statistical parameters, standard deviation and skewness, plotted against the mean reveal different groupings according to the method of deposition............................................................................................................ 42 Figure 14. Bathymetry and profile of San Juan de la Costa shelf margin area, which is located in the western portion of La Paz Bay. Unlike Alfonso Basin, the peninsular shelf is wide and the peninsular slope is short. Core BD is located at a depth of 140 m (modified from Nava-Sanchez, 1997)..............................................................................................45 Figure 15. A positive x-radiograph print representative of Core BD's highly bioturbated sediment............................................................................... 46 Figure 16. Sand percent, facies, mean size, organic carbon, and carbonate are plotted against age for easy comparison of the San Juan de la Costa shelf-margin record..........................................................................47 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 17. A. W eight percent frequency distributions of all the 16- ix channel grain size data per 10 cm sampled intervals from San Juan de la Costa. There were no turbidites or laminations present in this re-worked core. B. Statistical parameters, standard deviation and skewness, plotted against the mean show the range of depositional conditions present in this locality over the last 500 years.......................... 50 Figure 18. Bathymetry and profiles of Alfonso Basin show ing the steep peninsular slope and the location of Core CP at a depth of 390 m in die outer slope of the basin. Alfonso Basin, a silled basin within La Paz Bay, is separated from the deeper La Paz Basin by a sill at 250 m and the Espiritu Santo trough (modified from Nava-Sanchez, 1997)............................................................................................................................ 52 Figure 19. Bathymetry of Alfonso Basin show ing the location of the anoxic zone. Core CP is located at a depth of 390 m w ithin this zone (modified from Nava-Sanchez, 1997)...................................................... 54 Figure 20. Alfonso Basin's thin diatomaceous laminations are present in this representative positive x-radiograph print....................... 55 Figure 21. Sand percent, facies, mean size, organic carbon, and carbonate are plotted together against age for easy comparison of the Alfonso Basin record........................................................................................57 Figure 22. A. W eight percent frequency distributions of all the 16- channel grain size data per 10 cm sampled intervals from Alfonso Basin. The distributions change according to the m ode of deposition. B. Statistical parameters, standard deviation and skew ness, plotted against the mean show different groupings according to the method of deposition..............................................................................................................59 Figure 23. Age versus w eight percent opaline silica in Core CP from Alfonso Basin..................................................................................................62 Figure 24. Bathymetry and profile of Loreto, which is characterized by an irregular peninsular shelf and a steep peninsular slope caused by local faults. No bank or sill is present as at Alfonso Basin or La Giganta area. Core DB is located on the seaward side of the Loreto channel at a depth of 385 m (modified from Nava-Sanchez,1997).................................. 64 Figure 25. A positive x-radiograph print show ing Loreto's homogenized sediment. A vertical burrow is clearly visible from approximately 8-12 cm........................................................................................... 66 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 26. Sand percent, facies, mean size, organic carbon, and : carbonate plotted together versus age show the relative contribution changes through time in Loreto area................................................................ 68 Figure 27. A. W eight percent frequency distributions of all the 16- channel grain size data per 10 cm sampled intervals from Loreto area. There were no turbidites or laminations preserved in this re worked core. B. Statistical parameters, standard deviation and skewness, plotted against the mean reflect the high degree of hom ogenization that has occurred in this core.............................................69 Figure 28. Bathymetry and profile of La Giganta area, which is characterized by an irregular peninsular shelf, a steep slope, the adjacent San Bruno trough at the base of the nearshore slope and the Mangle bank. N ote Core EB's location at a depth of 560 m dow nslope and offshore from the Mangle bank (m odified from Nava-Sanchez, 1997).............................................................................................. 72 Figure 29. Bathymetry of the La Giganta shelf margin area, show ing the location of Core EB at a depth of 560 m within the anoxic zone (modified from Nava-Sanchez, 1997)....................................... 73 Figure 30. A positive x-radiograph print from 30-60 cm of Core EB, revealing well-preserved fine laminations characteristic of this core...75 Figure 31. Sand percent, facies, mean size, organic carbon, and carbonate plotted together versus age show the relative contribution changes through time for La Giganta area...................................................... 76 Figure 32. A. W eight percent frequency distributions of all the 16- channel grain size data per 10 cm sampled intervals from La Giganta area. The distribution is slightly bi-modal and reflects high input of fine material. B. Statistical parameters, standard deviation and skewness, plotted against the mean indicate the varied modes of deposition..................................................................................................................78 Figure 33. Bathymetry and profile of Santa Rosalia. This shelf margin area is characterized by irregular bathymetry. The peninsular shelf is almost absent and the peninsular slope is composed of steep scarps and gentle surfaces due to active faulting. Profile F-F' show s a narrow submarine terrace at a depth of 40 m. Core FF is located at a depth of 620 m (modified from Nava- Sanchez, 1997).......................................................................................................... 81 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 34. Bathymetry of Santa Rosalia shelf margin area : showing the location of Core FF at a depth of 620 m within the anoxic zone (modified from Nava-Sanchez, 1997)........................................83 Figure 35. A representative positive x-radiograph print from Santa Rosalia. An approximately 1 cm thick turbidite is located between 94.5-95.4 cm in the middle portion of core shown here..............................84 Figure 36. Sand percent, facies, mean size, organic carbon, and carbonate plotted together against age show the relative contribution changes through time for Santa Rosalia................................ 85 Figure 37. A. Weight percent frequency distributions of all the 16- channel grain size data per 10 cm sampled intervals from Santa Rosalia. B. Statistical parameters, standard deviation and skewness, are plotted against the mean. The distinct bi-modal distribution and statistical groupings show variations in the sedimentary facies of Santa Rosalia............................................................................................................ 87 Figure 38. Carbonate weight percentages for all of the areas are plotted together versus age to show regional trends...................................93 Figure 39. Organic carbon w eight percentages for all of the areas are plotted together versus age to show regional trends............................ 98 Figure 40. Organic carbon (% dry weight) contents of homgenous and laminated sediments from all the shelf margin areas in this study compared to Calvert's data from the central Gulf of California (modified from Calvert, 1987)........................................................................... 104 Figure 41. Water depth plotted against core-top values of opaline silica, carbonate, and organic carbon for all 6 areas....................................I l l R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. List of Tables xn Table 1. Geometric and morphologic characteristics of the drainage basins (data from Nava-Sanchez, 1997)............................................................ 10 Table 2. Summary of core locations and lengths........................................ 22 Table 3. Sedimentation rates based upon 210pb dates...............................32 Table 4. Differences between standard value and analysed value 32 Table 5. Turbidite interval depths and thicknesses for Santiago, Alfonso, La Giganta, and Santa Rosalia......................................................36-37 Table 6. Comparison of certain characteristics of Gulf of California shelf margin with Van Andel's study of basin and slope sediments of the Gulf of California and other m odem productive basins.........................................................................................................................95 Table 7. Comparison of average weight percent biogenic silica from Gulf of California shelf margin with California offshore basins....................................................................................................................... 108 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Abstract x iii Gravity core records of Late Holocene sediments from western shelf margin areas (Santiago, San Juan de la Costa, Alfonso, Loreto, La Giganta, and Santa Rosalia) in the southern half of the G ulf of California provide information about the spatial and temporal variation in centennial to m illenial basin sedim entation patterns and how they are affected by regional hydrography and climate. Cores contain three common facies: laminated sedim ents, turbidite deposits, and bioturbated sediments, w hich are evident from grain-size analyses and x-radiograph descriptions. Facies exhibit som e variation in composition between areas, w ith the southern locations (Santiago and San Juan de la Costa) containing higher amounts of terrigenous detritus and the more northern locations (La Giganta and Santa Rosalia) receiving more biogenic input. The materials being input into the shelf margin and measured in this study are terrigenous detritus, carbonate, organic carbon, and biogenic silica. Input variations correspond with small-scale climatic changes in the last millenium caused by the Little Ice Age and the M edieval Warm Period. Occurrence of the three facies in the areas is inconsistent. Areas w ith higher bottom water oxygen concentrations (San Juan de la Costa and Loreto) are thoroughly bioturbated. The remaining locations lie within an oxygen minimum zone (< 0.5 m l/L dissolved oxygen) which allows for the preservation of laminations. These locations also contain varying amounts of turbidite deposits and bioturbated sediments. Facies variations can be attributed to different basin bathymetries, depth, and proximity to major upwelling centers in the Gulf of California. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. XIV It is w id ely accepted that the aforementioned oxygen minimum zone lies between 200 and 1200 m depth (Calvert, 1964). The evidence of bioturbation within Loreto's core record taken at 385 m depth suggests that the regional oxygenation regime has been altered. Loreto's location within an upwelling center and surrounding local topography m ay contribute to this alteration. Also, strong local currents m ay sufficiently m ix waters to incur a high oxygen flux. The preferential preservation of organic matter in near-anoxic environments is not demonstrated in these western shelf margin areas. Mean total organic carbon values of bioturbated and laminated sediments from all six basins are very similar. As the majority of these areas are positively skewed, containing a high percentage o f fine materials, organic carbon contents increase, indicating that its presence is at least partially texture-controlled. This study reveals that biogenic silica preservation in these areas is also partially controlled by texture, as well as the presence of oxygen. Deeper locations with floors located within the oxygen minimum zone (Alfonso, La Giganta, and Santa Rosalia) have higher biogenic silica values than oxygenated basins. La Giganta, the m ost fine-grained area, has extremely high silica values, supplementing the idea that silica concentration is a function of texture. Productivity, as reflected by organic carbon, carbonate, and biogenic silica input variations, appears to have increased during the Little Ice Age and decreased throughout the M edieval Warm Period. Yet, due to the intricacies of this region (lateral transport into the basins as w ell as input from surface waters) and the complex proxies involved R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. in tracking productivity, it is difficult to use organic carbon and biogenic silica as paleoproductivity proxies. X V R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 1 Introduction S tatm en t of In ten t The purpose of this study is to investigate gravity core records of Late Holocene sediments collected from six shelf margin areas located along the western flank of the main trough in the Gulf of California. These areas represent a series of sedim ent traps aligned northwest to southeast in the southern half of the Gulf. They are immediately adjacent to peninsular sources and m ay also have received input from the Colorado River delta. Low bottom water oxygen concentrations preserve the original structures (turbidites and laminations) while high sedimentation rates provide exceptional resolution. The array of cores should provide information about the spatial and temporal variation in sedimentation patterns and how they are affected by regional hydrography and climate, as well as determine the amount of influence of local fan delta sources. Measurements of organic carbon, carbonate, and opaline silica have been made in an effort to estimate paleoproductivity and biogenic input. Productivity in the Gulf has been linked to changes in upwelling which can be attributed to seasonal shifts of the large-scale w ind pattern and increased El Nino Southern Oscillation (ENSO) affects in certain years (Bray and Robles, 1991). Variations in input of biogenic matter may also be attributed to small-scale climatic changes such as the Litde Ice Age and the Medieval Warm Period. X-radiography of the cores provides a detailed record of sedimentation modes, such as turbidity currents and the extent of bioturbation and lamination. Size analyses were made on both R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 2 turbidites and hemipelagic intervals. This data allow s for comparison of laminated intervals with organic carbon curves to test Calvert's (1987) hypothesis that the preservation of organic carbon may not necessarily be controlled by surface productivity and oxygen content in the waters, but may occur as a function of texture. Geologic S ettin g - G u lf o f California The continental margins of the Gulf of California combine high sedimentation rates (approximately 1-2 m m /yr.) and high productivity due to coastal upw elling to provide a high resolution framework in which to investigate regional and local oceanographic and depositional changes. Isolated from the Pacific Ocean by the rugged mountains extending the length of the arid Baja California peninsula, the Gulf of California is the only marginal sea rimming the Pacific Ocean which is evaporitic (Roden, 1964). The Gulf of California is an asymmetrical narrow structural trough approximately 1000 km long and an average of 150 km in width, with narrower peninsular shelves and steeper slopes on the western margin. This semi-enclosed marginal sea extends from the Colorado River delta in the northern region to the m outh of the Gulf by San Jose del Cabo, where it is in connection with Pacific waters (Figure 1). The Gulf of California floor is characterized by high relief; the general bathymetry consists of a series of silled deep basins increasing with depth southward from 1000 to almost 4000 m (Van Andel, 1964) and of shallower shelf margin areas, six of which w ill be emphasized in this study (Figure 2). The northern Gulf is at shelf depth and is separated R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. A H Q ft& o U NITED STATES ; * V OF ' . .KJ >\AMERICA Tiburon . 30 ' M EX I C O G U A Y M A S 'T Santa Rosalia 1 1 0 *, w La Giganta Loreto San Carloe ! Y A lf o n s o Y * “ "$-San Juan r* La Paz Santiago Figure 1 - Location of the Gulf of California and the six studied shelf margin basins (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. GULF ( J ) 0 * i l m y \! > | o • to o m * ’ 2 0 0 .1 w o rn I > o oo-20oom S i ] 2 0 0 0 . w o o m J — M l > oooom ■BAJA Figure 2 - General bathymetry of the Gulf of California showing the location of the shelf margin basins. The floor of the Gulf consists of a series of silled basins increasing with depth southward and of shallower shelf margin areas. From north to south, the areas of this study are: 1) Santa Rosalia, 2) La Giganta, 3) Loreto, 4) Alfonso, 5) San Juan de la Costa, and 6) Santiago. The three hydrographic portions of the Gulf are: 1) northern, extending north of the San Esteban sill, 2) central and southern, from Guaymas Basin to the mouth of the Gulf, and 3) the island region, which separates the northern Gulf from the southern Gulf, topographically and hydrographically (modified from Nava-Sanchez, 1997). 5 from the central and southern portions by a chain of islands known as the Midriff Islands (Tiburon Island, San Lorenzo Island, and San Esteban Island) and by the prominent San Esteban sill (designated as such by Bray, 1988a), which rises up to a depth of 439 m at the northern boundary of Guaymas Basin (Rusnak et al., 1964). Geologically, the province is a result of the interaction between the North American and Pacific plates. An assortment of en echelon right-lateral transform faults joined by small spreading ridges (oblique to the overall trend of the Gulf) accomodate slip or plate motion from the southern part of the San Andreas fault system and the East Pacific Rise (Figure 3). Before the western edge of North America overrode the East Pacific Rise (30 mya), the boundary was convergent (Hausback, 1984). Once the ridge contacted the subduction zone, located w est of the Baja California peninsula, subduction stopped and was progressively shut down to the north and south from the initial contact point during the late Miocene. After the cessation of subduction, normal faulting extended the region that would later become the Gulf of California in an east-west direction. When rifting of the Gulf began approximately 6-5.5 Ma (Curray and Moore, 1984), northwest-southeast transform faulting dominated over the east-west extension. Right step-overs along the transform faults linked motions on separate fault segments and began to form pull-apart basins (Lonsdale, 1989). Around 3.5 Ma, Baja California peninsula was severed from North America and became sutured to the Pacific plate, initiating the oblique pattern of en echelon transform faults linked by small spreading ridges present today R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. ^ Spreading axis a n d w W / / / / / / / / / / / v ' S k f ' N * * ^ / / / transform faults v v \ 30° N - NORTH AMERICAN PLATE 25° N - Diego PACIFIC PLATE Cabo San Lucas East Pacific Rise / / / / / / / S \ N \ \ N N ; . - - . a . . . \ N \ S \ \ ' / / / / / / / \ N N V \ \ // //<»// * . . , . . . \ \ N \ N S u u a y m a i . - v v w n n n n x w v \ V \ V V N V VVV V V \ V \ \.N ’ • A / / /•/ / / / / / / / / / / / / # * r r Guaymas'Basim / A / A a a A ✓ A / / / > / / A A / ~ * V V \ \ S% V \ >AN N \ \ N V V ' A AAA A A A A A / A A A A A A A N \ N ' A A N V \ w - ; \ \ v v \ \ v-v \ \ \ Carmen B a sm ssssv V A v W x A A A A A A A A A A iA \ \ VV V V \ A V \ V \ V \ N N A„ A, A. A. A. A. A A. A. / A A A 1 A- A A" c Faralion BasiriLyX'Xyy^ " V - V V V V V V s ' v ' V V A N J \ A A V A A A A A A A A A A " Vv V v V V V V V V V N \ ’ Pescadero B a s in y a v v v w v V A \ V \ V V VJ MazatfaivVv\ ' / V s ' V W s A A A- A A A , N V V V V \ v*- A 'A A A A - , V V V V - \ A A A A A .. V V \ \ \ u < « V s Tamayo TransformK> RIVERA: Figure 3 - Tectonic map of the Gulf of California show ing the extension occurring in a rifting transform system (from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 7 (Hausback, 1984). Rifting continues presently, w ith the basins extending enough to form oceanic crust, making the Gulf of California one of very few contemporary examples on Earth of active tranform- rift plate boundaries. Approximately 450-600 km of northward movem ent has occurred in this new rifting ocean basin along the the right-lateral system of transform faults which is essentially a continuation of the San Andreas transform fault system (Lyle and Mess, 1991). The shelf margin areas discussed herein are located in the southern half of the Gulf of California along its western margin between 23.5° and 27.5° North latitude and 109.5° and 112.3° West longitude (Figure 1 and 2). From north to south, the six regions are: 1) Santa Rosalia slope, just west of the northern edge of the extensively- studied deep Guaymas Basin, 2) La Giganta area, w est of the deep Carmen Basin, 3) Loreto area, offshore of the city Loreto and also west of Carmen Basin, 4) Alfonso Basin, in the northwest area of La Paz Bay, 5) San Juan de la Costa slope, in the western area of La Paz Bay, and 6) Santiago slope, approximately 35 km from the m outh of the Gulf. Santiago and Santa Rosalia are open slope areas, whereas La Giganta, San Juan, and Loreto are shelf margin basins. Alfonso is a perched margin basin. With the exception of San Juan de la Costa, all have basin floors or slopes in the depth range from 300 to 900 m and most have sills that range from 200 to 700 m, all within the oxygen minimum zone designated by Calvert (1964) as between 200-1200 m and containing <0.5 m l/L dissolved oxygen (Figure 4). The cores used in this research from these basins yield continuous high resolution R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 4, Longitudinal profile of the Gulf of California showing the vertical dissolved oxygen distribution in ml/I for April-May 1974. The shelf margins' basins floors all fall within the oxygen minimum zone (<0.5 m l/ 1 ) between 200-1200 m (from Alvarez-Borrego and Lara-Lara, 1991). oo 9 records ranging from 320-1210 years (Nava-Sanchez, 1997). These nearshore areas with similarly high sedimentation rates (1.89-3.14 m m /yr) are dominated by hem ipelagic diatomaceous m uds and terrigenous input from local rivers (Nava-Sanchez, 1997). Cores from both San Juan and Loreto localities are thoroughly bioturbated and no primary structures are preserved. Cores from within the remaining areas (Santa Rosalia, La Giganta, Alfonso and Santiago) contain turbidites of varying degrees of thickness and frequency of occurrence. These cores show preserved laminations because their slopes lie w ithin the oxygen minimum zone. Gulf sediments are immature and are derived from local and oftentimes unstable (due to rapid erosion) sources (van Andel, 1964). The Colorado River, which drains the Colorado Plateau, the southern Rocky Mountains, and the southwestern states of the United States, is the predominant source of sedim ent in the northern Gulf. Colorado River silts appears to be restricted to this region of the Gulf (Baba et al., 1991). Transport of sediment in the northern Gulf is longitudinally from the mouth of the Colorado towards the south; the central and southern Gulf receive sediments along their margins from ephemeral streams, and the configuration of province boundaries indicates little longitudinal transport (van Andel, 1964). It is possible that detritus supplied from substantial rivers (eg. Yaqui River, Mayo River) along the eastern margin of the Gulf m ay be present in sediments along the western margin but it is m ost likely not a major source. Table 1 outlines the geometrical and morphological characteristics of the R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 10 drainage basins along the eastern margin of the Baja California peninsula which supply detritus to the study area. Drainage Geometric Drainage Mean Watershed- Mean Slope of Relative Basin Form basin area max. coastline slope transfer stream (km2) height distance zone energv Santa Rosalia rectangular 606 1500 m 40 km 2.15° 0.7° moderate to high La Giganta triangular- rectangular 614 1600 m 25 km 3.7° 0.4° low Loreto triangular 114 800 m 19 km 2.4° 0.6° moderate Alfonso rectangular 58 800 m 11km 4-2° 0.9° high San Juan romboid 67 500m 11km 2.6° 1.0° moderate Santiago rectangular 760 2000 m 50 km 23° 03° low/mod. Table 1: Geometric and morphologic characteristics of the drainage