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Sedimentology of southeast Pacific deep-sea cores

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Sedimentology of southeast Pacific deep-sea cores

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Content SEDIMENTOLOGY OF SOUTHEAST It PACIFIC DEEP-SEA CORES by Thomas Francis Manera /// A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE (Geological Sciences) June 1969 UMI Number: EP58565 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. U M I Dissertation PublisNng UMI EP58565 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProOuest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 U N IV E R S IT Y O F S O U T H E R N C A L IF O 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 PA RK LO S A N G E L E S , C A L IF O R N IA 9 0 0 0 7 This thesis, w ritten by ................ under the direction of hi.5....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 fu lfillm e n t of the requirements fo r the degree of Master of_ _ S . qi enc . e. _ _ ( G e. o . l o . g i.c a 1 . . _ S . e . i ences) Dean Date.....June.J9.69. THESIS COMMITTEE Chairman ^ CONTENTS Chapter Page ABSTRACT ......................................... 1 INTRODUCTION ..................................... 4 Objectives and purpose ....................... 4 Location . ................................... 5 Sediment sampling methods • ................... 8 Bathymetry ...... ....................... 9 Bottom photography • • • • ................... 10 Previous work ......................... 10 Water masses and currents .••••••»••• 11 Acknowledgments ............................... 13 TECTONIC AND PHYSIOGRAPHIC PROVINCES ............ 15 General ................................... 15 Peru-Chile Trench ............................. 15 Nasca Ridge................................... 20 Fracture zones and volcanic ridges .......... 27 Island groups and seamounts • .............. 28 MICRORELIEF AND SURFICIAL SEDIMENTARY FEATURES . . 30 Peru-Chile Trench and continental margin off Callao, P e r u ........................... 30 Nasca Ridge................................... 30 Abyssal floor and island groups ........ . . . 42 Peru-Chile Trench and continental margin off Valparaiso, Chile ....................... 61 ii Chapter Page SURFACE SEDIMENTOLOGY ........................... 74 Laboratory techniques......................... 74 Calcium carbonate........................... 74 Organic carbon and nitrogen................ 74- Texture ..................................... 75 Gross clay mineralogy.................. 75 Chemical and textural data .......... .. 7 6 Clay mineralogy ............................. 94- STRATIGRAPHY OF DEEP-SEA CORES • . . .......... 98 General....................................... 98 Peru-Chile Trench, Callao ................ . . 99 Nasca Ridge........................ 104 Abyssal floor and island groups .............. 116 Pelagic sedimentation and Pleistocene carbonate deposition.................. . . 119 SUMMARY AND CONCLUSIONS ......................... 125 REFERENCES....................................... 129 APPENDICES....................................... 135 Appendix Is Station Data for Cruise 17* R/V Anton Bruun................. 136 Appendix II: Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen ...... 139 iii ILLUSTRATIONS Figure Page 1. Index map............................... 6 2. Topographic profiles, northern half of cruise................................. 16 3. Topographic profiles, southern half of cruise................................. 18 4. Bathymetric map of Nasca Ridge and Peru-Chile Trench ....................... 23 5* North-South precision echo sounder recorder profile across Nasca Ridge . . , 25 6. Photograph of coarse sediment and benthic l i f e ................ 31 7* Photograph of boulders and cobble • • • • 33 8* Photograph of sedimentary rock slab . . . 35 9. Photograph of worm tubes, mounds and debris ...................... 37 10. Photograph of benthic activity, Peru- Chile Trench........................... 39 11. Photograph of igneous rock outcrop . . . 44 12. Photograph of igneous rock outcrop and attached coral and crinoid ............ 46 13. Photograph of scattered manganese nodules 48 14. Photograph of bottom reworked by organisms............................... 50 15. Photograph of mounds in foraminiferal o o z e ................................... 52 16. Photograph of biologically reworked surface sediments ................ . . . 54 iv Figure Page 17. Photograph of fecal coils and sediment cloud • • • • • • ....................... 56 18. Photograph of manganese nodules ......... 58 19. Photograph of irregular bottom ......... 62 20. Photograph of slumped sediments and ripplemarks in Trench ................... 64 21. Photograph of slumped sediments in Trench •••••••• ................. 66 22. Photograph of sedimentary rock fragments, Trench ................... •• 68 23. Photograph of ripplemarks in Trench . . . 70 24. Chemical and textural parameters of surface sediments versus bathymetry . . . 77 25. Textural parameters of surface sediment . 80 26. Relationship of mean size, CaCO-, and bathymetry for surface sediments .... 83 27. Geographical relationship of CaCO^ and bathymetry for surface sediments .... 85 28. CaCO-z, bathymetry and distance from land of surface sediments ................... 88 29. Sequential plot of organic C and N in surface sediments ....................... 91 30. Physical and chemical parameters of core 14/664A........................... 100 31. Physical and chemical parameters of core 17/667G........................... 105 32. Physical and chemical parameters of cores 18/668F and 19/669D.............. 108 33. Physical and chemical parameters of cores 20/670F and 21/671F.............. Ill v Figure Page 34. Physical and chemical parameters of cores 22/672F, 23/673E and 33/678G . . . 114 35. Physical and chemical parameters of cores 34/679F and 46/682H... 117 36. CaCOj, size distribution and general correlation of carbonate stratigraphy • . 122 vi TABLES Table Page 1. Summary of observations - microrelief and surface sediments, Callao to Peru- Chile Trench........................... 41 2. Summary of observations - Nasca Ridge . . 43 3. Summary of observations - abyssal floor and island groups..................... 60 4. Summary of observations - Peru-Chile Trench and continental margin off Valparaiso, Chile ..................... 73 5. Occurrence of clay minerals............. 96 vii ABSTRACT Cores and bottom photographs collected along the continental margin and in the Peru-Chile Trench off Callao, Peru, show large amounts of organic material in the sediments, a direct reflection of the high product ivity in the surface waters of the Peru (Humboldt) Cur rent. Organic material ranges between 6.0 and 17.7 per cent by weight and is roughly seven times the amount found in samples seaward of the Trench. Values of c/N show a wide range but average 14.2 and 13*3 for sediments of the Trench-continental margin and seaward of the Trench, respectively. Sediment at water depth of 1000 m has larger CaCO^ content, mean size diameter and better sort ing than the sediments of the shelf and slope. These changes in chemical and textural parameters are the re sult of maximum abundance of foraminifera at this depth. Physical forces are at work on the margin as evidenced in bottom photographs by the presence of cobble and other coarse elastics at appreciable depths off Callao, and of slumped sediment, scour, "streams1 * of megarippled sedi ment and patches of thin-crested oscillation (?) ripple marks in the Trench axis (5200 m) off Valparaiso, Chile. Fracture zones, volcanic islands, seamounts, guyots and ridges indicate present and past tectonic 1 activity over much of the region. A zone of abrupt depth change and hackly to irregular microrelief approximately 150 km north of San Felix Island is probably the eastward extension of the Easter Island Fracture Zone. Seamounts between the islands of San Felix and Juan Fernandez ex hibit depressions at their bases similar to "moats" found along the base of larger volcanic island groups, which are attributed to crustal loading or plastic flow at depth. Profiles along Nasca Ridge show that faulting has occurred• Sediments south of the Nasca Ridge are generally brown calcareous and buff clays with fecal pellets, manganese micronodules and interlayered pyroclastics. Dredge hauls and bottom photographs indicate several regions of abundant manganese nodules. The distribution of CaCO^ is a function of productivity, water masses and currents, bathymetry and distance from land. Variations of carbonate with time indicate a trend similar to Arrhenius's model of lower CaCO^ production for Holocene and interglacial sediments in the equatorial Pacific. On the assumption that two cores, approximately 500 km apart, have a complete record of Quaternary sediments, a sedimentation rate for the total Pleistocene is calculated at 1.3 to 1.4 mm/1000 years. Along the Nasca Ridge, Holocene sediments have 3 accumulated at the rate of 1.4 to 2.7 mm/1000 years as a result of higher carbonate production. 4 INTRODUCTION Objectives and Purpose The composition and configuration of the sea floor provides the primary evidence for the development of tectonic theories. Although many expeditions have studied the ocean floor, the region studied is generally compara tively small in relation to the great area of the earth covered by water. The difficulties inherent in deep-sea sampling, navigational uncertainties and the diverse physiography of the sea floor are factors contributing to the relatively sparse data available. Studies of deep-sea sediments provide a means to judge the extent and relative influence of processes distributing, depositing and altering the sediments at present and in the geologic past. In this study the author has described and inter preted the environment, physiography and processes related to deep-sea sediments in the southeast Pacific Ocean. The use of bottom photographs, topographic pro files and chemical, textural and X-ray analyses of sedi ment were employed to evaluate the present and past ef fects of biologic, chemical and physical forces in the study area. In so doing, it is hoped that a better under standing of Holocene and Pleistocene sedimentary (and 5 biologic) environments will be attained. A second related objective is to determine rates of sedimentation which can be applied to geophysical studies involving the thickness and age of sedimentary layers which, in turn, have a bearing on hypotheses of spreading of the ocean floor. It should also be noted that a description of deep-sea sediments, their biological and chemical altera tions, composition and structures is necessary if we are to recognize deep-sea sedimentary rocks in the geologic column• Location Several areas of the southeast Pacific Ocean were studied during Cruise 17 of the National Science Founda tion R/V Anton Bruun Expeditions in 1966 by 0. L. Bandy and his scientific staff. The ship's track included a traverse across the Peru-Chile Trench off Callao, several crossings of the Nasca (Nazca) Ridge, a southern track between the Nasca Ridge and the volcanic islands of San Felix and Juan Fernandez, and an eastward line from Juan Fernandez Island, across the Peru-Chile Trench, to Valparaiso (Fig. 1). Designation of sampling locations followed previous Bruun procedure: general sampling locations are denoted by the first figure (53 locations during the cruise) followed by a three-numeral value (hydrographic Figure 1 Track of the Anton Bruun, cruise 17, showing generalized topography and sample locations. Large capital letters show location of topo graphic profiles. 