basins (data from Nava-Sanchez, 1997) The two geological subprovinces influencing sedimentation within the southern shelf margin basins of Baja California peninsula are the Sierra de la Giganta Range and the Del Cabo Region. The Sierra de la Giganta Range geological subprovince stretches from north of Santa Rosalia to the La Paz isthmus and supplies lithogenic material to Santa Rosalia, La Giganta Basin, Loreto Basin, Alfonso Basin, and San Juan de la Costa. It is characterized by high relief w ith mountains over 1200 m. The Sierra de la Giganta Range subprovince is composed of a thick sequence of volcanic and volcaniclastic rocks and subaerial sandstones that make up the "Comondu Group" (Hausback, 1984), which consists of the Oligocene Salto Formation, the late Oligocene San Gregorio Formation, the early Miocene San Isidro Formation, and R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. the early Miocene Comondu Formation. The fan deltas of Santa Rosalia, La Giganta Basin, and Loreto Basin drain the Comondu Formation, which consists of volcanic and volcaniclastic rocks with som e intrusions. La Giganta Basin also receives input from the adjacent onshore Loreto half-graben, which is filled with a marine sequence of Pliocene elastics (Dorsey et al., 1997). Alfonso Basin and San Juan de la Costa receive lithogenic materials from the marine sedimentary and volcaniclastic rocks of the San Gregorio and San Isidro Formations (Nava-Sanchez, 1997). The southernmost study area, Santiago, lies within the Del Cabo Region geological subprovince. This batholithic subprovince breaks the peninsular structural trend of right-lateral transform faulting with basin-range topography trending north-south. The left-lateral strike- slip fault system termed the "La Paz Fault" (Beal, 1948) juxtaposes this granitic subprovince against the volcanic-dominated Sierra de la Giganta Range to the north and west. The La Victoria Range is the m ost outstanding feature of the Del Cabo Region with heights reaching more than 2000 m. Del Cabo Region is composed of a Cretaceous granitic batholith which intrudes M esozoic metamorphic rocks (Nava- Sanchez, 1997). The Gulf's mountainous source areas combined with the arid climate and sparse vegetation results in little chemical weathering and rapid erosion. Baja California peninsula has no permanent streams and sediment is supplied by arroyos, alluvial fans, and coastal erosion (Donegan and Schrader, 1982). Overall, depositional patterns in the R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Gulf are controlled by tectonic, lithologic, and climatic influence, as w ell as the oxygen minimum zone and water circulation. General Circulation The Gulf of California differs from other evaporative basins (eg. the Mediterranean and the Red Sea) in that the evaporative excess is accompanied by a net heat gain from the atmosphere of a sufficient magnitude to reverse the evaporative buoyancy flux (ie. the water becomes more dense through evaporation but less dense through heating) (Bray, 1988b). Consequently, outflow from the Gulf is generally less dense than inflow from the Pacific and there is a net heat flux into the ocean. The resulting air-sea heat fluxes im ply a thermohaline circulation with colder, less salty inflow occurring deeper than warmer, salty outflow in order to balance the heat and salt. This is indeed the case, with inflow occurring betw een 500-250 m and outflow occurring between 250-50 m, with a surface layer (Gulf Surface Water) whose direction of transport changes w ith seasonal changes in the large-scale winds (Bray, 1988a) (Figure 5b). Deep inflow to the Gulf provides high levels of nutrients and m ay be the primary reason for enhanced productivity observed in the Gulf. This three-layered system dictates that the outflow must be an intermediate water mass, in depth and in T-S properties, between the deep fresh inflow and the surface layer made saline by evaporation (Bray 1988a). Surface circulation within the Gulf is a com plex combination of processes, including winds, tides, and remote effects such as coastally trapped waves. Wind patterns over the Gulf are monsoonal in nature, R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. DEPTH (m) 1 3 WATER MASS DISTRIBUTIONS IN THE GULF O F CAUFORMA DISTANCE (km) 200 400 600 500 1000 1500 _ 2000 — 2500 3000 CDW TSW SSW CCW NGW Wagner Basin Demn basin PDW : Farallon Basin Carmen Basin 1000 Guaymas Basin PACIFIC OCEAN TSW = Tropical Surface Water CGW = Central Gulf Water CCW = Calif. Current Water NGW = Northern Gulf Water SSW = Subtropical Subsurface WBW = Waaner Basin Water Water PIW = Pacific Intermediate CDW = Co,orado 08, 13 Wa,8r Water PDW = Pacific Deep Water WATER MASSES OF THE GULF O F CAU FORMA 3 0 2 6 22 < 1 8 1 1 1 X 1 4 10 6 2 TSW 1 \ ___________ I C C W / ____________ j " / ^ “ ~JbD W ___________________ ^ ------------ CGW / ' / ( n g w ' v 2 .5 / 1 f ------ ------------- ...— f / 1 t - — SSW 1 ' : — IT/ - _____ , , , \P D W , ' 1 * / S .______ 27 WBW,__________ _____— ______ 1 ______ 1 ______ 1 ----------1 --------- 1 -------- 3 4 TSW = Tropical Surface Water CCW = Calif. Current Water SSW = Subtropical Subsurface Water 3 5 SALINITY, psu PIW = Pacific Intermediate Water PDW = Pacific Deep Water 3 6 CGW = Central Gulf Water NGW = Northern Gulf Water WBW = Wagner Basin Water CDW = Colorado Delta Water Figure 5 - Schematic of water masses of the Gulf, (a) Longitudinal profile and the water mass distributions; arrows indicate the hypothesized thermohaline circulation, (b) T-S characteristics of the Gulf water masses. Vertical exaggeration = 5x (from Bray, 1988b). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 14 with southeasterly winds during the summer and northeasterly winds dow n the Gulf axis during the winter. Upwelling occurs along the western Gulf margin during the summer, when southeasterly winds predominate (Figure 6A). Generally, surface productivity increases in the northern half of the Gulf due to increased nutrients in this region. Yet in the southern Gulf, primary productivity is the m ost integrated as a result of increased euphotic zone depths (Alvarez-Borrego and Lara- Lara, 1991). Winds play a major role in causing upwelling along the margins of the Gulf, but it is tidal currents and coastally trapped waves which exert the largest influence on surface circulation. Molina-Cruz (1986) emphasizes the importance of the morphologic narrowing and the abrupt bathymetric changes near Angel de la Guarda and Tiburon Islands in intensifying tidal currents and water mixing, resulting in enhanced productivity. Prominent eddies in the Gulf of California also contribute to increased primary productivity. Upwelling areas are generally located near inter-eddy zones, indicating a significant relationship. Fernandez-Barajas et al. (1994) cite three eddies interrelated to the formation and distribution of water masses in the Gulf: a cyclonic eddy in Guaymas Basin, an anticyclonic eddy in Carmen Basin, and a cyclonic eddy in Farallon Basin (Figure 6B). Upwelling events and surface currents are intensified in these regions of the Gulf of California where two contiguous eddies combine to transport water away from the coast (Fernandez-Barajas et al., 1994). Under this regime, one of these regions is adjacent to Carmen Island, proximal to two basins in this study: Loreto and La Giganta. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. B A 3 0 *N ISLA ANGEL DE LA GUARDA IS L A TIBURON GUAY MAS TOPOLOBAMPO 2 5 *N LA PAZ MAZATLAN CABO SAN LUCAS CABO CO RRIENTES 20*N I0 5 *W IIO 'W II5*W Figure 6 - A) Schematic of upwelling patterns in the Gulf of California. Upwelling areas: a) with northwesterly winds, b) with southeasterly winds, and c) area characterized by intense tidal mixing (from Roden and Groves, 1959). B) Gyres in the Gulf of California. From north to south: the cyclonic Guaymas gyre, the anticyclonic Carmen gyre, and the cyclonic Farallon gyre (from Molina-Cruz, 1986). 1 6 The water masses in the Gulf of California are diverse and numerous (Figure 5a and b). The influx of Pacific Intermediate Water at depth into the Gulf and the subsequent extensive tidal m ixing of that water with saline surface waters from the northern Gulf leads to the creation of a distinct water mass, Gulf Water, which is exchanged with the Pacific (Bray and Robles, 1991). Gulf Water is further divided into Northern Gulf Water (NGW) and Central Gulf Water (CGW), the latter being a mixture of NGW and waters of Pacific origin, and filling the six basins in this study. Below 500 m in the southern region of the Gulf, the principal water masses are the Pacific Intermediate Water (PIW) and the underlying Pacific Deep Water (PDW). The top of PIW at 500 m is marked by a distinct foraminiferal faunal change with the appearance of B. argentea, Buliminella tenuata, Cassidulinoides cornuta, and other oxygen m inim um species (Nava-Sanchez et al., 1998). Hydrographically, the Gulf is divided into 3 different regions: 1) the northern third, where NGW is predominant, 2) the central and southern areas, where Pacific waters and CGW are predominant, and 3) the island region, where strong tidal m ixing and topographical constraints play a large role in determining the vertical structure of the water column (Figure 2) (Bray, 1988b). ENSOs influence circulation within the Gulf by introducing a greater amount of tropical waters. These waters generally consist of Tropical Surface Water (TSW) or Subtropical Subsurface Water (SSW) and are m uch warmer than normal, allow ing m ixing over an extensive area and causing lower salinity and higher temperatures in R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. the top 200 m of the water column in the central Gulf (Robles and Marinone, 1987). This results in increased primary productivity, unlike that which occurs along the Pacific Ocean margins. Rapid return to normal conditions in the northern Gulf after the 1973 ENSO suggests that waters are renewed annually (Bray and Robles, 1991). Previous Work While the deep-sea basins in the Gulf of California (ie. Guaymas Basin) have been studied extensively, no published works concerning the shelf margin areas exist. In this sense, this study is an exploratory one which should provide a helpful framework for further research. Past work in the deep basins of the Gulf has tended to concentrate on Guaymas Basin and its well-preserved varved diatomaceous sediments. Calvert (1964, 1966) investigated the water, organisms, and sediments in the deep Guaymas and San Pedro Martir Basins, which are sites of extremely abundant diatom accumulations. In contrast to previously described occurrences of laminated sediments, Calvert found that the laminated diatomaceous sediments of the Gulf of California occur on slopes of basins with free communication at all depths w ith the open ocean. The laminations' preservation can be attributed to an oxygen minimum zone found throughout the southern Gulf which comes in contact with the basin slopes where the laminated sediments occur (Figure 7). The presence of laminated sediments under these circumstances (ie. basins that are not stagnant) may be due to the presence of an intense oxygen m inim um in the eastern tropical Pacific (Calvert, 1966). Variations in the supply of R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. l i t * zr * R t O TA OU I Core EB _ _ HYDROGRAPHIC STATIONS: •ocroeeR -N O vE M aes. 1961 R/V HUGH M. SMITH oFEBRUARY, 1957 R/V SPENCER F. BAIRO 'SO PIE THS OF OXYGEN CONCENTRATION IN ibI/U Z 2 Z 2 a o x Y G E N MINIMUM: < 0 2 m i/L IS O B A T H S IN M E T R E S Figure 7 - Distribution of dissolved oxygen at, or close to, the bottom of the Guaymas and San Pedro Martir Basins. The points represent oxygen determinations within 200 m of the bottom. Locations of Cores FF and EB from this study are shown to faL I in the oxygen minimum zone of <0.2 ml/L designated by slanted lines (modified from Calvert, 1964). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 19 terrigenous and diatomaceous materials to the basin slopes are responsible for producing the regularly laminated sedim ents (Calvert, 1964). The absence of oxygen on these basin slopes prevents any destruction by the activities of burrowing and/or m ud-ingesting benthic organisms. More recently, Calvert (1987) investigated oceanographic controls on the accumulation of organic matter in marine sediments. The concentration of organic matter in marine sedim ents w ill depend upon the accumulation rates and how w ell it is preserved after burial. Primary productivity in surface waters and the depth to which particulate matter must settle control the supply of organic carbon to the sea floor. It is widely accepted that organic matter is preserved preferentially under anoxic conditions. Yet Calvert found no relationship between sedimentary carbon and the oxygen content of the bottom water in the Gulf of California. The carbon contents of the nearly anoxic, regularly-laminated sediments are indistinguishable from those of the oxic, bioturbated sediments located above and below the oxygen minimum zone (Calvert, 1987). Preservation of organic carbon in the Gulf of California m ay not necessarily be controlled by oxygen content of the waters, but may occur as a function of texture (Calvert, 1987). Furthermore, recent research suggests that high primary production and not water-column anoxia provides the first- order control on the accumulation of organic-rich deposits in modern ocean settings (Pedersen and Calvert, 1990). If primary production is the main control, then the preservation of organic matter within the sediments would be dependent upon the rate that sedim ent-dwelling R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 20 bacteria metabolized deposited organic matter (Pedersen and Calvert, 1990). These issues w ill be discussed further in "Synthesis - Organic Carbon and Paleoproductivity" in this study. Pride et al. (1998, in review) used the Gulf of California as a test area for evaluating productivity proxies, as it is one of the more productive regions of the world and its primary production undergoes large seasonal fluctuations (Alvarez-Borrego and Lara-Lara, 1991). Calcium carbonate and organic carbon were two of the many proxies tested. The study found it to be more comm on for central Gulf calcium carbonate and organic carbon fluxes to be higher in the summer than in the winter bloom events, suggesting that the fluxes represent coccolithophore production in the G ulf under oligotrophic (lower nutrient) conditions (Thunell et al., 1996). In light of these findings, calcium carbonate and organic carbon do not appear to be accurate productivity proxies on a seasonal scale. H owever, on an interannual scale, summer fluxes of biogenic sedim ents increased as the 1991-1994 ENSO diminished and tropical surface waters retreated back into the Pacific, indicating that calcium carbonate and organic carbon have merit as productivity proxies on longer time scales (Pride et al., 1998). The only written work dealing, if som ewhat indirectly, with the six areas studied in this project is an unpublished PhD. dissertation by Nava-Sanchez (1997). This dissertation focused upon the six local fan deltas which supply terrigenous sedim ent to the six areas of this study. Nava-Sanchez identified and nam ed these shelf margin areas, as he considered the whole fluvial system which w ould therefore include a receiving basin. Morphology and grain size distribution of the R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 21 southern western margin of the Gulf were studied in the six local regions. Nava-Sanchez (1997) identified gravitational processes that usually take place on the peninsular slopes in the southern half of the Gulf as slides, slum ps, fall of loose or solitary grains, and turbidity flows. He attributed these processes to active faults affecting pro-delta deposits. This study w ill focus on the relatively nearshore shelf margin areas that have generally been overlooked in the literature: namely, Santa Rosalia, La Giganta, Loreto, Alfonso, San Juan de la Costa, and Santiago. Due to their proximity to shore, location within or near the oxygen m inim um zone and CGW hydrographic zone, and high sedimentation rates, they should serve as excellent recorders and preservers of recent fluctuating climate regimes and sedimentation patterns of the southern western Gulf shelf margin. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 22 M ethods Cores and Curating The cores used in this study were collected during the PALEO VII and PALEO VET cruises on R.V. EL PUMA, a research vessel for the Universidad Nacional Autonoma de Mexico (UNAM), in 1994 and 1996, respectively (Table 2 below). These cruises were directed by Dr. Adolfo Molina-Cruz of UNAM. Of the six cores used in this study, five are gravity cores and one is a kasten core. In the gravity coring process, some top sediment, on the order of up to 10 cm, may be lost. The kasten core may also lose top sediment, but only on the order of up to 4-5 cm. All data reported in this study is from core-top, which might not necessarily be true sediment surface. Each core ranges in length from 100-275 cm. The cores were split and described aboard ship, then placed in core liners, labeled, and sealed for transport. After the cruises, the cores were transferred to a cold room at Centro Interdisdplinario de Ciendas Marinas (CICIMAR) - IPN. H alf of the cores remained at CICIMAR, while the remainder were transferred via Ensenada to USC. At USC, the cores are stored in a walk-in refrigerator. Water Length of Basin Latitude N Longitude W Depth fm) core fcm) AM-Santiago 23°39.326" 109°27.908" 480 129 BD-San Juan 24°23.9" 110°34.6" 140 104 CP-Alfonso 24°38.12" 110°33.242" 390 212 DB-Loreto 25°58.46" 111°15.126" 385 105 EB-La Giganta 26°15.11" m°13.89" 560 272 FF-Sta. Rosalia 27°21.462" 112°9.941" 620 220 Table 2- Summary of core locations and lengths. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 23 All X-radiography of these six cores was performed by Donn Gorsline and Enrique Nava-Sanchez. To X-ray the cores, one- centimeter thick slabs were cut and placed in labeled trays. The core slabs were x-rayed in a Penetrex industrial x-ray unit and then sealed and stored in the walk-in refrigerator. The remaining part of each core was partitioned into two-centimeter intervals (one-centimeter intervals for the kasten core), bagged, labeled, and stored in the walk-in refrigerator until sampling began. X-Radiograph Description The X-radiographs, which reveal density differences as preserved in the sedim ent column, were described in detail. Positive contact prints were m ade of the negatives. Differences in x-ray absorption show disturbances in the sediments, different modes of deposition, and laminated or varved intervals. The positive prints sh ow denser material as darker shades. Turbidite sequences, which are extremely dense, therefore show up as dark intervals on positives, while less dense materials such as hemipelagics appear much lighter. The X- radiographs were examined for laminations, bioturbation, turbidites, sedimentary structures, varves, and hemipelagic deposition. Sampling Subsampling was done every 10 cm downcore for organic carbon, carbonate, and grain size analyses. Subsampling for grain size was also performed at two-centimeter intervals for all turbidites present in each core. Each subsample was then dried at 60° Celsius in a R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 24 drying oven. After weighing the dried sample, it w as divided into two halves. One half w as powdered for organic carbon, carbonate, biogenic silica, and major and trace element analyses. The other half was separated by wet-sieving into coarse (> 63 pm) and fine (<63 pm) fractions to be used in grain size analyses. Core CP from Alfonso Basin, which is a perched margin basin, was selected for further analyses of biogenic silica at 10 cm intervals downcore. The same subsamples from Core CP which were used in organic carbon, carbonate, and grain size analyses were used in these analyses as well. Besides the Core CP samples, all core-tops except Core AM from Santiago were sampled for biogenic silica. Santiago was omitted because it receives mainly terrigenous silidclastic input. Organic Carbon and Carbonate A LECO Carbon Analyzer was used to determine both total carbon (TC) and inorganic carbonate (CaC03) percentages. TC was measured by complete combustion in an induction furnace of 0.5 g of powdered sample in a ceramic crucible. Iron and tin chip accelerators were added for increased mass to ensure total combustion. Calcium carbonate was determined with a gasometric acid digestion attachment to the LECO. For a more detailed description of this procedure, please refer to Kolpack and Bell (1968). Again, 0.5 g of pow dered sample w as used for each analysis. Analyses were repeated two times in order to drive all lurking CO2 from the system and to ensure complete digestion and therefore an accurate reading of the am ount of CO2 . The R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 25 total CO2 measured is the sum of the two runs. Total organic carbon is then calculated as a percentage based on this formula: TC - Total Inorganic Carbon = TOC where Total Inorganic Carbon = CaC 03/8.33 Grain Size Analysis The dry grain size sample (one of the two halves previously mentioned) was weighed and then re-suspended in approximately 5 ml of de-ionized water and 5 ml of acetone. The samples soaked in this solution for 2-3 days. (Samples from Core CP, however, usually needed increased acetone and soaking time). The sedim ent was then rinsed with de-ionized water and a dilute Calgon solution was added as a defloculant. Each suspended sample was sieved through a 63 pm screen. The coarse fraction (> 63 pm) was dried, weighed, and sand percentage was determined. The fine fraction (< 63 pm) was stored in a labeled plastic tub for later use at the US Geological Survey Laboratory at Menlo Park. The fine fraction grain size analysis was conducted using a 16- Channel Coulter Counter Tn at the United States Geological Survey Sediment Dynamics Laboratory in Menlo Park, CA. Approximately 10- 15 ml of the < 63 pm sediment in suspension was sieved through a 38 pm screen. The two suspensions were then drawn through the Coulter Counter, where the number of particles and volume is determined by relating spherical equivalence to electrical resistance and therefore volume. To conduct each analysis, a small amount of suspension is added to an electrically conductive liquid and then the R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 26 combined mixture is passed through an orifice of know n size to measure the subsequent changes in electrical resistivity. Two sizes of aperture tubes were used: the 70 pm and 280 pm orifice. Both sizes were necessary to obtain a complete size distribution of fine-grained particles from 1.3 - 200 pm. For a more detailed explanation of this procedure, please refer to McCave and Jarvis (1973). Biogenic Silica Determination of amorphous silica content w as performed by Na2C0 3 leaching of sediment samples from the core-tops of all basins and of the same sampled intervals downcore of Core CP (Alfonso Basin) which were previously analyzed for inorganic carbonate, organic carbon, and grain size. Alfonso Basin was focused upon as it is a silled basin with a high sedimentation rate and more work has been conducted there than in any of the other basins in this study. Amorphous silica was measured to give a proxy for productivity and its variations downcore. Previous silica measurements have concentrated only on the deep-sea basins of the Gulf of California, such as Guaymas Basin (Calvert, 1966). To measure % biogenic silica, amorphous silica was extracted from dry sediment samples using a Na2 C0 3 leaching solution. Approximately 60 micrograms of each pow dered sample was leached with 50 ml of a 5% Na2C0 3 solution in a capped plastic centrifuge tube at 80° Celsius. The sample solutions were placed into an 80° C water bath for four hours. Every 30 minutes the tubes were vigorously shaken, and every hour the progress of the leach was monitored by R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 27 removing the tube from the hot water bath, centrifuging it for 4 minutes at 5000 rpm, withdrawing 200 (il with a pipet, and diluting this aliquot w ith 1.8 ml of acidified water. A 0.9% HC1 solution was used as a dilutant rather than deionized water to allow the sam ple to de-gas. The diluted aliquot w as capped after 1 /2 hour had elapsed, allowing the gas to escape. This prevented any bubbles from forming, w hich could potentially become lodged in the cell of the spectrophotometer during future colorimetric analysis and alter its reading. Standards were prepared in 5% Na2 CC>3 and were diluted in the same manner. Dilutions were required to alter sample alkalinity and concentration to ranges proper for colorimetric analysis (Strickland and Parsons, 1972). Blanks containing only 5% Na2CC>3 were sampled in every run and showed only a very minor release of silica from glass reagent bottles. All measured concentrations were corrected for dilution effects which resulted from sequential sam pling in the spectrophotometer. Precision was monitored by drawing duplicates of every aliquot, by running one duplicate for every group of samples, and by running a duplicate of a sample from the previous day's group of samples. For a more detailed description of this procedure please refer to DeMaster (1979) and Hurd (1972). This method, w hich closely parallels that of DeMaster's (1979), is based on the assumption that biogenic silica dissolves within the first two hours of leaching and any increases in dissolved silica after this time frame are a result of the release of silica from clays. When leaching is initiated, no biogenic silica or silica from clays should be present in the solution. Therefore, a best-fit line drawn through the R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 28 linear portion of a w eight % biogenica silica versus time graph should result in an intercept along the y-axis (weight % biogenic silica) indicating the concentration of biogenic silica originally present in the sediments. This is shown in Figure 8. Colorimetric analysis of the diluted aliquots, blanks, and standards was performed w ith a Hitachi U-1100 spectrophotometer at 810 nanometers. Before running each aliquot through the spectrophotometer, 1.2 ml of a reducing reagent mixture and 0.8 ml of a molybdate solution were added to produce a silicomolybdate complex. This complex's blue color varies in intensity in proportion to the amount of silica present in the samples. Once the spiked sam ples had sat in a dark cupboard for two hours, colorimetric analysis w as conducted. Age Models The age model for each basin was constructed using a combination of AMS C-14 dates from planktonic foraminifera analyzed at Lawrence Livermore Laboratory, and 220pb dates analyzed at USC by Enrique Nava-Sanchez. The combination of the two provided a fairly accurate framework for establishing age downcore. AMS C-14 dates were needed to supplement the ^lOpb dates already available at USC because 2 21Opb dates had not been measured for all 6 basins and have a limited age range of about 100 years. Also, 2 1 1 Opb had been measured from the same basins in this study, but not necessarily from the same core used in this study. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. W eight % Silica vs. Time A lfonso Basin, CP 14-15 ra u C /i •§ > • H < u £ 5 4 3 2 1 3.0887 + 0.5i3575x R2= 0.9 0 4 3.5 1.5 2 2.5 3 1 0.5 0 Figure 8 - A representative plot of weight percent silica versus time from Alfonso Basin, Core CP 14-15. The best-fit line drawn through the linear portion of this plot results in an intercept at the weight percent of amorphous silica originally present in the sample. to V O 30 210pb is an intermediate member of the LT-238 decay chain, with a half-life of 22.3 years. 210pb is absorbed into particulate matter that settles onto the ocean floor and its activity decreases w ith depth in buried sediments. A sedimentation rate can be determined from the activity of 210pb by using this formula: Srate = 0 n 2 /T i/2 )/a where Srate is the sedimentation rate, T1 / 2 is the half-life of 210pb, and "a" is the activity of 210pb (Figure 9). Nava-Sanchez's (1997) sampling procedure involved analyzing 1.5 g of powdered sam ple every 2 cm for the top 12 cm of each core. Figure 9 shows the exponential correlation determined by this procedure from which a sedimentation rate is obtained for a sample from Alfonso Basin. To ensure accuracy, the presence of turbidites w as taken into account in the four basins where they are present: Santiago, Alfonso, La Giganta, and Santa Rosalia. Turbidite thicknesses as determined from the X-radiographs were subtracted out from each respective core's sampled interval depths, as turbidites essentially represent zero-time despite their thickness. The core bottoms ranged in age from 320 to 1215 years depending upon the length of the core. As the basins are all shelf margin basins and relatively close to shore, distance from the basin to the sediment source did not significantly impact sedimentation rates. The sedimentation rates for the 6 basins studied ranged from 1.9 m m /yr to R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Lead 210 Profile Station CA, Alfonso Basin 35 30 25 f § . 20 T3 I I I I ' I I I I I I I I I I I I I I I I © s A % w 15 10 5 0 y = 30,436 * eA (-0.16358x) B2 = 0.9664 sedimentation rate = 1,9 mm/yr , I I I I I j I I ( 0 2 4 6 8 10 12 14 Depth (cm) Figure 9 - Exponential correlation of the excess of 210pb determined from samples taken every 2 cm from Alfonso Basin, Core CA. From this correlation a sedimentation rate of 1.9 mm/year was obtained (from Nava-Sanchez, 1997). u > 3.1 m m /yr (Table 3). 32 Basin_______Core________Sed. Rate (mm/yr) Santiago AF 3.1 A lfonso CA 1.9 Loreto DD 1.9 La Giganta EA 2.1 Table 3: Sedimentation rates based on ^lOpb dates. Potential Errors Standard error for the calcium carbonate analyses is calculated based upon 20 runs of reagent grade CaC03 (Table 4) run periodically while performing analyses. The samples were replicated to a reliability within 2.5% of each other and average values were used. An attempt was made to prevent any compounded error from occurring in the total carbon standards by using two standard sample rings, each of which contained 0.823 % carbon. Standard error is calculated for both the standards used in the LECO analyses (Table 4). % CaC0 3 % TC ________________________ reagent____ rings Mean 0.005 0.042 Standard Deviation 0.006 0.010 Average Deviation 0.005 0.008 Table 4: Differences between standard value and analyzed value. Potential error associated with opaline silica analyses can be high. Precision, tracked by duplicates of each aliquot, duplicates within a run, and consecutive-day duplicates, is of the utmost importance in obtaining meaningful data. In this procedure, a 1% correction of R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 33 measured absorbance values was made for sequential draw effects. Freshly prepared standards were analyzed at the beginning, middle and end of each run to ensure accurate spectrophotometer absorbancy readings. Precision-tracking was accomplished by analyzing duplicates for each aliquot, sample duplicates on a daily basis for each non, and also analyzing consecutive-day duplicates throughout the entire block of time required for the analyses. Analysis of duplicate aliquots revealed that average precision ranged from 2-2.5%. Precision for consecutive-day duplicates of Core CP (Alfonso Basin) samples was calculated to be 5.86%. Precision for same-day duplicates was calculated to be 5.94%, except in the cases of core-top samples from Core BD 0-4 (San Juan Basin) and Core DB 0-4 (Loreto Basin). A precision value of 71.6% for BD 0-4 can be attributed to its extremely high average sand percent value of 56.32% and the intense level of bioturbation. For these reasons, it is doubtful that weight % silica values for Core BD could be accurately analyzed. A precision value of 17.9% for DB 0-4 is most likely a result of the bioturbation present throughout the complete length of this core. With the exception of these two samples, measured concentration values of duplicates were accurately reproduced. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 34 Results and Discussion Core AM - Santiago Core AM is located in the southeastern portion of Santiago at a depth of 480 m (Figure 10). Santiago is an open slope area w hose most prominent feature is the Las Palmas submarine canyon. It is situated approximately 35 km north from the mouth of the Gulf. The peninsular shelf is narrow and irregular, and the slope is generally steep with no breaks in gradient (Figure 10). Core A M from Santiago is characterized by an abundance of sandy turbidites, indicating the heavy influence of Las Palmas submarine canyon upon the sedimentation in this locality. Turbidites range in thickness from 0.3-6.3 cm and their frequency shows little variation downcore (Table 5). The largest turbidite occupies the last 6.3 cm of the core, from 122.7-129 cm depth and 321 yrs. in age, and has an average sand percentage of 55.12%. Due to the excessive turbidites, the Santiago core records only approximately 321 years despite its depth of 129 cm. The sedimentation rate of 3.15 m m /yr is the highest of the six shelf margin basins in this study and can be attributed to the presence of Las Palmas submarine canyon. X-radiographs of the entire core length allow for a more detailed look at the stratigraphy. There are three main facies present in the Santiago core: turbidite deposits, laminations, and bioturbated sediment. Turbidite deposits dominate the core at all depths, which a representative positive x-radiograph print in Figure 11 shows. Bioturbated intervals are more common than laminations throughout the core, and both facies are punctuated intermittently by dense R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 35 Profile A-A' 23° 44’ 200 400 1 1 0 0 1 n~ 600 23° ’ 40‘ 801 800 1000 AM 1200 LENGTH = 14.5 km km 109° 32' , , , f Figure 10 - Bathymetry and profile of Santiago shelf margin locality, showing the location of Core AM at a depth of 480 m. Sedimentation is influenced by the head of Las Palmas submarine canyon and by this area's close proximity to the Pacific ocean (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Table 5 - Turbidite interval depths and thicknesses for Santiago, Alfonso, La Giganta, and Santa Rosalia Basins. AM - Santiago CP - Alfonso EB - La Giganta FF - Santa Rosalia Sampled Turbidite Turb. Sampled Turbidite Turb. Sampled Turbidite Turb. Sampled Turbidite Turb. Interval Layer Thickness Interval Layer Thickness Interval Layer Thickness Interval Layer Thickness 10-12 10-10.5 0.5 154-155 154-154.5 0.5 12-14 13-13.5 0.5 94-96 94.5-95.2 0.7 11.8-12.3 0.5 179-180 179.5-180 0.5 16-18 16.3-16.6 0.3 108-110 109.2-110.1 0.9 12-14 13.7-14 0.3 202-203 201.9-202.3 0.4 96-98 97.5-98 0.5 162-164 162.7-163.5 0.8 16-18 16-16.7 0.7 208-209 208-208.8 0.8 124-126 124-124.7 0.7 18-20 18.8-19.6 0.8 125-126.3 1.3 20-22 21.3-22 0.7 126-128 127.2-128.8 1.6 24-26 24.1-24.9 0.8 128-130 127.2-128.8 1.6 26-28 27.1-27.3 0.2 136-138 137.2-138 0.8 28-30 28.1-28.7 0.6 138-140 138.8-139.8 1.0 30-32 31.4-31.6 0.2 204-206 203.9-204.4 0.5 34-36 35.2-35.5 0.3 208-210 208.5-208.9 0.4 36-38 37.5-37.8 0.3 40-42 40.7-41.2 0.5 52-54 52-52.7 0.7 68-70 68.7-69.7 1.0 72-74 72.1-73.1 1.0 78-80 78.5-78.9 0.4 82-84 81.8-82.4 82.7-83.1 0.6 0.4 84-86 84.2-85 0.8 90-92 91-92 1.0 96-98 95.6-97.6 2.0 100-102 100.3-101.5 1.2 37 T 3 < V P c U - i c 0 u 1 in < u 3 « H o 0 0 (3 • » 4 c < « cn s < cn c n QJ c -*5 u I S H T 3 jy s <d cn t N o o . c n v q i n o o O rH O O O O O C O v d i n CN O v r H O v 4 J v d r H C N v O Cn C O r H •* 4 "2 o o t-h r H r H r H r H 1 i n r H r H r H i O V r H C N r H i 2 a ; o o r H i n CN t-H i n r H C O i- l > * in d \ o C N in v d d \ o 3 c d o o r H r H r H r H r H < N H h - J T —< r H r H r H r H r H r H r H o v c n O O O C N T t« v O 00 O C N O r H r H r H r H r H C N C N r H r H r H r H r H r H r H r H v £ 0 0 O C N v £ .00 O O O r H r H r H r H r H C N r H r H r H r H r H r H r H r H t * v o o o o C N T ji C O R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 38 49 cm CORE AM 49-76 cm Santiago Area SLUMP 76 cm Figure 11 - A p ositive x-rad iograp h print representative o f Santiago's turbidite-dom inated. facies. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 39 turbidites of varying thicknesses. Laminations tend to be clustered into two peaks from 50-100 yrs BP and 190-240 yrs BP. Bioturbated sediments are mainly found between 0-50 yrs BP and 100-310 yrs BP (Figure 12). W eight percent sand downcore varies from 2.65-68.66% (Figure 12) w ith the most significant sand contributions occurring at the intervals of turbidite deposits. Despite the extensive range, the average sand percentage for laminated and bioturbated intervals is 3.8%. The average sand percentage for intervals containing turbidites reaches 10.4% only because of the presence of a very thick sandy turbidite at the end of the core. The mean grain size downcore is 6.5 0 (Figure 12). With the coarse-grained turbidite sample-means removed, the overall mean for the core is reduced to 6.55 0 , but this value still falls in the coarse silt category. There is only one significant decrease in grain size and that is from 6.1 0 to 7 0 between 130-160 yrs BP. This low size value corresponds to the end of the Little Ice Age, when coarse material was trapped on flooded or partially flooded shelves. The Little Ice Age, a world-wide expansion of glaciers, occurred from approximately A.D. 1400-1850 and resulted in 2° Celsius mean global cooling (Cowling et al., 1998). The end of the core records a substantial increase in size from 6.8 0 at 310 yrs BP to 4.6 0 at 320 yrs BP. This change can be attributed to the presence of the extremely sandy turbidite which occupies the last six centimeters of the core. Perhaps this thick turbidite reflects more sedim ent input during the Little Ice Age. Overall, size shows only R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Core AM - Santiago Sand Percent Facies Mean size Organic Carbon Carbonate T T T T T T T T TTTT TTTT TTTTTTTT[7TTTTUT TTTT IF TUT 100 ^ 150 & a ; W ) <• 200 250 300 350 Lmil iml.mil mil mil util mill 11 11 1111 11111 i i I i 0 10 20 30 40 50 60 0 20 40 60 80 ■Lll t i l l III II 111 1 1 1 l l l l . l l II I In 1 1 1 1 1 nil i ■ il ■ ■ i ili mini i In i n i lllllllllllllllllllliillll m l l i i i l m i 4.5 5 5.5 6 6.5 0 1 2 3 4 5 6 0 5 10 15 20 25 30 35 40 Weight % % structures phi Weight % Weight % Key: structures: X— % laminations O % bioturbated intervals -O — % turbidites Figure 12 - Sand percent, facies, mean size, organic carbon, and carbonate are plotted together against age for easy comparison of the Santiago open-slope record. o 41 slight variations downcore in Santiago, w ith the majority of values falling between 6.3 0 and 7.0 0 . It is very clear that all but a small minority of the fine fraction grain size samples came from intervals within the core which contained turbidites (Figure 13). The overall size distribution is platykurtic (stretching from very fine sands to very fine silts) but possesses a sharp peak in the very coarse silts between 5 and 6 0 with little or no tail past 4.2 0 other than the possible tail in the fine sand fraction. As the majority of these sampled intervals are turbidites, this could be a reflection of late stage sedimentation from residual suspension indicating decreased speed in the mass gravity flow and the subsequent onset of deposition of suspended fines. Dominance of silty beds m ay also be a function of the core location, which is laterally away from the submarine canyon axis (Figure 10) (Bouma, 1964). The turbidite-dominated distribution has strong positive skewness values towards the coarse and its standard deviation of 2.1-2.6 0 affirms that it is very poorly sorted (Figure 13B). Flemipelagic deposits such as AM 56-58 at 160 yrs BP have distributions with a tight peak in the coarse silts (6.2 0 ) and are much less positively skewed (Figure 13A). The more leptokurtic distribution indicates that the sedim ent has been sorted to a higher degree than the turbidite intervals. This effect may reflect flood discharges and a high suspended load of clays offshore. The amount of coarse silt is more than w ould normally be present in a more distal basin (Gorsline, pers. communication). N o clays are present in this core. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. A Weight Percent Frequency Distributions Core AM - Santiago § O J c u " § ) '3 12 10 8 4 2 0 8 9 10 3 4 5 6 7 phi —©—Wt%AM6-8 —a —Wt%AM16-18 — Wt%AM26-28 —H—Wt%AM36-38 -Wt%AM46-48 —A —Wt%AM56-58 - •• -Wt%AM66-68 - ■- -Wt%AM76-78 - ♦- -Wt%AM86-88 - A- -Wt%AM96-98 - *- -Wt%AM 106-108 - -0- -Wt%AM116-118 - H- -Wt%AM 126-128 Standard Deviation and Skewness vs. Mean Core AM - Santiago 4 o Standard Deviation - phi p Skew ness - phi________ 3 oi 2 1.5 1 0.5 0 6.5 7 4.5 5.5 6 5 mean (phi) Figure 13 - A. Weight percent frequency distributions of all the 16-channel grain size data per 10 cm sampled intervals from Santiago. The distributions change according to the mode of deposition. B. Statistical parameters, standard deviation and skewness, plotted against the mean reveal different groupings according to the method of deposition. to 43 Total organic carbon (TOC) ranges from 1.5 to 6.5 w eight percent (Figure 12) with a minima at the end of the core (320 yrs. BP) and a maxima at 20 yrs BP. TOC fluctuates horn 20 yrs BP dow n to 215 yrs BP, after which it begins a generally steady decline to the m inim um value previously cited. This decline corresponds to an increase in the amounts of bioturbated sediments present in the core, indicating that bottom waters were sufficiently oxygenated to support life. A decrease in TOC values also suggests a diagenetic effect downcore as TOC is mineralized. Since TOC input is more complicated than organic matter fa l l i n g from the surface, it is a complex and m ost likely not completely reliable proxy to use for productivity. H owever, if TOC does reflect productivity in these cores, high values should occur in colder periods and vice versa. From 320 yrs. BP to 215 yrs. BP, the latter part of the Little Ice Age, there is a definite increase in organic carbon, reflecting increased surface circulation and stronger w inds during glacial times which serve to enhance upwelling and productivity. Carbonate values range from 0.3 to 39 weight percent, but there is only one value higher than 10.5 weight percent (Figure 12). The sharp increase at 320 yrs. BP indicates that the sandy turbidite marking the base of the core is a carbonate turbidite. Carbonate can be a reflection of productivity, dissolution, or dilution, or a combination of all three. In Santiago, it appears to be a function of dilution, as Santiago is not located within the major upwelling centers in the Gulf (Roden and Groves, 1959), is subject to many mass gravity flows, and receives much detrital input. This open-slope is too shallow to be affected by the influence of corrosive Pacific Deep Water (Figure 5). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 44 The upper half of the core is virtually devoid of carbonate, and this m ay be a function of dilution from incoming terrigenous materials. There are 2 other peaks in the carbonate curve, one of 7.3 weight % at 260 yrs. BP and one of 10.5 w eight % at 215 yrs. BP. The former is a turbidite deposit while the latter is a hemipelagic deposit. It is feasible that the hemipelagic peak represents a large proportion of shell fragments and foraminifera tests sw ept across Santiago's narrow shelf and down its steep slope during a large storm event. Core BD - San Juan de la Costa Core BD is centrally located at a depth of 140 m within San Juan de la Costa, a shelf margin area found in the western portion of La Paz Bay (Figure 14). San Juan de la Costa is situated 140 km north of Santiago and is characterized by a w ide peninsular shelf and short gentle peninsular slope. Core BD from San Juan de la Costa is completely bioturbated, lacking laminations, turbidites, or any other type of sedimentary structure (Figure 15). Its distinguishing characteristic is its significant sand percentage found throughout the core with the lowest sand percentage at 53% (Figure 16). San Juan de la Costa's core records 490 yrs in 104 cm, which yields a sedimentation rate in this shelf margin basin of 1.9 m m /yr. This rate parallels sedimentation occurring in the adjacent Alfonso Basin. As previously mentioned, the stratigraphy revealed in x- radiographs shows bioturbated sedim ent the full length of the core. Such high levels of bioturbation at all intervals suggest that bottom R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 4 5 0.7' Shelf = 10 km 100 0.4 - 0.6‘ -see- 2 4 ' 200 LENGTH = 14.5 km v10°. 3 i Figure 14 - Bathymetry and profile of San Juan de la Costa shelf margin locality, which is located in the western area of La Paz Bay. Unlike the Alfonso Basin, the peninsular shelf is wide and the peninsular slope is short. Core BD is located at a depth of 140m (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 0 cm ■ * > • • fetv - A ." / " i -c. . ?;.*•.> v CORE BD 0-30 cm SAN JUAN DE LA COSTA AREA 30 cm Figure 15 - A positive x-radiograph print representative of C ore BD’ s h igh ly bioturbated sedim ent. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Core BD - San iuan de la Costa Sand Percent Facie9 Mean size Organic Carbon Carbonate < i 100 200 300 " I 400 () -. m iln n m i m i 11 n 500 4.54.64.74.84,9 5 5,15,2 1 1.2 1.4 1.6 1.8 20.521 21,52222.523 W eight % W eight % W eight % % structures Key: structures: X— % lam inations O % bioturbated intervals Q- — % turbidites Figure 16 - Sand percent, facies, m ean size, organic carbon, and carbonate are plotted together against age for easy com parison of the San Juan d e la Costa shelf-m argin record. -J 48 waters in this locality have been sufficiently oxygenated to support organisms during the last 500 yrs. This is to be expected in such a shallow area; San Juan de la Costa does not reach depths greater than 200m. The weight percent sand downcore show s high variations within a narrow range. San Juan de la Costa is by far the sandiest of the six study areas, with a range of 53-62 weight percent sand (Figure 16). The mean weight percent sand is 56% despite the core's lack of identifiable turbidites. Weight percent sand reaches a maximum of 62% at 330 yrs BP and a minimum of 53% at 435 yrs BP. The domination of sand within this core is likely a combined function of the shallow depth from which it was collected and the short peninsular slope which allowed coarse material to travel past the shelf-break. Wave action during large storms m ay also have contributed to sweeping sand off the shelf. The mean grain size downcore is 4.8 0 , highlighting the abundance of very fine sand in Core BD (Figure 16). Mean size varies only slightly throughout the length of the core, ranging from 4.5 to 5.25o. There is only one significant decrease in grain size and that is from 4.78 0 at 70 yrs BP to 5.25 0 at 120 yrs BP. Size remains relatively stable until it peaks at 4.5 0 at 330 yrs BP and then falls off again for a good remainder of the core. It is likely that the Little Ice A ge had only a minor effect upon sedimentation in this locality as Core BD at 140 m is just off the edge of the shelf-break and w ould still be capable of receiving coarse sediments even from a partially flooded shelf. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 49 Com pletely hemipelagic fine-size fractions show a platykurtic distribution, peaking fairly sharply in the very coarse silts at 5-5.4 0 (Figure 17A). The distribution is fairly uniform throughout the core, with the only variant being sample BD 22-24 at 120 yrs BP. It has a slightly higher peak, but its peak is still at the same phi value as the other sample intervals. The distribution is positively skew ed towards the coarse grain sizes and no tail is visible in the fine sands. The grouping evident in the statistical plot suggests that the range of depositional conditions present over this time period in San Juan de la Costa varies, probably varies only according to wet and dry years in the Gulf of California (Gorsline, pers. communication) (Figure 17B). The standard deviation ranges from 3.1-3.8 0 , suggesting that these hemipelagic sediments are extremely poorly sorted as a combined result of San Juan de la Costa's morphology, the mixing of flood events, and high wave stirring of the shelf. TOC w eight percent is quite low in Core BD, ranging from 1-1.8 weight percent (Figure 16). Such low organic carbon values are a partial function of the abundance of burrowing organisms which deplete the sediments of a substantial amount of organic matter and the relatively coarse sediments. Another possible biologic effect is the introduction of oxygen into the sediments through the bioturbating activities of burrowing organisms (infauna), causing oxidation of the existing organic matter. Calvert (1987) suggests that the amount of oxygen in bottom waters is not a controlling factor in determining if bioturbated sedim ent or laminations are prevalent, and this issue w ill be discussed in greater detail in the "Synthesis" of this thesis. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. ^ W eight Percent Frequency D istributions Core BD - San Juan de la Costa i i \ • \ i \ i X n iV . o "BD12-14Wt% —B -BD2-4Wt% —♦ — BD22-24Wt% —K— BD32-34Wt% --H— BD42-44Wt% —A—BD52-54Wt% - •• -BD62-64Wt% - *- -BD72-74Wt% - -BD82-84Wt% - A- -BD92-94Wt% B V) 8 Standard D eviation and S k ew n ess vs. M ean Core BD - San Juan de la Costa £ 3.5 ( / ) T J % 3 § S ' ’ ■ 2 & 2.5 V T l 2 T f S 2 1.5 in 1 p r.M .... • . ....... 1 i 0 • I i ! 1 o Standard Deviation - phi 1 D Skewness - phi | i l l : : : ! i i i i ! I ......... i .........i ..........i..........i..........i..........i....... a .... iffi*??.1 ? . . i .... i... ,1. P..- 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 m ean (phi) Figure 17 - A. Weight percent frequency distributions of all the 16-channel grain size data per 10 cm sampled intervals from San Juan de la Costa. There were no turbidites or laminations present in this re-worked core. B. Statistical parameters, standard deviation and skewness, plotted against the mean show the range of depostional conditions present in this locality over the last 500 years. 5 1 Carbonate values are all consistently high and show little variation , with a narrow range between 20.9 and 23.3 weight percent (Figure 16). The carbonate values of San Juan de la Costa are much higher than in any of the other six basins in this study. The reasons for this are two-fold: 1) Core BD is the shallowest core of the suite of cores and is located in a shelf margin basin with a short peninsular slope; therefore, it easily receives coarse shell fragments and foraminifera tests swept off the shelf; and 2) as depth increases, dissolution effects likewise increase; Core BD is at such a shallow depth (140 m) that dissolution does not effect preservation of carbonate in the sediments, making the carbonate values of Core BD good indicators of producitivity. It is also possible that it could simply be shelf accumulation of molluscans, echinoids, and other shell fragments. According to Core BD's record, productivity has stayed fairly high throughout the last 500 years in San Juan de la Costa. Core CP - Alfonso Basin Core CP is located at a depth of 390 m on the eastern edge of Alfonso Basin (Figure 18), which is situated approximately only 35 km north of San Juan de la Costa, in the outer edge of the northwestern area of La Paz Bay. Alfonso Basin is separated from the larger La Paz Basin by a sill at 275 m and the Espiritu Santo trough created by local active faulting. A steep peninsular slope, fairly narrow peninsular shelf, and generally flat basin floor characterize the morphology of Alfonso Basin. Core CP is one of three cores in the suite of cores studied that possesses extremely well-preserved laminations. This R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Profile C-C' 1.3° • in 100 £ 200 2.7‘ 400 CP 500 LENGTH = 14 km 36' Depth in meters Profile C -C "' 200 Espiritu Santo Trough\ A ALFONSO BASIN 600 800 30 20 LENGTH = 3 7 km Figure 18 - Bathymetry and profiles of Alfonso Basin showing the steep peninsular slope and the location of Core CP at a depth of 390 m in the outer rim of the basin. Alfonso Basin, a silled basin within La Paz Bay, is separated from the deeper La Paz Basin by a sill at 250 m and the Espiritu Santo trough (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. preservation results from the core's location in a poorly oxygenated zone, w hich inhibits burrowing organisms from hom ogenizing the sediments (Figure 19). Core CP also contains four turbidites concentrated in the lower quarter of the core ranging in thickness from 0.4-0.8 cm (Table 5). Alfonso Basin's core record extends back to approximately 1100 yrs BP, making its record the second-longest in the suite of cores. The core is 212 cm in length and its sedimentation rate of 1.9 m m /yr is the same as San Juan de la Costa's. X-radiographs of Core CP show three main facies: excellent laminations, slightly bioturbated sediment, and turbidites, though relatively few in number, are also present. Laminations are concentrated in the m iddle third of the core (325-750 yrs BP), with additional peaks at 1000 yrs BP in the base of the core and at 100 and 200 yrs BP towards the core-top (Figure 18). Laminated sections likely correspond to drier periods (decreased precipitation) of upwelling (Kelts and Niem itz, 1979). These very fine laminations have average thicknesses on the order of 1-2 mm, and generally consist of alternating light (biogenous material) and dark (terrigenous material) layers, suggesting the possibility that these could be varved sediments analogous to those in regional deep-sea basins, such as Guaymas Basin (Calvert, 1966). Alfonso Basin's relative proximity to shore combined with the Gulf of California's summer floods permits a variable supply of diatomaceous and terrigenous sediment to heavily infuence deposition and produce these laminations, shown in Figure 20. This inorganic/organic depositional cycle is considered to be annual and a R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 54 anoxic zone Figure 19 - Bathymetry of Alfonso Basin show ing the location of the anoxic zone. Core CP is located at a depth of 390 m within this zone (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Figure 20 - A lfonso Basin's thin diatom aceous lam inations are present in this representative positive x-radiograph print. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 56 function of summer and winter upw elling along both margins of the Gulf (Calvert, 1966). Slightly bioturbated intervals are sparse and distributed periodically throughout the core. The only somewhat substantial interval where they occur is from 655-705 yrs BP (Figure 21). Two lesser peaks are found at 130 yrs BP and 500 yrs BP. Of the four turbidites mentioned previously, only one falls into the 10 cm-interval sampling plan, and its presence at 810 yrs BP is marked by an increase in sand percent and mean size (Figure 21). Downcore weight percent sand is fairly stable, with a range of 0.4- 2 weight percent (Figure 21). The mean weight percent sand for laminated and bioturbated intervals is 0.8%; if all four turbidites are factored in, the average sand percentage increases to 3.4%. Sand percent shows two distinct increases in w eight percent, one from 0.4% at 450 yrs BP to 2% at 600 yrs BP, and one from 0.6% at 950 yrs BP to 1.5% at 1070 yrs BP at the bottom of the core. Still, the overall variability of sand percent is very small, and sand's low contribution to the composition of the core is likely due to Core CP's location on the Gulf-ward side of the basin. A ny coarse material getting washed downslope w ill be preferentially deposited on the nearshore basin slope, or if it makes it down to 400 m, on the basin floor. The mean grain size downcore is 6.88 0 (Figure 21), emphasizing the abundance of finer material which reaches the Gulf-ward slope of Alfonso. Removing the turbidite sample-means does little to change that value, resulting in a slightly finer value of 6.9 0 . These values illustrate the dramatic difference in population inputs w hen R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Core CP - Alfonso Basin Sand Percent Facies Mean size OrganicCarbon Carbonate ii nifc T TTT TTTT 200 • ••••<M (>••••1 1 • } < ,41- 400 < •< « < • i t t •} i — 600 v Ml < fl- 800 1000 ,11.11 1200 ■ ' I I n i l ■UlllllII 11 1111 11,1 0.5 1.5 20 40 60 80 Weight % %structures Weight % i Weight % Key: structures: X — % laminations -0~— % bioturbated intervals □ _.. % turbidites Figure 21 - Sand percent, facies, mean size, organic carbon, and carbonate are plotted together against age for easy comparison of the Alfonso Basin record. —i 58 comparing Alfonso to San Juan de la Costa, also in La Paz Bay. Mean size varies only slightly downcore, falling within a range of 6.7-7.1 0 for most of the core-length. There is only one significant increase in size, and that is from 7 0 at 915 yrs BP to 6.1 0 at 1070 yrs BP. A s the core record approaches the end of the Little Ice Age (at 200 yrs BP), size variations stabilize and a fine mean size hovers around 7 0 , suggesting that coarse material was trapped on the partially flooded shelf. The fine-size fraction distribution of Alfonso reveals a possible bi-modal population (Figure 22A). The distribution is m uch broader than those of Santiago and San Juan de la Costa, due to what appears to be the presence of two different size populations. The major peak occurs in the very coarse silts at 5.8 0 and the minor peak (for the possible second population) is at ~ 8 0 in the fine silts. The distribution is positively skewed towards the coarse grain sizes with an abundance of fine material (Figure 22A and B). A definite tail is visible in the fine sands. The only variant from this distribution is sample CP 184-185 at 965 yrs. BP. It has a very tight peak at 5.2 0 , considerably coarser than the general distribution even though it is part of a slightly bioturbated interval of Core CP, and it displays even stronger positive skewness than the general distribution. It is possible that this sampled interval with high carbonate values represents a fine-grained turbidite that was partially bioturbated by mud-ingesting organisms in the sediment. The x-radiographs reveal CP 184-185 to be slightly denser than the surrounding slightly bioturbated sediment. Standard deviation ranges from 2.1 to 2.45 0 , indicating that the sediments have been poorly sorted (Figure 22B). One main grouping R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Weight Percent Frequency Distributions Core CP - Alfonso Basin 4 5 6 7 8 9 10 phi — e —CP104-105Wt% —B—CP114-115Wt% —♦— CP124-125Wt% — * — CP134-135Wt% --+--CP14-15Wt% — * r - CP144-145Wt% - •- -CP164-165Wt% - ■- -CP174-175Wt% -CP154-155Wt% -CP184-185Wt% - -CP24-25Wt% • - o - •CP34-35Wt% - 1 9 - -CP4-5Wt% — CP44-45Wt% - - □- -CP54-55Wt% - o- -CP64-65Wt% - D- -CP74-75Wt% - o- -CP84-85Wt% - A- -CP94-95Wt% B I C / > S G < n s C o •43 ra V a i T > T J 1 -. ( 0 T 3 e rt Standard Deviation and Skewness vs. Mean Core CP - Alfonso Basin 2.5 2 1.5 1 0.5 -0.5 ' ' o I 1 1 j I i i i j i i r i i i h ~ ' ~ O * 1 i d>0 C C C O O Q O O D O D i I i : o Standard Deviation - phi 1 □ S kew n ess - phi | : i : i i D □ \ | ; i i i ............. j Z 2 5 5 . 4 h _ J ' i i . - .1 - 4 - 1 — 1 j i i i 1 i i i i i i .i ' 6 6.2 6.4 6.6 6.8 7 7.2 m ean (phi) Figure 22 - A. Weight percent frequency distributions of all the 16-channel grain size data per 10 cm sampled intervals from Alfonso Basin. The distributions change according to the mode of deposition, B , Statistical parameters, standard deviation and skewness, plotted against the mean show different groupings according to the method of deposition. L n V O 60 does occur in the statistical plot, with the majority of sam ples lumped in a slight continuum and representing the abundant laminated sections of Core CP. There are two samples that differ from the majority, and these are quite likely the bioturbated turbidite at 965 yrs BP and the turbidite at 810 yrs BP. TOC weight percent downcore is much higher than that of adjacent San Juan de la Costa shelf-margin basin. Organic carbon weight percent values have a wide range from 1.8 to 7.4% with a maxima at the top of the core and a minima at 600 yrs BP (Figure 21). The m ost significant increase in organic carbon is from 1.8% at 600 yrs BP to 6.5% at 400 yrs BP. This period may correspond to a period of higher productivity or may reflect the Little Ice Age, indicating that steeper stream gradients contributed more organic carbon in the form of terrigenous materials. For the most part, the TOC curve is the inverse of carbonate, reflecting the relationship that as organic carbon increases, oxygen is subsequently depleted, and the following production of CO2 increases dissolution, resulting in decreased carbonate values (Douglas, pers. communication). Carbonate values in Alfonso show much variability, ranging from 2.5-21% (Figure 21). The variations are a function of dissolution, dilution, and climatic changes. However, without corrections for downcore dissolution effects, it is hard to be sure what exactly the weight percent carbonate values indicate. A minima is found at 130 yrs BP, while the maxima of 21% is recorded at 600 yrs BP. A lesser peak of 16.5% is found at the base of the core (1070 yrs BP). Fairly low carbonate values from 1020 yrs BP to 800 yrs BP are indiciators of the Medieval R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 61 Warm Period, which endured from approximately A.D. 1000-1200 and resulted in 1° Celsius mean global warming (Cowling et al., 1998; Verschuren, 1998). During this period, wind-driven up welling was slowed, reducing productivity. The highest peak at 600 yrs BP signals the onset of the Little Ice Age. Circulation became more vigorous, increasing upw elling and therefore nutrients in the surface waters, therefore precipitating more carbonate from the water column. Thunnell et al. (1996) found from their sediment trap study in the Gulf of California that higher production results in increased diatoms; lower production (low nutrients) periods are dominated by coccoliths, which form the bulk of carbonate deposited on the sea floor. The high carbonate peak at 600 yrs BP is also characterized by a peak in silica values (Figure 23), supporting this time as a period of high productivity. Core CP is the only core of the suite of cores studied upon which biogenic silica analyses were performed downcore at 10 cm intervals. The analyses yielded fairly substantial amounts of biogenic silica present in the most representative shelf-margin basin (it being a perched margin basin). Biogenic silica is directly related to primary productivity, as it is an important nutrient for phytoplankton which incorporate it into their tests. Therefore, biogenic silica should generally mirror organic carbon. However, biogenic silica tends to dissolve in sea water because sea water everywhere is undersaturated with respect to this form of silica; rapid burial is necessary to preserve the original amount of biogenic silica. Previous studies of the Gulf of California found that north of latitude 26° N all silica is exclusively R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 200 400 (A W 600 to < 800 1000 1200 5 4 3 0 2 1 weight % Figure 23 - Age versus weight percent opaline silica in Core CP from Alfonso Basin. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 63 com posed of diatoms, while south of that parallel radiolarians are predominant but diatoms are still present (Van A ndel, 1964). This is due to a complex interplay between preferential preservation and ecologic occurrence (Douglas, pers. communication). The biogenic silica present in Alfonso Basin (south of latitude 26° N) is mainly from diatoms, w ith som e radiolarians present in the coarse fraction. Biogenic silica w eight percent in Core CP ranges from 0.5-4.4% (Figure 23), with the maxima at 24 yrs BP and the m inim um at 860 yrs BP. Such a high value of silica present near the top of the core m ay be time- related: not enough time has passed for much dissolution to occur. Also, this core interval is bioturbated, so burrowing organisms are introducing sea water into the surface sediments and dissolution should be actively taking place. The lowest silica values are clustered at the bottom of the core, when the Medieval Warm Period affected upwelling. The biogenic silica curve records the onset of the Little Ice Age with increasing values leading to a distinct peak at close to 2%. After this, biogenic silica weight percent varies but overall tapers off and does not begin to increase again until 180 yrs BP. The amount of silica present in Alfonso Basin is favorably influenced by its proximity to major upw elling centers in the Gulf of California and by its high sedimentation rate. Core DB - Loreto Basin Core DB is located at a depth of 385 m on the Gulf-ward side of Loreto area, which is approximately 160 km north of Alfonso Basin and adjacent to the small town of Loreto (Figure 24). This shelf-margin R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 64 s \ 02 ' . 100 / 3 200 i DB CL 5 CO 300 r . : 5 400 km LENGTH = 7 km Figure 24 - Bathymetry and profile of Loreto, which is characterized by an irregular peninsular shelf and a steep peninsular slope caused by local faults. No bank or sill is present as at Alfonso Basin or La Giganta area. Core DB is located on the seaward side of the Loreto channel at a depth of 385 m (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 65 area essentially sits in the Loreto channel and is bordered on the east by Carmen Island. Loreto is distinguished by an irregular peninsular shelf and an extremely steep peninsular slope caused by local faults. Core DB is completely hom ogenized, lacking in turbidites, laminated sediments, or any other sedimentary structures (Figure 25). Intense currents located in the Loreto channel provide adequate oxygen to the bottom waters. Therefore, despite its depth (though it is really too shallow for extremely low oxygen values), it is not situated in a poorly oxygenated zone, so the sediments are subsequently disturbed by infauna. Due to the confluence of the Guaymas cyclonic eddy and the Carmen anticydonic eddy (Figure 6B) in the vicinity of Loreto, upwelling and therefore productivity are enhanced. Loreto's core records 545 yrs in 105 cm. The sedimentation rate in this nearshore shelf-margin area is 1.9 m m /yr, similar to that in Core BD from San Juan de la Costa, the other completely bioturbated core. X-radiography of Core DB reveals thoroughly homogenized sedim ent the complete length of the core. This high amount of bioturbation at all intervals indicates that bottom waters in this area have been adequately oxygenated by strong currents in the Loreto channel during the last 545 yrs to support the presence of benthic and burrowing organisms. The area is not as shallow as San Juan de la Costa, yet it is likely that Carmen Island, whose axis is elongate to that of the Gulf, serves as a barrier between Loreto and the open waters of the Gulf of California. Because of the presence of Carmen Island, Loreto may receive more materials from lateral transport. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. CORE DB 0-24 cm Loreto Figure 25 - A positive x-radiograph print showing Loreto's homogenized sediment. A vertical burrow is clearly visible from approximately 8-12 cm. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 67 The weight percent sand downcore shows considerable variation within a narrow range, from 0.5-5.8% (Figure 26). Average weight percent sand is 2.18%. The variations in sand percent appear almost cyclic, and the reason for this is unknown. The lack of a short peninsular slope and absence of turbidites prevents significant sand contributions in Core DB. Coarse material gets trapped on the moderately wide peninsular shelf and fines are sw ept off the shelf and then rapidly re-deposited downslope in the basin. The mean grain size downcore is 6.67 0 (Figure 26). Mean size maintains stability throughout the 500 yr core record, varying only slightly within a narrow coarse silt range of 6.54-6.87 0 . A decrease in size is seen from 6.56 0 at 335 yrs BP to 6.87 0 at 440 yrs BP. Other than this slight decrease, mean size exhibits little variation in Loreto Basin in the past 500 yrs. Completely hemipelagic fine-size fractions display a somewhat platykurtic distribution similar to that exhibited by San Juan de la Costa, but peaking slightly finer at ~ 6 0 in the coarse silts (Figure 27A). While San Juan's peak is contained primarily below 8%, Loreto Basin's peak reaches 12%. The surface sample of DB 2-4 at 16 yrs. BP shows an even higher and sharper peak than the general distribution, but it is still located at 6 0 . The distribution is positively skewed, w ith an abundance of particles on the finer end, and a small tail is present in the fine sands at 3.8 0 . The extent of bioturbation results in a uniform distribution throughout the core. The statistical plot displays little grouping; rather, Core DB's samples are spread out in a continuum within a narrow range (Figure 27B). Standard deviation values are R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. C o re D B - Loreto 68 O j 1 3 c o H u e 0 X) ra U u 1 6 0 |M o M s c f S 0 ) .8 u ( 3 U U c 0 1 a V C h •a s C O in c o CD CM CO CO C O C O CO CM CM O O O CO O CM CO in J Z to i - C .£ P * S J Z a. 3 * u 3 (A 0 0 * S £ V (•SlX) 3 § V R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. structures: Figure 2 6 - S and percent, facies, m ean size, organic carbon, X— % laminations and carbonate plotted together versus age sh ow th e relative -O % bioturbated intervals contribution changes through tim e i n Loreto. Q — - % turbidites Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. A Weight Percent Frequency Distributions Core DB - Loreto 14 12 10 § a 8 < D C U X . 6 £ P 'S * 4 2 0 3 4 5 6 7 8 9 10 --- 6 - -DB102-104Wt% ------B - -DB12-14Wt% --- • — -DB2-4Wt% --- K — - DB22-24Wt% --+ - - DB32-34Wt% --- * r - - DB42-44Wt% — •- - DB52-54Wt% — o - - DB62-64Wt% — * - - DB72-74Wt% — »■ - DB82-84Wt% — B - - DB92-94Wt% B s < / > 3 I 0 ) XI c o •J3 I Q • p o j X3 X ) XJ Standard Deviation and Skewness vs. Mean Core DB - Loreto 2.5 1.5 0.5 0 T’T T ’T T T T T T ° 4 > o o I I I I | M I I ° « i > ■ 111111111 i oj ...i ■ 1 1 1 1 1 1 1 ■ : □ Skew ness - phi o Standard Deviation - phi EGfa ...! .... i i i | •~ aj i j r ; | ... I i I I . I I ■ H I I II I I I I I I I lnn 6,5 6.55 6.6 6.65 6,7 6,75 6.8 6.85 6.9 mean (phi) Figure 27 - A. Weight percent frequency distributions of all the 16-channel grain size data per 10 cm sampled intervals from Loreto. There were no turbidites or laminations present in this re-worked core. B . Statistical parameters, standard deviation and skewness, plotted against the mean reflect the high degree of homogenization that has occurred in this core. ON NO 70 from 2.2-2A 0 , indicating that not much sorting has occurred in Loreto Basin. Given that it is the most nearshore of all the six shelf-margin basins, this is to be expected. Loreto Basin's uniformity suggests that depositional conditions have remained constant throughout the past 545 yrs, and this can possibly be partially attributed to its isolation from the Gulf of California by Carmen Island. Looking carefully at the many peaks and troughs in the TOC and carbonate curves, it appears that higher organic carbon values correspond to lower carbonate values through the entire length of Core DB (Figure 26). As organic carbon is preserved and oxygen is used up, increased production of carbon dioxide will raise dissolution rates and less carbonate will be evident in the sediments. This appears to be the case in Loreto Basin. TOC values have a narrow range, with a maxima of 5.1 weight percent at 280 yrs BP and a minimum of 3.96 weight percent at 330 yrs BP. This decrease is the m ost significant downcore Core DB. Little variation can be seen due to the hom ogenization of the core by burrowing organisms. The organisms' presence also causes TOC values to be on the low side, yet they are higher than those of Core BD (San Juan), the other bioturbated core, because of Loreto's location in a major upwelling center and a higher clay content (Figure 6A) (Roden and Groves, 1959). The carbonate curve is also influenced by Loreto Basin's location within an upwelling center. Carbonate values are all consistently high, ranging from a minimum of 15.7 weight % at 70 yrs BP to a maxima of 19.4 weight % at 122 yrs BP (Figure 26). This increase is the most significant downcore Core DB. Loreto's core records the beginning of R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. the Little Ice Age, with a distinct peak (18.8 weight % carbonate) at -500 yrs BP, signifying the onset of increased circulation and upwelling. High carbonate values may also be a function of size, as larger shell fragments and foraminifera tests do not get trapped on the shelf and are easily transported down the steep slope to the floor of the basin. There is substantial biogenic carbonate input from surrounding shallow bays and banks as well. Core EB - La Giganta Basin Core EB is the longest gravity core of the suite of cores, with a length of 272 cm. This core is located on the Gulf-ward side of La Giganta area at 560 m (Figure 28). Mangle Bank, with a sill height of -120 m, separates the portion where Core EB is located from the La Giganta fan delta at shoreline. This shelf-margin basin is situated only 20 km north of Loreto, placing it in the sam e major upwelling center (Roden and Groves, 1959). La Giganta's bathymetry consists of an irregular peninsular shelf, a steep slope, and the nearshore San Bruno trough bordered on its Gulf-ward side by the Mangle Bank. Core EB's depth places it second only to Santa Rosalia, and Gulf-ward of the Mangle Bank a wide anoxic zone exists (Figure 29). Therefore, Core EB shows excellent laminations similar to those found in Core CP from Alfonso Basin. La Giganta’ s extensive core record extends back to 1215 yrs BP. The sedimentation rate in this shelf-margin basin is 2.1 m m /yr, slightly higher than all the other basins previously discussed except for Santiago. The presence of hemipelagic input is likely highlighted in La R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. km depth in meters 18' Grganfal !