6 7 R.V. ANTON BRUUN CRUISE 17, 1966 LEGEND Ships track and stations > -5 3 Locations W o °0\Bathymetry in fathoms v C a lla o >■ 20 90* W station) and ending with a letter designation for the particular operation following the hydro station: thus, 3/658A signifies general location 3> station 658, trigger core operation (A). Navigational positions for each station were derived from the ship's smooth plots based on the station's time. Astronomical fixes were hampered by overcast conditions. Star sights, when available, were used as new datum points for the dead reckoning plots. Sediment Sampling Methods Samples studied in this investigation were col lected with piston (6 m core barrel) and trigger corers, rock dredges and Campbell grabs. In most instances trigger cores were obtained at the same location along with piston cores. This enabled the recovery of sediment from the upper section of the sediment column which is usually lost during the operation of the piston corer (Arrhenius, 1952). At several locations along the flanks and crest of the Nasca Ridge the piston corer was used as a gravity corer in order to obtain a complete sediment section. Core samples were stored in core liners at the time of recovery and later extruded, split and described lithologically in the laboratory by personnel of the Department of Geological Sciences, University of Southern California. Grab samples were stored and later washed through 62 micron screens for studies of foraminifera in the coarse fraction. Some grab samples were also set aside for sedimentological studies. Although shore samples were collected from the San Felix and Juan Fernan dez Islands, the present study concerns itself only with deep-sea and continental margin sediments. Bathymetry Bottom profiles were obtained from an Alpine Co. Precision Echo Sound Recorder (PESR). All soundings are reported as uncorrected depths; a discussion of the methods for correction of depth is covered by Matthews (1939). Briefly, the corrections are greatest in very deep water where values give positive corrections on the order of 4 percent as determined for depths of 7645 m (4180 fm) in the Peru-Chile Trench (Zeigler and others, 1957). Since the PESR horizontal scale is constant with time, horizontal distortions caused by variations of the ship's speed must be corrected. These corrections were made by plotting closely spaced soundings on equal scale segments for the various pitometer log values. Final corrections were made for these segments after determin ing the absolute distance between stations from naviga tional fixes. Additional profiles were derived from compilations of bathymetric data by the Bureau of Com 10 mercial Fisheries for the Nasca Ridge and Peru-Chile Trench region. Bottom Photography- Oblique bottom photographs (black and white 35 mm) were taken with an Alpine multishot camera at 22 loca tions by Raphael Ouaknine. Thus, nearly all coring loca tions had photographic coverage within a short distance (Appendix 1). Since the camera angle, and distance above the trigger weight, remained constant for the cruise, the only variation of distance (represented by the base of the photograph) occurred when the negatives were en larged . Previous Work Studies of the mineralogy of the Peru-Chile Trench were made by Schmalz (1957) and Zen (1957; 1959). Bandy and Rodolfo (1964) studied the foraminifera, calcium carbonate and carbon and nitrogen content of the sedi ments from the surface layers. Topography and structure are covered in Zeigler and others (1957)» Revelle (1958)* Fisher and Raitt (1962), and Scholl and others (1968). The geophysics of the Trench is presented by Hayes (1966). Coastal geology is presented by Jenks (1956) and tectonic development of the coast by Childs and Beebe (1963). Data on the surface hydrography is given by Gunther (1936). 11 The bathymetry of Nasca Ridge has been compiled by the “Downwind” Expedition (Pisher, 1958) and more recently by Chase (1968). The relation between the Ridge and its continuation onto the Peruvian landmass is discussed by Ruegg (I960). Water Masses and Currents The most prominent current in the study area is the Peru (Humboldt) Current which probably originates from Subantarctic Water deflected north up the west coast of South America to latitudes 10-15°S (Gunther, 1936) and modified by upwelling. The Peru Current has a dif fuse western limit approximately 900 km from the coast and is characteristically a wide current marked by small transport of water, and low velocities. The well known upwelling of nutrient-rich cold water along Chile and Peru is caused by the prevailing south to south-southeast winds which carry warm, light surface waters away from the coast. Close to the coast, cold water, usually from 40-360 m depth level, is brought to the surface; no water from greater depths is involved and the over turning is intermittent and based on local winds (Gunther, 1936). Pour very general regions (between latitudes 3°S and 33°S) of overturning have been described (Gunther, 1936); the two regions of overturning in the northern half 12 (between latitudes 5°S and 15°S) are the most intense. At a distance of approximately 180 km from the coast the existence of a southward flowing and sinking counter- current has been shown. Found at less than 100 m at latitude 3°S and at 400 m at latitude 36°S, this counter- current is composed of water probably originating from the Pacific Equatorial Water. Part of the Peru Current joins with the South Equatorial Current in flowing west across the Pacific. During the northern summer a portion of the Peru Current converges with the eastward flowing Equatorial Counter- current which, in turn, begins to flow north near the coast. In northern winter the Equatorial Countercurrent is displaced, regularly in February and March, to the south. Part of it, warm, low salinity water, flows along the Equador coast and passes the Equator before converg ing with the Peru Current. This warm water, called HE1 Nino,1 ' has a southern limit only a few degrees south of the Equator. Occasionally this pattern is changed and HE1 Nino*' is displaced further south, sometimes past Callao (latitude 12°S), where its warm waters cause massive destruction of cold water marine life. This catastrophic condition is repeated, on the average, once every 12 years. The wholesale killing of marine life and sea birds causes vast amounts of hydrogen sulfide to be produced in the water, so that ships anchored in Callao 13 have their paint blackened. The term “Callao Painter” is given to this phenomenon. Heavy rains and flooding also accompany the extreme southerly displacement of warm water, an example being during March 1925 when 395 mm of rainfall was measured at Trujillo (latitude 7°S) compared to the March average of 4.4 mm during normal years. The increased productivity and decomposition of organisms in Peruvian coastal waters should also be reflected by low values of oxygen in these waters. The Bruun also traversed a general region of con verging currents— the Subtropical Convergence— in the middle latitudes between Nasca Ridge and Juan Fernandez Island. Acknowledgments Although the author was not a member of the scientific party during Cruise 17, he would like to thank the chief scientist of that cruise, Dr. Orville Bandy, and the many scientists and technicians from various academic and research institutions who accomplished such a fine job in the collection and preparation of data and samples. The author is indebted to the members of his com mittee, Drs. Donn S. Gorsline (Chairman), Orville L. Bandy, and Gregory A. Davis for helpful criticism, in valuable suggestions and thoughtful discussions during the 14 course of this study, and to Drs. Ronald L. Kolpack and David W. Scholl (U.S.G.S., Menlo Park) for their kind ad vice. Messrs. Peter Fleischer and Fritz Theyer and Mrs. Joan Stapleton gave valuable assistance and suggestions in the course of this study. The author would also like to thank the Computer Sciences Laboratory of the Univer sity of Southern California for the use of computer time and facilities in the textural analysis, the Department of Geological Sciences for the use of equipment and the helpful service of its staff members, Texaco, Inc., for use of reproduction facilities, and the author’s wife, Jane Manera, for assistance in the preparation of the manuscript and Mrs. June Brown for the final typing. Some aspects of this study were supported by the national Science Foundation (GA 730). 15 TECTONIC AND PHYSIOGRAPHIC PROVINCES General The Bruun traversed bathymetric ally high areas for a major part of its track. These areas are the con tinental margin off Callao, Peru and Valparaiso, Chile, the Nasca Ridge in the northern half of the track, a north-trending string of seamounts and islands (San Felix and San Ambrosio) between approximately 25°S and 30°S latitude and an east-trending ridge, including Juan Fernandez Island at 33°S latitude between 80°W and 75°W longitude (Figs. 1-3). These areas are generally shoaler than 3660 m (2000 fm). The remainder of the track was along depths between 3660-4500 m (2000-2500 fm), except in the Peru-Chile Trench off Callao where a maximum depth of 5520 m (3010 fm) was recorded. Peru-Chile Trench The Peru-Chile Trench parallels the west coast of South America from central Chile to southern Equador and is intercepted south of Callao, Peru by the Nasca Ridge. Here, the Trench is separated by a swell or "saddle" into a northern and southern portion. The Trench, however, is still well defined in this area and is 900-1500 m shallower than axial depths to the north and south (Fisher, 1958). The flat floors of the northern portion are evidences of Figure 2 Topographic profiles along track of R/V Anton Bruun* Water depths are uncorrected. Profile BA is un corrected for drift and course changes along stations. Vertical dashed lines at several loca tions represent larger off-sets in station posi tions at each location. Profile locations shown on index map (Fig. 1). 16 17 SO 100 150 K ilo m e te rs _________ L.________ I 25 50 N a u t i c a I M i Ies V e r t . E x a g . x 1 5.4 B Km P e r u C hile Trench N a s c a R i d g e Figure 3 Topographic profiles along ship's track, file locations shown on index map (Fig. Pro- ). 18 19 0 50 100 150 K i l o m e t e r s 1 i i . i V e r t . Exag. x 1 5.4 50 N a u t i c a l M i l e s the contribution of sediment from intermittent coastal rivers and the probable lack: of effective sediment traps on the continental slope. In the southern portion (off the Atacama Desert) little sediment is available, the Trench is narrow and depths greater than 7300 m occur (Fisher and Raitt, 1962). South of 27o30*S the Trench abruptly re-assumes its flat-floored character as a result of the increased number of streams discharging into the ocean and of the lack of sediment traps on the continental margin. South of Valparaiso horizontal beds of "turbidites" fill and extend across the offshore flank of the Trench (Scholl and others, 1968). Seismic refraction studies near 13°S latitude show less than 500 m of sediment in the Trench, crustal thinning beneath the offshore flank of the Trench, a maximum crustal thickness of 11 km and a depression of the Mohorovicic Discontinuity to 17 km below sea level at the axis (Fisher and Raitt, 1962; Hayes, 1966). Heat-flow studies at latitude 14°S indicate values well below those found over the general ocean basin (Fisher, 1958; Bullard, 1963). Nasca Ridge The Nasca Ridge is a northeast-trending submarine ridge approximately 148 km (80 nautical miles) in width and 1300 km (700 nautical miles) long. The Ridge extends from the southwest, branching off from the Easter Island 21 Fracture Zone between longitude 83°W and 84°¥ and latitude 23°50*S, to the Peru coast and possibly inland as part of the northeast trending Huricangana Mountains and surround ing areas (Ruegg, i960). L. R. Fisher (personal communi cation to Ruegg, I960) reported the dredging of a sheared alaskite from the northeast tip of the Ridge (Sample BD-9> "Downwind" expedition). Alaskite is found to be a constituent of the core of old structures from the Huricangana Mountains (Ruegg, i960). Fisher also reports that three seismic refraction profiles show a generally oceanic crust flanking the Ridge around its central region and a deep crust with depth to mantle possibly 15 km beneath the ocean floor. Gravity measurements indicate that the Ridge is essentially compensated and, together with the fact that the Ridge-Trench intersection does not greatly alter the character of the Trench, suggests that the Ridge is older (Hayes, 1966). It is difficult to explain the occurrence of alaskite in the northeast tip of Nasca Ridge as due to rafting since the Peru Current would carry material to the northeast. Since data on the composition of the Ridge is lacking, it is possible that the Ridge has a composite origin (volcanic and revitalized landmass)• The Ridge is well defined by the 3660 m (2000 fm) contour and is marked at its southwest extremity by a shallow, asymmetric area with a steep southeast and a 22 gentler northwest slope (Pig. 4). This region is also characterized by the presence of several seamounts, guyots, and a break in slope at the 1830 m (1000 fm) depth. The 1830 m (1000 fm) contour may represent a sur face truncated when the Ridge was partly emergent (Chase, 1968). Ruegg (i960) believes the Ridge was emergent and submergent several times in the past by analogy with the many terraces and geologic history of the Huricangana area. Peaks with depths of 311 and 322 m (170 and 1?6 fm) are located at latitude 23°4lfS, longitude 80°51,W, and at latitude 23°42'S, longitude 85°18!W, respectively. Due to the lack of detailed sounding the chance of later dis covery of additional new volcanic seamounts is high (Chase, 1968). A northeast trending ridge in the shoaler portion of Nasca Ridge at latitude 20°55'S and longitude 8l°4l!W (refer to Pig. 4) has a reported depth (Chase, 1968) of 1361 m (853 fm). A guyot or flat-topped ridge was observed at this position, approximately 92 km (50 nautical miles) due north of location 22 (Pig. 1). This feature (Pig. 5) rises 2000 m (1100 fm) to a depth of 1610 m (883 fm). The steep walls and step-like levels of both flat and hilly areas shown by the PESR indicate extensive faulting on the Ridge. Debris of late Tertiary to Holocene age dredged from Nasca Ridge guyots at a depth of approximately 400 m (216 fm) suggests that these Figure 4 Bathymetric map of Nasca Ridge and Peru-Chile Trench, 23 9Q°W 151 S BATHYMETRIC CHART OF NASCA RIDGE (AFTER BUREAU OF COMMERCIAL F IS H E R IE S , C IR C U L A R 291, T .E .C H A S E , 1 9 6 8 ) —2 0 0 0 —^ CONTOURS IN FATHOMS CALLAO PROFILE ACROSS p e r u - c h ile t r e n c h AXIS OF PERU-CHILE TRENCH = 3 0 0 0 FATHOMS ISLAND FRACTURE 90 ° W Figure 5 North-South Precision Echo Sounder Recorder profile across part of the Nasca Ridge between locations 21 and 22, See Figure 4 for loca tion. 25 NASCA RIDGE 000 2000 — 500 Fm — 1000 Fm / a 3000 UJ o 4 0 0 0 1 0 NAUTICAL MILES 20 N 500 Fm — 1000 Fm — 1500 Fm __ 1000 2 QOC r o O N 27 guyots developed as a result of volcanism continuing through the Tertiary (Menard and Ladd, 1963). Practure Zones and Volcanic Ridges The Clipperton, Galapagos and Easter Island