_Fah . D elta J Profile E-E' 3.5' M angle Bank 100 200 2.5' 1300 i- 0- LU Q400 500 600 LENGTH = 14.0 km Figure 28 - Bathymetry and profile of La Giganta, which is characterized by an irregular peninsular shelf, a steep slope, the adjacent San Bruno trough at the base of the nearshore slope and the Mangle bank. Note Core EB's location at a depth of 560 m downslope and offshore from the Mangle bank (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. depth in meters Figure 29 - Bathymetry of the La Giganta shelf margin area, showing the location of Core EB at a depth of 560 m within the anoxic zone (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 74 Giganta, as Core EB is blocked by the Mangle Bank from receiving potentially high amounts of terrigenous input via rivers. X-radiographs of Core EB exhibit fine diatomaceous laminations (Figure 30), a fairly large number of turbidites, and sm all sections of bioturbated sediment. Laminations are prevalent throughout the majority of the core, but especially in the upper third, from 400-122 yrs BP (Figure 31). Bioturbated intervals are scattered intermittently downcore, from 356 to 1166 yrs BP. La Giganta possesses the highest number of turbidites after Santiago. The majority of turbidites are found deeper than 450 yrs BP in Core EB and range in thickness from 0.3-1.6 cm (Table 5). The weight percent sand downcore shows high variation, but it is within such a narrow range as to limit its significance (Figure 31). The average sand percentage for hemipelagic intervals is 0.97%; including the sandier turbidite intervals raises the average sand percentage up to 1.8%. M ost of the sand percentage peaks occur where turbidites are present in Core EB. Sand values are low because the Mangle Bank screens out coarse detrital particles com ing off the shelf. La Giganta Basin's mean grain size is 7.4 a (Figure 31). Removing the turbidites from the equation only yields a slightiy finer mean grain size of 7.45 a. There are numerous peaks and troughs in the mean size curve, but the limited range in which they occur decreases their significance. The decrease in size dow n to 7.48 a at 122 yrs BP corresponds to the end of the Little Ice Age, w hen coarser material was trapped on the partially flooded shelf. A distinct increase in size to 7.25 a at 580 yrs BP signals the beginning of the Little Ice Age, R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 7 5 CORE E B 30-60 cm LA GIGANTA AREA Figure 30 - A positive x-radiograph print from 30-60 cm of Core EB, revealing well-preserved fine laminations characteristic of this core. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without perm ission. 0 200 4 0 0 6 0 0 & < D W ) < 8 0 0 1000 1200 7 7 .17.27.37.47.57.67.7 2 2 .5 3 3 ,5 4 4 .5 0 2 4 6 8 10 p hi Weight % Weight % Figure 31 - Sand percent, facies, mean size, organic carbon, and carbonate plotted together versus age show the relative contribution changes through time for La Giganta. -j o\ 0 0 .5 1 1 .5 2 0 2 0 4 0 6 0 8 0 Weight % %structures Key: structures: X — % laminations O % bioturbated intervals □- — % turbidites Core EB - La Giganta Sand Percent Facies Mean size OrganicCarbon Carbonate TTTT T n T |in i[m T | r i iT |i i n Tin r i i i i i r i i i TTTT TTTT TTTT 1 r t r tm lim liiniiiiiiinilini ■ t . i n i u n i n n l i n i H U U 1L l i U I H 1Jill 77 w hen pro grading shorelines steepened stream gradients, increasing terrigenous flux into shelf-margin basins. Core EB's mean size in the medium silts is by far the finest of all the six shelf-margin basins. Hemipelagic input is em phasized here due to Mangle Bank shielding the basin from local terrigenous input. La Giganta is the only shelf-margin area which displays negative skewness towards the fines (Figure 32A and B). The fine-size fractions show a bi-modal distribution peaking once in the fine silts at ~ 8 0 and again in the coarse silts at - 6.5 0 . There is some variability in the distribution from the m ixing of two different populations. The finer population likely consists of som e clays, w hile coccoliths and nannofossils compose the slightly coarser population (Gorsline, pers. communication). La Giganta and Santa Rosalia are the furthest north and it is possible that they receive some fine suspended load in the form of fine silts or clays from the Colorado River delta. A variable tail in the distribution exists in the fine and very fine sands, from 3.7-4.8 0 and could be caused by foraminifera. Despite the dissolution occurring in La Giganta, foraminifera w ould tend to be a bigger proportion here than in a shallower area w ith more terrigenous input. Turbidite distributions are not distinguishable from the general trend, and that is because La Giganta's turbidites are fine-grained, w ith the sandiest deposit having a sand percentage of 4.7% (Appendix IV). Core EB's standard deviation remains constant at all mean sizes with a value of ~ 2.15 0 , indicating poor sorting in all intervals of the core (Figure 32B). All of the cores for this area contain much re-worked and displaced microfossils (Douglas, pers. communication). The explanation for such R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. O J a, • * - * ' 5 3 Weight Percent Frequency Distributions Core EB - La Giganta B 12 10 8 6 4 2 0 phi — < * — EB116-118Wt% — B— EB126-128Wt% — • — EB136-138Wt% — H — EB 156-158Wt% - - - EB 166-168Wt% — *— EB16-18Wt% - •• -EB176-178Wt% - - EB196-198Wt% - - EB206-208Wt% - - EB226-228Wt% - *- - EB236-238Wt% - - o - - EB246-248Wt% - B - - EB256-258Wt% - - B- - EB36-38Wt% - - - EB46-48Wt% - O - - EB56-58Wt% - - EB6-8Wt% - - EB66-68Wt% - A - - EB86-88Wt% - - EB96-98Wt% Standard Deviation and Skewness vs. Mean Core EB - La Giganta 2.5 / ■ —s ' £ c x Q J 1 1 C ° 0.5 r s o Standard Deviation - phi d Skewness - phi________ > 0 ) T J 6.8 7 7.2 7.4 7.6 7.8 mean (phi) Figure 32 - A. Weight percent frequency distributions of all the 16-channel grain size data per 10 cm sampled intervals from La Giganta. The distribution is slightly bi-modal and reflects high input of fine material. B . Statistical parameters, standard deviation and skewness, plotted against the mean indicate the varied modes of deposition. -j 00 79 uniform sorting in all grain sizes from two different populations is unknown. The statistical parameters of skewness and mean reveal groupings related to the three facies types present in this core. They appear to fall on a line, as do all the statistical parameters of these shelf- margin basins, with turbidites and bioturbated sediments being the end-members and laminated sedim ents clustered in the middle (Figure 32B). Organic carbon values are moderate in La Giganta, with a highly variable TOC curve ranging between 2.2-4.8 weight percent (Figure 31). An inverse correlation between TOC and carbonate is present that is similar to that seen in Loreto Basin's core record. Two maximums of -4.8 weight % occur in the surface sediment and at 540 yrs BP. TOC values fluctuate slightly but hover between 4-4.5 weight % in all intervals of the core except one. TOC drops from 4.4 to 2.1 weight percent between 800 and 656 yrs BP, signalling the onset of the Little Ice Age. Increased upwelling brings more nutrients which can support larger numbers of organisms; these organisms in turn deplete the sediments of organic matter. Constantly higher values of organic carbon from 1213-1026 yrs BP reflect the Medieval Warm Period, indicating slowed mineralization of organic carbon. Production is occurring, but there is less utilization at the bottom, resulting in lower bottom water oxygen values which aid in preserving the organic carbon. Carbonate values vary w idely in Core EB, with values ranging from 0-9.2 weight percent (Figure 31). The significant increase from 1.5 to 8.8 weight percent at 1070-890 yrs BP occurs when the effects of the R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 80 Medieval Warm Period are diminishing and oceanic circulation is picking up. La Giganta's carbonate values are the low est of the six shelf-margin areas studied, despite its location w ithin the same major upwelling center affecting Loreto Basin, created by the combination of the Guaymas cyclonic and Carmen anticyclonic eddies m oving water away from the coast (Figure 6A and B). Perhaps this can be attributed to the Mangle Bank screening out the carbonate proportion that comes from river detritus. A ny of this that is swept off the shelf w ill be deposited in the shoreward San Bruno trough adjacent to the Mangle Bank. Also, the large proportion of re-worked and displaced carbonate sediments cannot be overlooked. Dissolution is high and m ay quite easily have altered the values. Carbonate values w hich come close to reaching 10 weight percent ideally represent the proportion of carbonate precipitated from the water column but m ay be also altered by increased dilution or clay content. Even though carbonate might be lowest in La Giganta relative to the other areas and m uch dissolution is occurring, this area should by no means be characterized carbonate- deficient. Core FF - Santa Rosalia Core FF is the deepest core of the suite of cores at 620 m (Figure 33). It is centrally located within Santa Rosalia, an open-slope area approximately 160 km north of La Giganta. Guaymas Basin, a deep-sea basin known for its diatomaceous laminated sedim ents is located just to the east of Santa Rosalia, in the center of the Gulf of California. Santa Rosalia's irregular bathymetry consists of a very narrow near- R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 5 Km i _____ i depth in meters ST ROSALIA FAN.DELTA - 1 1 2 .1 5 San Marcos 1 0 ' y\lsland - - nun r • I ■ Profile F-F' 0 200 U J Q 600 800 1000 LENGTH =20.5 km Figure 33 - Bathymetry and profile of Santa Rosalia. This shelf margin area is characterized by irregular bathymetry. The peninsular shelf is almost absent and the peninsular slope is composed of steep scarps and gentle surfaces due to active faulting. Profile F-F' shows a narrow submarine terrace at a depth of 40 m. Core FF is located at a depth of 620 m (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 82 absent peninsular shelf and a peninsular slope m ade up of undulating surfaces and steep scarps caused by active local faulting. This northern m ost basin of the six shelf-margin basins studied lies in the most northern major upwelling center in the Gulf of California with southeasterly windes (Figure 6A) (Roden and Groves, 1959). This factor, combined with its depth and location in an oxygen minimum zone (Figure 34), results in diatomaceous laminated sediments similar to Core EB in La Giganta dominating Core FF (Figure 35). Santa Rosalia's core records 1000 yrs in 220 cm, which yields a sedimentation rate in this shelf-margin basin of 2.1 m m /yr. This rate parallels the sedimentation occurring in La Giganta area to the south. Stratigraphy as revealed by x-radiographs shows a core with three main facies: distinct diatomaceous laminations, bioturbated sediments, and scattered turbidites. Three turbidite deposits ranging from 0.7-0.9 cm in thickness are found in the m iddle third portion of Core FF (Table 5) (Figure 35). Bioturbated sediments are concentrated in the core intervals corresponding to 210-487 yrs BP (Figure 36). Diatomaceous laminations are more common than bioturbated sediments in Core FF, with this facies especially prevalent between 116- 257 and 530-807 yrs BP. W eight percent sand downcore varies w idely within a broad range (Figure 36). A maxima of 26 weight percent sand is found at 160 yrs BP, with sand contributions almost reaching that value again at the base of the core. A minimum of 1.3 weight percent sand marks 807 yrs BP. The mean weight percent sand value for hemipelagic intervals is 12.08%; including the turbidite deposits raises that value only slightly R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. t o salKI 'A N D ES / / / ’•’ ''' Figure 34 - Bathymetry of Santa Rosalia shelf margin area showing the location of Core FF at a depth of 620 m within the anoxic zone (modified from Nava-Sanchez, 1997). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 84 80 cm CORE FF 80-108 cm SANTA ROSALIA AREA Figure 35 - A representative positive x-radiograph print from Santa Rosalia. An approximately 1cm thick turbidite is located between 94.5-95.4 cm in the middle portion of core shown here. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Core FF - Santa Rosalia Sand Percent Facies Mean size OrganicCarbon Carbonate TTTT TTTT TTTTJ TTTT TTTT TTTT 11 n i n i ip 111 | »i» i T T T TT T T T T T T T 1 200 •* * _ 400 i < V o o ^ 600 800 I ' 1 1 1000 ± i± J-LL I'll ± 1 1 1 1 1 1 1 ■ i i i i I i i i ilm tliiii liiii li n i r 8 9 101112 Weight % Weight % % structures phi Weight % Key: structures: X % laminations O -— % bioturbated intervals - -- -D- -- - % turbidites Figure 36 - Sand percent, facies, mean size, organic carbon, and carbonate plotted together against age show the relative contribution changes through time for Santa Rosalia, oo U l 86 to 12.72%. Core FFs relatively dose proximity to shore and Santa Rosalia's bathymetry are key factors in this core receiving such high sand input. Core FF is from what could almost be termed a "submarine peninsula," with three surrounding sides dramatically falling off and reaching depth of 900 m in some places (Figure 33). Sand can easily be swept from the shore down the initial steep slope to be deposited on the quasi-plateau where Core FF is located. The average grain size downcore is 6.53 0 (Figure 36). As turbidites make up such a small fraction of the core, removing the turbidite sample-means does little to change this value in the coarse silts, yielding 6.52 0 . This slightly coarser value emphasizes the sand contribution from local terrigenous sources. Santa Rosalia's average grain size is similar to that of Loreto, Alfonso Basin, and Santiago. Mean size varies relatively widely downcore, ranging from 5.1-7.3 0 . The m ost significant decrease in size, from 5.1 0 at 947 yrs BP to 7.3 0 at 807 yrs BP corresponds to the sharpest decrease in weight sand percent. The fine-size fraction distribution of Santa Rosalia show s a distinctly bi-modal distribution, like La Giganta, and even suggests the possibility of multitiple populations being mixed (Figure 37A and B). There is some variability within the distribution as a result of the mixing of 2 or more populations. The anomalous distribution has no distinguishable skewness, with two peaks representing the two populations occurring at ~ 7.7 0 in the medium silts and ~ 6.3 0 in the coarse silts (Figure 37A). Only one of the three turbidites mentioned previously fell into the 10 cm sampled intervals and it can be seen peaking tightly and distinctly higher in the coarser population at R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. W eight Percent Frequency Distributions Core FF - Santa Rosalia 3 4 5 6 7 8 9 10 phi “ * —FF104-106Wt% —Q— FF114-116Wt% — • — FF124-126Wt% — H— FF134-136Wt% --+--FF14-16W t% —Ar-FF144-146Wt% - • - -FF154-156Wt% - m- -FF164-166Wt% - ♦- •FF174-176Wt% -FF184-186Wt% -FF194-196Wt% - - o - -FF24-26Wt% - H- -FF34-36Wt% - -BB- -FF44-46Wt% - - 0 - -FF54-56Wt% - o- -FF6-8Wt% - a- -FF64-66Wt% - -FF74-76Wt% - it- -FF84-86Wt% - -FF94-96Wt% B Standard D eviation and Skew ness vs. Mean Core FF - Santa Rosalia 2 -& m s c £ < u < / I T J C O 'D I Q > 0 ) T 3 r o T ) 3.5 3 o - o standard Deviation - phi p Skewness - phi________ 1 0,5 0 -0.5 5 5,5 6 6,5 7.5 7 mean (phi) Figure 37 - A. Weight percent frequency distributions of all the 16-channel grain size data per 10 cm sampled intervals from Santa Rosalia. B . Statistical parameters, standard deviation and skewness, are plotted against the mean. The distinct bi-modal distribution and statistical groupings show variations in the sedimentary facies of Santa Rosalia. oo 88 ~ 6.2 0. A moderate tail is visible in the fine sands at ~ 3.8 0. The presence of two samples with high peaks in the very fine sands at ~ 4.6 0 suggests multiple populations in Santa Rosalia. Their positively skew ed distributions resemble coarser turbidite deposits, but they are from bioturbated intervals of the core. Closer inspection of the x- radiographs indicate that though these samples are from bioturbated intervals of the core, the said intervals appear darker and m ottled and one shows signs of slumping. This suggests the presence of turbidites that since deposition have been re-worked by the local faulting or slightly homogenized by infauna. Core FF's standard deviation values range w idely from 2.1-3.250, indicating all intervals are very poorly sorted but that the degree of sorting did vary (Figure 37B). Three groupings occur within the statistical plot, with two of these groupings falling into curved continuums. This lends credence to the possibility of multiple populations being mixed in Santa Rosalia. There are two samples that make up one grouping found at the far left of the plot. These are likely the two bioturbated turbidites w hose frequency distribution shows positive skewness and goes against the general trend of the overall distribution in Core FF. TOC weight percent downcore falls into a range similar to that of La Giganta's, with a maxima of 4% at 623 yrs BP and a minim um of 1.1% at 33 yrs BP (Figure 36). There is no apparent relationship between the organic carbon and carbonate curves. TOC values basically fall into two stages consisting each of a decrease, a peak, and an increase as they progress downcore. The trough at 442 yrs BP occurs in the Little R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 89 Ice Age, where increased mineralization of organic carbon and higher bottom water oxygen contents combine to decrease organic carbon values. Carbonate values display moderate variation in Santa Rosalia, with values ranging from 5.2-12.9 weight percent (Figure 36). The carbonate curve looks similar to that of La Giganta's. The variations in Santa Rosalia are a result of dissolution at this depth of 620 m, dilution by incoming detrital materials, and re-transport of materials. A miminum in carbonate weight percent occurs at the base of the core, with a maxima occurring at ~ 650 yrs BP. This increase from the base of the core to ~ 650 yrs BP is the m ost pronounced change in the carbonate curve and the high value of 12.9% at ~ 650 yrs BP signals the transition from the Medieval Warm Period to the cooler Little Ice A ge, where increased upwelling and productivity is reflected by higher rates of carbonate precipitation from the water column. The subsequent variations from 650 to 200 yrs BP mirror the minor climatic variations that occur during glacial times. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 90 Synthesis The six areas in this study are situated along the same shelf margin in the southern half of the Gulf of California, receive similar bottom waters from both Central Gulf Water and Pacific Intermediate Water, have similar sedimentation rates, and most share the same surface waters, those of the Central Gulf Water (Santiago, near the m outh of the Gulf, is influenced by California Current Water, Subtropical Subsurface Water, and Tropical Surface Water). Within this regional setting there are local features unique to each area which shape its depositional history. The areas vary in bathymetry, distance from shore, the amount and com position of biogenic materials, the amount and size of terrigenous input, the preservation rates of inorganic and organic carbon, and the influence of turbidity currents. A drawback in this research that must be noted is the values presented in this paper are w eight percent values; there is sim ply not enough data as of yet to have MAR's (mass accumulation rates). As w eight percent values are highly influenced by sedimentation rates, MAR's would provide a much clearer and accurate picutre and may give a different perspective on what is occurring in these shelf margin areas. It is therefore imperative that the reader understand there is only one core to represent each region in this study, and the parameters (weight percent values) studied in each locality are not well- constrained. Also, chronology is "best estimate" based on few determinations and large amounts of re-worked turbiditic materials. As no concrete dates are available below 10 cm downcore, all correlations drawn from this data are strictly tentative. Peaks are R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 9 1 apparent, however it is possible to be looking at the same events and having more or less time represented w ithin the cores than is show n by these age models. Carbonate While carbonate cycles in many productive areas of the world's seas and oceans have been described numerous times, they have not been previously studied along the shelf margins of the Gulf of California. The carbonate cycles as recorded in cores from western shelf margin basins in the Gulf of California are affected by the basins' proximity to shore and subsequent coarser terrigenous input. Carbonate content shows some variability in all six of the records due to preservation and re-transport. Generally, most of the localities show a pattern of high CaCC>3 content during the onset of the Little Ice Age, commonly thought to reflect increased productivity. This is followed by variation in the carbonate values as a result of varying terrigenous dilution during the glacial. Recent sedim ent trap results in the Gulf of California, however, suggest that carbonate accumulates in lower nutrient regimes and is not necessarily due to rates of production (Thunnell, et al., 1996). If this is indeed the case, then carbonate peaks from the cores studied herein indicate lower nutrient regimes where the presence of a thermocline inhibits the advection of nutrients; this does not mean that the nutrient content of the water is variable, only that the advection of available nutrients is controlled by the physical oceanography of the region. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 92 Also apparent in all cores is a decrease in carbonate associated w ith the M edieval Warm Period. Even though the sill depths for the silled basins and all basin floor depths for open slope basins are above the lysocline, dissolution does play a major role in the carbonate sedimentation pattern of these shelf margin areas. There is enormous carbonate dissolution occurring within all the cores below the shelf and there m ay be dissolution occurring there as well (Douglas, pers. communication). A mixture of up w elling and tropical species of planktonic foraminifera (Globigerina bulloides, Neogloboquadrina dutertrei, Globigerinoides, Globorotalia menardii, and Pulleniatina ) are abundant and preferentially well-preserved at 400 m but they dissolve rapidly with increasing depth, especially in depths greater than 800 m; few tests are present below 1000 m (Nava-Sanchez et al., 1998; Douglas et al., 1998). Dissolution occurs at some rate, whether fixed or variable, as a result of the input and oxidation of organic matter, and the basin floors of Santiago, Alfonso, La Giganta, and Santa Rosalia are at 400 m or deeper. The spike in carbonate values at 400-500 yrs BP (m entioned above) which occurs at the onset of the Little Ice Age can be found in all of the basins except for Santiago (Figure 38). Santiago does n ot record the beginning of this cooler period sim ply because it's core record is dominated by turbidites to such a degree that it only records approximately 300 years in its 129 cm length. An attempt at correlating this event is show n by dashed lines on Figure 38 and substantiates the possibility that the age models m ay cause more or less time to be represented in a section of a given core. Only three of the six cores R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Santiago Core AM San Juan Core BD Weight Percent Carbonate Alfonso Loreto Core CP CoreDB La Giganta Santa Rosalia Core EB Core FF TT T T ]IT T IT ][T T T T im r TTTT TTTT 'Tl'T I | T I T T| Till TTTT TTTT TTTT T T T IITT| IIII| I IT T T T T T ] [T T T T ] 200 4 0 0 60 0 a > W > < 1 80 0 1000 1200 LIU U U [uu l l l l l l l l l l l l l l l l l l l T l l l l l i m U l ll ill m l i n il ii ii III ii I liml mill mini iliiiilimli mini ill u T i i i i I i i i I i i i 1 1 21 2 2 2 3 0 5 10 15 2 0 16 17 18 19 0 2 4 6 8 0 10 20 30 Weigh t% Weight % Weight% Weight % Weight % Weight % Figure 38 - Carbonate weight percentages for all of the localities are plotted together versus age to show regional trends. V O CO 94 possess records that extend back past 800 yrs BP. These three cores, from Alfonso, La Giganta, and Santa Rosalia areas, all show a decrease in carbonate values at approximately 900-1000 yrs BP signalling the Medieval Warm Period, w hen currents and upwelling were sluggish. Overall, San Juan de la Costa and Loreto have higher carbonate contents than any of the other areas (Table 6). This is a function of several factors: 1) San Juan and Loreto are both fairly nearshore areas with bathyme tries conducive to collecting high amounts of coarser materials and cores that are located at depths relatively shallow to those of the other areas, inhibiting dissolution; and 2) skeletal carbonate is an important constituent in shelf sands (and is the most abundant in coarser fractions) along the western side of the central and southern Gulf of California, with carbonate weight percentages commonly reaching and exceeding 20% (Van Andel, 1964). San Juan is by far the sandiest of the six areas, with sand percentages ranging from 53-62%. It would appear that skeletal carbonate makes up an appreciable proportion of the sand in Core BD from San Juan. San Juan is also extremely shallow with a wide peninsular shelf. Loreto, while not possessing noteworthy sand contributions, does have an extremely steep slope and narrow peninsular shelf, allowing the fairly shallow basin to catch coarse materials such as skeletal carbonate. It is also located within a major upwelling center of the Gulf of California. Slopes of