Practure Zones offset the East Pacific Rise, Three major volcanic ridges branch to the northeast from the fracture zones and extend nearly to the edge of the continent. The Tehuantepec Ridge branches off from the Clipper ton Practure Zone and intersects the Middle America Trench in a manner very similar to the intersection of the Peru- Chile Trench by Nasca Ridge. Cocos Ridge extends from the Galapagos Practure Zone to the southern end of the Middle America Trench off Costa Rica. A fourth ridge, Carnegie Ridge, trends east-west and strongly alters the topographic character of the Trench between latitudes 1°N and 4°S. Menard (1964) believes each ridge is the result of movement along its own fracture zone. Por each of the four ridges, the intersection with the fracture zones to the southwest and with the continent or trenches to the northeast, has produced large bounded basins on the southeastern sides of the ridges. The differential forces of an eastward moving oceanic crust produced by angular ities in the South and Central American coastlines could possibly explain the trend of fracture zones, volcanic ridges and trenches (Menard, 1964). Recently Menard and 28 Atwater (1968) postulated that the great fracture zones in the northeast Pacific Ocean represent transform faults formed at the edges of rigid moving crustal blocks and that variations in the configuration and direction of the fracture zones are the result of changes in the direction of sea floor spreading. It is not known if this relation ship can be applied to the southeast Pacific; however, until more data can be accumulated, this hypothesis should be borne in mind. Island Groups and Seamounts The volcanic island of San Felix, latitude 26°17'S, longitude 80°05'W, and the active volcanic is land of Juan Fernandez, latitude 33°38'S, longitude 78°48’W, lie between Nasca Ridge and the southern limit of the cruise. Juan Fernandez Island is the locale for the story of Robinson Crusoe based on the exploits of Alexander Selkirk, one of several inhabitants who occupied the Island in the 19th century. Several seamounts were observed along the ship's track south of San Felix Island. One seamount (refer to Fig. 3, profile GF) has a relief of nearly 3660 m (2000 fm) and also exhibits a slight basining at its base. This "moat-like" feature is better observed in a smaller sea mount to the south (Fig. 3» profile HG) which also ex hibits an outer "arch." Moats and outer arches were first 29 observed by Vening-Meinesz (194-8) in the Hawaiian Islands. Other examples of moats and arches around large volcanic island groups and seamounts have been described in the Hawaiian Islands, Line Islands and Emperor Seamounts (Dietz and Menard, 1953; Emery, 1955; Hamilton, 1956; Menard, 1964). The formation of moat and arch structures is generally attributed to subsidence in response to the large, local load on the sea floor (Menard, 1964). Since there is only one traverse across both of these seamounts, it may also be possible that these seamounts lack an en circling depression. If they are moats, then the previous ly reported occurrence of these features can be extended to include these smaller solitary seamounts in the south east Pacific. 30 MICRORELIEF AND SURFICIAL SEDIMENTARY FEATURES Peru-Chile Trench and Continental Margin Off Callao, Peru Both physical forces and biologic activity are at work on the sediments as shown by the striking abundance of large cobbles, slabs of rock, and benthic organisms in Figs. 6-10. The presence of crabs, fish, brittle stars, etc., reworking the sediments attest to the high organic content related to the overturning in the Peru Current. The occurrence of boulders, cobble and rock slabs, some with adhering sea anemones, at depths of 1000-2000 m, indicates some downslope movement of coarse debris by slumping or other mechanisms. Many of the cores contain numerous glass fragments and grab, dredge and trawl samples reveal sedimentary and volcanic rock at a variety of depths (Table 1). The presence of sedi mentary rock at these locations is an argument against volcanic activity as the sole argument for the formation of coarse elastics and debris at these depths. Nasca Ridge Sediment on the flanks and crest of Nasca Ridge reflect the effectiveness of the Peru-Chile Trench as a Pigure 6 Coarse nature of bottom sediment consisting of glauconitic sand mixed with organic remains and volcanic glass. Spider crabs, fish (Halosaurid) and gastropods browsing on organic matter. Location: 7/659J. Depth: 550 m. Base of photograph: approximately 1.4 m. Note: Dimensions for the base of all following photographs refer to the right-hand margin of the page. Photograph by R. Ouaknine. 31 Figure 7 Boulders, cobble, and slabs of sedimentary and volcanic rook resting on sandy, glauconitic silt* Legged worm is visible in center fore ground in front of boulder. Brittle stars are attached to boulders. Location; 10/661D. Depth: 1750 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine. 33 34 Figure 8 Slab of sedimentary (?) rock protruding from silty clay. Grab sample from immediate area contained a slab of sedimentary rock, however, occurrences of slabs of volcanic ash have been reported for this region (Worzel, 1959). Location: 12/662D. Depth: 3230 m. Base of photograph: approxi mately 0.5 nu Photograph by R. Ouaknine. 35 36 Figure 9 Mounds, worm tubes protruding from bottom and scattered organic debris (?) in clayey silt. Location; 13/663D. Depth: 3930 m. Base of photograph; 1.4 m. Photograph by R. Ouaknine. 37 38 Figure 10 Mounds, pits, worm tubes, and tracks made by- feeding holothurian in clayey silt of Peru- Chile Trench. Location: 14/6640. Depth: 5430 m. Base of photograph: 1.4 m. Photo graph by R. Ouaknine. 39 40 Table 1. Summary of observations of mlcrorellef and surface sediments - continental margin and Peru-Chile Trench of:' Callao, Peru. Location and Device Bottom Photographs; Mlcrorellef Coarse Fraction and Color Remarks 1 T Sandy slit.* Large numbers of diatoms; lesser amounts of foramlnifera; mod erate amounts of organic debris: fish teeth, vertebrae, etc. Angular quartz, micas, magnetite. 2 T Silty sand.* b(J-9U£ well-sorted angular quartz; remainder of diatoms, magntitie. R T Silty sand.* Same as location 2. 3-p cm dlsc-snaped pebbles of con solidated sedimentary rocks found in Campbell grab (optj). 0 T Coarse-textured sediment; surface furrowed by possible ripple marks; fish Silty sand, olive-brown silt aggregates and glauconite; re mainder of' organic materials; fish ver tebrae, diatoms, magnetite, quartz and a sedimentary rock fragment (lx.p cm). Large Claps of consolidated sedi mentary rocks (2L'Xlo-9 cm) re covered from grab (099H). jedi- nentary and volcanic rocks from, grao (btyP), 7 Irregular surface; large shell and rock fragments; gastropods, fish and abundant 3plder crabs. 9 T Silty sand.* yof. glauconite pellets with septaria-liKe vein fillings. Organic material: vertebrae, etc.; remainder of glass, quartz, chert fragments, siliceous aggregates and volcanic rock fragments. Sedimentary anJ volcanic pocks from dredge and Campbell ^raoc. 10 T idound Shells, shell fragments, boulders, cobble, angular' rock slabs; brittle stars, worms; 3ea anemones attached at odd angles to boulder3 and cobble. 11 T Sandy silt. 1UYR2/2-. Approximately Sob of silt aggregates; 40£ glauconite pel lets; remainder of foramlnifera, a few diatoms, quartz, volcanic shards, dark minerals, mica, rock fragments and orgarli material. c 12 Generally smooth bottom; large slab of sedimentary rock protruding from sediment; organic (?) debris. Sedimentary rock iron: grab (bti2A ) . 13 T Several mounds and burrows, worm tubes; scattered organic (?0 debris. Clayey silt.* Large numbers of radio- ) larians, diatoms and di3coa3ters; 2 mm muscovite flake; some foramlnifera (Y)rbulina universa). 14 T Mounds, burrows and trails; abun dant worm tubes protruding from sur face; Holothurians Drowsing on sedi ment surface. Clayey silt, 3>YR2/l3. Approximately biogenic (mostly radiolarlans) ; quartz, micas, dark minerals; 1U£. glau conite, Fe-stairied crusts, and organic:,. * Rose 3engal added to top of core as a stain 1 1. Dusky brown; ^ Dusky yellowish brown; 3 Olive T Trigger corer; ?: Piston corer or organles black 42 sediment trap. Surface sediments exhibit a general color change from the olive-green, darker silts and sands of the Callao-Trench samples, to lighter, buff-colored clayey silts and clays along the Nasca Ridge (Table 2). Some of the coarser-textured sediments (locations 15-19) are due to the contribution of foraminiferal tests or aggregates of silt derived either from preexisting sedimentary rocks or from fecal pellets of benthic organisms. Manganese nodules dredged from Ridge crest loca tions and micronodules found in the surface samples indicate an association with volcanic activity (Figs. 11 and 12). Many of the volcanic rocks dredged from this general area are encrusted by manganese and iron oxide. Although manganese micronodules were found with depth in the cores, only one location has visible evidence of large nodules at the surface (Fig. 13). Subsurface burrowing (presumably by worms) is evident in the bottom photographs by pits and mounds (Figs. 14 and 15) and spiral burrows (Fig. 16). Oblong coils of fecal matter (Fig. 17) also occur over much of the area. Abyssal Floor and Island Groups Sediment recovery from trawls and dredges sup plemented by four photographic locations indicate large numbers of manganese nodules (Fig. 18) lying both below and on the surface (Table 3) in the area between San Felix Table 2. o-rer.ary if observations - Nasca Ridge Location anti Lev ice 3ottorr. Photographs; Micro re lief Coarse Fraction and Color Remarks 1; T Outcrops of extrusive volcanic rook; sediment filling in low areas. dome roughly spheroidal outcrops; Alyconarian coral and crinold ("Sea lilly"). Clayey silt.* Approximately f'0% forami- nlfera, 20% radiolaria, 10% discoasters. Some glauconite casta, glass, quartz and mica. Manganese nodules, sedimentary and volcanic rocks recovered from trawl (66%E). 16 T Mounds, burrows and trails. Clayey silt.* Approximately 00% forami- nifera, 20% radiolaria, discoasters, glauconite, glass, quartz and mica. (oti'2) Generally 3mooth but surface broken Dy a few mounds and burrows including spiral our- rows; worm tube or crinold. Clayey silt. 10YR6/a1. Approximately 70% of silt aggregates (fecal pellets). 20% foraminlfera, 10% quartz fragments, dark minerals, radiolaria and one 1-2 ram angular rock fragment encrusted with Fe-oxide. T ( LO : ’ u ) Clayey silt. bYRb/l^- Same as (667B). Clayey silt IOYRr/4^. tiC% silt ag gregates, 30% foraminlfera, 3% quartz, glass, dark minerals, mica, teeth, etc., 3% dark gray colled fecal " ribbons" . lb T Generally smooth, with mounds, Durrows (spiral), trail3 and small pits. Sandy silt. 3YR3/24. Same as 17 T (667B) but contains less dark minerals. Sandy silt. 10YRb/2u. Approximately 96% foraminlfera, 2%' dark gray fecal "ribbons". Manganese nodules from trawl (66bC). 19 FG Relatively smooth surface; small ridge with medial "rift" probably the result of burrowing, pits, tracks and oblong fecal coils. Clayey silt, lOYRb/2^1. Thin layer of 3VR3/4? at 0-2cm. Approximately 60% silt aggregates, 10% foraminlfera and radiolaria, 10% dark gray fecal "ribbons". cU ?G . “ slightly irregular surface with a few large mounds; pits, scat tered manganese nodules; rope- like fecal droppings or worms. Silty clay. 3YR3/4^. Approximately 40% silt aggregates, 30% quartz fragments, magnetite and other dark minerals, talc, manganese nodules radiolaria and fish teeth, 30% dark gray fecal "ribbons". 11 F Smooth surface with a few cratered mounds. Silty Clay. 10YRb/2^-3potted with 10YR7,/4r and 3YR3/47. Approximately 90% foraminlfera, 2% fecal "ribbons" and radiolaria. Sedimentary rocks recovered from trawl (672G). 21 PG Same as location 21. Silty clay p YR3/4^. Approximately 99% foraminlfera, 1& dark gray fecal "ribbons". Manganese nodules recovered from trawl (672G). 23 ?G Smooth; long, winding burrows; pits . Silty clay. 3YR3/4^. Approximately 99% foraminlfera, 1% dark gray fecal "ribbons". * Hose Bengal v 1 Light yellowish brown; “ -Moderate orange Drown; Moderate yellowish brown; Pale brown; 'H/ery pale orange; Moderate yellowish crown; ^Moderate brown; ‘ '’ Moderate yellowish brown; ^Grayish orange T Trigger carer; : • > Piston eorer; PG Piston _sed as gravity corer Figure 11 Outcrop of extrusive igneous rock crusted with manganese oxide. Irregular surface of sedi ments on slope in background. Note sediments filling in joints and other depressions of rock. Location: 15/665D. Depth: 2680 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine. 44 45 Figure 12 Outcrop of slightly rounded extrusive rock (pillow basalt). Orientation of "sea lilly" (crinoid) and alcyanarian coral (in foreground) indicates camera probably tilted 45° from the vertical. Calyx of crinoid directed towards direction of current. Sediment filling in depressions and also mantling the upper surfaces of some rocks. A milliped-like animal, or legged-holothurian is visible in right fore ground. Location: 15/665D. Depth: 2680 m. Base of photographs: 1.3 Photograph by R. Ouaknine. 46 47 Figure 13 Scattering of manganese nodules thinly covered by silty clay. A few large mounds and smaller pits as well as fecal dropping (center back ground) from worms, are visible. Location: 20/670E, Depth: 4400 m. Base of photograph: 1.4 m. Photograph by H. Ouaknine. 48 49 Figure 14 Mounds, pits, worm tubes, tracks and trails, and fecal droppings indicate the extent of sediment reworking* Location: 16/666F. Depth: 2932 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine* 50 Figure 15 Scattering of cratered mounds and smaller pits in foraminiferal ooze. The feeding sac, pos sibly of a worm, is visible in lower right-hand corner; note the similarity in shape between mounds and this animal. Location: 22/672C. Depth: 1870 m. Base of photograph: 1.3 m. Photograph by R. Ouaknine. 52 53 Figure 16 Preponderance of browsing and burrowing organ isms denoted by spiral markings from sub surface burrower, and the winding and grooved ridges formed by a pycnogonid (Msea spider”) one of which is visible in upper left-hand section of photograph. Location; 18/668D. Depth: 3165 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine. 54 55 Figure 17 Sediment cloud stirred up either by trigger weight of camera or animal. Visible are ob long coils of fecal matter, small pits, tracks (lower right of photo) and a ridge with medial crack probably caused by a burrowing animal (top center). Location: 19/669F. Depth: 4260 m. Base of photograph: approximately 1.4 m. Photograph by R. Ouaknine. 5 6 57 Figure 18 Large number of manganese nodules. Little organic activity visible. Location: 45/6811. Depth: 4200 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine. 53 59 r K Table 3 . Summary of observations - abyssal floors and islands Location and Device Bottom Photographs: Microrelief Coarse Fraction and Color Remarks 24 Both irregular, hackly and smooth regions (with worm tuoes). Manganese nodules dredge (674G). from rock 31 Scoured mounds asymmetrically shaped by currents 33 P Silty Clay. FYRb/^. Approximately 9b% foraminlfera, b% silt aggregates, mica, manganese nodules and dark gray fecal "ri obons". Manganese nodules rocks from dredge and volcanic (67tiE). 34 p Silty clay. bYR3/42. 90%- radiolaria, b% foraminlfera, 9% manganese noduis o Manganese nodules (6790). from trawl Lb T Large numbers of manganese nodules lying on smooth surface; only a few indistinct mounds visible. Silty clay.* Radiolaria, foraminlfera. Manganese nodules (68lD). from grab 4b T Irregular and hilly; surface marked by a few cratered mounds, worm tubes and trails. Clayey silt.* Mainly foraminlfera and radiolaria; some glauconite. Manganese nodules, volcanic and sedimentary rocks re covered from trawl (6821). P Clayey silt. Nb^. 90% radiolaria, b% foraminlfera, b% manganese nouules, glass, teeth, fecal "ribbons", cocoliths (?). * Rose Bengal T Trigger corer; p Piston corer x Grayish brown; 2 Moderate brown; Medium gray C T \ O 61 and Valparaiso, Chile, Much of this region is slightly hilly and has an average depth of about 4000 m. A sur face of hackly microrelief (Pig, 19) may attest to either faulting or volcanic disturbance at location 24, The abrupt slope at this location (see Pig, 3, profile FE may represent an extension of the Easter Island Fracture Zone to the east. With the exception of location 46, chemical activity at the surface appears to predominate over physical and biologic forces. The presence of volcanic islands and seamounts with "moats** indicate the recent volcanic exhalates (Bonatti and Nayudu, 1965)# The presence of manganese nodules is also an indication of the slow sedimentation rate in this region. A fast sedimentation rate would result in the formation of archipelagic aprons (Menard, 1964). Peru-Chile Trench and Continental Margin Off Valparaiso, Chile Recovery in the Peru-Chile Trench was small and probably due to the coarse texture of the surface sedi ment. The piston corer brought up several grams of sedi ment which contained approximately 86 percent sand-sized particles (Table 4). Bottom photographs at location 47 (Trench) reveal the surprisingly strong effect of physical forces such as deep currents, creep and slump, in creating the relief. These features (shown in Pigs. 20-23) are Figure 19 Irregular, hackly bottom showing little visible evidence of bottom activity except for spiral burrow (center left-hand edge of photo) and two light-colored animals with branching forms (possibly bryozoa) next to spiral burrow and in the center foreground. Location: 24/674E. Depth: 4198 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine. 62 63 Figure 20 Irregular hills and knobs of sediment in Peru- Chile Trench, off Valparaiso, Chile, A channel like mass of sediment runs obliquely across the field of view. The sediment in this "channel1 1 appears to be asymmetrically ripple-marked or perhaps piled into a series of minor drape like folds through downslope movement in a coherent or semi-coherent mass. Wave length of the ripples appears constant at about 0.3 m. Sediment surface is littered with oblong fecal droppings. Note prominent trail at base of photograph. Location: 47/683D. Depth: 5200 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine. 64 65 Figure 21 Irregular surface in Trench. Steep downslope portions of knots may indicate slumping of sediments. Fecal coils evident. Location: 47/683D. Depth: 5200 m. Base of photograph: 1.4 m. Photograph by R. Ouaknine. 66 67 Figure 22 Chunks and fragments of semiconsolidated sedi mentary rocks protruding from sediment on slope (Peru-Chile Trench). Also visible are stippled trails, tracks and fecal matter. Location: 47/683D. Depth: 5200 m. Base of photograph: approximately 1.0 m but may be less because of slope. Next photograph in sequence (not shown; indicates camera has been knocked over. Photograph by R. Ouaknine. 68 69 §si§I ' V'- GEE*BN; 4pfe V - | R t ■ ' * > . - • Figure 23 Long-crested oscillation (?) ripples in Trench. Pattern shown in upper right-hand corner of photograph may he interference ripple. Abundant fecal droppings are oriented pre dominantly at oblique or right angles to the direction of ripple crests. Location: 47/683D. Depth: 5200 m. Base of photograph: 1.3 m. Photograph by R. Ouaknine. 70 71 72 also being modified by the activity of benthic organisms, A channel of mega-rippled sediment (Fig. 20) runs oblique ly across a slumped terrain. Evidence of well-defined thin-crested ripplemarks (Fig. 23) indicates that deep currents as well as downslope movements due to gravity are operative in the Trench. The mega-rippled sediment was at first thought to be a slope-drape or sag feature, how ever Buffington (personal communication, 1969), on the basis of direct observations from over 35 dives in various deep submersibles off southern California, expressed the opinion that the ripples shown here (Fig. 23) probably represent some sort of current activity superimposed on a larger slump. Table 4. Summary of Observations - Peru Valparaiso, Chile -Chile Trench and Continental Margin off Location and Depth Bottom Photographs: Microrelief Coarse Fraction and Color Remarks 47 Hilly, irregular surface possible slump features; knobs; sediment-filled channel with "mega-ripples*1; one area of well-defined long-crested ripples. Piston corer (683F) recovered only 6.5 g of sediment: Washed sediment equals 5.6 g (approximately 86^ sand). Small recovery also on Campbell grab (683E) 50 P Abundant pits and mounds, coarser textured surface; abundant shrimp. Silty sand (5YR2/11). P - Piston corer. - Brownish-black. 74 SURFACE SEDIMENTOLOGY Laboratory Techniques Calcium Carbonate The determination of calcium carbonate content by the gasometric method followed procedures outlined in Bien (1952) and Kolpack and Bell (1968). The analytical error of this method is plus or minus 0.5 percent (Gors- line and others, 1968). Organic Carbon and Nitrogen Organic carbon is determined by analyzing the sediment for weight of total carbon and then subtracting the weight carbonate carbon from total carbon. Total carbon analysis entailed the use of a LECO induction fur nace (Laboratory Equipment Corporation, 1959) and results are plus or minus 0.4 percent as determined by the author on replicate analyses of known amounts of carbon. Organic nitrogen, another relative measure of the organic content of sediments, is determined by the Kjeldahl technique (Nierderl and Nierderl, 1947). Barnes (1967) found that the total recovery from 35 replicate samples was plus or minus 5 percent of the nitrogen present. Kolpack (1968) found that the accuracy involved 75 in the digestion of marine sediments is difficult to assay, but that the distillation procedure had an ac curacy of plus or minus 3.0 percent and a precision of plus or minus 2.0 percent. Texture Textural parameters were determined through hydro meter analysis of the grain-size distribution. Sternberg and Oreager (1961) show hydrometer cumulative curves to vary by no more than an average of 5*5 percent from replicate analyses made with the pipette; the accuracy and precision of the hydrometer increases with sediment concentrations greater than 12 gm/l. Calculation of mean diameter (M ), phi standard deviation (SDJ2f) and phi skewness (Sk 0) was accomplished with a Honeywell computer utilizing a Fortran IV statistical program for standard size analysis of unconsolidated sediment (Pierce and Good, 1961). Gross Cla.y Mineralogy Pipettes of the less than 2 micron fraction were drawn after hydrometer analysis was completed. These samples were sedimented onto glass slides and analyzed with a Norelco X-ray diffractometer for clay-mineral con tent after the methods of Warshaw and Roy (1961). Chemical and Textural Data 76 Textural trends show a marked reduction in mean grain size and a corresponding decrease in the sand-sized fraction below 2000 m (Pig. 24). Some of the larger quantities of sand-sized fraction below and above this depth are the product of the contribution of CaCO^ from foraminiferal tests larger than 62 microns (Pig. 24). At a depth of 4000 m nearly all of the CaCO-^ is dissolved and only resistant or rapidly deposited foraminifera are usually preserved (Peterson, 1966; Berger, 1967, 1968). Values of organic carbon and nitrogen (Pig. 24) show no apparent trend with depth except in the coastal region off Callao where the high productivity is reflected in the bottom photographs (Pigs. 6-10). An apparent relationship is shown between organic carbon and nitrogen content and CaCO^ content. Organic carbon is roughly inversely pro portional to CaCO^; this may be a reflection of the greater amounts of organic material present in the low carbonate, terrigenous sediments and in the low carbonate deep-sea clays. In deep-sea clays below the compensation depth organic material ionically fixed by colloidal particles result in a higher organic carbon content at the expense of calcium carbonate. It should be pointed out that the trends, if any, represent several different environments and that interpretations must be more care fully analyzed on the basis of physiography. Figure 24 Relationship of CaCO^, organic carbon and nitrogen, size distribution and mean diameter plotted against depth for surface sediments. 77 78 5 0 100 ( ft a c u I - L U 2 v cr h - L i J Z > • X h - < O D I 000 2 000 3000- 4 0 00 5000- 6000 % C a C 0 3 10 0 50 100 % Organic C Size Distrib. < f t a: UJ ( - UJ 2 > c c H - U J 2 > • X H < CD 1000 2000 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 50 100 % Organ ic N Mean Diameter (My) in microns When mean particle diameter (microns) is plotted against phi standard deviation (sorting) and against phi skewness, for each location, it becomes evident that the terrigenous sediments from the continental margin off Callao have coarser texture, slightly poorer sorting and are skewed towards the fine particle sizes in comparison with sediments in the Trench and seaward (Fig. 25). The coarse texture of the former group is explained by proximity to both source and higher energy environments. The presence of boulders, cobble and pebbles, as shown in the bottom photographs, serves to show that the sampling method does not accurately account for the actual range of sizes in this region. A larger sampling would pro bably reveal a tendency towards a bimodal size distribu tion. In the low-energy deep ocean environment only fine sediment is transported by suspension in water, or air, and finally deposited. Sand-sized foraminifera make up a large proportion of some samples, especially those on the crest of Nasca Ridge. Therefore, it is not surprising to find that the sediment from the shoalest portion of the Ridge, location 22, has a mean particle size within the range of the shallower terrigenous sedi ments. Location 18 (Fig. 25) represents analyses made on the upper 2 cm of a piston core. Since the associated trigger core shows a smaller CaCO^ content (approximately 39%) and, most likely, a smaller mean size, the actual Figure 25 Plot of mean diameter in microns versus standard deviation (phi) and skewness (phi). Location 17b and 17g refer to trigger cores 17/667B and 17/667G, respectively. 