the Gulf of California tend to have high concentrations of coarse skeletal remains (diatoms, Radiolaria, and benthic foraminifera) due to greater rates of biogenous material produced near the margins and sorting processes which concentrate coarse material on the slope R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Table 6: Comparison of certain characteristics of Gulf of California shelf margin basins w ith Van Andel's study of basin and slope sediments of the Gulf of California and other m odem productive basins 95 Basins % CaC03 % Organic Carbon Distance from Continent (miles) G ulf of California Shelf Margin Basins: Santiago 5.64 (13) 4(13) 6 San Juan de la Costa 21.94 (10) 1.54 (10) 7.2 Alfonso 9.8 (22) 5.03 (22) 10.6 Loreto 17.21 (11) 4.44 (11) 5.6 La Giganta 3.32 (28) 3.94 (28) 9.4 Santa Rosalia 8.64 (22) 2.73 (22) 6.3 (V an Andel, 1964) Basin 4.6 (30) 2.54 (30) 20-70 Western slope 12.7 (17) 4.22 (15) 5-25 G ulf of Mexico (Stetson, 1953; Trask, 1953) Slope 21.3 (750) 1.02 (750) 35-300 Peru-Chile Trench (Trask, 1961) Upper Slope 0.5 (21) 2.43 (31) 30-60 Lower slope and basin 0.5 (21) 0.63 (51) 60-120 California Offshore Basins (Emery, 1960) Slope 19 (63) 1.6 (30) n /a Basin (summary) 20 (420) 3.9 (80) n /a San Pedro Basin 10.2 (30) 3.6 (14) 2-17 Santa Barbara Basin 11.6 (43) 3.2 (10) 5-20 Santa Monica Basin 8.6 (42) 3.2 (13) 5-25 San Clemente Basin 14.4 (57) 3.2 (4) 40-60 San Nicolas Basin 26.1 (29) 4.5 (4) 60-95 East Cortes Basin 26.1 (27) 3.6 (3) 80-100 Tanner Basin 34.4 (21) 6.5 (4) 100-115 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 96 (Calvert, 1964). San Juan and Loreto areas, w ith average carbonate values of 22% and 17%, respectively, reflect Calvert's observation (Table 6). Alfonso and Santa Rosalia have moderate average carbonate values of 9.8% and 8.6%, respectively (Table 6). Santiago’s carbonate record does not accurately reflect carbonate input into the area; it is nearshore but the majority of the sediments being deposited are in the form of turbidites and this excessive detritus obliterates the carbonate signal. La Giganta has the low est average carbonate value of all six areas, with 3.3%, despite its location within a major upw elling center of the Gulf of California. La Giganta and Santa Rosalia are the deepest cores and may experience increased dissolution. The location of Core EB is shielded from the shore and all incoming detritus from the shelf by the Mangle Bank, so, assuming that the carbonate values recorded in these basins are mainly from coarse skeletal foraminifera, it is to be expected that La Giganta's record w ould show this deficiency. When comparing these six shelf margin areas to previous studies in the Gulf of California and other modern productive basins, they have comparable, or in many cases, higher carbonate values (Table 6). Van Andel (1964) found the western slope of the Gulf of California to have an average of 12.7% carbonate. The average carbonate value for all six shelf margin areas in this study is 11.1%. The six localities can be favorably compared to the California offshore basins, namely San Pedro Basin, Santa Barbara Basin, and Santa Monica Basin, as they are also located relatively close to shore. San Juan and Loreto's carbonate percentages are nearly double that of these three California R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 97 basins, and only Santa Barbara Basin's carbonate percentage is higher than the average for the six shelf margin areas studied. This shows how considerable are the amounts of biogenous material produced along the western margin of the Gulf of California and how much less is the terrigenous material being input into these areas. Organic Carbon and Paleoprodnctivity TOC records for all six of the localities are quite variable. There may be slight errors associated with using TOC as a good indicator of productivity; as previously mentioned, MAR (mass accumulation rate) of carbon would be the only extremely reliable index, due to diagenesis and varying sedimentation rates. Santiago's turbidite-dominated record is not extensive enough to record productivity changes related to the Little Ice Age or the Medieval Warm Period. The other five areas show a general pattern of decreasing TOC values at 400-500 yrs BP indicating increasing surface circulation as the Little Ice Age begins (Figure 39). This more vigorous circulation introduces oxygenated waters to the basin bottom, oxidizing the organic matter. The variability in the records throughout the Little Ice Age can be attributed to enhanced or altered preservation regimes caused by slight shifts in sedimentation rates from glacially-induced increased terrigenous input. An increase in TOC is found after the aforementioned decrease and tentative correlation of this event is shown by the dashed lines in Figure 39. The three longest cores from Alfonso, La Giganta, and Santa Rosalia display increased organic carbon values at ~ 800 yrs BP and this is also shown by dashed lines (Figure 39). This is likely a reflection of R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Weight Percent Organic Carbon Santiago Core AM San Juan Core BD Alfonso Core CP Loreto Core DB La Giganta Core EB Santa Rosalia CoreFF inii uniiiii|iiii|im T TT TIT T TT TIT T T T T T T TT T T T ] III f[ IIII "IIIII1111 T T T T 200 400 S * w 600 v W > < 800 1000 jui uu. mini luuluiiliniliiiiliiiilinilniilliiiliiiliii I n il m liiil iiilliiiilinilm .li n i l i m l m i 3 5 7 3.8 4.2 4.6 5 2.5 3.5 4.5 Weight % Weight % Weight % llll 1200 1.4 1.8 Weight % Weight % Weight % Figure 39 - Organic carbon weight percentages for all of the localities are plotted together versus age to show regional trends. M D 0 0 99 the end of the Medieval Warm Period, which was marked by a sharp warm ing trend at ~ 1200 AD (Zhongwei, 1998). In warmer periods, circulation is sluggish and it is possible that lower bottom water oxygen values m ay create an effective preservation regime. However, at these water depths a small variation in oxygen content w ould not be com pletely effective in controlling carbon consum ption rates (Calvert, 1987). In recent research, it has been debated as to whether anoxia or productivity controls the formation of organic carbon-rich sediments (Pedersen and Calvert, 1990). It may be that increased primary production in the surface layers of the ocean plays a greater role than was originally thought. It has been w idely assumed that organic matter oxidation does not take place in the absence of oxygen, and hence preservation of organic matter occurs in anoxic environments. However, once oxygen has been exhausted, nitrate and sulfate are used by bacteria as oxidants; oxidation reactions continue in oxygen-deficient environments even w hen oxygen is not the oxidant (Pedersen and Calvert, 1990). Pedesen and Calvert (1990) state that oxygen levels in marine waters are inconsequential w hen bacterial metabolic rates in anoxic and oxic environments are approximately the same. Waters in the Gulf of California with low oxygen contents m ay not be the cause of the high organic carbon contents in the sediments but may be the consequence of very high productivity in the surface waters. Van Andel (1964) stated that high organic carbon concentrations indicate high productivity; to use TOC as a measure of surface water productivity it w ould also have to be assum ed that all organic carbon R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 100 input is from the surface waters (Samthein, 1987). Lateral input from basin slopes complicates using TOC as a paleoproductivity proxy. Keeping these constraints in mind, organic carbon can be used as a paleoproductivity proxy if factors controlling its concentration are considered. These factors include water depth, rate of organic production, rate of deposition, and rate of decomposition (a function of the amount of dissolved oxygen in the bottom waters). The Gulf of California, with its primary productivity rate of 1-4 gC /m ^ /d ay, has very high organic carbon contents in its marine sediments comparable to other recent marine sediments such as those from the Gulf of Mexico, the Peru-Chile Trench, and California's offshore basins (Douglas et al., in press) (Table 6). Organic carbon contents in marine sediments from these regions are in the same range as those from the Gulf of California; it is the in the uptake that carbon is exceptionally high (Douglas, pers. communication). Van Andel found the western slope of the Gulf of California to have, on average, 4.22% organic carbon, which compares favorably w ith an average value of 3.61% for the shelf margin areas in this study (Table 6). Such high rates can be attributed to the fact that most of the areas in this study and the majority of slope areas in the Gulf of California fall into the oxygen minimum zone designated by Calvert (1964) as between 200-1200 m and containing < 0.5 m l/L dissolved oxygen, and at some depths < 0.2 m l/L dissolved oxygen. The existence of the oxygen m inimum zone is considered to be biologically controlled (Richards, 1957), w ith oxygen consumed by organisms and settling organic detritus, while its position in the water column is determined by the circulation of the region R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 101 concerned (Wyrtki, 1962). Below 200 m in the Gulf of California, Subtropical Subsurface Water marks the rapid decline in dissolved oxygen, substantiating Calvert's (1964) estimation of the position of the oxygen minimum zone in this region (Nava-Sanchez et al., 1998). Cores from all of the areas except for San Juan de la Costa are located within the oxygen minimum zone and this is reflected by their average organic carbon contents (Table 6). Core BD from San Juan de la Costa is located at 140 m water depth, considerably shallower than the oxygen minimum zone, and so preservation of organic carbon does not occur. Overall, Loreto and Alfonso have the highest average organic carbon content of all the six areas, with values of 4.4% and 5%, respectively (Table 6). Loreto is anomalous as it's core is completely bioturbated despite its location at 385 m water depth, in the supposed oxygen minimum zone. Loreto m ay be in the oxygen minimum zone but the most critical factor remains the level of oxygen; <0.5 m l/L may place the area in the oxygen minimum zone, but m uch biological activity can still occur, as the Core DB indicates. Critical oxygen values, which serve to preserve organic carbon contents and inhibit burrowing, are <0.2 m l/L (Douglas, pers. communication). It is also possible that higher oxygen values may be attributed to the strong current effect in Loreto channel. Possibly the presence of Carmen Island to the east of Core DB, shielding it from the open waters of the Gulf of California, alters the oxygenation regime. If different oxygenation regimes that control the presence of organic materials exist it is difficult to measure productivity from organic carbon concentrations (Cai and Reimers, 1995). Also, Loreto's location within R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 102 a major Gulf of California upwelling center w ill influence its record of organic carbon. Alfonso is the only perched basin of this study (making it the best trap - it has a considerable clay proportion) and its near- anoxic bottom waters preserve the highest average organic carbon value of the six basins. The other 3 areas located within the oxygen m inim um zone (Santiago, La Giganta, and Santa Rosalia) all possess similar relatively high organic carbon values ranging horn 2.7-4% (Table 6). La Giganta is located within the sam e major upwelling center as Loreto, and Santa Rosalia is located w ithin another major upw elling center to the north. Upwelling centers replenish depleted surface waters w ith nutrient-rich waters and so these are areas are bound to record the enhanced productivity in the sediments. Comparing these six shelf margin areas to previous studies in other m odem highly productive regions only em phasizes the w ell- known fact that the G ulf of California is extremely productive (Table 6). The average value of 5% organic carbon for Alfonso Basin is higher than all other basins and slopes in Table 6 w ith the exception of Tanner Basin, which is located directly downstream of Point Conception's nutrients and super-productive waters and has lo w terrigenous input (Robinson, 1997). Even the combined average organic carbon content (3.6%) for all six shelf margin basins is a quite comparable, or in many cases higher, value than other modern productive regions, demonstrating that the Gulf of California is a natural laboratory for studying sedim entology and oceanography. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 103 It is w idely accepted that organic matter is preferentially preserved under near-anoxic or anoxic conditions. Under this assumption, a correlation should exist between sedimentary organic carbon content and the oxygen content of bottom waters. As w as demonstrated above, all basins located within the oxygen m inim um zone have high concentrations of preserved organic matter. However, though Loreto's depth places it within the oxygen minimum zone, x- radiographs of the core reveal it to be thoroughly bioturbated. The oxygen minimum zone is not at a fixed position throughout the entire Gulf of California, and Loreto's hom ogenized sediments indicate that it is not in place here. Calvert's study (1987) in the central Gulf of California found that the organic carbon contents of nearly anoxic laminated sedim ents are undifferentiable from those of oxic bioturbated sediments (Figure 40). Calvert concluded that whatever process is deemed effective in preserving carbon under oxygen-deficient conditions, it does not operate or does not dominate in this region. In other regions explored in Calvert's study, organic carbon content was found to be a function of texture more so than the oxygen content of the waters. In the Gulf of Mexico, the maximum for organic carbon of surface sedim ent is coincident to the oxygen m inim um zone (Calvert, 1987). This observation is misleading w hen sediment texture is considered. Sediments on the outer shelf and the upper slope are coarser- grained and the organic carbon content of this facies is very low. Grain- size decreases in the m odem silts and m uds of deeper waters and consequently the organic carbon content increases to levels R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Shelf Margin Localities Laminated Sediments Mean=4.02% n=47 a I t o •* 4 o u 0 » S i a 9 z Bioturbated Sediments Mean=3,54% n=56 : : 2 3 4 5 6 Organic Carbon (%) Central G ulf of California Laminated Sediments Mean 2,9*/. ( n = 3 6 ) 10 C H a 6 ro l O 0 < _ c # o E D z Hom ogeneous Sediments Mean : 2 , 9 V . ( n = 38 ) 1 2 3 4 Organic Carbon (Vo) 1 5 Figure 40 - Organic carbon (% dry weight) contents of homogenous and laminated sediments from all of the shelf margin localities in this study compared to Calvert's data from the central Gulf of California (from Calvert, 1987). 1 0 4 105 characteristic of this facies (Calvert, 1987). To test the idea of texture influencing organic carbon levels, I compared the organic carbon contents of homogenous and laminated sediments from all six shelf margin areas (Figure 40). The mean organic carbon values of laminated sediments and bioturbated sediments for shelf margin areas are extremely similar, with laminated sediments' value higher by only 0.5%; the mean values in Calvert's (1987) data are exactly the same. The histograms representing data from the shelf margin areas are extremely similar to Calvert's histograms; the only major difference being the increased concentration of organic carbon in the shelf margin basins as compared to the central Gulf of California. In general, the southern basins of the Gulf of California are very fine-grained notwithstanding the nearness of terrigenous sediment sources (Van Andel, 1964). With the exception of La Giganta, all the shelf margin areas are positively skewed with an abundance of particles on the fine end of the distribution. La Giganta, while negatively skewed, possesses the finest mean grain size value. San Juan de la Costa, the only locality w ith low organic carbon content, is much coarser-grained and has a significantly higher sand percentage than the other areas. All of the observations and data combined demonstrate that the preservation of organic carbon in the shelf margin areas is not necessarily controlled by oxygen content of the waters, but occurs as a function of texture. Texture should be added to the factors considered w hen investigating controls on organic carbon concentrations. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 106 Biogenic Silica Dissolved silica in seawater is a crucial nutrient for phytoplankton which incorporate it into their tests. Ninety-nine percent of all silica incorporated by organisms into their skeletons is recycled (Wollast, 1974). Diatoms, Radiolaria, sponges, and silicoflagellates metabolize dissolved silica and secrete it in solid form as amorphous silica, also known as opaline or biogenic silica. Distribution of biogenic silica is influenced by three m ain factors: distance from shore, sedimentation rates, and upwelling. Silica content in sedim ent tends to increase as distance from shore increases. H igh terrigenous sedimentation rates can reduce silica accumulation rates, but these same high rates have the ability to enhance preservation of microfossils. Silica content is also favorably influenced by proximity to upwelling centers. As previously mentioned, seawater is undersaturated w ith respect to biogenic silica so dissolution begins to occur immediately upon the death of an organism. M ost siliceous particles are covered w ith various metallic oxides or organic films by the time they reach the sedim ent (Kunze, 1980). Such coverings on the surface of tests can decrease the surface area available for dissolution, therefore decreasing dissolution itself. It is also logical to assume that as the most easily dissolved tests are removed from the sedim ent by dissolution, the dissolution rate of biogenic silica will slow ly decrease. In this study, it is assum ed that no change in dissolution occurs with depth in the core, an assumption made in previous studies (Hurd, 1973). R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 107 H igh biogenic and total sedimentation rates, which increase during upw elling, help preservation by rem oving biogenic silica from the sediment-water interface. W hile this rapid burial can enhance the preservation of biogenic silica in the sediments, slow sedimentation rates can help to increase dissolution. Greater sedimentation rates also improve the preservation of tests because the concentration of silica in pore waters surrounding each test w ill increase more quickly and the sedim ent at a given depth w ill have less time for diagenesis (Boucher, 1984). Silica data therefore reflects not only productivity but the mix of different siliceous organisms' tests, sedimentation rates, and texture. Rea (1981) found a dependence of the concentration of silica on the presence of oxygen, w ith anoxic environments containing higher concentrations of silica. Increased silica concentrations in anoxic sediments are attributed to higher dissolution rate constants in anoxic environments. Comparison with these previous findings indicates that San Juan de la Costa and Loreto, which are oxygenated environments, should have lower w eight percent silica values than the sediments from Alfonso Basin, Santa Rosalia, and La Giganta. This can clearly be seen in Table 7, where San Juan de la Costa and Loreto possess core-top w eight percent biogenic silica values of 0.11% and 0.73%, respectively. Generally, biogenic sedim ent input is highest in regions of upw elling and terrigenous sedim ent accumulation is highest nearshore. Although the actual percentage of biogenic material in sediments increases as distance from shore increases, areas with the highest rates of biogenic sedimentation occur where there are high R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 108 Table 7: Comparison of average w eight percent biogenic silica from Gulf of California shelf margin basins with California offshore basins Basins Core and sampled interval (cm) Average silica (weight % ) G ulf of California Shelf Margin Basins: (core-tops only) Santiago San Juan de la Costa Alfonso Loreto La Giganta Santa Rosalia n /a Core BD, 0-4 Core CP, 0-1 Core DB, 0-4 Core EB, 0-6 Core FF, 8-10 n /a 0.11 2.88 0.73 16.35 5.85 Alfonso Core CP, 0-205 1.38 California Offshore Basins (Boucher, 1984) San Nicholas San Pedro San Clemente Santa Cruz Santa Monica Santa Barbara Santa Catalina AHF 29622,0-21 AHF 29584,0-33 MANOP, 0-16 AHF 26341,6-32 AHF 25504,4-16 AHF 28283,8-47 AHF 27058,0-14 0.41 0.43 0.18 0.66 0.30 1.90 0.53 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 109 rates of terrigenous deposition (Schwalbach, 1982). Terrigenous material in the western Gulf of California is supplied by peninsular stream s/rivers and the Colorado River delta. According to Calvert (1964), there are appreciable quantities of biogenic opal (Radiolarian skeletons and diatom frustules and fragments) in the central and southern Gulf of California, w ith considerably more biogenic silica on the western margin than the east. N ot only are deep-sea basins like Guaymas rich in diatoms (Calvert, 1966), but significant amounts of diatom s are found in nearshore areas of the western margin. The w estern shelf margin areas also have high terrigenous sedimentation rates and are located close to, or within, major Gulf of California upw elling centers. All these factors combined make these localities excellent study sites for biogenic silica. Core-tops from all cores except Core AM from Santiago were analyzed for weight percent biogenic silica. Because Santiago receives m ainly siliciclastic terrigenous input it was omitted from biogenic silica analyses. Core CP from Alfonso Basin was the only core where biogenic silica analyses were completed downcore at 10 cm intervals. Table 7 shows the weight percent biogenic silica values of the shelf margin basins and selected California offshore basins. Only Alfonso Basin can be compared to the California offshore basins, as an average downcore weight percent biogenic silica value exists for this basin. This average silica value for Alfonso, 1.38%, is eclipsed only by Santa Barbara Basin, which has an average silica value of 1.90% (Table 7). Santa Barbara's high silica value can be attributed to strong upwelling R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 110 and its lack of bioturbation, which, along w ith the high sedimentation rate, contributes to rapid burial of biogenic silica (Boucher, 1984). Alfonso Basin's sill at 250 m does not allow silica-rich Pacific Intermediate Water (PIW) to enter the basin and replace depleted surface waters; this could account for Alfonso's core-top weight percent biogenic silica (2.88%) being considerably lower than La Giganta (16.35%) and Santa Rosalia (5.85%) (Table 7). Core locations from both La Giganta and Santa Rosalia (areas w ith the highest core-top silica values) are deeper than 500 m and have no sills, allow ing PIW to enter the basin and replace depleted surface waters. This replacement of nutrients by PIW is, in its turn, depleted b y subsequent diatoms bloom s, leading to continuous accumulation of silica on the Gulf of California floor, with the Gulf acting as a sink for Pacific silica (Revelle, 1950). La Giganta's unusually high core-top w eight percent silica m ay be a combined function of texture (it w as the m ost fine-grained core studied), transport, and re-working. A large portion of biogenic silica in the Gulf of California consists of finely comminuted or very sm all diatoms; this smaller size-fraction accounts for approximately 10-30 times more of the biogenic silica than the amount of coarse opal present (Calvert, 1964). The location of both La Giganta and Santa Rosalia within major Gulf of California upw elling centers should also contribute to their significantly high biogenic silica values. Plotting water depth against core-top values of opaline silica, carbonate, and organic carbon for all six areas revealed the dependence of silica upon the presence of oxygen in the waters (Figure 41). Silica concentration increases with depth, reaching a maximum at R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without perm ission. All Regions - Core Tops Water Depth vs. SiO^CaCO , and Organic Carbon — • — S i l i c a - - B - - C a r b o n a t e - o - - O r g a n i c C a r b o n 100 200 I £ 300 < 1 > P Q J 4-i £ 500 400 600 700 10 15 20 0 5 25 Weight Percent Figure 41 - Water depth plotted against core-top values of opaline silica, carbonate, and organic carbon for all six areas. 