80 81 Sk0 46 J___i — l.i / \ L r L i 17? I7t £3r] 0 Mu 23 16 • Mu versus SD0 A Mu versus Sk0 33 COf<E LOCATION 82 position of the sample from location 18 should be shifted to the finer-sized, better sorted pelagic sediment group. An interesting trend within the terrigenous sediments is noted for locations 1, 2, 6 and 9. Mean size increases with depth, culminates in a maximum mean size of 94- microns for location 9 and subsequently decreases with increasing depth below 1000 m (Pigs. 25 and 26). Loca tion 9 is characterized by abundant glauconite casts of Bolivina sp. and Uvigerlna sp. It should also be noted that sorting Is measurably better (Pig. 25) and a rela tively large percent of CaCO^ is found (Pig. 26) in this sample. The CaCO^ is derived from test fragments and from the vein fillings observed in the glauconite casts. The well-sorted coarse material of location 9 then is the result of large biogenous accumulations at this depth. The relatively high CaCO^ content agrees with studies which show a maximum abundance of foraminifera (which are larger than 62 microns) at about the 1000 m depth on the west coast of South America (Bandy and Rodolfo, 1964). The greatest CaCO^ content is also noted to occur at this depth for the continental margin samples. When CaCO^ is plotted against depth and the resulting plots grouped as to region (Pig. 27), the effect of physiography on CaCO^ is better defined. CaCO^ is shown to decrease appreciably with depth and to be sharply controlled by the compensa tion depth. The area flanking Nasca Ridge has a wide Figure 26 Graph of mean diameter versus bathymetry, CaGO^ content plotted as an independent variable. Black circles represent zero CaCQ-z content. Location 18 represents top of a piston core; associated trigger core has 39 percent CaCO^ but was not analyzed for size. 83 0 1000-3 in tr 2 0 0 0 - LU h- L lI Z Z 3 0 0 0 - >■ tr 1^400 0 - >- X I- < 5 0 0 0 - tn 100 75^5 50 0<2KSS % C g C 0 3 Continental mar gin, Callao — Crest of Nasca Rid ge Nasca Ridge flank area 3 4 O 20 a » ■■" -r1 10 5 MEA N DIA M ETER , u (microns) oo 4> Figure 27 Graph of CaC03 versus bathymetry. plots grouped'geographically. Resultant C o n t i n e n t a l Margin l OOO c n K 2 000 - UJ H LU Nasca Ridge Crest Z 3 0 0 0 >- £T Abyssal Floor 2 3 UJ 5 > 4 0 0 0 X I- < CD 3 3 17b 5 0 0 0 P e r u - Chile T rench, C a l l a o 6 0 0 0 100 5 0 7 5 0 % Co C 0 3 • Trigger core X Piston core ® p iston corer used as a gravity c o r e r 87 range of CaCO_ content. Higher values are roughly related 5 to distance from the continent and reflect the reduced amounts of terrigenous material which would otherwise dilute the amount of carbonate (Pig. 28). Organic matter in sediment is affected by the oxygen content of the water, benthonic and bacterial activity, the resistance and type of organic material and the Eh of the sediments (Emery, i960). Trask (1932) and Revelle and Shepard (1939) found that total organic matter is less than 1 percent for bank tops and for continental and island shelves, whereas values between 5 and 10 percent are present in the basin and trough areas off southern California. The dilution of organic nitro gen by sediment which is rapidly deposited and the rela tive increase of nitrogen in fine, undiluted, and slowly- deposited sediments has been noted by several workers (Emery and Rittenberg, 1952; Emery, i960; Gorsline and others, 1968). Based on studies off southern California, a ratio of 1.7 for total organic matter to organic carbon in sediments has been cited. Emery (i960) points out that because of uncertainties this ratio should be used only for the sake of consistency and not be accepted as necessarily correct. Organic nitrogen roughly parallels organic carbon content but the ratio c/N is not fixed and in fact varies with the particular type of environment. Along the continental margin off Peru, the trends Figure 28 Relationship between OaCO^ content, bathymetry and distance from land. 88 Depth: • 0- 2000 m O 2-4 00 0 m O 4-6000 m 23 O 6 00 22 33 34 o ‘ 18 p O l8t 20 O f 9 O f 45 |6 o o | 7 b I7g 15 r 100 4 6 % Co CO 3 5 0 25 500 400 300 200 100 D IS TA N C E FROM LAND (nautical miles) 90 observed in southern California basins are not observed (Fig. 29). Organic carbon content is exceedingly high and if a ratio of 1.7 is employed to determine the amount of total organic matter, values range between 6.0 and 17.7 weight percent. Furthermore, carbon and nitrogen are seen to attain maximum values in the coarser sediments. The best explanation for this trend is that maximum over turning and greatest productivity in the Peru Current occurs at about 300 m along the Bruun track. Extensive reworking of the finer abyssal sediments of locations 13 and 14 (Trench) is shown by bottom photo graphy (Figs. 9 and 10) and the moderate organic carbon content (Fig. 29). Values of zero percent nitrogen for these locations appear to be an operatorfs error in the analysis. Comparison with the base of the piston core for location 14 shows a value of 0*32% nitrogen, which parallels both the carbon and nitrogen trends of the slope sediments and tends to confirm the operational error. Although several of the trigger cores were treated, after recovery, with a solution of Hose Bengal, alcohol and sea water, a plot of these samples (Fig. 29) with untreated specimens from the same station shows little, if any, effect on the organic carbon and nitrogen contents. A noticeable decrease in organic carbon and nitro gen occurs in the pelagic sediments seaward of the Trench. Values of organic carbon and nitrogen content for loca- Figure 29 Relationship of organic carbon and nitrogen plotted sequentially along ship's track. Question marks indicate operator's error for locations 13 and 14. 91 (% ) ORGANIC C (%) ORGANIC N 10 8 6 4 2 0 0 .200 4 0 0 .600 .800 1.000 Mean 1 1 1 1 1 1 1 1 1 1 Location 1 1 1 1 1 1 1 1 1 1 Depth(m) Diam.(u) CONTINENTAL MARGIN, CALLAO • 1 • 95 14.5 • 2 • 140 48.0 • 5 • 2 8 7 o 6 O 4 2 0 44.0 • 9 • 1 0 0 0 94.0 • 1 1 • 2110 25.5 * 13 4 2 0 0 5.4 TRENCH,CALLAO • CD 14 C 9— ■*? □ 5 5 2 0 5.4 NASCA RIDGE • 15 • 3 0 7 0 3.0 • 16 • 2 9 8 0 3.9 ° I7B ° 4 0 5 0 3.7 O L 1 17 G ( 4 0 9 0 3 .0 ,4 4 £ | 18 ( 2] ° 3170 14.0 0 3 19 £ ) □ 4 2 8 0 2.2 c r 2 0 E© 4 4 5 0 1.8 o 21 [o 4 01 0 2.5 i 2 2 E D 1 7 6 0 4 0 .0 £ ) 2 3 [ 3© 3 7 0 0 4.2 J.FERNANDEZ- SAN FELIX ISLAND AREA £ h 3 3 [0 3 8 0 0 2.5 £!) 3 4 [ 4 5 0 3 9 2 0 1.7 • • s 3 8 5 0 TRENCH SEAWARD OF VALPARAISO □o • 4 6 3 9 6 0 7.0 C O N T IN E N T A L MAR GIN, V A L P A R A IS O □ 5 0 o 4 8 5 O TRIGGER CORE • TRIGG ER CORE TREATED WITH ROSE BENGA L-ALCOHOL SOLUTION 0.0 PISTON CORE : TOP ; BOTTOM 0 , 0 PISTON CORER USED ASA GRAVITY CORER 93 tions 15-20 average approximately 0.8 and 0.06$, respectively. This is compared with corresponding average values of 5.7 and 0.40$ for the continental margin and Trench samples. The following relationship between pela gic and terrigenous sediment in this area gives an indica tion of the magnitude of organic matter: A • B • Trench and Seaward of Shoreward Trench A/B Average $ Org. C 5*7 0.8 7*1 Average $ Org. N 0.40 0.06 6.6 Average c/R 14.2 13.3 Owing to the greater precision and accuracy in determining organic carbon content, the ratio value of 7 indicates that organic matter is seven times more abundant in terrigenous and Trench sediments off Callao than in sediments seaward. Average values of C/N are somewhat lower seaward of the Trench. Some individual samples show a wide range of c/N values ranging from 60.0 and 0.9 for locations seaward of the Trench to 19.4 and 9.4 shoreward. Values of C/N appear more consistent for individual samples on the continental margin, and erratic ratios become more prominent approaching, and seaward of, the Trench. Al though an average C/N ratio of 6.60 for 12 samples along the Trench was reported by Bandy and Rodolfo (1964), their value of 12.0 for Eltanin station 41 (3495 m) off Callao is in the general range found in this study. Some of the 94 low C/N values possibly reflect a relative increase of N with respect to C in increasingly clayey sediments (Arrhenius, 1952). Locations on the southeastern side of Nasca Ridge and in the island region south show generally lower organic carbon and nitrogen values. No apparent trend with mean grain size was noted in these areas (Pig. 29). On approaching the continental margin off Val paraiso, Ohile, organic carbon and nitrogen show an in crease which may be correlated with increased grain size. However, more samples from this region would have to be studied to determine actual trends. Clay Mineralogy Six major groups of clay minerals were qualitative ly identified in the surface sediments: Illlte - Platy minerals which give diffraction o peaks at approximately 10 A and are not affected by treat ment with ethylene glycol. This group also includes glauconite and the micas (Grim, 1953). 2. Montmorillonlte - Identifiable by a broad peak o between 15 and 12 A which expands with ethylene glycol o treatment to approximately 17 A. o 3* Kaolinite - This group includes any platy 7 A mineral which retains its basal reflection after heating to 450°C (Zen, 1959). No attempt was made to distinguish the various phases of kaolinite. 95 o Chlorite - 14 A clay mineral; determined by heat treatments as described in Warshaw and Roy (1961), 5. Kaolinite-Chlorite - Based on basal reflections only; probably contains both minerals. 6. Mixed Layer Minerals - Several different interstratified clay minerals giving peaks between 10 and o o 14 A. Bo not fully expand to 17 A with ethylene glycol treatment. The distribution of clay-minerals shows no ap parent trend with depth or location except perhaps the mixed layer and illite groups (Table 5). The mixed layer minerals do not appear in any of the continental margin samples above 4000 m and illite seems to be more abundant on Nasca Ridge and north towards Callao. Montmorillonite is either present in small quantities, or poorly crystal lized, northeast of Nasca Ridge. Numerous fragments of volcanic glass were observed in the surface sediments of this region. The alteration of volcanic ash to mont morillonite (Ross and Hendricks, 1945), however, may be strongly affected by either physical factors (currents, etc.) or biologic alteration (organic complexing) of the clay mineral. The lack of definite trends in the south Pacific, compared to the strongly developed patterns and source areas in the north Pacific, has been noted by Griffin and Goldberg (1963). They explain this dif ference as the result of small amounts of detrital 96 Table 5* Occurrence of clay minerals Location I M C K K-C ML Location I M C K I-Q ML 1 X ? X 18 X X X 2 S ? X 19 X X X X X 6 X X X 20 ? X X X X 9 X 9 • X 21 ? X X X X 11 X ? X 22 X X 13 X ? X s X 23 X X X 14 X ? X X X 33 X X X X 15 X X X X 34 X X X 16 X 9 • X X X 46 X X X 17 X X X s X X - present S - present in small amounts ? - may be present I - illite M - montmorillonite C - chlorite K - kaolinite K-C- kaolinite-chlorite ML - mixed layer minerals being deposited today in the south Pacific com pared to the faster sedimentation rate and abundant source areas in the north Pacific, The better-defined mont- morillonite peaks in the south Pacific are also explained by the greater amounts of pyroclastics contributed there. 98 STRATIGRAPHY OP DEEP-SEA CORES General Among the many problems inherent in determining sedimentation rates and correlation of Pleistocene carbonate depositional events, distortion and omission of sediment in the coring procedure is significant, Arrhenius (1952) developed a Pleistocene chronology based on CaCO-j for the equatorial Pacific and found that a highly increased rate of productivity in the upper water level is related to high CaCO^ content. He subdivided high and low CaCO^ zones into glacial and interglacial periods, respectively. This is thought to be exactly opposite to cores studied in the Atlantic and north Pacific and may be the result of not accounting for the loss of sediment in the upper portion of the piston corers (Shepard, 1963); on the other hand, the chronology may be correct for equatorial sediments. To complicate matters, it was assumed that piston corers obtained a relatively undistorted (unshortened) section of sediment in compari son to gravity corers at the same location (Emery and Hulsemann, 1964). Recent investigation has found an opposite relationship to exist: piston cores were shortened relative to gravity cores (Ross and Reidel, 1967). The amount of distortion was also found to be 99 highly variable and affected by the individual sampling technique, dimensions of the corers and sediment type. Upon consideration of the problems it should also be realized that sedimentation rates expressed in length per years is biased by both natural compaction of the sedi ments and by distortion during sampling. One technique described by Scholl (1958) utilizes the amount of salt in the sample to determine the original amount of sea water. In this way, one can express sedimentation rates in terms of dry weight per unit per year. The use of absolute radiometric dates in conjunc tion with paleontological and lithologic markers can be used to correlate events between cores. Since no ab solute dates and only limited paleontological data are available in this study, the author has attempted only a generalized interpretation of past events on the basis of sedimentological and chemical parameters and by comparison to published chronologies. Peru-Ohile Trench, Callao Both a piston and a trigger core were obtained from the shoreward portion of the Trench axis at location 14, CaCO^ and organic content for both cores indicate that little if any surface sediment was lost in the coring operation. A relatively large amount of CaCO^ is found in the piston core with depth (Pig. 30) when the water Figure 30 Physical and chemical parameters of piston core 14/664A. Coarse fraction (greater than 62 microns) is divided into 3 general groups of sediment: (1) Biotic (blank portion of pie diagram) consisting of foraminifera (f), radiolarians (r), diatoms (d) and coccoliths and discoasters (c); (2) Biogenous (black) made up of glauconite casts (g), undifferenti- ated organic debris (o), fecal pellets (p), fish scales (s), and teeth (t); (3) Detrital (stippled) consisting of quartz (q), glass (g), mica (m), dark minerals (dk), sedimentary (s) and volcanic (v) rocks, G.S.A. color codes (Goddard, 1948): 512/1, olive black; 5Y3/1, dark olive gray; 514/1, olive gray, Note: Symbols for three components of coarse fraction will also hold for pie diagrams in succeeding figures. Lower case letters for components of each group are listed in decreasing order of abundance. 100 2 C I 4 664A-P % C a C C 3 I 0 I 5 SIZE PI S T R I BU T I 0 N 0 5 0 100 > 6 2 u CO LO R % O R E C 0 0 J f,, q . m ,d k 5 Y 2 / I op p r ■ - q ,m,d k Y 4/1 q ,m(dk,s,v w, Pj 1, o q k(s (v Y3/ I and > Y 4 / I G G £ R CORE 101 102 depth (5520 m) is considered. Tests of the foraminifera Bolivina sp, occur in the calcareous sections. These tests may have been displaced from the upper regions of the continental slope since they are associated with sand and silty sand. The occurrence of glauconite foraminiferal casts and detrital quartz, mica and heavy minerals further supports the displacement even though several species of Bolivina inhabit bathyal to abyssal depths in this region (Bandy and Rodolfo, 1964). It is surprising to find any amount of C&COj below the compensation depth. However, if sedimentation is sufficiently rapid, succeeding layers will protect calcareous forms, already deposited, from solution. For example, the occurrence of the calcareous shallow-water alga Hallmeda in coarse layers interbedded with red clay has been noted (Heezen, 1963) in the bottom sediments of the Puerto Rico Trench at 8380 m (4580 fm). Radiolarians dominate the coarse fraction of the surface sediment and reappear at all other low CaCO^ intervals. Numerous sand layers at the 200 cm level also coincide with the CaOO^ maximum and indicate that the upper 230 cm of the core is largely composed of Hturbi- dites.H The reappearance of worm tubes, fecal pellets and dominant numbers of radiolarians below 230 cm demonstrates a return to conditions of slow deposition and benthic re working of sediments. The presence of abundant volcanic glass in the surface sediments of the continental margin 103 and throughout most of the core (both above and below the 230 cm depth) attests to recurring volcanic activity in this region and may correspond to the widespread occur rence of volcanic ash here and to the north (Worzel, 1959). Organic carbon content in the core shows a good relationship with the grain size distribution. Low values of organic carbon correlate with coarser sediments and indicate either dilution of organic material by an in crease of detrital material, or sorting in transport of two different density components. Due to the lack of paleontologic or radiometric data it is difficult to ascertain the age between the "turbidite” and pelagic sequence. If this "turbidite" sequence is the result of an increased supply of sediments resulting from lowered sea level, increased stream gradients and intensified meteorological conditions dur ing the Pleistocene glacial stages, then one must also consider the length of the pelagic clays below and question whether this represents Pliocene or interglacial sedi ments. A sedimentation rate of 1.2 mm/1000 years for an expected Pleistocene time span of 2 million years appears within the range ascribed for the southeast Pacific. Once more, the possibility that the piston core has been measurably shortened should not be overlooked, or that sediment is sufficiently trapped on the continental margin 104 to allow a slow sedimentation rate for the Trench, Nasca Ridge Piston core 17/6670* on the flank of the northern portion of Nasca Ridge, is an homogenous chocolate brown clay with some mottling in its lower half (Pig. 31). The remarkable fact about this core is its CaCO^ content which bears a striking resemblance to the pattern observed in the Trench core. Both cores have a CaCO^ maximum in the upper 30 cm followed by a minimum interval below. Bandy (personal communication), in a preliminary study, observed some left-coiling Globigerina pachyderma at the 20 cm core depth (667G) CaCO^ peak and more than 50^ sinistral forms at the 95 cm CaCO^ peak. Both cores also have the great est CaCO^ content at about 240 cm and zero CaCO^ below. Although core 667G lacks the high percentage of sand noted in 664a , both cores have the same increase of CaCO^ with particle size and the presence of radiolarians in low CaCO-j intervals. Fluctuations of the OaOO^ content in 17/667G are, however, better defined and show distinct intervals of zero CaCO^. The down-slope position of 17/667G from the cal careous ooze of core 16/666B on the crest and the high percentage of silt in 17/667G also indicate that the latter may be receiving sediment from higher regions in a manner similar to the Trench core. The bioturbation of Figure 31 Physical and chemical parameters of piston core 17/667G. Biotic coarse fraction: fora- minifera (f), radiolarians (r) and coccoliths (c). gjLoeenous_: fecal pellets (ps), fecal coils (fc), fish teeth (t) and undifferentiated organic debris (o). Petrital: quartz (q), glass (g), mica (m), chlorite (c), rock frag ments (r), talc (t) and dark minerals (dk). Color codes: 10YR5/4, moderate yellowish brown; 10YR6/2, pale yellowish brown. 105 D t : f - T H N r J b V . SAND CLAY CO LLO ID 901 > 6 2 a COLOR % ORG 107 sediment by benthic organisms (Table 2) in this region may have destroyed any layering of turbidites originally pre sent, Organic carbon content generally follows the same trends as 14/664A but is decidedly smaller. Further south, core 18/668F (piston and trigger) on the crest shows a sharp increase in OaOO^ content below the surface sediment (Fig. 32) and a minor increase below 25 cm. Blackman and Somayajulu (1966, p. 887) reported a gravity core (DWBG 114) nearby to the southwest at 3090 m which had a surface CaCO^ content of 82.0 percent. This measurement was at the 0-4 cm interval and it is possible that the 0-2 cm interval would have registered a drop in CaCO^ content such as that shown for the 0-1.5 cm inter- 3 val of trigger core 18/668F. Organic carbon is 0.23 per cent at the surface and decreases to less than 0.10 per cent below. Core 19/669D, on the north flank, has only one CaCO^ peak between 0-30 cm (Fig. 32). Organic carbon also shows a similar increase and is considerably higher than the previous crest sample. Trends in the size dis tribution appear to depart from the higher CaCO-^-coarser size of cores 14/664A and 17/6670 in that the CaCO^ peak is associated with a low silt fraction. However, the sand fraction for the 5-10 cm interval contains at least 70 percent foraminifera, and together with coccoliths and foraminifera in the silt fraction should account for the Figure 32 Chemical and physical parameters of piston core 18/668F and gravity core 19/669D. Biotic coarse fraction: foraminifera (f), radiolarians (r) and coccoliths (c). Biogenous: fecal pellets (ps), fecal coils (fc; and fish teeth (t). Detrital: quartz (q), mica (m), talc (t), chlorite (c) and dark minerals (dk). Color codes: 10YR6/2, pale yellowish brown; 10YR5/2, moderate yellowish brown; 5YR5/2, pale brown; 5Y5/l> medium olive gray. 108 8/668F-P % C o C 0 3 30 6 0 9 0 J 1 I J , . J i f 5 J . E {.1ST PI B .. i I O N i oo > 6 2 g / h , X - TRIGGER COR E C O O R % ORG C 0 10 0 r R 6/2 1 9 /6 6 9 D — P6 5 0 100 ® 0 ' w ' “0 - q ,m t, c ,d k ~ ~ T ~ I0YR5/2 5 V 5/1 I grades evenly t o 10 Y R 5 / 2 __yi_ 5 Y R 5 /2 H O VO 110 observed OaCO^ content. Below this peak radiolarians are the dominant forms in the sand-sized fraction; at the base, a large percentage of this fraction is represented by fecal pellets. A color change occurs between the cal careous interval (moderate yellowish brown) and the 50-110 cm interval (medium olive gray). At 110 cm an even downward gradation to moderate yellowish brown is ac companied by a maximum increase of the silt fraction. Core 20/670F (Big. 33) is a brown deep-sea clay containing no CaCO^. Although the 0-10 cm interval was not available for analysis, it is doubtful that it is calcareous since the 10-12 cm interval should carry through at least a small amount of CaCO^ and the water depth (4450 m) is well below the compensation depth. The larger than 62 micron size fraction revealed sponge spicules below 160 cm and manganese micronodules (40^) near the base (340 cm). On the north flank, but southwest of location 20, core 21/671F is a calcareous silty clay from 0 cm to the 80 cm depth and is a foraminiferal ooze between 80 and 110 cm. Since no trigger core was taken at this location it is assumed that some of the surface sediment was lost during coring. The many CaCO^ peaks indicate fluctuations in productivity probably associated with climatic changes. A large peak at 100 cm may be related to the maximum CaCO^ peak seen at locations 14 and 17* The percentage Figure 33 Chemical and physical parameters of gravity- core 20/670F and piston core 21/671F. Biotic coarse fraction: foraminifera (f) and radiolarians (r). Biogenous: fecal pellets (ps), fecal coils (fc), fish teeth (t) and sponge spicules (sp). Detrital-authigenic: quartz (q), glass (g), dark minerals (die), mica (m), talc (t) and manganese micronodules (mn). Color codes: 5YR3/3, moderate grayish brown; 5YR3/4, moderate brown; 10YR7/4, grayish orange; 10YR5/4, moderate yellowish brown; 10YR4/4, yellowish brown; 10YR6/2, pale yellow ish brown; 10YR5/2, moderate yellowish brown. 111 112 20/670 F— PG I 0 0 2 C 0 — P * , 1 c , ♦ p».fc, t SI ZE D I S T R I B U T I O N COLOR > S 2 n ORG. C 1,0* , m n 5 YR 3, in m ol t es o f 10 l R 5/4 d kV-; r * P S | ! . * p 10 YR 5/2 10 Y R 4/4 I 0 Y R 5/2 ICYR 6 / 2 10 YR5/2 {zero % C q C 0 3 ) P s,*,sp 113 and size of manganese micronodules in the coarse fraction increases (from 15 to 20%) below the 150 cm depth. Organic carbon, CaCO^ and size distribution do not seem to show any interrelated trends. Core 22/672F (Fig* 34) on the crest at a water depth of 1760 m is a pale yellowish brown, foraminiferal ooze. A definite increase in OaCO^ takes place below the 5 m core depth and little variation is seen below. Organic carbon exhibits minimum values in association with the small clay and colloidal size fractions. This core is similar to one reported by Blackman and Somayajulu (1966)— DWBG98C— to the southwest at 2300 m, which does not show a decrease in CaCO^ at the surface. Blackman and Somayajulu (1966) have calculated a sedimentation rate of 6.9 mm/1000 and 6.1 mm/lOOO years for cores DWBG114 and 98c, respectively, on the basis of the thorium-230: thorium 232 method. Core 23/673E, located on the south flank in 3700 m of water and nearly due south of location 22, is a moderate to pale yellowish brown foraminiferal ooze (Fig. 34). CaCO^ content decreases below the surface and develops a maximum peak at approximately 140 cm. A thin (0.2 cm) sand layer is present at this depth and spotted sediment and fecal pellets throughout the core indicate benthic reworking. This location is situated at the base of the steep southeast flank of Nasca Ridge and the pre- Figure 34- Chemical and physical parameters of gravity cores 22/672F and 23/673E and piston core 33/678G. Biotic coarse fraction: fora- minifera (f) and radiolarians (r). Biogenous: fecal coils (fc), fecal pellets (ps) and fish teeth (t). Detrital-authigenic: quartz (q), glass (g), talc (t), volcanic rocks (rv), mica (m) and manganese micronodules (mn). Color codes: 10YR7/2, pale orange; 10YR6/2, pale yellowish brown; 10YR7/4, grayish orange; 5YR6/4, light brown; 5YR4/4 and 5YR3/3, moderate brown; 5YR3/2, grayish brown. 114 u / o C a C 0 3 Vo ORG. C 2 2 / 6 7 2 F PG SIZ E Dl S T R i U U T I O N 115 C O LO ft 80 100 0 1.0 0 — 1 —L-i— l _____ 50 I 00 I 0 0 0 1 P7/2 10 Y R 7/2 mottled with ! C Y R 6,' 2 .. O ' 50 I 0 0 80 5 YR 3/4 . 0 YR 6/2 v - ■ t h spots of I 0 YR 7/4 and vi ’ hr d vole r c o k ( and glass 5 YR 3/4 0 0 S Y R 4 / 4 ps spotted ""sand ktyer 0 2 cm ttik nn n ,r v, g,t, m 5 Y R 4/4 ps with spots of 1 0 Y R T / 4 0 2 3 /6 7 3 E—PG m n , m 100 .0 20 40 rs.t 5 YR 3/2 p s , t 3 3/.6 7 8G-P 116 sence of sand layers, volcanic glass and rocks indicate a contribution of material from the Ridge. Abyssal Floor and Island Groups Core 33/678G (Fig. 34) was collected on the crest of one of several small seamounts south of San Felix Is land. The surface sediment is a grayish brown foraminifer al ooze ranging from silty clay above to clayey silts be low. A sharp increase in CaCO^ at approximately 162 cm may be related to a similar peak in core 22/672F. At a core depth of 30 cm a manganese nodule was found which was nearly 2 cm in diameter. It did not appear to have been displaced from another horizon during coring. Manganese micronodules are also distributed throughout the length of the core and radiolarians are dominant in the 30-50 cm interval. This interval is also characterized by an in creased sand fraction as a result of the increase of radiolarians. Radiolarians are also in abundance in the upper 25 cm of core 34/679F (Fig. 35) to the south. As in location 33» this sediment is a brown foraminiferal ooze and grades to calcareous clayey silts and silty clays below. Manganese micronodules, glass and fecal pellets are dessiminated throughout the core and low values (0.17- 0.01 percent) of organic carbon are observed. The basal CaCO^ peak at 165 cm may correspond with the peaks noted at 140 and 162 cm for locations 23 and 33, respectively. Figure 35 Chemical and physical parameters of piston cores 34/679F and 46/682H. Biotic coarse fraction: foraminifera (f), radiolarians (4) and coccoliths (c). Biqgenous: fecal pellets (ps), fecal coils (fc) and fish teeth (t). Detrital-authigenlc: quartz (q), glass (g), mica (m),volcanic rocks (rv) and manganese micronodules (mn). Color codes: 5YB3/4, moderate brown; 5YR5/2, pale brown; 5R5/2, 5R4/2, grayish red; 10R5/4, pale red dish brown; IT4, medium dark gray; R5> medium gray; R6, medium light gray; R7> light gray. 117 (cm) 118 % C a C 0 3 S I Z E D I S T R I B U T I O N O 2 0 40 0 Of J I L I 0 0 ^ 6 2 u p s m n ,g ) ( o r g a n i c C m a x i mu m of 0 .1 7 % of s u r f a c e ,0.0 I below) 3 4 / 6 7 9 F— P COLOR 5 Y R 3/4 5 K 5 / 2 D R4/2 [ps,t with u p o t s c f I 0 R D/4 % Or g. C 20 50 0 0 P5 2 0 0 p jrnice eng P s 3 0 0 ■ I 6 ' J 0 N o and N7 . 