112 approximately 620 m, which corresponds to the base of Gulf Water and the top of Pacific Intermediate Water. As previously mentioned in "Introduction-General Circulation," the top of PIW is marked by a distinct foraminiferal faunal change with the appearance of oxygen m inim um species. Silica's m axim um is coincident with a m inim um in carbonate at depth. This relationship is produced by dissolution of carbonate with depth, which in turn introduces carbon dioxide into the waters. Increased CO2 results in increased pH, preserving silica which is more insoluble in higher pH levels. Organic carbon levels also mark the onset of the oxygen minim um zone with a maximum at approximately 500 m. All the regions studied show trends downcore, but the fact that the cores' trends don't mirror each other is largely a function of depth, as shown in Figure 41. Comparing records of organic carbon and biogenic silica downcore Core CP determined that both organic carbon and biogenic silica show a similar pattern in the 200 yrs. BP; however, in the majority of the core no similar patterns were revealed. Organic carbon and biogenic silica both recorded low values during 800-1000 yrs. BP, signalling the less productive Medieval Warm Period. A distinct peak in biogenic silica at 600 yrs. BP correlates precisely with a very sharp percent sand peak and a significant carbonate peak, indicating the beginning of the Little Ice Age. It is likely that the increased terrigenous volume contributed to preserving biogenic silica. Carbonate values and biogenic silica values are high in this period, reflecting increased upwelling and productivity. But, at the sam e time, organic carbon values are low. Due to all the complexities associated R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. w ith using either organic carbon or biogenic silica as a productivity proxy in the Gulf of California, it is difficult to accurately estimate paleoproductivity changes. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 1 14 Conclusions 1. X-radiograph descriptions and grain size analyses reveal three sedimentary facies present with varying degrees in all six shelf margin areas: diatomaceous laminated sediments, bioturbated sediment, and turbidite deposits. These facies possess distinct grain-size distributions related to their mode of deposition, contributing to a w eight percent frequency curve unique to each individual locality. 2. Carbonate and total organic carbon records for the shelf margin areas record small-scale climatic changes such as the Little Ice Age and Medieval Warm Period (Santiago is the exception due to insufficient core length and excessive turbidite deposits) and exhibit distinct variations reflecting variable biogenic input at generally high levels in the Gulf of California during the last millenium. 3. Loreto's core record taken at 385 m depth should place it in the oxygen minimum zone, how ever the sediments are thoroughly bioturbated and contain high amounts of organic carbon. It is located within an upwelling center with a strong current regime and local topography shields it from the open waters of the Gulf of California, altering the regional oxygenation regime. With differing oxygenation regimes controlling the presence of organic matter w ithin the Gulf of California and lateral inputs into the basins, it is difficult to use organic carbon as a productivity proxy. 4. Mean total organic carbon values of homogenous and laminated sediments in the six shelf margin areas correspond very closely. The preservation of organic carbon in shelf margin areas is not necessarily R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 115 controlled by the oxygen content of the waters but may occur as a function of texture and extremely high levels of primary productivity in the surface waters. With the decreased grain size of silts in deeper waters, organic carbon contents increase to levels characteristic of this facies. 5. Oxygenated basins have lower biogenic silica values demonstrating a dependence of silica concentration on the presence of oxygen. Alfonso Basin’ s biogenic silica record indicates an area of high productivity w ith input variations of finely comminuted or very small diatoms corresponding to small-scale climatic changes. In the deeper La Giganta and Santa Rosalia localities, biogenic silica preservation is enhanced by the influx of silica-rich Pacific Intermediate Water. Significantly high concentrations of biogenic silica w ithin extremely fine-grained La Giganta area suggest that silica preservation is also a function of texture. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 116 References Alvar ez-Borrego, S., and Lara-Lara, J. R., 1991, The physical environment and primary productivity of the Gulf of California: In Dauphin, J. P., and Simoneit, B. R. T. (eds.)/ The Gidf and Peninsular Province of the Calif or nias, Am erican A ssociation of Petroleum Geologists Memoir 47, p. 555-567. Baba, J., C. D. Peterson, and H. J. Schrader, 1991, Fine-grained terrigenous sediment supply and dispersal in the Gulf of California during the last century: In Dauphin, J. P., and Simoneit, B. R. T. (eds.), The Gulf and Peninsular Province of the Californias, American Association of Petroleum Geologists Memoir 47, p. 589-602. Beal, C. H., 1948, Reconnaissance of the geology and oil possibilities of Baja California, Mexico: Geological Society of America, Memoir 31:138 p. Boucher, J. M., 1984, Silica dissolution and reaction kinetics in southern California Borderland sediments: unpublished Masters thesis, University of Southern California, Los Angeles, CA., 149 P- Bouma, A. H., 1964, Turbidites: In Bouma, A. H., and Brouwer, A. (eds.), Developments in Sedimentology: Turbidites, p. 247-256. Bray, N. A., 1988a, Water mass formation in the Gulf of California: Journal o f Geophysical Research, v. 93, p. 9223-9240. Bray, N. A., 1988b, Thermohaline circulation in the Gulf of California: Journal of Geophysical Research, v. 93, p. 4993-5020. Bray, N. A., and Robles, 1991, Physical oceanography of the Gulf of California: In Dauphin, J. P., and Simoneit, B. R. T. (eds.), The Gulf and Peninsular Province of the Californias, American Association of Petroleum Geologists Memoir 47, p. 511-553. Cai, W. J., and C. E. Reimers, 1995, Benthic oxygen flux, bottom water oxygen concentration and core top organic carbon content in the deep northeast Pacific Ocean: Deep-Sea Research, v. 42, p. 1681- 1700. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 117 Calvert, S. E., 1964, Factors affecting distribution of laminated diatomaceous sediments in the Gulf of California: In T. H. van Andel and G. G. Shor (eds.)/- Marine Geology of the Gulf of California, American Association of Petroleum Geologists Memoir 3, p. 311-330. Calvert, S. E., 1966, Origin of diatom-rich varved sediments from the Gulf of California: Journal of G eology, v. 74, p. 546-565. Calvert, S. E., 1987, Oceanographic controls on the accumulation of organic matter in marine sediments: In J. Brooks and A. J. Fleet (eds.)Marine Petroleum Source Rocks, Geological Society of America Special Publication N o. 26, p. 137-151. Cowling, S. A., R. H. W. Brashaw, and M. T. Sykes, 1998, The importance of the M edieval Warm Period and the Little Ice A ge for species com position of Scandinavian temperate forests, International Global Project (IGBP) - Past Global Changes (PAGES) Open Science M eeting Abstracts. Curray, J. R., and Moore, D. G., 1984, Geologic history of the m outh of the Gulf of California: In Crouch, J. K., and Bachman, S. B. (eds.),Tectonics and Sedimentation Along the California Margin, Pacific Section Society of Economic Paleontologists and Mineralogists, v. 38, p. 17-36. DeMaster, D. J., 1979, The marine budgets of silica and Si^2: unpublished PhD. dissertation, Yale University, N ew Haven, CT. Donegan, D., and Schrader, H., 1982, Biogenic and abiogenic components of laminated hem ipelagic sediments in the central Gulf of California: Marine Geology, v. 48, p. 215-237. Dorsey, R. J., K. A. Stone, and P. J. Umhoefer, 1997, Stratigraphy, sedimentology, and tectonic developm ent of the southeastern Pliocene Loreto basin, Baja California Sur, Mexico: In M. E. Johnson and J. Ledesma (eds.), Pliocene carbonates and related facies flanking the Gulf of California, Baja California Sur, Mexico, Geological Society of America Special Paper. Douglas, R., T. DeDiego, D. Gorsline, and E. Nava-Sanchez, in press, M odem 'black shales" in the Gulf of California, Geological Society of America Abstracts for Fall 1998 Annual Meeting. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 118 Emery, K. O., I960, The sea off Southern California: John W iley and Sons, N ew York, 366 p. Femandez-Barajas, M. E., M. A. Monreal-Gomez, and A. Molina-Cruz, 1994, Thermohaline structure and geostrophic flow in the Gulf of California, during 1992: Ciendas Marinas, 20 (2): 267-286. Hausback, B. P., 1984, Cenozoic volcanic and tectonic evolution of Baja California Sur, Mexico: In Frizell, V. A., Jr. (ed.), Geology of the Baja California Peninsula, Padfic Section Sodety of Economic Paleontologists and Mineralogists, v. 36, p. 219-236. Hurd, D. C., 1972, Factors affecting solution rate of biogenic opal in seawater: Earth and Planetary Sdence Letters, v. 15, p. 411-417. Hurd, D. C., 1973, Interactions of biogenic opal, sedim ent and seawater in the central equatorial Pacific: Geochimica et Cosmochimica Acta, v. 37, p. 2257-2282. 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(eds.), The Gulf and Peninsular Provinces of the Californias, American A ssodation of Petroleum Geologists Memoir 47, p. 403-423. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 119 McCave, I. N T ., and Jarvis, J., 1973, Use of the M odel T Coulter Counter in size analysis of the fine to coarse sand: Sedimentology, v. 20, p. 305-315. Molina-Cruz, A., 1986, Evoludon oceanografica de la boca del golfo de California: Anales del Instituto de Ciendas del Mar y Limnologia, Universidad N adonal Autonoma de Mexico, 13 (2): 95-120. Nava-Sanchez, E. H., 1997, M odem fan deltas of the west coast of the Gulf of California, Mexico: unpublished PhD. dissertation, University of Southern California, Los Angeles, CA., 229 p. Nava-Sanchez, E. H., D. S. Gorsline, R. G. Douglas, K. Rikansrud, and T. DeDiego, 1998. Paleodimatic/paleooceanographic studies of Gulf of California margin basins, Baja California Sur, Mexico, International Global Project (IGBP) - Past Global Changes (PAGES) Open Sdence Meeting Abstracts, p. 97-98. Pedersen, T. F., and Calvert, S. E., 1990, Anoxia vs. productivity: what controls the formation of organic-carbon-rich sediments and sedimentary rocks?: American A ssodation of Petroleum Geologists Bulletin, v. 74, no. 4, p. 454-466. Pride, C., R. Thunell, and E. Tappa, 1998, Evaluating productivity proxies: results from the Gulf of California, in review: M icropaleontology. Rea, R. L., 1981, The flux of dissolved silica from South San Frandsco Bay sediments: observations and models: unpublished Master's thesis, University of Southern California, Los Angeles, CA., 88 P- Revelle, R. R., 1950, Sedimentation and oceanography - survey of field observations, pt. 5 of The 1940 E. W. Scripps cruise to the Gulf of California: Geological Sodety of America Memoir 43, 6 p. Richards, F. 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A., R. L. Fisher, and F. P. Shepard, 1964, Bathymetry and faults of the Gulf of California: In T. H. van Andel and G. G. Shor (eds.),Marine Geology of the Gulf of California, , AAPG Memoir 3, p. 59-75. Sam thein, M., K. Winn, and R. Zahn, 1987, Paleoproductivity of oceanic upwelling and the effect on atmospheric C 02 and climate change during deglaciation times: In W. H. Berger and L. Labeyrie (eds.), Abrupt Climate Change, Dordreicht (Reidel), p. 311-337. Schwalbach, J., 1982, A sediment budget for the northern California continental borderland: unpublished Master's thesis, University of Southern California, Los A ngeles, CA., 212 p. Stetson, H. C., 1953, The continental terrace of the western Gulf of Mexico - its surface sediments, origin, and development, part 1: The sediments of the western Gulf of Mexico: Papers in Physical Oceanography and Meteorology, Massachusetts Institute of Technology and W oods Hole Oceanographical Institute, v. 12, no. 4, p. 1-45. Strickland, J. D. H., and Parsons, T. R., 1968, A practical handbook of seawater analysis: Fisheries Resource Board of Canada, Bulletin 167. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 121 Thunell, R., C. Pride, P. Ziveri, F. Muller-Karger, C. Sancetta, and D. Murray, 1996, Plankton response to physical forcing in the Gulf of California: Journal of Plankton Research, v. 18 (11), p. 2017- 2026. Trask, P. D., 1953, Chemical studies of sediments of the western Gulf of Mexico: part 2, The sediments of the western Gulf of Mexico: Papers in Phys. Oceanog.raphy and Meteor.ology, M assachusetts Institute of Technology and Woods H ole Oceanographical Institute, v. 12, no. 4, p. 49-120. Trask, P. D., 1961, Sedimentation in a m odem geosyncline off the arid coast of Peru and northern Chile: International Geological Congress, 21st, Copenhagen, Denmark, Repts., v. 23, p. 103-118. Van Andel, T. H., 1964, Recent marine sedim ents of the Gulf of California: In T. H. van Andel and G. G. Shor (eds.), Marine Geology of the Gulf of California, , American Association of Petroleum Geologists Memoir 3, p. 216-310. Verschuren, D., 1998, A 1800-yr. record of lake level and climate from equatorial E. Africa with tropical equivalents of the 'Medieval Warm Period' and 'Little Ice Age,' International Global Project (IGBP) - Past Global Changes (PAGES) Open Science Meeting Abstracts, p. 129-130. Wollast, R., 1974, The silica problem: In E. D. Goldber, (ed.). The Sea, Vol. 5, p. 359-392. Wyrtki, K., 1962, The oxygen minimum in relation to ocean circulation: Deep-Sea Research, v. 9, p. 11-23. Zhongwei, Y., 1998, Comparative analysis o f climatic scenarios in M edieval times between China and Europe, International Global Project (IGBP) - Past Global Changes (PAGES) Open Science M eeting Abstracts, p. 137. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. APPENDIX I - Table of % carbonate, organic carbon, silica, and grain siz e param eters per 10 cm intervals for h em ip elagic sam p les depth in mean standard age (yr) core (cm) %C03 OrgC % Si diameter deviation skewness kurtosis Core AM Santiago Basin 22.26 7 0.00 6.44 n/a 6.37 2,34 0.76 1.36 47.69 17 0.00 4.60 n/a 6.54 2.26 0.60 1,34 72.18 27 0.31 3.38 n/a 6.78 2,18 0.33 1.33 99.84 37 0,00 4.83 n/a 6.67 2.21 0.47 1.33 129,09 47 0.31 3,76 n/a 6.12 2,47 0,93 1.40 158.66 57 0.79 6.10 n/a 6.99 2,13 0.05 1.36 190.46 67 7.01 3.80 n/a 6.66 2,22 0.48 1.34 215.90 77 10.44 5.01 n/a 6.61 2,23 0.53 1.33 240.70 87 3.57 4.03 n/a 6.69 2,21 0.45 1.33 264.86 97 7.31 3.24 n/a 6.99 2.13 0.06 1.36 288.71 107 2.93 2.50 n/a 6.59 2,24 0.55 1.33 309.70 1 1 7 1.37 2.70 n/a 6.82 2,17 0,28 1.33 321,46 127 39.22 1.57 n/a 4.63 3,67 1,12 1.34 Core BD San Juan de la Costa Basin 15.79 3 21.42 1.66 n/a 4.74 3.56 1.13 1.36 68.42 1 3 22.48 1.66 n/a 4.78 3.52 1.13 1.37 121.05 23 22.72 1.63 n/a 5.25 3.11 1.13 1.43 173.68 33 21.16 1.63 n/a 4.73 3.57 1.13 1.36 226,32 43 21.91 1.71 n/a 4.80 3.51 1.13 1.37 278,95 53 20.93 1.83 n/a 4.72 3,58 1.13 1.36 331.58 63 21.28 1.47 n/a 4.52 3,78 1.12 1.32 384,21 73 21.79 1.34 n/a 4.84 3,47 1.13 1.37 436.84 83 22.55 1.40 n/a 4.90 3,42 1.14 1.38 Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. depth in age (yr) core (cm) %C03 OrgC 489.47 93 23.18 1.03 Core CP Alfonso Basin 2.63 0.5 11.36 6.38 23.68 4.5 8,25 7.36 76.32 14.5 9.76 6.96 128.95 24.5 2,58 6.77 181.58 34.5 8.33 6.22 234.21 44.5 7.22 6.44 286.84 54.5 4.60 5.88 339.47 64.5 7.33 2.71 392.1 1 74,5 5.67 6.50 444.74 84.5 11.31 5.42 497.37 94.5 10.27 3.27 550.00 104.5 12.42 2.96 602.63 1 14,5 21.28 1.79 655.26 124.5 10.75 2.32 707.89 134.5 9.47 6,05 760.53 144.5 12.95 5.05 810.53 154.5 8.64 5.01 863.16 164.5 10.85 3.12 915.79 174.5 10.82 6.27 965.79 184.5 8.05 4.93 1018.42 194.5 7.17 5.21 1068.95 204.5 16.43 4.08 Core DB Loreto Basin 15,87 3 17.01 4.61 68.78 1 3 15.76 4.78 121.69 23 19.40 4.47 mean standard % Si diameter deviation skewness kurtosi n/a 4.75 3.55 1.13 1.36 2.875 n/a n/a n/a n/a 4.377 7.03 2.13 0,00 1.37 3.089 7.01 2.13 0.03 1.37 2.725 7.04 2.13 -0.02 1.38 0.610 7.07 2.12 -0.06 1.39 0,786 7.09 2.12 -0.09 1.39 0.863 7,08 2,12 -0.07 1.39 1.108 6.96 2.14 0.10 1.35 1.372 7.01 2.13 0.03 1.37 1.390 7.03 2.13 -0.01 1.38 0.924 6.76 2.18 0.36 1.33 1.042 6.87 2.16 0.22 1.34 1.881 6.90 2.15 0.17 1.34 1.426 7.01 2.13 0,03 1.37 1.480 6.94 2.14 0.12 1.35 0.873 6.85 2.16 0.24 1.34 0.588 6.81 2.17 0.29 1.33 0.471 7.01 2.13 0.02 1.37 0.627 7.02 2.13 0.01 1.37 0.634 6.72 2,19 0.40 1.33 0.689 6.52 2,27 0.62 1.34 0.636 6.14 2.46 0.92 1.40 n/a 6.54 2,26 0.61 1.34 n/a 6.55 2.25 0.59 1.34 n/a 6.63 2.23 0.51 1.33 depth i n m ean standard age (yr) core (cm ) % C03 O rg C % S i diameter deviation skewness kurtosis 174.60 33 17.57 4.46 n/a 6.65 2,22 0.49 1.33 124 CO c o -O ' CO -O ' CO c o 0 3 T -- CO CO CO CO CO CO CO CO ID - T — T — - - - 1 0 5 ID CD C M C M C M CD C M -O- ID CD -O ' C M CO CO O O o’ o " O O o " O o ’ i o * C V 1 - o - CD O CO 0 0 0 0 C M CM CM CM CM C M CM CM CM C M C M CM CM C M C M LO 0 3 CD O 0 3 0 3 N - C M CD CD CD r - CD r - O CO C D * CO CD CO C D * CD CD r - r - - re re re re re re re rt re C c c e c C C c CD t ^ - CD -O ' C M r - I D ID CO o C3 -O ' -O' o CM - - CO -O ' c o C O * ■O' -O' -0 " -O' -O - CO o c o o f - C O LO r-~ C M 1 — C M r-~ ID ID r-- C D C M ID CD C D C D c o ’ c o ’ 03 ID c tn C O CO C O C O C O C O C O ca 1^ -O' C D CD C D 03 o re c re M l 5 CM CO ID CD re _ 1 -0" ID -0 - CO C M , — O 0 3 CD o CO CD 0 3 CM -O ' CD C M ID CM CD CO CD CO 0 3 < 1 3 CO CM CM CO CO -O ' -O ' LO O U C M C D -O' ID 00 -O' O ID CD ID -O ' h - 00 03 -O' C O CO "O' LD - ’ -~ - - - r - C O CD - o - C O C O O - 0 - C M LD ID CO CO C D C O LD C O 00 ■ 0 - o ’ o ’ 1 o ’ 1 o * o ’ « O 1 o 1 o ’ o ’ o ’ i -O' C M C M C M CO C O C M C M - o - C M - - - — -— ' — -— - — -— -— C M C M C M C M C M C M C M C M c m’ C M CO CD CD o r - - 0 0 o r - - -O ' CO CM CO -O ' CD CM CM ID c o r - r - r a r e r e r e r e r e r e r e r e r a c o ' c ' c ' c c c c c c c C D C M C O 00 C O 03 -O- 00 T — C M o O C D 03 C O CO ID C O -O' -O' ■ M - -O' C O -O' -o- -O' C O -0- ■ M - T - CM t" - CO CD CM -O ' 0 3 LD O CD CM 00 0 3 CD -O ' o 00 CO CO T“ o’ o "O' -o- -O ' CM o ’ -o- co’ r^ - r - - t-~ r - CM CO -O ' LD CD 0 0 0 3 o - - -O ' CM 03 CD -O ' T — 0 0 LD 03 CD ID CO O 0 0 CD -o- 03 CO C M 03 CD CM 03 c o c o 03 ■ -O ' CM CD *— CD O ID o -O ' 03 -O ' CM CM CO CO -O ' •O ' -O ' ID R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 578.58 127 1.55 4.26 n/a 7.25 2.12 -0.32 1,47 617.87 137 0.44 2.91 n/a 7.46 2.13 -0.60 1.60 656.22 147 2.77 2.17 n/a 7.53 2.15 -0.69 1.65 702.99 157 1.92 2.45 n/a 7.67 2.18 -0.84 1.74 749.77 167 3.23 2.38 n/a 7.50 2,14 -0.65 1,63 depth i n m ean standard age (yr) core (cm ) % C03 O rg C % S i diameter deviation skewness kurtosis 125 ( DO Ni n ^ f r - O t ' < t N n o) n t - co co co w v n T - a 3 o n i o o o v n o ^ n n n c o n v c o n ^ O T - t-' - co O I D N t O T - f f i O O N C M ( O a ) C O ' < r o O ' < t o o o o o o o o o o o o o o o o o o o o o CM O • m - cn o o o IflM-inCMM-r-rfWOO t— i— i— t— -— ■ C M i— C M C M C M C M C M C M C M C M C M CM CO CM CM 0 5 CO CM CO M - CM •M’ i — t — CM CM CM CM CM CM CM O N O V C O N l O O t n CM CM CM CM CM CM CM CM C M V C O f f l i - C M S C O O O C O l O M - l O C M l D K V O C O r~ — r~- i— t— r-— r— r— c o cm o LO 05 o co CO CO C M C O O O 1 — t^ . CD CO CD C D S M C M O M O > - 0 ) t -(0 CV(ONO)O t- ( O N t - (O CO CO (£) N N co’ CO co' a c CO c co c CO CO V V C C CO CO C C CO CO C C CO ~ C CO C CO C CO co c c CO CO c c co co 1: CO CO cT CO C CO C m co m- M in in co c\i N S 0 5 M V M - O C li co ' < 3 - 0 0 S CO CO C M O co r - m M ’ i— o ^ "M- -O- 'O- 1— CO o m- c m m o a> 05 Ifl O Ifl r* i— CM CO C M C M CO C O * 1 - M N N f f l i n C O t o N C M _ W r - O ) O) CM T — CO CO CO CO C M 05 co f'- t" - O C O C M O C O O O C D O O i n O OD OO NS rt cll in O CO M " M CM i — N - t — - O M -m ocoM -m aicM coin’- ' f i - O ' t NM-COnCMWCOCBCOT-NCKinc-CO C J ) 0 3 C J ) 0 ) ( 0 ( 0 0 5 S 0 ) ( 0 ' " O O O C M c ^ — c— r — c — c — N 0 0 0 5 O c - C M C 0 M l O < 0 t- t- t-CMCMCMC MCM CMC M c n CO co N i n i fi i f i i n m i n i n i n i n i f i i o i n i f l i n ’- C J C O M ’ l f l C D N O O l O ' - C M C O c f ■ M - T - m co c o ' c o " 05 -M- N - CO C O C M C M O ) N M " t- oO O l f l V c - O N l O C M O T f 0 5 CO CM 05* CO CO* 0 5 CO N CM N ^— CO i — CO 0 5 0 5 O O i — i — CM c C O CO u. t i ll) u , o < J • c f c o c o o m m w o s o v o N B N N ^ 05 N ct W O CO ui o E 'l; 05 N- C O N r-( 0' -in 00 05 MO «^ «^ ^ ^ C M N n c o n M ' f ' - f> in(010 R eproduced with perm ission o f the copyright ow ner. Further reproduction prohibited without perm ission depth i n m ean standard age (yr) core (cm ) % C03 O rg C % S i diameter deviation skewness kurtosis 717.49 155 9.03 2.84 n/a 6.78 2.18 0.34 1.33 126 w O ) ■ * 3 " C M C M ■ o - ■ ’ 3 - ^r - ' 3 " 'r — T — T — T _ C O N - C M O ) cn C M C O cn cn O i o’ 1 -r_ o ’ o ’ CM CM e' in C M m en in C M in C V I C M C M C M C O C M T — cn T — o C M o C M C M o ■ * - o N - in C O * in c o ’ a co CO CO co CO "c C C C C C o CM m CM 00 CO CO C O CM CM cn o CO CM CM CM c m ’ CO o in CO CO h- CO N. 0 0 in 00 CM c o ’ 0 0 c o ’ i n’ in in in in m m C O e- 00 cn o T — i— T— T - i— C M C M CM o r- • < 3 - — cn m C O o 00 C O co o ’ o r- ■ < 3 - C O o in o cn 0 0 00 cn cn cn R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. A PPENDIX II - T able o f % carbonate, organic carbon, and grain size param eters per 10 cm intervals for turbidite sam p les depth in mean standard age (yr) core (cm) % C03 OrgC diameter deviation skewness kurtosis Core AM Santiago Basin 33.39 1 1 n/a n/a 6.41 2.32 0.73 1.36 38.16 13 n/a n/a 6.52 2.27 0.63 1.34 47.69 1 7 0 4.6 6.54 2.26 0.6 1.34 53.42 1 9 n/a n/a 6.64 2.22 0.5 1.33 57.87 21 n/a n/a 6.26 2.39 0.84 1.38 65.82 25 n/a n/a 6.62 2.23 0,52 1.33 72.18 27 0.31 3.38 6.78 2.18 0.33 1.33 75.99 29 n/a n/a 6.49 2.28 0.65 1.35 82.35 31 n/a n/a 5.92 2.59 1.02 1.43 94.44 35 n/a n/a 5.99 2.55 0,99 1.42 99.84 37 n/a n/a 6.67 2.21 0.47 1.33 110.65 41 n/a n/a 6.62 2.23 0.52 1.33 145.95 53 n/a n/a 6.44 2.3 0.7 1.35 195,87 69 n/a n/a 6.66 2.22 0.48 1,33 203.50 73 n/a n/a 6.56 2,25 0.58 1.34 220.99 79 n/a n/a 6.77 2.18 0.34 1.33 230.84 83 n/a n/a 6.7 2.2 0,43 1.33 234.34 85 n/a n/a 6.75 2.19 0.37 1.33 253.42 91 n/a n/a 6.69 2.2 0.44 1.33 264.86 97 7.31 3.24 6.99 2.13 0.06 1.36 273.45 101 n/a n/a 6.94 2.14 0.12 1.35 288,71 107 2,93 2.5 6.59 2.24 0.55 1.33 295.07 109 n/a n/a 6.78 2.18 0.34 1.33 296.66 111 n/a n/a 6.71 2.2 0.42 1.33 127 Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. depth in age (yr) core (cm) % C03 OrgC 300.16 113 n/a n/a 306.52 115 n/a n/a 309.70 117 1.37 2.7 315.74 119 n/a n/a 318.92 121 n/a n/a 321.46 123 n/a n/a 321.46 125 n/a n/a 321.46 127 39.22 1.57 321.46 128.5 n/a n/a Core BD San Juan de la Costa Basin -100% bioturbated Core CP Alfonso Basin 810.53 154.5 8.64 5.01 939.47 179.5 n/a n/a 1058.42 202.5 n/a n/a 1085.79 208.5 n/a n/a Core DB Loreto Basin -100% bioturbated Core EB La Giganta Biisin 58.47 1 3 n/a n/a 75.77 17 5.51 3.35 449.95 97 0.89 3.38 575.30 125 n/a n/a 578,58 127 1.55 4.26 580.45 129 n/a n/a 617.87 137 0.44 2.91 618.80 139 n/a n/a 925.16 205 n/a n/a 942.00 209 n/a n/a mean standard diameter deviation skewness kurtosis 6.69 2.2 0.44 1,33 6.74 2.19 0.38 1.33 6.82 2.17 0.28 1.33 6.6 2.24 0.55 1.33 6.66 2.21 0.47 1.33 6.69 2.21 0.45 1.33 5.91 2.6 1.02 1.43 4.63 3.67 1.12 1.34 4.62 3.67 1.12 1.34 6.81 2.17 0.29 1.33 6.83 2.16 0.27 1.33 6.7 2.2 0.43 1.33 6.72 2.19 0.41 1.33 6.95 2.14 0.11 1.35 7.32 2.12 -0.42 1.51 7.28 2.12 -0.36 1.49 7.07 2.12 -0.06 1.39 7.25 2.12 -0.32 1.47 7.25 2.12 -0.31 1.47 7.46 2.13 C O o 1 1.6 7.51 2.14 -0.66 1.63 7.35 2.12 -0.45 1.53 7.49 2.14 -0.64 1.62 depth i n m ean standard age (yr) core (cm ) % C03 O rg C diameter deviation skewness kurtosis C ore F F Santa Rosalia Basin 129 to C O C - - C O C O c o T— y— 1— C O o > N- o’ o’ o ■ m - C M ■ ' 3 ' C M C O O J C M C M to C O 0 5 C O C O C O c o ’ C D T f r-- C 3 c to C O ta c to 05 05 CO O CO O to q to T — c m ’ C O T— - o to LO I*- R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. APPENDIX III - T abic of w eight percents and class m eans for hem ipclagic and turbidite sam ples Class Means 9,83 9.50 9,17 8,83 8,50 8,17 < 4 phi (> 63 mm) 7,83 7.50 7.17 6,83 6,50 6,17 5.83 5,50 5,17 4,83 4.50 4,17 >4 phi 3,83 3,75 Core AM Santiago Basin AM 6-8 1,3 1.6 2,6 3.0 3.4 4.0 4.6 4,7 5,6 6.1 7.7 9.1 10,0 10.6 10.2 7.4 3.4 0.0 0.0 0,0 AM 10-12 1.5 1.8 2.8 3,3 3.9 4,3 5.0 4.9 5,3 5.9 7.1 8.3 9.3 9.5 9.6 8.1 4.6 1.4 0,6 0.0 AM 12-14 1.6 2.1 3,2 3.8 4,5 5.0 5,6 5.5 5,9 6.2 7,3 7.9 9.1 8.3 8,3 5.0 3.9 0.3 0,0 0.0 AM 16-18 1.8 2.1 3.1 3.8 4.5 5.1 5.3 5,6 6.2 6.1 7.3 8.0 8.6 9.1 9,3 5.7 1.4 0.0 0,0 0.0 AM 18-20 2.1 2,6 3.8 4.3 5,0 5.3 5.7 6.0 5.8 6,1 7.0 7.4 8.4 8.8 7.9 4.5 1,7 0.0 0.6 0.0 AM 20-22 1.5 1.7 2.5 3.0 3.5 3.9 4.6 4.6 5.4 5.7 6.8 7.8 8.6 9.0 9,7 8.1 3.3 0,9 1.2 0.0 AM 24-26 1.9 2.4 3.6 4.2 4.8 5.4 6.0 6.0 6.4 6.4 7,5 7.9 8.4 7.0 7,4 4.3 0.9 0,0 0.0 0,0 AM 26-28 2.2 2.6 3.7 4.4 5.1 5,6 6,1 6.5 7.1 7,5 8.5 8.6 8,0 7.4 6.5 3.9 0.8 0.0 0.0 0.0 AM 28-30 1.9 2,3 3.4 3,9 4.6 5.1 5.5 5.7 6.3 6.7 7.7 7.8 8.1 7.8 6.3 4.8 1.9 1.8 0.0 1.4 AM 30-32 1.3 1,6 2,4 2.8 3.2 3,5 3.8 4.1 4.7 4.7 5.7 7.0 7.7 8.4 9.7 7.3 7.4 2.2 3.5 3.0 AM 34-36 1.2 1.5 2.3 2.6 3.1 3.4 3.6 3.8 4.0 4.3 5.3 6.2 7.9 9.1 11.0 11.8 8.2 1.1 0.0 0.0 AM 36-38 2.1 2.6 3.8 4.3 4.9 5.2 5.5 5,7 6.4 