1 N 5 - L CR5 '2 mott lee N b with s p o *' j f N 4 X = T R I G G E R CORE 4 6 / 6 8 2 H— P 119 Core 46/682H (Fig. 35 )> located nearly 150 km sea ward of the Peru-Chile Trench off Valparaiso (Fig. 3* profile I-J) is in a region of low hills and irregular topography. The surface sediment is a slightly cal careous, gray clayey silt. CaCO^ content increases with depth to 35 cm and fluctuates between 3 and 17 percent below. Thin alternating layers of light and medium gray clayey silt occur within the 30-70 cm interval. Volcanic rocks, glass, manganese and assorted minerals are pre sent above the 230 cm depth. Due to the smaller, less defined peaks of CaCO^, it is difficult to attempt cor relations with previous cores. Large contributions of sediment have been derived from the glaciated Andes off Chile and a high sedimentation rate should be expected in this area (Scholl, personal communication, 1969). Pelagic Sedimentation and Pleistocene Carbonate Deposition Several well defined CaCO^ peaks are available for a general correlation although there is some doubt as to their climatic significance. Previous explanations of the high CaCO^ content call upon upwelling and the in creased productivity associated with intensified meteoro logical conditions during glacial stages, at least in the equatorial Pacific (Arrhenius, 1952). The CaCO^ maxima can also result from a reduction in solution during the warmer, interglacial stages. Gravity cores, and piston 120 and trigger cores taken simultaneously, have in most cases sampled a complete section of surface and subsurface sedi ment. These profiles indicate that present (warm) condi tions are characterized by slow deposition, lower CaCO^, and generally lower organic content. This is true at least north of location 22 (assuming that core 21/6711? has lost the upper 10-20 cm of sediment). The piston and trigger cores seaward of the Trench off Valparaiso show this general pattern. The intermediate cores (locations 23> 33 and 34) show an increase in CaCO^ at the surface which can be explained by (1) loss of surface sediment during coring (no trigger core taken) even though a gravity core (23/673E) was taken, or (2) nearly all sur face sediment is represented, productivity was relatively minor in influence and CaCO^ content was directly in fluenced by reduced solution during interglacial periods. Arrhenius (1952) states that a greater loss of surficial sediment occurs when coring calcareous oozes. Since the cores in question have between 40 and 80 percent CaCO-^, it can be argued that this loss has occurred and that a CaCO-, decrease at the surface would be observed had a com- 3 plete section been sampled. The occurrence of a manganese nodule at the 25-30 cm interval of core 33/678G corresponds to a low CaCO^ content and greater numbers of radiolarians. This indicates the slower sedimentation rate associated with interglacial times. 121 Under the hypothesis that GaCO^ peaks represent glacial (cold) stages, several maxima can be traced across the study area. Cores 14/664A and 17/6670 show an upper CaCO- 3 peak (“W”) which is interpreted as the last glacial stage (Fig. 36). This hypothesis is further strengthened by the presence of some left-coiling Globigerina pachyderma in the latter core at this peak and by frequent numbers of radiolarians in the warm water sediments above and below this peak. The sediment thickness between the surface and the initial CaCO^ increase is taken as representing Holo- cene sedimentation. Seismic profiles in the Trench off Antofagasto, Chile, show a sequence of Pleistocene turbidites overlying pelagic sediment both of which thin towards the north (Scholl, personal communication, 1969). Although seismic data is lacking in the vicinity of core 14/664A, a select core could conceivably sample both layers. In all cores north of location 22 the Holocene interval is between 1.5 and approximately 3 cm thick, which indicates a sedimentation rate of 1.4 to 2.7 mm/1000 years, if the inflection point is taken as 11,000 years B.P. This peak is correlated with the tops of cores 21, 23* 33 and 34 for reasons discussed previously. CaCO^ peaks "X" and hY" are also roughly correlated across the cores (Fig. 36). The peak , f Z, f in cores 14 and 17 is thought to represent initial glaciation at the Pleistocene-Pliocene boundary. If true, this would repre- Figure 36 CjaC03 content, size distribution, and generalized carbonate correlations of A. Bruun cores. V represents last Glacial Stage and MZn is thought to be Pleistocene-Pliocene boundary. f , Xf * and , 1 Y” do not represent any specific Pleistocene horizon but are only attempted correlations from core to core. 122 I 4/6 6 4 A- P I 7 / 6 6 7 G - P w ■ z —t- K L 22/672F-PG 23/673E-PG 3 3 /6 7 8 G -P 1 ft I8/668F-P IS/669D-PG 2I/67IF-P 3 4 /6 7 9 F -P 4 6 /6 8 2 H -P r , W ? X _ _ Y 123 124 sent a total Pleistocene sedimentation rate of 1.2 and 1.3 mm/years for each core, respectively, based on a span of 2 million years for the Pleistocene. These rates are considered relatively low when compared to the Holocene rates derived earlier which may result from the relatively high sediment rates (related to high carbonate production) on the Nasca Ridge. The effectiveness of sediment traps on the continental slope off Callao can also explain the low rates observed for Locations 14 and 17* Locations 33 and 34 are in the region of the Sub tropical Convergence. CaCO^ content ranges between 30 and 75 percent in this area (Bramlette, 1961) and decreases towards the coast. It is possible that climatic condi tions during glacial stages could have affected this con vergence and resulted in lower CaCO^ production than that presently observed. 125 SUMMARY AND CONCLUSIONS In the area of study, Holocene and Pleistocene pelagic sediments are dominantly foraminiferal oozes ex cept where controlled by depth and low productivity, A decrease in CaCO^ for the surface sediments of gravity cores indicates a lower rate of deposition during Holocene and interglacial time than in glacial times and is in accord with Arrhenius's model of equatorial sedimentation. This observation is better documented for cores taken along the Nasca Ridge and in the Peru-Chile Trench. The effect of the Nasca Ridge on currents and general water circulation is not well known but maximum percentages of CaCO- 5 occur in sediments on this feature. Sedimentation rates on the Ridge are higher than the 0.4 to 0.5 mm/1000 years calculated for the southeastern Pacific (Menard, 1964) but lower than the 10 mm/1000 years calculated for the equatorial belt of high carbonate by Arrhenius (1952). A core from the Peru-Chile Trench and one from the Nasca Ridge, 500 km distant, show similar sedimentation patterns interpreted as representing the Pleistocene section. Although sedimentation rates along the South American coast, off Peru and Chile, are in excess of 10 mm/1000 years (Goldberg and Koide, 1962) the effectiveness of sediment traps for the Trench sample and the distance of the Nasca Ridge sample from large terrigenous sediment 126 sources indicate a complete Pleistocene record and a sedimentation rate of 1.3-1*4 mm/1000 years. The relationship in time and space of the Peru Current may be demonstrated by the cores from the Trench off Callao and the northern tip of Nasca Ridge. In this region a westward shift or increase in intensity of over turning during glacial periods may be shown by periods of greater sedimentation and CaCO^ content, although not necessarily increased organic content. Both Mturbidites” and higher CaCO-^ production would account for the sediment- CaCO-^ pattern seen in the cores. In general, benthic organisms are continually removing organic material from sediments. Organic material is seven times more abundant on the continental margin and Trench off Callao than seaward of the Trench off Callao, Peru where bottom photographs indicate extensive re working of sediment. Physical forces such as gravity, deep currents, etc. are at work depositing and moving sediment along the continental margins at a wide range of depths. Sediment contribution from submerged topographic highs such as the Nasca Ridge was also greater during the lower sea levels of the Pleistocene. Seamounts and related volcanic activity account for a large amount of pyroclastics in the cores and the widespread occurrence of montmorillonite as an alteration product. Chemical activity is also widespread as shown by 127 manganese oxide encrustations on outcrops and on dredge samples of volcanic rocks. Several regions associated with lower productivity and sedimentation rates have abundant surface distribution of manganese nodules. Manganese micronodules are found disseminated through cores in these regions and the occurrence of a nodule at the 25-30 cm interval of one core may indicate a period of very slow sedimentation similar to present conditions. Sediment in cores from the continental margin off Callao, Peru and Valparaiso, Chile are dominantly brown ish black, olive black and dusky yellowish brown silty sands and silts. The dark hues of these sediments are the result of greater concentrations of organic material than found further offshore. Calcareous oozes from depths of less than 4000 m are typically tan to yellowish brown silts and sands. Their color and texture is a function of large amounts of foraminifera larger than 62 microns and other finer calcareous remains. Sediment deeper than 4000 m contain little or no CaCO-^, greater amounts of authigenic minerals (manganese and iron oxides) and have amounts of organic material ranging in value between sediments from the continental margin and those from the deep-sea (but less than 4000 m depth). They are usually chocolate brown silty clays and have the lowest rates of accumulation of the samples studied. This slow rate of sedimentation is a function of depth (solution of CaCO^), distance from land 128 (decrease in terrigenous component) and distance from bathymetrically high area (related to carbonate production in surface waters). REFERENCES 129 REFERENCES Arrhenius, G., 1952, Sediment cores from the east Pacific: Reps. Swed. Deep-Sea Expedition, 1947-1948, v. 5, no. 1. Bandy, 0. L., 1967, Cruise report, R/V Anton Bruun, cruise 17: Spec. Rept. 7, Texas A & M Univ., p. 16. Bandy, 0. L. and Rodolfo, K. S., 1964, Distribution of foraminifera and sediments, Peru-Chile Trench area: Deep-Sea Research, v. 11, pp. 817-837. Barnes, P. W., 1967, Volumetric determination of aminoid nitrogen: unpublished report, Dept. Geological Sciences, Univ. of Southern Calif., 11 pp. Berger, W. H., 1967, Foraminiferal ooze: solution at depths: Science, v. 156, pp. 383-385* Berger, W. H., 1968, Planktonic foraminifera: selective solution and paleoclimatic interpretation: Deep-Sea Research, v. 15, pp. 31-43. Bien, G. S., 1952, Chemical analysis method: Univ. of Calif., Scripps Institute of Oceanography, Ann. Rep. Director, SIO Ref. 52-58, 9 PP. Blackman, A. and Somayajulu, B. L. K., 1966, Pacific Pleistocene cores: faunal analysis and geochronology: Science, v. 154, pp. 886-889. Bonatti, E. and Nayudu, Y. R., 1965, The origin of manganese nodules on the ocean floor: Amer. Jour. Sci., v. 263, pp. 17-39. Bramlette, M. N., 1961, Pelagic sediments, pp. 345-366, in Sears, M., Editor, Oceanography: Wash., D. C., Amer. Assoc. Adv. Sci., publ. 67, 654 pp. Bullard, E. C., 1963, The flow of heat through the floor of the ocean, pp. 218-232, in Hill, M. N., Editor, The Sea, v. 3: New York and London, Interscience Publishers, 963 pp. 130 131 Chase, T. E., 1968, Sea floor topography of the central eastern Pacific Ocean: Bureau of Commercial Fisheries, circ. 291, U. S. Dept. Interior, 33 pp. Childs, 0., and Beebe, B. W., 1963, The backbone of the Americas— tectonic history from pole to pole, a symposium: Mem., Amer. Assoc. Petrol. Geol., no. 2, 320 pp. Dietz, R. S. and Menard, H. W., 1953, Hawaiian swell, deep and arch, and subsidence of the Hawaiian Islands: Jour. Geology, v. 61, pp. 99-113. Emery, K. 0., 1955, Submarine topography south of Hawaii: Pacific Sci., pp. 286-291. Emery, K. 0., i960, The sea off southern California: New York, John Wiley and Sons, Inc., 366 pp. Emery, K. 0. and Hulsemann, J., 1964, Shortening of sedi ment cores collected in open barrel gravity corers: Sedimentology, v. 3, pp. 144-154. Emery, K. 0. and Rittenberg, S. C., 1952, Early dia genesis of California basin sediments in relation to origin of oil: Bull. Am. Assoc. Petroleum Geologists, v. 36, pp. 735-806. Fisher, R. L., 1958, Downwind investigation of the Nasca Ridge: IGY General Report Series, pp. 20-23. Fisher, R. L. and Raitt, R. W., 1962, Topography and structure of the Peru-Chile Trench: Deep-Sea Re search, v. 9, PP. 423-443. Goddard, E. N., 1948, Rock color chart: National Research Council, Wash., D. C. Goldberg, E. D. and Koide, M., 1962, Geochronological studies of deep-sea sediments by the ionium-thorium method: Geochim. et Cosmochim. Acta, v. 26, pp. 417-450. Gorsline, D. S., Drake, D. E. and Barnes, P. W., 1968, Holocene sedimentation in Tanner Basin, Calif. Continental Borderland: Geol. Soc. America Bull., v. 79, PP. 659-674. Griffin, J. J. and Goldberg, E. D., 1963, Clay-mineral distributions in the Pacific Ocean, pp. 728-741, in 132 Hill, M. N., Editor, The Sea, v. 3: New York and London, Interscience Publishers, 963 pp. Grim, R. E., 1953, Clay mineralogy: New York, McGraw- Hill Book Co., 384 pp. Gunther, E. R., 1936, A report on oceanographical investi gations in the Peru coastal current: Discovery Reports, v. 13: London, Cambridge Univ. Press, pp. 107-276. Hayes, D. E., 1966, A geophysical investigation of the Peru-Chile Trench: Marine Geology, v. 4, pp. 309- 351. Hamilton, E. L., 1956, Sunken islands of the Mid-Pacific Mountains: Geol. Soc. America Mem. 64, 97 pp. Heezen, B. C., 1963, Turbidity currents, pp. 742-775, in Hill, M. N., Editor, The Sea, v. 3: New York and London, Interscience Publishers, 963 pp. Jenks, W. P., 1956, Peru, pp. 215-247, in Jenks, V/. P., Editor, Handbook of South American geology: Geol. Soc. America Mem. 65, 378 pp. Kolpack, R. L., 1968, Oceanography and sedimentology of Drake Passage, Antarctica: Ph.D. dissert., Univ. of Southern Calif., 232 pp. Kolpack, R. L. and Bell, S. A., 1968, Gasometric deter mination of carbon in sediments by hydroxide ab sorption: Jour. Sed. Petrology, v. 38, pp. 617-620. Laboratory Equipment Corporation, 1959, Instruction Manual for operation of LECO carbon analyzer: Laboratory Equipment Corporation, St. Joseph, Michigan, 20 pp. Matthews, D. J., 1939, Tables of the velocity of sound in pure water and sea water for use in echo-sounding and sound-ranging: Brit. Admiralty Hydrogr. Dept. Publ., H. D. 282, 2nd ed. Menard, H. VT., 1964, Marine geology of the Pacific: New York, McGraw-Hill Book Co., 271 pp. Menard, H. W• and Ladd, H. S., 1963, Oceanic islands, seamounts, guyots and atolls, pp. 365, in Hill, M. N., Editor, The Sea, v. 3: New York and LonJon, Inter science Publishers, 963 pp. 133 Menard, H. W. and Atwater, T. M., 1968, Origin of fracture zone topography: Mexico City: Program Abstracts, Geol, Soc. America Ann. Mtg., 334- pp. Niederl, J. B. and Niederl, V., 1947, Micromethods of quantitative organic analysis: New York, John Wiley and Sons, 147 pp. Peterson, M. N., 1966, Calcite: rates of dissolution in a vertical profile in the central Pacific: Science, v. 154, pp. 1542-1544. Pierce, J. W. and Good, D. I., 1961, Fortran II program for standard size analysis of unconsolidated sedi ments using an IBM 1620 computer: State Geol. Survey, Univ. of Kansas, Spec. Dist. Publ. 28, 21 pp. Revelle, R. R., 1958, The Downwind Expedition to the South-east Pacific: Trans. Amer. Geophys. Un., v. 39, PP. 529-530. Revelle, R. R. and Shepard, F. P., 1939, Sediments off the California coast, pp. 245-282, in Trask, P. D., Editor, Recent marine sediments: Tulsa, Okla., Am. Assoc. Petroleum Geologists, 736 pp. Ross, C. S. and Hendricks, S. B., 1945, Minerals of the montmorillonite group: U. S. Geol. Survey Prof. Paper 205B, 77 pp. Ross, D. A. and Riedel, W. R., 1967, Comparison of upper parts of some piston cores with simultaneously col lected open-barrel cores: Deep-Sea Research, v. 14, pp. 285-294. Ruegg, W., I960, An intra-Pacific ridge, its continuation onto the Peruvian mainland, and its bearing on the hypothetical Pacific landmass: 21st Intern. Geol. Congr., Copenhagen, pt. X, Proc. sec. 10, pp. 29-38. Schmalz, R. F., 1957, Quantitative X-ray modal analysis of sediments from the Peru-Chile Trench (abstract): Geol. Soc. America Bull., v. 68, p. 1793. Scholl, D. W., 1958, A comparison of moisture contents derived from saturated and dried Recent marine muds: The Compass, v. 35, PP. 110-121. Scholl, D. W., von Huene, R. and Ridlon, J. B., 1968, Spreading of the ocean floor: undeformed sediments in the Peru-Chile Trench: Science, v. 159, pp. 869- 871. 134 Shepard, P. P., 1963, Submarine geology, 2nd edition: New York, Harper & Row Publishers, 557 PP. Sternberg, R. i f f . and Creager, J. S., 1961, Comparative efficiencies of size analysis by hydrometer and pipette methods: Jour, Sed. Petrology, v. 31, pp. 96-100. Trask, P. P., 1932, Origin and environment of source sediments of petroleum: Houston, Gulf Publishing Co., 323 pp. Vening Meinesz, P. A., 1948, Gravity expeditions at sea, 1923-1938: Pub. Neth. Geod. Comm., Waltman, Delft, v. 4. Warshaw, C. M. and Roy, R., 1961, Classification and a scheme for the identification of layer silicates: Geol. Soc. America 3ull., v. 72, pp. 1455-1492. Worzel, J. L., 1959, Extensive deep-sea sub-bottom reflections identified as whiteash: Proc. Nat. Acad. Sci., v. 45, no. 3, pp. 349-355. Zeigler, J. M., Athearn, W. D., and Small, H., 1957, Profiles across the Peru-Chile Trench: Deep-Sea Research, v. 4, pp. 238-249. Zen, E., 1957, Preliminary report on the mineralogy and petrology of some marine bottom samples off the coast of Peru and Chile: Amer. Mineral, v. 42, pp. 889- 903. Zen, E., 1957, Mineralogy and petrography of some marine bottom samples of west coast of Peru and Chile: Jour. Sed. Petrology, v. 29, pp. 513-539. APPENDIC APPENDIX I Station Data for Cruise 17> R/V Anton Bruun 136 137 Appendix I Station data for Cruise 17, R/V Anton Bruun (Bandy, 1967) Location Device ” 15TT" Depth Lat. (S) ..long . (W) 1/657B Trigger corer 95 12° 03' 77° 181 2/6571 Trigger corer 140 12° 09' •jrjO 25' 5/6581 Trigger corer 287 12° 25' 77° 27' 6/659B Camera 410 12° 30' 77° 281 6/6590 Trigger corer 420 12° 30’ 77° 28' 7/659J Camera 550 12° 35' 77° 27* 9/660E Trigger corer 1000 12° 54' 77° 161 10/661B Camera 1750 13° 16' 77° 301 11/661G Trigger corer 2110 12° 23' 77° 291 12/662D Camera 3230 12° 33' 77° 26' 13/66 3A trigger corer 4200 13° 45' 77° 32* 13/663D Camera 3930 130 44> 770 33’ 14/664A Trigger corer 5520 13° 45' 770 45* 14/664A Piston corer 5520 13° 45' 77° 45* 14/664C Camera 5430 13° 41' 77° 501 15/665A Trigger corer 3070 15° 33' 77° 37’ 15/665D Camera 2680 15° 36' 77° 341 16/666B Trigger corer 2980 16° 44' 77° 14' 16/66 6F Camera 2932 16° 42' 77° 161 17/667B Trigger corer 4050 17° 55' 77° 14’ 17/6670 Camera 4050 17° 56' 77° 13' 17/667G Trigger corer 4090 17° 57' rjfj 0 08’ 17/667G Piston corer 4090 17° 57' 77° 08’ 18/668B Camera 3165 17° 49' 78° 40' 18/668F Trigger corer 3170 17° 47' 78° 391 18/668P Piston corer 3170 17° 47' 78° 39’ 19/669B Piston corer* 4280 17° 20' 80° 02’ 19/669P Camera 4260 17° 22’ 80° 00' 20/670E Camera 4400 18° 32' 81° 15 1 20/670F Piston corer& 4450 18° 32' 81° 151 21/671P Piston corer 4010 19° 35' 81° 51' 21/671H Camera 3985 19° 36' 81° 46' 22/6720 Camera 1870 21° 36' 81° 35' 22/672F Piston corer* 1760 21° 33' 81° 3 2 * 23/673D Camera 3760 22° 33' 81° 31' 23/673B Piston corer* 3700 22° 33' 81° 31' 24/674E Camera 4198 24° 23' 80° 511 31/6760 Camera 410 26° 21' 80° 02' 33/678G Piston corer 3800 29° 21' 80° 02* 34/679P Piston corer 3920 30° 38' 80° 30’ 138 Appendix I. Station data for Cruise 17, R/V Anton Bruun (Bandy, 1967), Continued Location 45/681C 45/6811 46/682D 46/682F 46/682H 46/682H 47/683D 50/683K 50/683L Device (m) Depth Lat. (S) Lone;. (W) Trigger corer 3850 33° 20' 750 03' Camera 4200 33° 14' 75° 06' Camera 4320 33° 04' 73° 18' Camera 4005 33° 08' 73° 15' Trigger corer 3960 33° 10' 73° 16' Piston corer 3960 33° 10' 73° 16' Camera 5200 33° 12' 72° 33' Camera 495 330 09' 71° 52' Piston corer 485 33° 09' 71° 52' * Piston corer used as gravity corer. APPENDIX II Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen 139 140 Appendix II. Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen Percent Average Depth in Total Organic Location Core (cm) CaCO^ C C N 1/657B* 0-2 1.98 3.72 3.48 0.180 2/6571* 0-3.5 0.48 4.79 4.31 0.458 5/6581* 0-2 0.12 10.38 10.36 1.016 6/659C* 0-2 1.12 6.79 6.66 0.569 9/660E* 0-2 35.52 8.23 4.00 0.320 10/661G* 0-2 9.10 6.45 5.34 0.355 13/663A* 0-4 0.12 7.22 7.20 0.000 14/664A* 0-2 0.36 4.56 4.52 0.000 14/664a top 0-5 10-15 0.00 4.54 3.53 3.30 3.30 0.000 20-25 3.82 1.48 1.03 25-30.5 5.12 30.5-35 0.00 40-45 0.37 2.57 2.53 50-55 3.17 60-65 5.55 3.33 2.67 70-75 7.72 80-85 6.06 3.28 2.56 90-95 6.80 100-105 7.04 110-115 7.43 120-125 8.03 2.53 1.57 130-135 5.85 140-144 6.89 150-155 7.36 160-165 7.64 2.55 1.64 170-175 8.83 180-185 11.87 190-195 11.67 200-205 10.86 3.25 1.96 220-224 9.61 3.50 2.36 224-230 1.93 230-235 0.00 240-245 0.00 3.70 3.70 260-265 0.00 281-289 0.00 5.43 5.43 300-305 0.00 3.01 3.01 320-325 0.00 3.71 3.71 340-345 0.00 3.19 3.19 141 Appendix II. Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen, Continued Percent Average Location Depth in Core (cm) CaCOx Total C Organic C N 360-364.5 0.16 4.41 4.39 380-385 0.00 3.78 3.78 402-407 0.00 3.72 3.72 407-413 0.00 2.95 2.95 418-424 0.00 3.74 3.74 424-435 0.00 3.70 3.70 0.319 15/6651* 0-3 11.60 3.22 1.84 0.031 16/666B* 0-2 40.36 5.71 0.90 0.043 17/667B* 0-2 10.50 2.03 0.79 0.090 17/6676* 0-2 0.64 0.88 0.80 0.046 5-7.5 5.22 10-15 0.00 17/667G 0-2 7.49 1.86 0.98 0.000 2-5 9.10 5-10 6.25 10-15 6.25 15-20 9.51 20-25 3.90 30-35 1.44 40-45 0.00 0.51 0.51 50-55 0.00 60-65 0.25 70-75 0.00 80-85 1.92 0.74 0.51 90-95 8.45 95-100 11.94 100-105 7 • 68 105-110 7.58 110-115 3.15 120-125 0.00 0.42 0.42 130-135 0.00 140-145 2.84 150-155 6.58 160-165 0.40 0.58 0.53 170-175 6.39 180-185 1.33 190-195 3.44 200-205 4.17 1.02 0.52 208-215 2.67 220-225 2.02 230-237 8.90 142 Appendix II. Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen, Continued Location Depth in Core (cm) CaCO^ Percent Average Total Organic C C N 18/668F* 18/668P 19/669D 20/670F 240-245 250-254 260-265 270-275 280-286.5 0-1.5 1.5-5 5-10 10-15 0-2 20-25 40-45 60-65 70-76 0-2 5-10 10-15 20-25 30-35 40-44 50-55 80-85 120-125 160-165 200-205 240-245 254-257 10-12 20-25 40-45 80-85 100-105 120-125 160-165 200-203 240-245 280-284 320-325 340-345 24.02 11.25 0.00 0.00 0.16 39.10 80.27 81.80 78.12 79.24 81.90 89.04 88.02 88.59 0.47 4.81 4.52 1.24 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.64 0.20 4.89 9.49 9.82 10.61 10.53 10.58 0.67 1.53 0.89 0.52 0.50 0.62 0.59 0.48 0.37 0.45 0.43 0.27 0.35 0.25 0.38 0.38 0.24 0.31 0.19 0.23 0.17 0.78 0.16 0.23 0.06 0.07 0.01 0.05 0.03 0.61 0.96 0.89 0.52 0.50 0.62 0.59 0.48 0.37 0.45 0.43 0.27 0.35 0.25 0.38 0.38 0.24 0.31 0.19 0.23 0.17 0.032 0.114 0.000 0.005 0.000 0.056 0.057 0.038 143 Appendix II. Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen, Continued Location 21/67IP 22/672F 23/673E Percent Average Depth in Core (cm) CaCO^ Total C Organic C H 0-2 2-5 10-15 40.67 39.46 36.82 5.04 0.20 0.025 20-25 30-35 40-45 50-55 23.79 31.39 11.67 21.70 3.40 0.57 60-65 70-72 80-85 90-95 95-100 12.20 16.20 19.64 37.09 44.68 1.72 0.27 100-105 107-110 110-115 120-125 130-135 62.45 46.26 19.06 27.98 11.88 7.90 0.47 140-145 150-155 160-165 170-175 18.56 17.19 18.88 9.66 2.40 0.19 180-185 190-195 200-205 210-215 19.21 9.96 19.62 27.54 2.37 0.08 220-222 17.68 2.28 0.18 0.015 0-2 2-5 10-15 20-25 81.86 94.34 94.13 93.75 9.87 0.13 0.013 40-46 93.54 11.32 0.18 80-85 93.64 11.18 0.02 120-125 94.85 11.33 0.04 160-165 95.85 11.42 0.01 190-196 94.12 11.34 0.14 0.000 0-2 81.40 9.71 0.02 0.036 10-12 20-25 30-35 74.97 73.13 62.02 9.14 0.22 144 Appendix II. Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen, Continued Location 33/678G Depth in Core (cm) Percent Average CaCO^ Total C Organic C N 40-45 55.07 6.61 0.05 50-55 63.00 6O-65 70.72 70-75 68.68 80-85 57.56 6.99 0.13 90-94 66.73 99-104 65.88 109-114 59.93 119-124 55.17 6.61 0.11 129-134 57.90 134-139 47.20 139-144 73.60 8.76 0.00 149-154 70.50 159-164 60.09 7.34 0.19 169-174 66.91 179-184 66.64 189-194 62.82 199-204 68.46 8.33 0.18 219-224 61.28 229-234 56.75 230-244 59.41 7.11 0.04 0.000 0-2 63.15 7.65 0.13 0.009 2-5 56.51 10-15 44.10 20-25 38.75 4.85 0.24 25-30 26.88 30-35 26.41 40-45 24.82 3.02 0.06 50-55 26.17 60-65 30.45 70-75 18.98 2.42 0.16 8O-85 8.26 102-105 25.87 3.11 0.03 120-125 28.12 140-145 27.18 3.32 0.08 160-165 61.67 180-185 52.03 6.22 0.02 200-205 33.77 220-225 33.26 3.96 0.00 145 Appendix II. Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen, Continued Percent Average Location 34/679F 45/681C* 46/682H* 46/682H Depth in Dore (cm) CaCO-z Total C Organic C N 250-255 j ' 33.29 270-275 55.05 6.56 0.01 280-284 0.006 0-2 38.36 4.74 0.17 0.010 2-5 36.86 10-15 11.14 1.34 0.01 20-25 8.10 40-42 3.32 0.40 0.00 50-55 6.80 60-65 7.45 0.90 0.01 70-75 7.65 80-85 4.51 90-95 6.60 100-105 15.31 1.83 0.01 110-115 19.47 120-125 18.18 130-135 16.32 140-145 6.74 0.81 0.01 150-155 15.40 160-165 16.92 170-175 11.54 180-185 5.56 0.67 0.01 0.005 0-2 42.46 5.47 0.41 0.031 0-2 4.29 1.99 0.48 0.066 0-2 4.62 1.64 1.09 0.000 2-5 6.14 10-15 15.22 2.45 0.64 20-25 20.23 28-29 26.86 29-35 27.00 40-45 20.60 3.16 0.71 50-54.5 13.04 59-62 8.96 1.93 0.86 70-75 9.56 80-85 10.34 2.02 0.79 100-105 3.32 120-125 6.50 1.80 1.03 140-145 6.65 150-155 11.36 146 Appendix II. Average Weight Percent Calcium Carbonate Total Carbon, Organic Carbon, and Nitrogen, Continued Location Depth in Core (cm) Percent Average CaCO^t Total C Organic 0 N 158-162 j 11.05 2.58 1.26 170-175 3.63 200-205 5.97 1.76 1.05 215-220 5.04 240-245 5.36 1.84 1.20 250-255 11.12 260-265 10.54 270-275 14.19 280-285 16.04 2.98 1.07 290-295 15.75 300-305 12.32 310-315 8.54 320-325 16.28 3.10 1.16 0.058 50/683L 0-2 1.98 1.26 1.02 0.068 20-25 3.41 0.84 0.43 * Trigger cores.

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