6.4 7.5 8.0 8.6 8.2 7.1 5,3 2.3 1.7 0.7 0.0 AM 40-42 2.0 2,4 3.5 4.1 4.7 5.1 5.9 5.7 6.2 6.4 7.4 7.7 8.5 7.3 8.0 6.8 2.9 1.0 0,0 0.0 AM 46-48 1.2 1.6 2.5 2.9 3.6 3.9 4.5 4.9 5.6 6.2 7.3 8.1 9.0 8.8 8,9 6.9 1.6 2.4 2.4 3.6 AM 52-54 1.7 2.1 3.1 3.8 4.3 4.8 4.9 5.6 6.4 6.4 7.3 7.8 8.0 7.1 7.6 5,2 2.9 1.0 2,6 0.0 AM 56-58 2.1 2.6 4.0 4,5 5.3 6.0 6.5 7.6 7.7 8.6 10.7 12,0 7.1 6.4 4.5 1.9 0.0 0.0 0.0 0.0 AM 66-68 1.3 1.7 2.7 3.0 3.6 4.3 5.0 5.4 6,4 7.6 9.1 10.0 10.7 10.0 9.3 5.0 1.8 0,4 0.0 0.0 AM 68-70 2.1 2.6 3.7 4,3 5.0 5,6 6.2 6,5 6.5 6.8 7.7 7.6 8.0 7.4 7.5 4.4 1.5 0,8 0.0 1,5 AM 72-74 2.0 2,5 3.7 4.1 4.6 5.3 5.5 6.0 6.4 6.8 7.6 8,6 8.1 7.6 6.5 4.0 1.6 0.4 0.0 1.4 AM 76-78 1.7 2.2 3.4 3.8 4.5 4,9 5.4 5.8 6.6 6.6 8.1 8.2 9.5 9.1 8.3 4.4 1.9 0,0 0,0 0,0 AM 78-80 2.3 2,8 4.2 4.7 5.3 5.8 6.0 5.9 6,5 6,6 7.3 8.1 8.6 8.5 5.9 4.0 1.4 0.0 0.7 0.0 AM 82-84 2.1 2.7 3.7 4.3 4.9 5.3 5.6 6.0 6.7 6.8 7.6 8.2 8.4 7.9 8.1 4.0 2.1 0.4 0.7 0.0 AM 84-86 2.2 2.8 3.9 4.5 5.0 5.5 5.6 6.1 6.1 6.5 7.5 8.5 8.8 8.8 6.9 5.5 2.9 0.3 0.0 0.0 AM 86-88 1.9 2,3 3,5 3.8 4.3 4.8 5.3 6.1 6,6 7.1 8.2 9.3 9.8 9.6 9.1 3,7 1.5 0.3 0.0 0.0 AM 90-92 2.0 2.5 3,7 4.3 5.0 5.3 5.9 5.7 6.5 6,8 7.8 8.1 8.5 9.4 7.2 3.3 1.4 0.4 0.0 0.0 AM 96-98 2.7 3.3 4.8 5.4 5.9 6.2 6.8 6.5 6.9 7.1 7.8 7.8 8.3 7.2 5,7 3.3 0,4 0.0 0.0 0,0 AM 100-102 2,7 3.2 4.6 5,1 5.5 5,8 6.3 6.2 6.5 6.8 8.0 8.2 9.1 8.0 6.6 3,9 1.1 0.0 0,0 0.0 AM 106-108 2,2 2.6 3.8 4.2 4,8 5.0 5.4 5.7 5.6 6.3 7.1 7.5 8.1 7.6 7.6 6.1 2,2 0.0 0.6 0.0 AM 108-110 2.4 3.1 4.4 4.9 5,4 5.4 5.8 5.9 6.3 6.2 6.9 7.7 8,3 7.1 7.9 5,2 2.3 0.3 0,0 0,0 AM 110-112 2,4 2.8 3.0 4.5 5.1 5.3 5.7 5.4 6.3 6.3 7.6 8.0 8.6 7,9 6.8 5.4 1.8 1.3 0.0 0,0 AM 112-114 2,3 2.8 3,8 4.4 5.0 5,3 6.0 6.1 6.3 6,6 7.5 7.8 7.7 6.9 7.0 4.3 2,9 1.0 1.4 0.0 O J O Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without perm ission. Class Means 9.8 9.5 9.2 8.8 8.5 8.2 7.8 AM 114-116 2.1 2.9 4.1 4.4 5.0 5.2 5.9 AM 116-118 2.6 3.0 4.2 4.7 5.0 5.5 6.0 AM 118-120 2.2 2.7 3.9 4.3 4.7 4.9 5.3 AM 120-122 2.4 2.9 4.1 4.5 5.1 5.4 5.9 AM 122-124 2.2 2.7 3.8 4.4 5.0 5.3 5.7 AM 124-126 1.5 1.9 2.9 3.2 3.6 3.8 4.3 AM 126-128 0.6 0.7 1.0 1.2 1.3 1.4 1.6 AM 128-129 0,5 0.6 0.9 1.0 1.1 1.2 1.5 Core BD San Juan de la Costa Basin BD 2-4 0.5 0.6 0.8 0.8 0.9 1.0 1.2 BD 12-14 0.6 0.6 0.9 0.9 1.0 1.1 1.3 BD 22-24 0.8 0.9 1.2 1.3 1.4 1.5 1.8 BD 32-34 0.6 0.6 0.9 0.9 1.0 1.1 1.3 BD 42-44 0.6 0.7 0.9 0.9 1.0 1.2 1.3 BD 52-54 0.7 0.7 0.9 0.9 0.9 1.0 1.2 BD 62-64 0.3 0.4 0.5 0.5 0.6 0.7 0.8 BD 72-74 0.7 0.8 1.0 1.0 1.2 1.3 1.5 BD 82-84 0.8 0.9 1.1 1.2 1.3 1.4 1.6 BD 92-94 0.7 0.7 1.0 1.0 1.0 1.2 1.4 Core CP Alfonso Basin CP 4-5 2.9 3.6 5.1 5.1 5,5 6.1 6.6 CP 14-15 2.7 3.5 4.9 5.1 5.6 6.0 6.7 CP 24-25 3.0 3.6 4.8 5.0 5,7 6.1 6.6 CP 34-35 2.9 3.7 5.1 5.5 5.9 6.4 6.5 CP 44-45 2.8 3.4 4.7 5.3 6.6 6.5 6.8 CP 54-55 3.4 3.7 4.9 5.1 5.6 6.1 6.9 CP 64-65 2.8 3.4 4.5 4.8 5.4 5.9 6.4 CP 74-75 2.8 3.4 4.6 5.0 5.8 6.1 6.8 CP 84-85 3.0 3.8 5.1 5.3 5.9 6.4 6.7 CP 94-95 2.6 3.2 4.6 4.9 5.5 6.1 6.5 CP 104-105 2.7 3.3 4.6 4.8 5.3 5.6 6.7 CP 114-115 2.4 2.9 4.4 4.8 5.3 6.1 6.4 CP 124-125 2.7 3.3 4.7 5.1 5.8 6.0 6.4 < 4 phi (> 63 mm) 7.5 7.2 6.8 6.5 6.2 5,8 5.5 5.2 4.8 4.5 4.2 3.8 3.8 5.7 5.8 7.2 7.8 8.6 8.5 8.6 7.4 4.6 0.7 0.4 0,0 0.0 6.4 7.0 6.7 7.7 8.1 8,6 7.3 6.9 4.1 1,4 0.0 0.0 0.0 5.6 6.6 7.1 7.9 8.3 9.0 7.7 6.4 2.8 1,8 0.4 0.7 1.5 6.1 6.2 6.9 7.5 8.3 8.3 7.1 5.9 4.0 0,4 0.4 0.7 1.4 5.9 6.4 6.8 7.7 8.4 8,3 7.1 6.2 4.6 2.1 0.0 0.0 0.0 4.4 4.7 4.8 5.3 5.9 6,4 6.4 5.2 3.2 2.1 0,3 0.0 0.0 1.7 1.6 1.9 2.3 2,6 3.0 3.2 3.1 2.5 1.6 0.3 0.0 0.0 1.6 1.8 1.9 2.5 2.9 3.2 3.3 3.3 2.3 3.2 0.1 0.6 0.0 1.5 1.5 2.0 2.6 3.5 4.6 5.4 6.4 6.6 3.3 0.8 0.2 0.0 1.4 1.7 2.1 3.0 3.9 5.0 5.9 6.5 5.6 2.4 0.1 0.2 0,0 2.1 2.6 2.9 4.0 4.9 6.9 8.0 10.1 10.0 6.1 1.0 0.5 0.0 1.5 1.6 1.9 2.6 3.5 4.7 5.0 5,9 5,4 2.5 0,1 0.0 0.0 1.4 1.7 2.1 2.9 3.8 4.8 5.8 6.8 5.8 3,0 0.2 0,0 0.0 1.2 1.5 1.7 2.5 3.1 4.4 5.2 6.2 7,3 4.2 0.4 0.4 0.3 0.9 1.2 1.4 2.0 2.7 3.7 4.7 6.0 5.9 4.5 ' 0.9 0,1 0.2 1.7 2.0 2.2 3.0 3.0 5.1 6.0 5.7 5.3 2.7 0.7 0,0 0.0 1.8 1.9 2.2 3.0 3,6 4.8 5.6 6.0 6.0 3.9 0.1 0.0 0.0 1.5 1.8 2.0 2.7 3.4 4.1 4.9 5.2 5.1 3.7 0.8 0.2 0.0 6.7 6.8 7.0 7.5 7.9 8.9 7.9 7.2 2.9 1.2 0.0 0.8 0.0 6.3 6.5 7.0 7.7 8.1 8.6 8.5 8.7 3.0 0.8 0.0 0.0 0.0 6.6 7.6 6.8 7.6 8.0 7.8 8.1 7.5 4.3 0.6 0.0 0.0 0.0 7.2 6.5 6.7 7.5 7.9 8.2 8.3 7.5 3.8 0.2 0.0 0,0 0,0 6.4 7.5 7.3 7.5 8.4 8.2 8.2 6.3 3,0 0.6 0.0 0.0 0.0 6.6 7.2 7.2 7.6 7.9 8.8 8.4 6.8 1.8 0.2 1.2 0.0 0.0 6.2 6.9 6.8 7.7 7.9 8.8 8.3 8.0 3.9 0.8 1.1 0.0 0.0 6,5 7.1 6.8 7.5 7.5 9.0 8.5 8.5 3.3 0.4 0.0 0,0 0.0 6,4 7,1 6,5 7.1 7.5 7.7 7.0 6.8 5.2 1.2 0.4 0,8 0.0 6.3 6.5 6.6 7.3 8.0 7.7 6.4 7.0 4.0 1.1 0.4 1.5 3,0 6.2 7.5 6.9 7.5 7.9 8.3 7.3 7.2 4.4 0,8 0.4 0.0 1,6 6.2 6.7 6.8 8.0 8.6 8.9 9.1 4,9 4.8 0,9 0,0 0.7 0.0 6.9 7.2 6.9 7.6 8,1 9.2 8.2 6,2 3.4 0.9 0.4 0.0 0,0 I — 1 OJ h-1 >4 phi Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Class Means 9.8 9.5 9.2 8.8 8.5 8.2 7.8 < 4 phi (; 7.5 7.2 CP 134-135 2.7 3.2 4.5 4.7 5.3 5.9 6.3 6.7 6.4 CP 144-145 2.7 3.4 4.8 5.1 5.5 6.2 7.0 6.2 6.2 CP 154-155 2.1 2,6 3.7 4.2 5.0 5,5 6.1 6.3 6.9 CP 164-165 2.8 3.4 4.6 4.8 5.5 5.9 6.7 6.6 6.9 CP 174-175 3.1 3.5 4.8 4.8 5.4 5.6 6.2 6.4 7.2 CP 179-180 2.2 2.7 3.9 4.4 5.3 6.0 6.4 6.4 5.9 CP 184-185 2.5 2.9 3.9 4.2 4.8 5.4 5,6 5.2 6.0 CP 194-195 2.8 3.3 4.3 4.4 4.9 5.3 5.4 5.7 6.7 CP 202-203 2.3 2.8 4.0 4.4 5.1 6.0 6.2 6.5 6.1 CP 204-205 1.5 1.8 2.5 2.7 3.0 3.4 3.7 3.5 3.4 CP 208-209 2.2 Core DB Loreto Basin 2.5 3.8 4.1 4.7 5.5 6.1 6.6 6.7 DB 2-4 1.1 1.3 1.9 2.3 3.0 3.9 5.2 6.0 7.1 DB 12-14 1.2 1.4 2.3 2.7 3.6 4.7 5.8 6.4 7.6 DB 22-24 1.4 1.7 2.6 3.1 3.7 4.6 5.6 6.4 7.3 DB 32-34 1.4 1.8 2.8 3.4 4.1 5.1 5.8 6.3 7.3 DB 42-44 1.2 1.5 2.4 3,0 3.8 4.8 5.9 7.2 7.4 DB 52-54 1.3 1.6 2.4 2,9 3.7 4.5 5.7 6,3 7.1 DB 62-64 1.4 1.8 2.7 3.2 4.0 5.0 5.8 6.2 7.5 DB 72-74 1.6 2.1 3.1 3.7 4.3 5.0 5.6 5.8 7.2 DB 82-84 2.0 2.4 3.6 4.1 5.1 6.1 7.1 7.4 8.0 DB 92-94 1.4 1.8 2.7 3.3 4.2 5.3 6.5 7.0 8,1 DB 102-104 1.6 2.0 3.0 3.6 4.4 5.4 6.5 7.3 7.9 Core EB La Giganta Basin EB 6-8 2,6 3.4 4.9 5.8 7,0 7.8 7.9 7.5 7.4 EB 12-14 2.5 2.9 4.2 5.3 6.3 7.3 8.4 8,7 8,5 EB 16-18 3.2 3.8 5,2 6.1 7.2 7.8 8.5 8.9 8.1 EB 26-28 3.4 4.2 6.2 7.5 8.7 9.2 9.4 8.6 8.5 EB 36-38 2.7 3.5 5.0 6.2 7.5 8.6 9.7 8.6 9.2 EB 46-48 2.6 3.3 4.7 5.7 6,8 7.8 8.7 8.6 8.6 EB 56-58 3.1 3.9 5.6 6.2 7.0 7.8 8.6 8.7 8.6 EB 66-68 3.0 4.0 5.6 6.7 7.6 8.6 8.5 8.7 8.9 EB 76-78 3.8 4.9 6.8 8.1 9.2 9.9 10.0 10.5 7.6 53 mm) 6.8 6.5 6.2 5.8 5.5 5.2 4.8 4.5 4.2 >4 phi 3,8 3.8 6.7 7.6 8.5 8.7 9.2 8.0 4.5 0.4 0,0 0.0 0.0 6.4 7.1 7.1 7.7 7.7 7.3 3.8 1.8 0.4 1.5 1.5 7.4 7.8 8.7 9.1 9.1 7.3 5.4 1.0 0,0 0.8 0.0 7.1 8.0 8.2 8.6 9.0 7.8 3.2 0.2 0.0 0.0 0.0 7.0 8.1 8,5 9.5 9.3 6.6 3.0 0.4 0.0 0.0 0.0 6.8 7.4 8.2 9.6 8.8 7.7 5.4 1.5 0,0 0,7 0.0 5.7 6.4 7.3 8.8 9.2 11.5 7.2 2.2 0.6 0,0 0.0 6.2 7.0 7.0 7.5 7.6 6.3 4.2 1.4 0,4 4,3 4.3 6.1 6.8 7.3 7.7 7.0 7.0 4.8 0.9 1.1 0,7 0.0 3.7 4.8 6.6 9.6 13.4 18.6 12.6 3.0 0.0 0.0 0.7 6.4 7.7 7.9 8.7 8.0 7.3 4.7 2.6 0.0 0,7 0.0 7.8 10.1 12.3 12.8 10.7 8.5 3.2 0.6 0.3 0,0 0.0 8.1 9.6 9.9 10.4 9.0 7.3 3.7 0.7 0.0 0,0 0.0 8.1 9.5 10.1 10.6 8.8 8.9 3.1 1.1 0.4 0.7 0.0 7.6 9.2 10.2 9.9 8.7 7.6 3.7 0.9 0.0 0.7 0.0 8.0 9.2 10.4 10.5 9.6 8.2 3.3 0.5 0.3 1.4 0.0 8.0 9.6 10.8 11.3 8.7 8.1 3,2 0.5 0.7 0.7 0.0 7.9 9.4 9.7 10.2 7.2 7.0 4.1 2.3 1.6 0.8 1.6 6.9 8.7 10.1 11.3 9.9 8.3 3.4 0.7 0.4 0.0 0.0 8.3 9.9 10.3 9.5 6.5 4.7 1.5 0.0 0,0 0.0 1.5 8.3 10.0 10,2 11.1 8,7 6.8 3.7 0.4 0,0 0,0 0.0 7.8 9.0 9.2 9.8 8.1 8.0 3.8 1.7 0,4 0,0 0.0 7.0 7.1 6.6 5.8 4,2 2.7 3.7 2.0 4.3 1,6 0,0 7.1 7.4 6.8 5.6 3.5 3.2 2,1 2.1 1.1 2.3 1.5 7.8 8.0 7.8 7.4 4.5 2.4 0.8 0.2 0.0 0.0 0.0 7.1 7.0 5.9 4.8 2.5 1.9 1.5 1.1 0.8 0.8 0.0 8.1 8,0 7.4 6.0 4.1 2.3 1.4 0.2 0.4 0,0 0.0 8.1 8.3 8.1 6.8 5.2 4,1 0.6 0.9 0,0 0.0 0.0 7.6 8.0 6.9 6.2 4.2 2.6 0.8 1.7 0.8 0.8 0,0 7.3 7.9 7.4 5.8 3.7 3.2 1.0 0,8 0,4 0.0 0.0 6.4 6.1 5.5 4.9 2.9 1.6 0.7 0.6 0,0 0,0 0,0 O J N O Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Class Means 9.8 9.5 9.2 8.8 8.5 8.2 7.8 EB 86-88 3.1 4.0 5.7 6.8 8.0 8.7 9.2 EB 96-98 2.9 3.1 4.6 5.6 6.7 7.5 8.4 EB 106-108 3.4 4.5 6.4 7.2 8.2 8.2 8.6 EB 116-118 2,9 3.7 5.2 6.4 7.5 8.6 9.1 EB 124-126 2.1 2.5 3.6 4.5 5.5 6.8 8.0 EB 126-128 2.3 3.1 4.6 5.7 7.0 8.0 8.8 EB 128-130 2.6 3.3 4.7 5.6 6.8 7.6 8.5 EB 136-138 2.1 3.0 5.0 6.9 9.0 10.2 10.8 EB 138-140 3.6 4.6 6.5 7.5 8.6 9.6 10.0 EB 146-148 3.5 4.3 6.1 7.2 8.6 9.2 9.9 EB 156-158 3.9 4.8 6.7 8.0 9.4 10.1 10.6 EB 166-168 3.3 4.2 5.9 7.3 8.4 9.8 10.2 EB 176-178 3.6 4.4 6.1 7.2 8.5 9.4 9.6 EB 186-188 3.1 3.9 5.6 6.8 8.1 8.8 9.3 EB 196-198 3.7 4.7 6.5 7.6 8.4 9.5 9.2 EB 204-206 3.2 4.1 5.9 6.8 7.9 8.5 8.6 EB 206-208 3.2 3.8 5.2 6.2 7.2 7.9 8.9 EB 208-210 3.4 4.3 6.3 7.6 9.1 10.1 9.9 EB 216-218 3.2 4.2 6.2 7.3 8.4 9.3 9.6 EB 226-228 3.8 4.8 6.9 8.5 10.2 11.2 11.6 EB 236-238 3.3 4.2 5.9 7.5 8.9 10.6 11.3 EB 246-248 3.3 4,2 5.9 6.8 7.9 9.4 9.4 EB 256-258 3.9 4.8 6.5 7.8 9.5 10.0 9.9 EB 266-268 3.2 4.1 5.7 6.7 8.2 9.1 9.9 Core FF Santa Rosalia Basin FF 6-8 1.9 2.3 3.2 4.0 4.9 5.4 5.9 FF 14-16 1.8 2.2 3.0 3.7 4.4 4.9 5.3 FF 24-26 2.3 2.8 3.9 4.9 5.7 6.3 6.8 FF 34-36 1.6 1.9 2.7 3.2 4.0 4.7 5.2 FF 44-46 2.2 2.8 3.9 4.9 6.1 7.1 7.8 FF 54-56 2.9 3.5 5.0 5.9 7.4 7.9 8.4 FF 64-66 1.6 1.8 2.7 3.4 4.3 5.0 5.7 FF 74-76 2.1 2.7 4.0 4.8 5.7 6.6 7.0 < 4 phi (> 63 mm) 7.5 7.2 6.8 6.5 6.2 5,8 8.7 7.6 6.9 6.8 6.1 4.8 8.9 9.0 8.6 9,0 8,4 7.5 9.0 8.6 7.8 7.8 6.8 5.3 8.8 8.1 8.3 8.4 7.4 6.8 8.8 9.2 8.8 9.8 9.2 7.7 8,6 9.0 8.2 8.8 8.0 7.5 8.1 9.3 8.4 9.0 8.1 7.3 9.2 9.2 8.2 7.7 6.4 5.4 9.4 8.9 7.2 7.0 5.6 4.1 9.2 8.4 7.0 7.1 6,2 5.3 8.8 7.8 7.0 6.8 5.7 4.9 9.7 7.8 7.0 6.6 6.0 4.8 9.0 8.1 7.2 7.3 6.2 6.0 9.1 8.7 8.0 8.1 7.3 5.5 8.5 8.6 7.4 7.4 5.7 5.1 7.8 7.9 7.8 7.0 6.8 5.7 8.6 8.7 7.5 7.7 6.8 5.2 9.9 8.1 7.0 6.1 4.9 3.6 8.9 8.6 7.4 7.6 6.5 5.4 10.3 7.9 6.3 6.1 4.8 3.6 9.8 6.8 6.0 5.4 4.4 3.3 8.9 7.4 6.8 6.7 5.8 5.1 9.7 8.6 7.4 6.9 5.4 4.1 9.2 8.3 6.7 6.6 5.6 5,3 5.8 6.2 5.7 6.2 6.5 6.3 5.5 5.6 5.5 6.5 7.2 6.7 6.8 6.4 6.4 6.8 6.7 7.4 5.6 5.9 5.5 5.9 6.6 6.5 8.3 7.8 7.6 8.2 8,0 7.9 7.5 7.7 7.1 7.5 6.9 6.3 5.4 5.6 5.7 6.6 7.2 7.4 6.9 7.3 6.5 7.6 7.6 7.6 5.5 5.2 4.8 4,5 4.2 >4 phi 3.8 3.8 3.4 2.2 0.9 3,3 1.3 0,0 1.7 4.5 3.4 0.3 0.0 0.4 0,0 0.0 3.7 1.8 1.3 0.9 0.4 0.0 0.0 3.8 2.2 1.1 0,2 0.0 0.0 0.0 5.3 4.7 1.7 0.4 0.0 0.8 0.0 4.5 2.8 0.8 0.0 0.4 0.9 0.0 4.7 3.0 0.4 0.2 0.4 0.9 0.0 2.9 1.9 0.4 0.2 0,5 0.0 0.0 2.6 1.8 0,6 0.2 0,0 0.0 1.8 3.6 2.3 0,8 0.4 0.0 0,0 0.0 2.6 1.5 0.3 0.0 0,5 0,0 0.0 3.4 2.1 0,9 0.2 0.4 0.8 0,0 3.6 1.8 0.7 0.2 0.4 0.0 0.0 3.7 1.7 0.9 0.2 0.0 0.0 0.0 3.1 1.8 1.2 0.2 0.4 0.0 0.0 4.2 2.3 0.5 0,7 , 1.5 1.0 0.0 4.1 2.5 1.1 0,2 1.3 0.9 1.7 2.1 1.3 0.0 0.2 0.5 0.9 0.0 3.0 1.7 0.5 0.2 0.9 0.0 0,0 2.0 0.8 0.1 0,0 0,0 0,0 0.0 2.7 2.6 1,2 1.0 1.2 3,3 0.0 3.2 2.3 1,4 1.6 0.8 2.3 0.0 2.2 1.0 0.5 0.0 0.0 0.0 0.0 3.4 2.0 1.2 0.9 0.0 1.7 1.7 4.8 3.0 2.6 1.5 0.9 0,6 0.0 5.7 4.4 2.7 2.7 0.3 0,0 1.1 5.5 4.4 2.4 0.5 1.8 1.4 1.4 5,2 3.7 2,5 1.6 1.4 0.0 0.0 5.8 3.2 2,2 0,6 0.0 0,0 0.0 4.5 2.1 1.5 0.6 0.0 0.0 0.0 7.0 4.6 3.6 1.8 0.6 0.6 0.0 6.2 4.6 1.9 1.6 0.7 0.0 0.0 Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Class Means 9.8 9.5 9.2 8.8 8.5 8.2 7.8 F 84-86 2.1 2.6 3.7 4.7 5.6 6.3 6.6 F 94-96 2.1 2.4 3.4 4.3 5.2 6.1 7.2 F 104-106 2.3 3.0 4.4 5.4 6.3 7.3 7.9 F 108-110 1.9 2.2 3.1 3.8 4.8 5.5 6.4 F 114-116 2,6 3.3 4.7 5.8 6.6 7.5 8.6 F 124-126 2.5 2.9 4.1 5.0 6.1 6.7 7.5 F 134-136 1.9 2.5 3.7 4.5 5.4 6.1 7.1 F 144-146 1.8 2.2 3.0 3.6 4.3 4.8 5.4 F 154-156 1.9 2.7 3.9 4.8 5.7 6.6 7.5 F 162-164 2.5 2.5 3.4 4.1 4.8 5.7 6.0 F 164-166 3.4 4.2 5.7 6.7 7.4 8.0 8.8 F 174-176 3.2 3.8 5.4 6.3 7.2 7.9 8.1 F 184-186 0.9 1.0 1.3 1.6 1.9 2.1 2.3 F 194-196 1.6 1.8 2.5 2.9 3.4 3.7 4.0 F 204-206 0.8 0.9 1.3 1.5 1.8 2.0 2.2 F 214-216 1.7 2.0 2,7 3.3 3.9 4.3 5.0 < 4 phi (> 63 mm) >4 phi 7.5 7.2 6.8 6.5 6.2 5.8 5.5 5.2 4.8 4.5 4.2 3.8 3.8 6.3 6.9 6.6 7.4 7.4 7.4 5.7 4.7 2.8 1.0 0.3 0.0 0.0 7.8 8.0 8.3 9.5 9.6 8.8 7.1 4.0 1.7 1.3 0.0 0.0 0.0 8,2 7.6 7.4 8.4 8.0 7.2 5.7 3.5 0.9 0.6 0.4 0.0 0.0 6.5 7.1 7.3 8.1 8.8 8.4 7.8 5.1 2.4 0.7 0.4 0.0 0,0 8,2 8.2 6.8 7.5 6.9 6.8 5.3 3.2 1.2 0.7 1.1 0.0 0.0 7.6 7.2 7.1 7.9 8.0 7.4 5.0 2.4 1.2 0.4 0.0 0.0 0.0 6.7 7.1 6.5 7.3 7.6 7.6 6.6 4,4 2.5 1.7 0.7 1.3 0.0 5.5 5.7 5.4 6.4 6.9 7.2 6.0 5.2 4,3 3.0 3.3 1.1 3.3 7.5 7.7 6.8 7.4 7.6 6.9 5.5 4.7 2.8 1.1 0.4 1.4 1.4 6.5 6.6 5.6 6.0 5.8 5.7 3.7 2.8 1.9 1.1 0.3 0.0 0.0 7.6 7.5 6.9 6.5 5.8 5.0 3.6 2.6 1.0 1.1 0.9 0.0 0.0 8.4 8.0 7.3 7.9 7.1 6.7 4.4 3.0 2.4 0.6 1.3 0.0 0.0 2.4 2.6 2.6 3.6 4.6 6.5 8.7 12.2 14.8 14.4 4.5 2.5 2,5 4.0 4.2 4.1 4.9 5.4 6.6 7.6 8.8 9.6 10.0 4.0 1.3 0.0 2.2 2.5 2.3 2.9 3.4 4.2 5.5 7.9 11.9 14.0 4.6 2.4 2.4 4.9 5.2 5.1 5.7 6.1 6.1 5.4 4.6 3.8 3.1 , 1.0 1.0 1.0 O J Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Appendix IV - Sand percentages of hemipelagic and turbidite sample intervals Age Depth in Total Wt. Powder Wt. Texture > 63 Wt. Sand % (yrs.) Core (cm) (g) (g) Total Wt. (g) (note: turbidite sand percentages are in bold.) AM 22,26 6-8 4.199 3.116 1.083 0.052 4.80 10-12 6.620 4.492 2.128 0.061 2.87 12-14 6.330 3.842 2.488 0.168 6.75 47.69 16-18 7.489 4.080 3.409 0.240 7.04 18-20 8.373 4.636 3.737 0.267 7.14 20-22 9.051 4.947 4.104 0.336 8.19 24-26 6.227 3.730 2.497 0.236 9.45 72.18 26-28 7.611 4.519 3.092 0.178 5.76 28-30 7.360 4.248 3.112 0.221 7.10 30-32 8.939 5.212 3.727 0.225 6.04 34-36 8.021 4.585 3.436 0.332 9.66 99.84 36-38 9.329 5.184 4.145 0.157 3.79 40-42 10.025 5.289 4.736 0.212 4.48 129.09 46-48 5.560 4.142 1.418 0.059 4.16 52-54 10.969 5.990 4.979 0.373 7.49 158.66 56-58 7.082 5.235 1.847 0.049 2.65 190.46 66-68 7.812 5.056 2.756 0.074 2.69 68-70 7.741 4.409 3.332 0.151 4.53 72-74 10.148 5.511 4.637 0.350 7.55 215.9 76-78 6.344 3.950 2.394 0.137 5.72 78-80 12.759 5.859 6.900 0.390 5.65 82-84 12.281 6.928 5.353 0.251 4.69 84-86 11.866 7.484 4.382 0.125 2.85 240.7 86-88 8.989 6.405 2.584 0.073 2.83 90-92 11.177 7.222 3.955 0.248 6.27 Age Depth i n Total Wt. Powder Wt. Texture > 6 3 Wt. Sand % (yrs.) Core (cm) (g) (g) Total Wt. (g) 136 05 rr C O 05 o C M C O C O y— O C O C O in o © C O C O C O C O * T C M in in in C O C O e-’ C O C O C O C M C M T — C O • > 3 - r- 0 5 T — in in C O in C O y — o C O C O e > - C M o o d C O C O in’ C D c o ’ o i in’ in’ r — in’ C D C O C O C O C O in in in in in in C D in in m 05 m in o ’ o ’ o C O •'t C O o y— C O C O in C O o y— C M C O T — 05 in C O C O y— C O 05 C M C M T — T— C O in Tf C O N- o C O in ^3- C O ■ '3 - C O C O C M T — C O C M C O C O C O C M y — *3- C M C M C M C M C M C M C O C M C O C M C O C O in in I"- C O • M " in o o ’ o o ’ o ’ o ’ o ’ d o ’ o ’ o o 1 - ^ C O c m ’ C O M- C M c o ’ C M ■d i n ’ 00 05 o o o ' o ’ C O C O in C O C O o in C O 05 C O C O C O ’3’ T — y— C O in y— c - C O r > » C O t — C O o C O 05 o C O C O C O O 05 i'- 05 N- r r o e' C M ■ ' S ’ y — C O r» C O o in * 3 " C O in in r r M ' 05 O ^ 3 - f - C O in C O en o L O in in M - ’ in’ in ^ 3 - d C O d c o ’ i f in C O d d d c o ’ C O 00 co r'- ^ y — o ’ c m C M 05 C O C O C O C O C O • ' 3 - in 0 5 • ' S - C O T “* C O C O r - C M O in f" 0 5 C O o 0 5 t — C O 0 5 o C O .— in C M C O C O C M C M C O ' 3' ■ 3 ’ t — e- C M C M C O C O in C O i ' ' - ■ o - in t i - .— ■'f’ C5 r * - C M 05 in o O C O CD C M C M co C M f'- T “ o C M C O C M C M y ~ _ d d d d d d d h-’ ^ 3 - M - d d d d d d 1^ d d d f - 00 00 M - 05 h- 'S ' d ■ ^ r o in C M in C O C O C O in in C O C O C O 00 05 C M C O C O C O C M O C O in 00 t— ■ M - C O tt r - C O in t— C O C O T— ^ r C M C M C O r - C M C O C O C O 05 O .— 05 in in in L O N C O •3; cq in C M 05 e * - C O ' 3 _ C O M- C O C M C M c m ’ C O T — C M 1 — o t— 05 d d T — 0 5 * T — C O c m ’ c m ’ o C M * I— C O d d y — T — T — * T “ ■ r - T — T— T — T“ T“ t — T “ ' — ' — y~ co in N- C O C O T- 00 C O CM C O o C M ■ 'S ' C O c o o CM ^ 3 ' c o C O 0 5 0 0 O o T— y— y— T — y— CM CM CM CM CM CM 0 5 ■ * — y- * T ---- y— y— ▼ ” y— i - y~ T— C O o d C O o CM ■O’ d C O d CM •M - d d 0 5 o o o T — T— T— t— CM CM CM CM C M * — f — T— . ---- T * T— T---- ■ .— r - ' — i t ’- w c o v i n c o s c o f f i „ in in ■ » V M V J >4 W I ^ A My i i i i i i i i i t C U * . CMCMCMCMCMCMCMCMCMCMCJ • ' 3 - _ L < - o i c o ^ i n c o s c o o ) ^ C O T — C O 05 r - ' - C M in C O C M in C O T ~ N- C O h- r-- 05 • ^ 3 ’ o C O C O 05 to C M cq > 3 - d d t — d d C O T — d d d t — d d a i C O C O o C O C M C M h- C M r- C O C O C O C O C M C M C O t— C M C M C O C O ■ ^ r 00 C M C O C O C O C O C M f" R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. A ge Depth in Total W t. Powder W t. Texture > 6 3 W t. Sand % (yrs.) C ore (cm ) (g) (g) Total W t. (g) 128.95 24-25 10.051 5.490 4.561 0.018 0.39 137 o ■ M - o V — t^ - r -» in C O 0 5 C O o C M 0 5 0 5 0 T — if C MC M c o C O in r- C O o 05 q q 00 o q C O q q q if in © o ' o’ o’ o’ o’ o’ o’ o’ o’ o T “ o’ o 0 0’ n! <f C M o r- C O 0 5 C M C O C O C M00 o C O C M00 C M C O in C O c- 00 C MC M y — C M ■ . — C MC O C O C MC MC M T — C M T - T —C O m I f r- o O o o o o o o o o O o o o o O O q q 0 0 o ’ o o o o’ o o’ o’ o’ o o o’ o o’ o* O O’ 0 0 0 d C O i-- C O in " d - in in C O o r > - 0 5 C O 05 in in 0 5 C MI f T — C O 0 5 00 o T — r-. in o C M in 00 C O Tf T — '4 ‘ 0 5 00 i f T T C O C M■ * — • * — C MC O * - C Mq q 00 o 0 C O C O 00 0 q C O c o ’ C MC O ^f C O c o ' c o ’ C O C MC M c m ' C O d c m ’ c m ’ d d C O C Mr» o C O ■ M - ■ m - C O N - C Mo r- rf in C M 0 5 00 in 0 5 C Mr- C O C MC O I s- C O oo in C O ■ M " C O 0 5 0 0 in 00 0 0 0 in T —o C O C Min M - C O o 0 5 ▼ —C O o y —o T — 00 T — y — C M 0 00 o in in in m in in • d - in • < 4 - • ' 4 - in in C O lO i f i f 0 5 0 5 o 00 0 5 00 c o C Mt-- c o in 0 C O 00 O 05 0 C O o C O C MC O 00 05 r^ 00 C O o C O in 0 5 00 O 00 0 lO ■ ' 3 ’ 05 • < r q C O • « — T — 0 5 q 0 5 q 0 O q 00 c o ’ c o ’ d 00 0 5 00 d d d d d d r-’ d d d d M - in in in in in in in 0 in in C O in 0 5 in in in in in m in O C M C O ■ * 4 ’ in C O r» 00 00 0 5 0 0 0 C O ■ O ' in C O N- 00 0 5 ■ » — T- ■ * - ■ * - y — t— T j- C M C M cm pa 4 T ti- ■ ^ r • * r • M " ■ M - -4- * T • M " 0 5 • * 4 - C M i f c o D C O M - in C O r- C O 0 5 O T — C M c o - < 4 - in C O r > - 00 0 5 O 0 0 r — C M C M C M 0 0 r- ■ M - r - - C O C O 05 c o C O C O 0 5 0 5 C M in 0 5 w C M C O q T — C O o C O q 0 0 in q q ■ M " C O 0 5 c m ’ N - ’ in c m " in o ’ o ’ C O d in’ d d f f t C O C O C O C O 0 5 ■cr 0 5 in o in o CD y— C O T — C O 0 ■ * “ C M C M C O C O -M - '4 - C O C O C O 0 0 0 5 0 5 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 15.87 2-4 5.308 4.575 0.733 0.014 1.91 68.78 12-14 5.156 4.130 1.026 0.059 5.75 121.69 22-24 5.999 4.544 1.455 0.033 2.27 174.60 32-34 7.900 5.731 2.169 0.078 3.60 227.51 42-44 7.326 5.145 2.181 0.030 1.38 138 5 s * T 3 f— 05 o > t o O I C O 05 ' t - 'S ’ i n i n o o U ) CM p«. CO CO CD 0 01 CO o o o c o 0 0 i n 0 0 CO T— T l- c o CD r - - r« - 0 5 © © CM c o CD o o r ^ 05 n C /5 c m ’ o ’ T “ c m ’ o ’ o ’ c d c \i o ’ T“ o o d o ’ o * - T" o o ’ • 3 - C O r « - C O C O C O C N J C O y— 00 in C O C M in 5 — C M 00 o ' S’ in C M C M C O 05 '3’ C O *— 0 0 C O y — T — T — C O ' S’ o T — T — T — o ^— C M o C O y — C M C M C M T— T — o ^— o o o o o_ o o o o o o o o o o o q o o o o o o o o O o o o ’ o o d o o ’ o ’ o o o ’ o o ' o ’ o o ’ o o o ’ o ’ o ’ o ’ o o ' o ’ o ’ d 00 • r»- •3- o y— •"S’ C O C M 0 0 0 5 0 0 C M CO C M 0 5 T - CO C M 0 5 T - 0 5 CO CO N - C O 0 0 o 0 0 f '- C M O T — C O C M 'S ’ i n o 'S ’ c o T — •3- CO C M 0 0 c o CO 'S ’ o T — CO LO o 0 5 0 0 C M o N - 0 5 C M C M C M f ' - i n CO 0 5 CO CO 0 0 C M T — 0 5 r» - t — A o H T _ C O C M C M O T “ C M C M C M C M % CO 00 CO 00 CO v - 00 t ' - 05 f '- s - 05 i n 05 •3 - o h - ' S ’ o CO N - y - •M" 05 M - « V 05 1— •"S’ o 00 05 05 00 CM i n i n CO CO CO CO CO CO o 00 3 ’ i n r>- o c o CD 3 ’ CO V • o « 2 P CO 05 q q c q o q CM CO 05 CO in o CO i n 05 ' S ’ CD q CO f» o 00 05 T “ CO CM 5 CO ■ < 3 - i n d i n i n c m ’ c m ’ CO T - ’ CM c m ’ CM c m ’ c m ’ • 3 - c m ’ CM C M CM CO CM c m ’ c m ’ c m ’ CM o cu o in T“ y— 3 ’ CM CO in o in 0 0 in 0 5 in CM y - CO y— CO CO 0 5 3- CO r-- in CM y— , ___. CO o in 0 0 in CM 0 5 0 5 CO CO o CM CO CO CO 0 0 M - 3 * r» CO CO in r - - 0 0 CM 3 “ _ 6 0 oo q q 0 5 CO 0 5 oo CM o CO 0 5 q CM o ■ « — in 3 - in 3 o CM r^- c o q 0 0 3 ’ p ■ M " CO 0 5 0 5 CO co’ co’ in CM cm’ CO co’ 3- 3 ’ ■d c d i d 3 ’ 3 ’ in’ in 3" in cd CO CO c ? •'S’ 0 0 oo CD 00 o o o o C D CO 00 3 ^3- ^3" O q ’ 3 ’ o o 00 00 00 00 o o C O 00 0 0 o T — C M C M C O C O 'S ’ 'S ’ in C O JC u in C O C O 0 5 T - a a i C M C O •M - in C O h - 00 0 5 T - ▼ “ T — D . O J b C M C M C M C M C M C M c u cd C M cd c d cd cd cd cd cd cd c d c d cd '3 ’ cd o o cd 00 cd c d cd Q J □ O m C O N . 00 0 5 O y— C M C O •'3' in C O r«» C O 0 5 o T — C M C M C M C O C O ■3" in C O u y— 1 - " i— ' — *— T - T —■ * — — CM CO 'S ’ in CO 0 5 CO ' 3 ’ T ” 0 0 in 0 5 CO 0 0 CM 0 5 r^ - q CO CM q 0 5 i^ - P 1 * 1^- q o 0 0 q ■ q 0 5 q ■ q w CD CM 0 5 q 6 0 w d c d c d d CM 'S ’ CM CO in c m ’ c d c m ’ d d CO d ' S ’ d d c m ’ d < ^ CD CO o o CO 0 5 ■ ' S ’ CM ^— CO o in o 'S’ 0 5 ' S ’ T — in o ' S ’ CM CO CO ' S ’ • ' S ’ in T ~ CM CM CO CO ^ r 'S’ in in CO CO r ~ - R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. 139 p '' r » T - r * T — 00 in CD o in [■*- C M . CD •M - n C O ■ f o C M m C D C M 00 C O O O 03 in r-~ 03 C M •a co •»- 03 0) M - r» O C M in 03 CO w in N 1 ''. • m- ■ M " C M C O C O T — 03 c « C /3 o T~ O " T~ - - - o o — o C M C M C M 03 d C M in 03 d C D d 03 d o d o in t-'- C M in C M h- in 03 T — r > - in i — ■ M " C M in C O C D in in C D i— o o -r—. T— in C M T— t — o C M o C M m in T — ■ D - C D ■ M " C M oo C O C O r». o o o o o T - o o o o O o ■ 'S ' C O O C D C M o C M o o d o o o o d o d o d d o o o o d d d o o o d d o o 60 o > 'T i ? £ l H C O o C O N > o o T T 0 3 C O in • M - • » 3 - CD in o CD in O o 0 3 o o in r>~ CM o o in in in CD C D o o '< • o ■ M - T — T — • M - in CM • D - h - T— C O o C O ■ D " in CD 00 r>- C O CD CO C M C O in 0 3 C O CD C M 0 3 r>- CD O 00 0 3 in in • d T - " T * CM ■ d C M * i —’ 1 — " t —• T - ’ • r - i — •*- CM f - cm’ i — T * t - i — CM CD CM 1— i— i — > Q C D O O C O W ^ ^ f f i l O t O W W i* ^ w n c o o T - n o T - n i o n o •a M o o s o r - i f l n t f l o > 0 ) 0 ) 0 ) n 5 c m c m co d d d c v j c\i c\i c m ■ * - co o c_ T - a 3 C 0 C 0 0 3 C 0 i n C 0 C M O C n C M 0 3 a 0 i n i - i - O ) T - N m ( D ( D T - ( O ( D ( M ^ N 0 3 c o o o o i i o n n i f l i f l i o n n i o f f l S N crj ^ co m- n" n ^ co Tf to M - to cd cd r r vv uj u; w w* uj u; W c D O f l l f f l ' - O t - O H 03 03 in r-- m C D C M 03 • M " C D CO CO i n i n C D C M C D i n CO CO 03 C M C D v— CO y— C M C M T — o o C M 00 C M C M T — C M i n i n ■D" T — m C M 03 i n C D CO C D C M 03 i n . OO 00 C D C D d d C D i n d i n d i n ' d M’ d o i n d ■ M - d d -S s s * s ^ ° D < j ao 00 00 C O 00 O ao 00 O O O O O O 00 C O o C O C O t"- 00 03 o O T — T— C M C D •<r in C O C O C O C O C O C O C O C O C O C O O t — T — C M T ~ C M C M C M C M C M C M C M C M C M u> 00 1 T — C M C D M- in C O t"- ao 03 ■ * “ ' r - I C O 1 C O C O C O C O C O C O C O C O C O C O u. C O ■ M - •M- ■D- M - ■D- •D- oo r-- oo 03 O O O C M CD ■D- in C O T - C M C D i n C O ao 03 o o T — C M T— t — T ” “ C M C M C M C M C M C M C M C M C M T — ai & o T —0 0 C M C M in C D o in M ’ d d o ■ d a i 03 ■ M - 03 C D r - » i'- 0 0 0 0 03 03 03 h- T l- ■ » — 0 0 t — 03 t ^ - in C M CO d C M 03 d C D r ^ T — C M ^ — CO t — c m ’ d o o C M C D N- C D oo in C M C O i*. rr h» 03 I " * C M o in C M 0 0 > 4 T — d d C O o d m d o o in C D N -’ 03 'S- 1 ^ - ’ oo o C D in d 1 C M C M C D C D m m 03 C D CM R eproduced with perm ission o f the copyright owner. Further reproduction prohibited without perm ission. A ge Depth in Total W t. Powder W t. Texture > 6 3 W t. S a n d % (yrs. ) C o r e (cm ) (g) (g) Total W t. (g) 670.72 144-146 7.215 5.466 1.749 0.208 11.89 140 r- ” t- s n w oo in CM t- CO CM 'M ' CM ■ < * o S- T - o in 05 C O l " » 05 O CM in C O in T — o o CM CO C O r - ~ o o ’ o o d o ’ o ’ o ’ in C O 0 5 C O '3- C O N - t ' ~ - C O C O o • M - C M in C M q in N - C O 0 5 t - ’ c o ’ T “ T ~ co c o ’ C M C M in C O C O h- in V— C O C O 0 0 . — C O oo T — o r - - q C M C O C M q in C O o c o ’ in’ c m ’ C O rr c o ’ c d 0 5 0 0 C O C O • « — in C M i " - in C O o o 0 5 in C O C M 0 5 C O q o o in C M vr o ' S ' 0 0 c o ’ o o ' d 0 5 C O C O C O in C O C O r > » r— f - ■ * “ CM 4 • ' S ’ in C O C O r ^ T “ T— T " CO CO CO CO o o 0 5 o i— C M C M ■M - 00 0 5 o T— T— T— C M C M 05 C M C O h - r r 05 q q q q C O o d M - ’ ^ — C O U o o in o 05 o o 05 05 05 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. IMAGE EVALUATION TEST TARGET (Q A -3 ) 1 . 0 l.l 2.8 3 2 . Li IS SI 2.2 2.0 1 . 8 1 .2 5 1.4 1 . 6 150m m 6" A P P L I E D IIW 1 G E . I n c — 1653 East Main Street ■ = '■ Rochester, NY 14609 USA ^=SS=I=S Phone: 716/482-0300 - = ' - ^ = Fax: 716/288-5989 0 1993. Applied Image. Inc.. All Rights Reserved R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission.

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Creator Rikansrud, Kristi Anne (author)

Core Title Late Holocene depositional history of western shelf margin, Gulf of California, Mexico

Degree Master of Science

Degree Program Geological Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-30528

Unique identifier UC11337110

Identifier 1394794.pdf (filename),usctheses-c16-30528 (legacy record id)

Legacy Identifier 1394794.pdf

Dmrecord 30528

Document Type Thesis

Rights Rikansrud, Kristi Anne

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA