Close
About
FAQ
Home
Collections
Login
USC Login
Register
0
Selected
Invert selection
Deselect all
Deselect all
Click here to refresh results
Click here to refresh results
USC
/
Digital Library
/
University of Southern California Dissertations and Theses
/
Environmental analysis of sediment from the sea floor off Point Arguello, California
(USC Thesis Other)
Environmental analysis of sediment from the sea floor off Point Arguello, California
PDF
Download
Share
Open document
Flip pages
Contact Us
Contact Us
Copy asset link
Request this asset
Transcript (if available)
Content
VIRONMENTAL ANALYSIS OP SEDIMENT PROP THE SEA FLOOR OFF POINT ARGUELLO, CALIFORNIA A Thesis Presented to the Faculty of the Department of Geology The University of Southern California In Partial Fulfillment of the requirements for the Degree Master of Science in Geology t>y Robert Floyd Dill June 1952 UMI Number: EP58437 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 Publishing UMI EP58437 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 ProQuest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 Ge. D51? T h is thesis, w ritte n by ............ H o b e r Di_ll.......... u nde r the guidance o f h is . —F a c u lty C o m m itte e f and a pp ro ve d by a ll its m em bers, has been presented to and accepted by the C o u n c il on G raduate S tu d y and Research in p a r tia l f u l lf ill- m ent o f the requirem ents f o r the degree o f Master or Science D a te ............ Faculty Committee Chairman ii ENVIRONMENTAL ANALYSIS OF SEDIMENT FROM THE SEA FLOOR OFF POINT ARGUELLO, CALIFORNIA Robert F. Dill ABSTRACT Eleven cores were taken along a profile across the continental terrace off Point Arguello, California. Chemi cal analyses of some of the more important constituents of the sediments such as, organic carbon, nitrogen, ferric and ferrous iron, and carbonate were determined and compared with the pH, E^, water content, grain size, depth of burial, and distance from shore in order to determine the environ ment of deposition in this area. Glauconite was found to form in an oxidizing environment in an area of slow sedimen tation half way across the continental terrace. Ferrous iron predominated over ferric Iron, a condition which is attributed to the reduction of Iron to its lower valence state during the oxidation of organic material. Sediments with sufficient organic material to form source rocks were found on the outer portion of the continental terrace. In this area the organic material is not diluted by detrital sediments and Is deposited with sufficient rapidity to pre vent Its destruction by organic oxidation. iii TABLE OF CONTENTS .Page | ! ABSTRACT............................................... ii INTRODUCTION........................................... 1 ACKNOWLEDGMENTS ...................................... 3 CHOICE OF POINT ARGUELLO AREA ....................... 4 GEOLOGICAL SETTING.................................... 5 , Geology of the Inland Region....................... 5 1 Offshore Seismic Activities ....... 7; Offshore Topography . .......................... 8 : Oceanography........................................ 10 METHODS OF SAMPLING...................... -.......... 13 GRAIN SIZE ANALYSIS.................................. 13 Methods ................... • 13 Median Diameter . .......... ... .. ... .. . 16 ? Sorting............................................ 20: Skewness.................................... .. 23 Microscopic...................................... .. 24 WATER CONTENT...................................... .. 24 ORGANIC MATERIAL IN TEE SEDIMENTS .................... 26 Organic Carbon..................... ................ 29 Organic Nitrogen.................................... 31 BYDROOEN-1ON CONCENTRATION (pH)...................... 34 THE 0 XI DA TI ON - R E D UC TI ON POTENTIAL (Eh)................ 38 Environmental Evidence from Analysis of the 0 he rn i c a 1 E or mu la.................................... Field Evidence of Environraental Conditions. . . . . Ori ■in of Olauconite................................ V LIST OF LISURES Figure Page 1. Diagram Showing Typical Cumulative ;*>, Grain Size Starves Across Shelf and Slope.............. 18 2. Cumulative , b curve showing decrease in glauconite with depth in the core.........t.................. 19 3. Cumulative curve plotted on probability graph paper showing various constituent of the sediment . . . .................................22 4. Relationship of percent of water content per whole sample with depth in the core and distance across the continental terrace..................... . . 27 5. COg/N Ration showing Rapid Decrease in N in the First Few Inches of Depth. .....................33 6. Way in which the pE of sediments can be changed by organic activity.............................36 7. Values for the Iron content, and pH plotted against distance from shore.................... 44 8. Division of the continental terrace and the deep sea basin into three zones on the basis of the states of oxidation of iron In the sediment. . . 49 9. Relationship of Calcium Carbonate with Depth in the core....................................... 51 Figure 10, Percent of CaCO^ in the sediment showing range per core and CaCO^ content for surface sample, as a solid line . . . Vll LIST OP TABLES Table Page 1. Median diameter, sorting, skewness for the surface samples across the Continental Terrace........................................ 25 2. Nitrogen, Carbon, Carbon Nitrogen Ratio, Carbonate Nitrogen Ratio, and Carbonate Carbon Ratio plotted against surface samples which run consecutively across the Continental Terrace........ . ....................... . • . 30 5. and pH values of cores....................... 42 4. Relationship of ferric and ferrous iron in glauconite and their relationship to other elements in the mineral ................ 57 5. Relationship of glauconite to water depth and Oxidation-Reduction potential of sediments. . . 57 viil LIST OP PLATES Plate Page 1. Chart of Offshore Topography Showing position of Cores with Inset Showing Relation to California Coast ................. • 2 2. Current Pattern Off Southern California During Summer, Pall, and Winter. . ........... 11 3. Phleger Corer....................................... 14 4. Organic Activity at a depth of 300 fathoms. .................................. 38 INTRODUCTION It is becoming ever more apparent that the Interpreta tion of ancient sediments demands a fuller knowledge of sedimentary processes which are acting at the present time. Physical and chemical measurements of the environments of deposition and erosion must be made so that the geologist may have facts on which to base his interpretations of ancient sediments. The realization that some of the ancient sediments now rich in oil, were deposited under conditions similar to those which now exist on the conti nental shelf has enhanced the value of an environmental study such as is presented in this paper. Some of the important factors which control the environment of the continental shelf and slope are measurable and the presen tation of results of such measurements is the purpose of this paper. Dietz and Menard (1951) define a continental terrace as the submarine part of the continent consisting of a continental shelf and slope. This term, will be used throughout this paper with the same meaning whenever it is more convenient to refer to the entire continental shelf and slope. A series of cores were taken along a line running seaward from Point Arguello (Plate 1). Grain size analyses and distribution of sediments are presented in order to understand more clearly the relationship between these II ·----·············---·--·----·--""····-·-·---------------------------------------------""-------------,-·------------------------------------------------- ~------......._ '" ~\ \ \ -io 0\ \ I \ \., \\ //? \ . , __ _/ r I \ \ \ '· I 1. I I \ I \ I I I '.,_ I I I I i ! I -' I I I I ---.......... LOCATION MAP OF CORES SHOWING RELATIONSHIP TO TOPOGRAPHY SOURCE U.S.C.&G.S. 5202 CONTOUR INTERVAL 100 FMS. 0 SCALE 4 NAUTICAL MILES -----1 I I I I ' ' ' ' ',, ', I > I I -- __, I '· I 3 physical features and the chemistry of sediments. Chemical analyses of some of the more important constituents of the sediments, such as organic carbon, nitrogen, ferric and ferrous iron, and carbonates are presented in order to show how they vary with pH, grain size, depth of burial, and distance from shore. Environmental analyses of the type presented in this thesis have not been done previously in the Point Arguello region. Most work on continental terraces elsewhere deals mainly with sediment distribution and geomorphic features; this study furnishes a different and more detailed approach to the study of recent sediments# ACKNOWLEDGMENTS The generous cooperation of the Scripps Institution of Oceanography in making available its research vessel, E. W. Scripps, permitted the field work necessary for collecting the cores which serve as a basis for this study. Necessary laboratory facilities for the majority of sedimentary and chemical analyses of the cores acquired in the field research were provided by the Allen Hancock Foundation of Marine Research at the University of Southern California. The writer is grateful to David Moore, Richard Terry, and David Wozab for their help v/ith the shipboard work involved in collecting the cores. The advice and k suggestions of Drs. K. 0. Emery, 0. L. Bandy and S. C. Rittenberg have greatly helped in solving many of the problems which have arisen during the course of the in vestigation and the writing of this thesis. The study of chemistry of the sediments was greatly aided by Wilson Orr, chemist for the Hancock Foundation. CHOICE OF POINT ARGUELLO AREA In this type of study it is desirable to select a topographically uncomplicated area because submarine canyons and borderland type topography influence sediment distribution and characteristics. In addition, it is necessary that an adequate supply of sedimentary material be available, and that there be no local changes In slope which might mask the regional characteristics. The terrace off Point Arguello fits the requirements as set forth, and was chosen as the location for the line of cores across the continental terrace. It has no sub marine canyons and has an even gradient across the slope and shelf. The Santa Ynez River furnishes an abundant sup ply of sedimentary material. Emery and Rittenberg (1952) investigated the sedimen- tology and chemistry in the offshore basins along the coast of southern California. The present study extends many of the techniques and ideas developed in their investigation 5 to the continental terrace. The study also enabled Dr. 0. L. Bandy to compare the foraminiferal fauna inhabiting different depths and environments with those of similar profiles along the Pacific Coast of North America. Some of his results are presented in the text under Carbonate, and show the relationship between the fauna and carbonate distribution. GEOLOGICAL SETTING Geology of the Inland Region The geology of inland areas which supply the sedi ment to the continental terrace play a role In the nature of offshore sediments. Point Arguello and neighboring Point Conception mark an abrupt change in the entire structure of California. They form the western most extension of the continental portion of the Transverse Ranges, which run at right angles to the main northwest- southwest trending structures of the remainder of the Pacific coast of North America. Structurally, the Point Conception-Point Arguello region is a series of dissected anticlines and synclines which have a general east-west trend. The main faults which are associated with the anticlinal mountains also have a east-west trend. Because of the dissection of the structures by the Santa Ynez river and its tributaries there is an interesting association between the structure features and the age of the outcropping rocks. Eocene rocks crop out along the axis of the anticlines, Sespe (Oligocene) on the flanks, and Miocene and Pliocene in the lower foothills. Farther inland rocks of the Franciscan- Knoxville series (Jurassic and Cretaceous) crop out and probably furnish some of the material which is carried to the sea by the Santa Ynez River (Upson, 19^4-9) • The main physiographic feature in the region is a broadening of the Santa Ynez River Valley, this feature is called the Lompoc Plain. It is filled with a thick section of Pleistocene gravels which are slightly dissected by the present day Santa vnez River channel, indicating that they have furnished material to the offshore sediments. One hundred and ninety to two hundred and twenty feet of alluvium underlies the flood plain of the Santa Ynez River in the region of the Lompoc plain, this in turn overlies truncated and warped sedimentary rocks of Miocene and Upper Pleistocene age. The alluvium appears to be deposited in an ancient river valley cut by the Santa Ynez River in "post-Wisconsin times" (Upson, 1914-9)* The base of the alluvium is now approximately two hundred feet below sea level. It follows that sea level during the cutting of the ancient valley also was lower by at least two hundred feet. In areas of nondeposition, as at station 7 (see plate 1), such a lowering is probably still reflected in the sediments. At present, the Santa Ynez River is aggrading its channel and the amount of material transported to the continental terrace must be less than when the ancient valley was carved. The aggradation shows that the river no longer is in equilibrium and the filling of its channel has also caused the offshore irregularities to fill, thus possibly accounting for the smooth appearance of the sea floor in this region. Sediments off the Santa Ynez River show a distinct break in composition at about the 300 fathom contour line. This break could correspond to the furthermost extension of the detrital material. Upson (19h9)> extended the base of the ancient valley to a distance of thirteen miles off the present shoreline by extending the gradient of the base of the alluvium out ward until it coincides with the surface of the present day sea floor. Assuming an area of nondeposition at station 7> the sediments in this area may have been deposited under conditions similar to those found on the inner portion of the profile today, with time the only difference between the two • OFFSHORE SEISMIC ACTIVITIES Earthquake epicenters are common between the shoreline and 3^0 fathoms. These shocks might be expected to be represented by changes in the sediments, but there is no indication of an abrupt change in the sedimentation or topography in this area. The magnitude of the shocks ranges between 3 to Il.5 (Gutenberg and Richter, I9I 4 .I) • Of the twenty-nine shocks reported in this area by the Seismological Laboratory at Pasadena from January 1, 193^1 to March 3>±, 19I+6, the location is known to be fairly accurate for four shocks and within 15 kilometers for the remainder. Pew conclusions can be drawn from the seismic data other than the fact that there is an active area on the inshore portion of the profile, which is probably re lated to the main fault system inland. Of interest, and possibly connected to this seismic activity, is a newly discovered escarpment as large as the Mendocino Escarpment (Menard and Dietz, in press) extending toward Point Arguello from the deep sea and may be associ ated with the Transverse Ranges (Menard, personal communica tion ) . OFFSHORE TOPOGRAPHY The main character of the continental terrace off Point Arguello is the smooth and relatively simple topogra phy which extends from shore to the floor of the oceanic basin, approximately sixty miles offshore. The smooth portion of the terrace is bounded on the north by the Santa 9 Lucia Bank and the Arguello Canyon on the south. Large scale features of the terrace follow major structural trends in the region and reflect structural influences from the Transverse Ranges* The terrace has been greatly modified by faulting and canyon formation, however, the general trends of the Transverse Ranges are seen in the presence of Rodriguez Seamount and the topographic high to the north of Santa Lucia Escarpment which has been re ported to be a fault scarp by Shepard and Emery (I9I 4-I, p • ) • Breaks in slope on the terrace are found at 50 fath oms, 3^0 fathoms, and 1000 fathoms. Between the shore and the 50 fathom contour there is a broad submarine terrace with an average slope of 0° 23 ’ • Beyond this, the slope increases slightly to 0° 53* to the 300 fathom contour which is 25 miles offshore. Here the slope increases to 8° 27T for a distance of IpJ miles which in turn is followed by a decrease in slope to 5° 55’ for a distance of 5tf miles. Then, the final shelf break begins, and the slope increases to 10° 05’ and is constant to the base of the continental terrace, which in this area is 60 miles offshore. The part of the terrace with which this paper is con cerned lies between the major topographic forms, and the transportation and deposition of sediment probably is not affected by their presence. 10 OCEANOGRAPHY Current activity and the resulting organic production brought about by upwelling are Important In determining the amount of organic material in the sediment. Nutrients brought to the surface by upwelling waters are utilized by the plants which live in the photosynthetic zone, or upper 100 meters of the ocean. Currents then in turn determine the distribution and distance of transporta tioxi of these non- swimming plants and organisms which feed upon the plants. Oceanographic conditions in the region of Point Arguello are variable and depend upon the seasonal changes of wind and shifts in the major current systems. The distribution of current patters is such that they can be devided into three zones (Plate 2), which will be discussed individually. The first of these, the California Current, is the eastern expression of the North Pacific gyral, a steady flowing stream v/hich has relatively high surface tempera tures and low salinities when compared with the other zones. The mixed layers in this current system are relatively thick. This current is responsible for movement of water masses in the surface layers in the area north of Point Conception (See Plate 2) in all but the winter months of the year. Due to bottom and coastal topography and the predominant northwesterly winds, there is a seaward deflect ion resulting in the development of large eddies which are 3 5 34 33 I I carried southward alonn; the coast with the main current drift. Orran ic production is related to these eddies (Sverdrup and Allen, 193$) which in turn affects the organic material supplied, to the sea floor. The second zone, brought about by the outward move ment of the California Current, causes a shift in the dynamic balance of the region and results in a compensa ting upwelling of water from depth to take its place. This zone of upwelling necessarily is dependent on the winds and the magnitude of the eddies, and as a result, there is not a constant area of upwelling but instead a migrating zone which varies in intensity depending upon the seasonal winds. As would be expected in areas of upwelling, the water of this zone is characterized by low surface temperatures and high salinities. The convection layer in this zone is thin and in some cases may be absent entirely. The California Counter Current, which represents the third zone, lies between the California Current and the coast, and in general flows to the north. Its waters are characterized by temperatures similar to the California Current, but its salinity lies between that of the Upwell ing Zone and that of the California Current. This current is not present in the surface layers in the spring when the upwelling is predominant. It is, however, present in the lower levels and remains the dominant current activity at 13 depth throughout the year. The generalized pattern of surface flow is shown in Figure 2 along with the names and relationships of the three surface currents. METHOD OF SAMPLING Cores were taken with a Phleger corer (Plate 3) which combines light weight, speed of operation, a high percent age of recovery, and. nondeformation of cores. It has a Ip foot core barrel lined with a plastic tube. The instrument is driven into the sediment by gravity, and the sediment prevented from sliding back out of the barrel by means of a core catcher in the nose and a valve at the top of the barrel• The pH, Eft, ferric iron content and. field descriptions were made as soon as the cores were brought to the surface. After measuring the changeable properties, the samples were stored in mason jars so that the water content would not change, and transported back to the Allen Hancock Foundation for further study. Grain size, total iron, water content, nitrogen, organic carbon, carbonate; properties which do not vary appreciably with time, and microscopic examination of the sediment were determined later in the laboratory. GRAIN SIZE ANALYSIS Methods Grain size was determined by a combination screening Plate 3# Phleger Corer ready to be dropped overboard* 15 and pipette method. Sediment samples were taken from the core every few inches, usually in the following intervals: 0-1 inch, 1-5 inch, 5-10 inch, 10-15 inch, 15-20 inch, and at the bottom of the core. The sediment was then wet screened on a 0,062 mm screen. The coarse fraction was retained and weighed, and if it composed more than 10 per cent of the sediment by weight, it was sieved in a set of Tyler screens with openings corresponding to the 7/entworth Size Scale. The fine fraction, containing particles smaller than 0,062 mm, was treated with a 0.0035 N solution of sodium hexametaphosphate and placed in a "malt” mixer for a period of 10 minutes. The sample was then transferred to a 1000 ml graduate cylinder and filtered twice by Pasteur filter tubes. The volume was then made up to 1000 ml with 0.0035 N sodium hexametaphosphate solution which acts as a dis persion agent, and a routine pipette analysis was made of the sediment. Results of the sieving and pipette analysis were plotted on a cumulative weight percentage basis for each size grade. The median diameter, skewness, and sorting were determined from the resulting curve. After sieving the coarse fraction and computing the statistical data, each grade size was examined under a microscope; in this way the relationship between grain size and sedimentary 16 characteristics was determined. The coarse fraction was then used for the determination of the foraminiferal dis tribution in the sediment by Dr. 0. L. Bandy. Median Diameter The median diameters of the sediments on the contin ental terrace are a complex function of the differently derived material of which they are composed. Detrital minerals, or material derived directly from the rivers of the region are predominant on the inner portion of the shelf. These give way to authigenic minerals in a broad zone that is approximately half way across the terrace. On the outer edge of the terra.ce the sediments consist of poor ly sorted muds. The transition from one zone to another is gradual. This gradual change results in the median diame ter representing a mixture rather than singularly derived sediment. It is important that this transition be recog nized before any conclusion as to the distribution of sedi ments of the continental terrace is attempted. The median of the detrital sediments decreases with distance from shore. This decrease is not expressed in the median diameter in all of the sanples, however, because of the presence of foraminiferal tests and authigenic minerals, such as glauconite and phosphorite. Mixtures of materials of different derivation cause a deviation from, the normal expected decrease in grain size in the area 17 where this mixing is more pronounced* Figure 1 shows the typical cumulative percentage curve, median diameter, and sorting of the three sediments zones of the continental terrace. The median size for the sediments in the inner portion of the traverse (Stations 1-5) was 0.056 mm. The maximum median grain size was 0.115 mm for core 1 and the smallest median grain size was at the bottom of core 2. These two extreme values were definitely the exception, and, in general, the material in the inner por tion of the continental terrace was quite uniform. In the mid-terrace zone (Station 6 -7 ) where there is a predominance of authigenic minerals, the average median dia meter is O.5I 4 - mm, the largest median grain size found on the terrace. The grain size of the material, however, is vari able due to the different types of material of which it is composed. In core 6, the decrease in the abundance of glauconite (Figure 2) with depth, as shown in the cumulative percentage curves for various sections of the core can be interpreted in several ways: (1) the sediment cored is one sedimentary unit which is undergoing glauconitization, and conditions are more favorable at the surface for the forma tion of glauconite than at depth; (2) the rate of sedimen tation is slower at the present time, and glauconite can form for a longer time before burial than it could in the lower portions of the core; (3) glauconite breaks down with OUTER TERRACE ZONE MID TERRACE ZONE NNER TERRACE ZONE 100 % 00 % 00 % .001 MM 001 MM .001 MM CORE 8-11 S = 3.9 AVE. MED. GS = 0.009 CORE 1-5 $°A =1.5 0 .5 4 AVE.MED.GS = 0.056 CORE 6 -7 S Ofa =3.5 AVE. MED. GS 500 000 1500 2000 60 50 40 30 0 20 10 MILES FROM SHORE Figure 1. rrofile of the Continental terrace showing sediment zones which are determined hv cumulative percentage grain size curves, average sorting (Co.), and average median grain size of the sediment, in these zones • DEPTH IN FATHOMS Lr Hi ?- O' / / hi / 0 $■ *9" /, //O 0 !i 20 depth in the core after being formed at the surface. Phosphorite which was abundant in core 7 was not found in core 6. This lack probably is caused by a slight topo graphic high at station 7 which caused a change in envi ronment. No definite conclusion can be made however, be cause pH and Eft measurements were not determined for core 6, to compare with the ones found in core 7« The outer terrace zone (Stations 8-11) is composed of fine grained clay with an medium grain size of 0.009 mm, and a range in size from 0.013 ram to 0.003 mm in diameter for the clay particles. Sorting Sorting is a measurement of the dimensional spread of the grain sizes of a sediment (Twenhofel and Tyler, I9I 4-I) • The sorting coefficient (SQ) is defined as the square root of the third quartile diameter ( ) divided by the first quartile diameter, or SQ = / Qy ~ Ql The sorting coefficient of the sediment increases with distance from shore. Values ranged from 1.2 for the near shore samples, to Ip.9 for the fine material on the outer edge of the continental terrace(Table 1). The values of sorting coefficients along the sampled profile fall into three zones: the nearshore zone with an average sorting coefficient of 1.5 for five cores, the mid-terrace zone 21 with an average sorting coefficient of 3*5 fo r two cores, and the outer terrace zone which has an average sorting coefficient of 3*9 f°r four cores* Figure 1 shows typical cumulative curves and average sorting coefficients, (So ), JrL in these zones compared with the profile along which the cores were taken. The decrease in sorting, indicated by an increase in the sorting coefficient, is brought about by the mixing of two to four differently derived constituents of the sedi ments. Phosphorite, glauconite, foraminiferal and radio- larian tests, diatom frustules, and detrital minerals all are present in some of the cores and have a normal distri bution about their respective distribution nodes. However, when mixed, the results are the decrease in the sorting found in all cores containing constituents of different sources. If the cumulative percentages of the sediment are plotted on probability paper, the various constituents become apparent (Figure 3)* Glauconite, phosphorite, and detrital-foraminiferal nodal curves become straight lines, each with its own distinctive slope. The nearshore cores contain no authigenic minerals or abundant foraminiferal tests and are, as to be expected, well sorted. As the distance from shore becomes greater and the rate of sedi mentation becomes retarded, phosphorite and glauconite become abundant and the sorting becomes increasingly poorer. CUMULATIVE PERCENT 9 9 98 D E T R IT A L - FORAM I NI FERAL (.0-3") 95 ^ DETRITAL FORAM I N I FERAL ( 3 - 5 " ) 90 GLAUCONITE (3' - 5") 80 PHOSPHORITE —^ 70 60 50 4 0 GLAUCONITE (o"-3") 30 20 O CORE 7 (0"-3") + 5 - 5 0 UNITS ■lottod on . 1 o j. v e c ur v 23 Beyond the zone of glauconite and phosphorite formation there is little or no coarse detrital material in the sediments, only clay and foraminiferal tests. However, even though composed of only one constituent, marine clay, the sediments are more poorly sorted in this area than any other place in the line of cores. This can be explained in two ways; one, the mechanical analysis of the clay-sized particles is inadequate due to differential breaking apart of clay particles by dispersion agents; and two, (probably the most likely) the lack of hydraulic agencies for sorting sediments of extremely small grain size. Crystallization of clay minerals in different size particles during dia genesis may be a minor factor in the poor sorting of the fine grained sediments in the outer cores. Skewness The coefficient of geometrical quartile skewness indi cates the degree of symmetry of the size distribution re lated to the median (Twenhofel and Tyler, 19^4-1) • Skewness is determined by dividing the product of the two quartile diameters by the square of the median diameter, or On 0>2 If the skewness be greater than unity the maximum sorting of the sediment lies on the fine side of the median diameter; if it is less than unity the maximum sorting lies 21) . on the coarse side of the median diameter* The further the value deviates from unity the further the position of maxi mum sorting (mode) is from the median grain size* Values for skewness ranged from O.jp to Ip.I 4. and in gen eral decrease with depth. Results of the calculations of skewness, median grain size, and sorting are presented in Table 1* Microscopic Examination Microscopic examination of screened portions shows that the^detrital material which is predominant in the nearshore areas decreases in grain size and abundance with distance from shore. Glauconite, which was not found in the near shore cores (1-5?)* does not occur in any appreciable amount in sizes below 0.062 mm in any of the samples. Necessarily, its presence increases the mean grain size of sediments in which it is found. Phosphorite also exists only in the size fractions above 0.062 mm and has the same effect on the median grain size as does the glauconite. WATER CONTENT The water content of the sediment was determined by measuring the weight difference between wet and dried samples. Two to five grams of sediment from various depths in the core were weighed wet and placed in an oven which was kept at a temperature of 9^° C for a period of twenty- four hours. The sample was again weighed after cooling in 25 Gore Nr. Median Diameter Sorting Skewness 1 0.115 mm 1.32 0.97 2 O.O3I 4 . mm 1.56 0.90 3 O.OI4 .5 mm 2.11 0J4.0 k 0 • 0i _ j _5 mm 1.20 1.10 5 0.01^3 mm 1.1 4 - 2 1.10 6 O.38 mm 3.1+6 2.00 7 0.70 mm 3.60 1 +.1+0 8 0.009 beb 2.60 0.81 9 0.013 Ym- 1+.86 0.25 10 0.006 mm 1+.70 0.70 11 0.008 mm 3.1+0 0.72 Table 1. Median diameter, Sorting, and Skewness for the surface samples across the continental terrace* 26 a dessicator; the difference between the first and second weighings is the weight of the water in the sediment. The water content of the cores ranged from 2l j . percent of the wet sample for the sandy above detrital sediments to 67*7 percent of the wet sample in the outermost fine grained sediments. In general, the water content of the cores de creased with depth in the cores. The decrease in water content was most noticeable in the top few inches of the core; below this zone it was hardly noticeable. Tops of some cores were so ”soupy" that it was difficult to deter mine where the core began and the overlying water stopped. The decrease in water content of the cores is attrib uted to an increased compaction with depth. The cores are noticeably stiffer at the bottom than they are at the top. The grain size, while decreasing somewhat with depth in the cores, is inadequate to explain the observed decrease in water content. Compaction must therefore be the cause. Figure l \ . gives the water contents of the cores off Point Arguello. ORGANIC MATERIAL IN THE SEDIMENTS The high production of plant and animal life in the photosynthetic zone of the ocean produces a never ending "rain" of organic material on the ocean floor. On the sea floor it becomes incorporated in the sediments and, with the passing of time, becomes buried deeper and deeper in DEPTH IN INCHES c r 5 10 20 L 25 0 0 r 10 15 20 25 0 5 I 0 15 20 25 0 20 40 60 CORE 2 ..i________ i _____ 2 0 4 0 CORE 5 —j 60 PERCENTAGE o r 20 , 40 60 CORE 3 / 1 20 40 60 CORE 6 0 20 4 0 60 0 20 4 0 6C COR E 8 CORE 9 JL 2 0 40 60 CORE 4 20 i i 40 60 CORE 7 i . -i ~i 0 20 40 60 CORE 10 FIGURE 4. RELATION IN PERCENT OF WATER CONTENT WITH DEPTH IN THE CORE CO <3 28 the sediment. The burial, however, is not uneventful, as a multitude of organisms use this material for food. These scavengers continually grub through the sediment, gradually turn it over and pass it through their digestive tracts, changing the composition of the sediments by their actions. Bacteria are present in great numbers and continually attack organic material, changing it into various compounds. This activity cannot go on indefinitely, however, because most of the organisms depend on oxygen for their metabolic processes. As the sedimentary material becomes buried, the interstitial water becomes exhausted and renewal from above is too slow to be of any significance. The remaining buried organic material then changes more slowly with time or depth in the sediment, as it can be attacked only by anaerobic organisms. Thus, the rate of deposition and the length of exposure to biological attack, becomes important in determining environmental conditions. The biological oxidation of organic material in oxygen containing sea water will change most of it to water and carbon dioxide. This reaction is indicated in red clays by the low organic content of these sediments. One explan ation for this low organic content is that organic material produced in the surface water is completely oxidized before it reaches the ocean bottom. Another explanation is that the production of organic matter in the regions bf red clay 29 Is insurficient to furnish organic material to the ocean bottom. Measurements of organic nitrogen and organic carbon are essential for the determination of the post-deposition- al history of organic material. lost organic carbon material in the sediments is less readily broken down than the nitrogenous compounds (Emery and Rittenberg, 1952). It is therefore important to study the carbon-nitrogen ratio (Table 2) to determine what happens to the organic content of the sediment during diagenesls. Organic Carbon Organic carbon measurements were made by a modified Allison (1939) method. This method involves the oxidation of organic matter by sulfuric acid in the presence of excess potassium dichrornate. The rate of oxidation is controlled by heating the solution to 175° 0 in 90 seconds. After cooling, the unused dichrornate is titrated with a standard solution, of ferrous ammonium sulfate, using barium diphenylarnine sulfonate as an Internal indicator. Values for organic carbon in the sediment ranged from '0.37/i to 2.77%, Maximum values were found in the sediments which had the smallest median grain size and those which were farthest from shore. Minimum value was in core number one which was a fine grained sand. Values for the surface s ample s are presented in Tab.le. 2 30 Core Nitrogen Carbon c/n co5/n co3/c 2 0.096% 1•30/a 13.50 67 4.96 3 0.105% 1.22% 11.80 87 7.45 4 0.115% 0.79# 5.10 50 4.10 5 0.155% 1.04# 7.05 83 11.70 6 0.210% 0.59# 2.80 51 18.30 7 0.295# 1.10# 3.73 38 10.20 8 0.256# 2.48# 9.65 93 9.60 ' 9 0.222# 1.79# 8.05 109 13.60 10 2.77# ---- -- 8.00 11 0.308# 2.77# 9.00 49 5.50 Table 2. Nitrogen, Carbon, Carbon Nitrogen Ratio, Carbon- ate Nitrogen ratio, and Carbonate Carbon ratio for surface i samples run consecutively across the continental terrace. Organic Nitrogen 31 Organic nitrogen in the sediment was measured by the Ejeldahl process. A sample weighing 0.200 gm was placed in a digestion flask and oxidized with concentrated sulfuric acid. This process oxidizes the carbon and hydrogen in organic compounds to carbon dioxide and water and forms ammonium sulfate from the nitrogen in the organic material. Two to three selenized granules were used as a catalyst for speeding up the digestive process. After the formation of the ammonium sulfate by digestion and boiling off the GOg, the sample was placed in a Kleldahl generator and made basic with concentrated sodium hydroxide. The liberated ammonia brought about by the alkalinization of the solution was distilled into a known volume of standard sulfuric acid solution which in turn was titrated with a standard solution of sodium hydroxide. The difference between the normali ties of the standard acid solution before and after titra tion was due to liberated ammonia and the equivalent amount of organic nitrogen needed to form the ammonia taking place in such a reaction could be computed. Results of the nitrogen determinations are presented in Table 2. Organic nitrogen percentages ranged from less than 0.05 to 0.308 and averaged 0.205. Changes in the percentage of nitrogen correspond closely to changes in the carbonate content and grain size. In all samples the nitrogen content of the sediments decreased with depth in the core and increased 32 with distance from shore* Rittenberg (19I 4.O) and Zobell (19^2) have shown that there is a rapid decrease in the abundance of bacteria with depth in recent marine sediments, and it can be assumed that the amount of biological activity decreases with depth in the core. It is therefore desirable to com pare change in organic material to a substance which will change very slowly if at all with depth, such as calcium carbonate. Such an approach was used by Emery and Rittenberg in their study of basin sediments (1952). Assuming that the calcium carbonate, deposited in the form of shells and skeletal material, is essentially unchanged by burial, it is possible to use this compound as a con stant with which to compare changeable substances such as carbon and nitrogen* By this method changes in organic material can be determined indirectly by plotting a ratio of carbonate to the changeable compound as in Figure 5* The assumption that the carbonate will be relatively un changed Is valid in sediments which are alkaline, as are most marine sediments (Emery and Rittenberg, 1952). Changes in organic nitrogen with depth In a core serve to indicate changes in the organic material which take place after deposition. Carbonate-nitrogen ratio profiles like those presented in Figure 5 show that the amount of organic nitrogen decreases with depth. This A 0 10 15 20 (0 Ld X o z \ CORE z CORE X h- CL LlI O O CORE 8 A CORE II 25 i O 95 A 50 100 55 105 60 110 65 115 70 120 125 75 80 130 85 135 90 140 95 145 100 150 105 Pip/ure 3* Carbonate-nit: showing a rapid decrease Pen inodes of sedinent • n rat . :a ins u in the tii st 3k decrease is most pronounced in the first six inches of core, indicating that it is in this zone that the greatest changes in the organic material take place* Figure 5 shows that approximately 80 percent of the breakdov/n of nitrogen com pounds takes place in the top six inches of core 8. Core 11 shows the same decrease in nitrogen content but the lack of an intermediate point of nitrogen content prevents the drawing of a curve similar to that for core 2. Emery and Rittenberg (1952) have reported an increase in the CO^/rJ ratio with depth in their samples of the basin sediments off southern California, and attribute it to the breakdown of organic nitrogen by bacterial activity. In all probability the same process Is active In the cores off point Arguello and changes in both organic carbon and nitrogen are due to micro-organisms. HYDROGEN-ION CONCENTRATION (pH) The acidity or alkalinity of a sediment is expressed by Its hydrogen-ion concentration or its pH. This value is import a n . t because it gives clues as to the amount and nature of biological activity and chemical changes which are tak ing place In the sediment. Conditions which can change the pH of bottom sediments are closely connected with the life processes of benthonic organisms particularly bacteria, be cause they produce organic acids, carbon dioxide, and hydrogen sulfide which In turn change the pH of the sediment. 3$ A Beckman pH meter was used to measure the pH of the sediment. Samples to be measured were placed in a 5 ml beaker and the electrodes of the meter placed directly into the sediment. The samples were then allowed to come to equilibrium, and the pH read directly from, the instrument. The period of time needed for the instrument to reach equilibrium never exceeded one minute. Measurements were made on nine of the eleven cores at various depths in the cores, usually corresponding to 0-1 inches, 1-5 inches, 5-10 inches, 10-15 inches and the bottom of the core if it was deeper than 15 inches. Samples were taken from the middle of each section and assumed to represent the entire section if there were no variation in texture, color, or grain size to warrant a closer division. The instrument was standardized against a standard solution of pH 7 both before and after each series of measurements on each core. Table 3 shows the pH of the sediments taken on the profile* In general the pH of the sediments off Point Arguello increased with depth in the core. This means that the sed iments become more basic after burial. Figure 6, shows some of the important processes which will cause such a change in pH. These changes, when compared with the or oxidation-reduction potential, give clues as to what type of processes are taking place. Because no hydrogen sulfide was found in any of the cores, the production of hydrogen 36 Decrease In pH 1. Production of carbon dioxide by bacteria during the breakdown of organic matter. 2. Breakdown of sulfate by bacteria during the decomposition of organic matter. 3. Production of organic acids. ! [ . . Assimilation of HH^ by bacteria. 5?. Liberation of phosphates by bacteria during the decomposition of organic matter. Increase in pH 1. Production of HH^ by bacteria. 2. Reduction of sulfate to hydrogen sulfide. 3* Consumption of phosphates and carbon dioxide. 1|. Breakdown of nitrates, to nitrites, to ammonia. Figure 6. Ways in which the pH of sediments can be changed by organic activity. 37 sulfide from sulfates can be eliminated as one of the causes in the changes of pH in the sediments off Point Arguello. The E^ in all of the cores was positive, thus ruling out processes which bring about reducing conditions as being responsible for changes of pH* These being elim inated the following mechanisms are the most likely to explain changes in pH with depth in the cores. The in creased pH in the samples could be brought about by the breakdown of organic material by bacterial activity to ammonia. The utilization of carbon dioxide, phosphates, and organic acids which are the by-products of many organic functions would also bring about an increase in pH. De crease in pH could be caused by the production of carbon dioxide by animals during respiration and oxidation of organic material by bacterial activity. As the pH at the top of the cores is more acidic than at the bottom there is an indication that with time organisms change the sediments from an environment of acidic conditions to one of basic conditions, assuming, of course, that an increase in depth in the sediment is equivalent to a longer time of burial. Bacteria are one of the main types of organisms which change the chemistry, including the pH, of the sediments. Their ability to ^reak down organic compounds to ammonia, hydrogen sulfide, carbon dioxide, and many other simple compounds makes their role extremely important in 38 diagenetic changes. Abundant bacteria have been reported by ZoBell (19/4-9) sediments from cores taken off southern California. Mud-eating and bottom dwelling scavengers are another important group of animals which change the chemistry of bottom sediments. The passage of mud through the digestive tract of these animals reduces the organic content and forms by-products which affect the pH. Brittle stars were found at a depth of I 4. inches in one of the cores from the Point Arguello profile and their presence undoubtedly changed the composition of the muds by the simple process of mixing, as they traveled through the sediment. Worms and other burrowing organisms are continually stirring and eating the sediment and thus affecting the chemistry of sediments in their path. Submarine photographs on the continental terrace of southern California show that organisms are active in turning the sediments over, and in turn changing its chemistry. Plate l \ . 9 taken off southern California on the continental slope' shows abundant organic activity at a depth of 300 fathoms. THE OX ID AT 10 PI- R EDU C T10 N POTENTIAL (Eh) The state of oxidation of marine sediments has been until recently a matter of speculation. Very few measure ments of the E^, which is an expression of the state of oxidation or reduction of any material related to the Plate 4* Organic Actibity at a depth of 300 fathoms on the continental slope off southern California* hydrogen half cell, have been made. The is important in the study of the environment of sediments because it, like the pH, is affected by the biological and chemical activi ties which take place in sediments (Zobell, 19^-6) • The oxidation potential (3^) waa measured by a Beckman pH meter equipped to measure E^. Platimum and calomel electrodes were used for the measurements and were placed directly in the sample of mud; similar to the method used in measuring the pH. The system was then allowed to come to equilibrium and the uncorrected E^ of the sediment read from the instrument. In order to relate the instrument reading to the standard hydrogen half cell a correction of plus 21\5 millivolts was added to the value recorded by the meter. An appreciable instrument drift is associated with the measurements of the Eft in sediments and a special technique has to be used to get reproducible results. When the electrodes are first placed in the sediment the value drifts quite rapidly; after this initial rapid change, the drift, which is brought about by a non-equilibrium existing between the instrument and the mud, slows down. It is at this slowing down point that the E^ is read because at that moment the sediment is in equilibrium with the instrument and sufficient time has not elapsed for oxygen in the atmosphere to begin oxidizing the sediment. kx All of the samples taken on the profile were in a positive environment. The term "positive" indicates that the samples were in an oxidizing condition rather than a reducing one. Variations in the magnitude of the positive potential did exist however, with the most highly oxidized material at the top of the cores and the less oxidized material at the bottom. This change can be attributed to the activities of organisms because the life processes of many of the bacteria tend to reduce the organic material in the sediments and in turn lower the oxidation potential of the sediment. The samples from Point Arguello become increasingly more oxidized with distance from shore, which in turn is probably an expression of exposure to the oxidizing environ ment of sea water and because of the slower burial rate in deep water. This indicates that the longer sediments are exposed to the oxidizing effect of sea water the more oxi dized they become. The transition of the sedimentary material in the line of cores and the increase in the oxi dation potential across the continental terrace substanti ates this reaction on the area off Point Arguello. Table 3 presents the values of 3^ for the sediments of the traverse• IRON The samples in which the total iron content was to be Gore 1. 2 . 3. k- 5. 6 . 7. 8, 9- 10. _________________________________________________________k2 Depth pH Uncorr. Corrected 0-2" 6.62 + 102 t 3l±7 0-1" 7 .5 0 - 182 t 63 1-5" 7.31 - 211 + 34 3-10" 7.71 - 205 t [j.0 10-12" 3.08 - 223 + 20 0-1" 7 .9 0 - 192 •* 33 1 -4 t" 7 .7 6 - 193 * 52 k'.-6" 7 .6 7 - 197 r U -8 8-12" 7 .6 9 ■ - 137 * 88 0-1" 7.39 - 20V + I4 .1 1-2" 7 .4 0 - 114 f 131 2-3" 7 .5 0 - 223 •* 20 3-10" 7 .6 3 - 173 * 72 0-1" 7.07 - 78 ■ » 167 1- 3" 7 . lo - 132 •» 93 3-10" 7 .6 3 - li+o ■ * 103 10-12" 7 .3 2 - 135 ■ * 110 12-15" 7.67 - 136 •» 109 15-10" 7.27 - 129 ■ * 116 No pH and R Left in core tube. 0-3" 7.05 + 70 ■ » 315 3- 5" 7.11 + 5 0 ■ » 295 0-1" 7 .0 8 - 1I4.3 f 102 1-2" 7.28 - 157 -* 88 2 -5" 7.28 - 157 f 88 5-10 " 6.9!). - 20 * 225 10-15" 6.82 - 32 ■ * 213 15-21" 7 .3 0 - 118 ■ » 127 21-23" 7 .0 - 121 -» 121). 0 - l" 7.17 * 1 5 ’ 260 1-5" 7.18 16 •* 261 5-10" 7 .1 0 - ll|. ■ * 231 10-15" 7 .3 0 - 11 -* 234 0-1" 7.42 - 12 f 233 1-5" 7 .6 1 - 60 * 185 5-10" 7.85 ♦ 35 " 280 i o - i 5” 7.83 ■ » 82 * 327 15-20" 8.10 + 15 * 260 Table 3* pH and Values for cores. U measured were made acid by hydrochloric acid and oxidized by potassium permanganate in order that all iron be in the ferric state. Excess permanganate was removed with bromine water which was in turn driven out of the solution by boil ing for 15 minutes. Fifty ml of a solution containing 2 gms of potassium iodide per SO ml of solution was added to the oxidized sample. The iron in the solution, which is in the ferric state, was reduced, freeing which was then titra ted by a standard solution of thiosulfate. The amount of thiosulfate needed to titrate the iodine is equivalent to the amount of iron in the sediment. The ferric ion content of the sediments was measured in the same manner as the total iron except the sediment sample was not oxidized before the addition of the KI solution. Organic matter was considered to have little effect in the reaction, and the main oxidizing agent in the sediment was assumed to be iron in the ferric state. In both ferric and total iron analyses, blanks were run to determine the amount of oxidation by atmospheric oxygen. Ferrous iron was then determined indirectly by subtracting the ferric iron from the total iron of the sediment. The total iron in the sediments ranged between 7*^1 and 16.6 mg. per gram of dry sediment. The iron content in creases with distance from shore (Figure 7) and in general, decreases with depth in the core* +++ I I I I 2 5 CORES 8 10 DISTANCE FROM SHORE IRON Eh +++ 230- Fe PH . 220- 4 -15 210- 200- 190- PH 7.60 E o U) I 70- 160- 7.50 3 -10 150- 7.40 - 8 130- ISO- 7.30 .2 lio- loo- 7.20 © / -4 9 0 - 8 0 - 7. I 0 - 2 70- 60-1 7.00 k5 Most of the iron which is found in recent marine sedi ments is originally deposited in its ferric state, usually as ferric hydroxide. Gorrens (19^ 4-1 > 19^ 4 - 2, 19^1-7} states that the oxygen content of sea water is high enough to oxidize all iron present in sea water to the ferric state, and because the pK of the sea water is always higher than 6, iron is precipitated as ferric hydroxide. The ionic state of iron in the sediments taken off of Point Arguello however was predominately in its lower valence state (ferrous iron) which indicates that the iron has had to undergo a change in ionic form after deposition. Rankama and Sahama (195>0, p. 662) state that iron in ) the ferric state is reduced to iron in the ferrous state during the oxidation of organic material in soils. This action suggests a possible explanation of the preponderance of ferrous over ferric iron on the continental terrace. If one assumes the reduction of ferric iron to ferrous iron during the oxidation of organic material in the sea, as do Rankama and Sahama (195°) in soils, the following reactions can be postulated: Ferric Iron in complex organic com pounds or adhered to clay particles may be reduced during the oxidation of organic matter to the ferrous state. Iron in the ferrous state could then be oxidized back to the ferric state If sufficient oxygen remained in the inter stitial water to oxidize it to its higher valence. Iron would in this way act as a continuous oxidizing agent, and be partly responsible for the oxidation of carbon compounds into carbon dioxide. Thus, iron could serve as a catalyst in the carbon cycle. The oxidation of organic matter could cause the CO2 content of the sediment to become higher and the pH of the sediment to decrease. In areas of low pH caused by oxidizing organic material to 0C>2 the ferric iron should also be low, showing that it is affected by organic activity. The ferric Iron content of the sediments off Point Arguello decreases with distance from shore indicat ing that such a reaction might be active in these sediments. Figure 7 shows the ferric iron content plotted against the pH of the sediment. The organic material which is continually being de posited on the sea floor seems to have an effect on the state of the iron in the sediments, and the reduction of iron from the ferric state can be explained by its action as a catalyst in the carbon cycle. The supply of oxygen In the sediments also controls the state of oxidation of iron. Free 0x7 7 p:en in the sediments is limited to that which was contained in the interstitial water upon burial and that which, by the process of diffusion, Is added to the sediments from the overlying oxygenated bottom water. The amount of oxygen added by the process of diffusion is probably very small, however, and the major portion of oxygen present in the sediment after burial is probably that which was incorporated in the interstitial water at burial. This oxygen is used by aerobic bacteria in their basic metabolism to oxidize material for food and energy. Thus, there is a continuous demand for the oxygen in the interstitial water of the sediments where there is bacterial activity. Iron which is assumed to be reduced to the ferrous state upon oxidation of organic material is not able to compete for the oxygen in the sediment and is, therefore, continually kept in the reduced state after its initial reduction by organic material In the sediments. This condition will prevail until the organic material is completely oxidized or has been oxidized to a stable com pound, when this state Is reached by the organic matter In the sediments the iron may then be oxidized back to the ferric state. In most continental terrace sediments this condition is never reached because the sediment becomes buried beyond a source of oxygen before the complete oxida tion of organic matter. This process, however, nearly goes to completion at the base of the terrace and is indicated by an increase in the ferric iron content of the sediments. Red clays (which were not found in the traverse) are known to contain little organic matter and a predominance of ferric Iron, thus indicating a complete oxidation of organic material in these areas and a completion of the iron cycle 2 4 - 8 in sediments. It is possible to divide the continental terrace and the deep sea basin at its base into three zones (Figure 8) on the basis of the state of iron in the sediments: 1. The Continental Terrace Zone, where deposition is relatively rapid and the abundant supply of organic material reduces iron to the ferrous state. 2. The Base of the Continental Terrace Zone, where the supply of organic material is small and is nearly balanced to the iron in the sediment. Here the iron, when in excess, may begin to be oxidized to ferric iron before it is buried beyond the supply of oxygen in the sediment. 3. The Oceanic Abyssal Zone, is found where the organic material is either completely oxidized before reaching the bottom or is in a stable compound when it reaches the bottom, resulting in a high ferric iron content because of the lack of organic material to reduce it to the ferrous state. Two of these three zones were sampled in the cores from Point Arguello, and if cores farther from shore could have been taken, the third, would undoubtedly have been encountered. The contact between red clay and sediments which contain ferrous iron should be sharp, and dependent on the organic material in the sediment. To the knowledge of the writer the contact of terrigenous and red clay Figure 8* Division of the continental terrace and the deeposea basin into three zones on the basis of the states of oxidation of iron in the sediments. OCEANIC ABYSSAL BASE OF THE CONTINENTAL TERRACE ZCNE CONTINENTAL TERRACE ZONE ZONE //// / 50 sediments has not been described. It Is, therefore, sug gested that this zone be further investigated for valuable information about the sedimentology of material as it passes from a terrigenous to a deep sea sediment. CALCIUM CARBONATE The amount of carbonate in the sediment was determined by a weight loss method. Five to seven grams of dried sediments were placed in a 500 ml beaker and treated with dilute hydrochloric acid. Acid was added until carbon dioxide stopped forming from the breakdown of the carbonate. The sample was then filtered with Pasteur filter tubes several times using distilled water as the diluent. The samples were then placed in an oven at a temperature of 9^° C until the sediment was dry. The residue was then weighed and the loss during the treatment assumed to be the weight of carbonate in the sediment. Because most of the carbonate in the sediments is combined with calcium in the shells of organisms, carbonate is reported as calcium carbonate. Calcium carbonate values, Figure 9* ranged from to 3 k and show an increase with distance from shore. Figure 10 shows the relationship of calcium carbonate to distance from shore along with the range encountered in each core. The calcium carbonate content was quite vari able with depth in the core and related to local concentra tions of foraminiferal tests. The carbonate concentration CALCIUM CARBONATE 25 20 ON 0 RANGE IN CARBONATE PERCENTAGE PER CORE PERCENT OF SURFACE SEDIMENT CARBONATE INCREASE IN DEPTH 4 _ L 5 i CORES 8 10 _ l_ 11 Figure 10, Percent of CaCOo in the sediment showing range per core and CaCO^ content for surface sample, as a dotted line. 53 In the sediments is much greater than the carbonate in sea water and represents a concentration of this compound in the sediments. The increase in the amount of carbonate in the sediment with distance from shore is not due to a higher production of carbonate in the offshore areas, but the result of a decrease In the dilution of organic carbonate by detrital material. Thus, the carbonate is probably being deposited at essentially the same rate over the entire continental terrace but the abundance of detrital material in the inshore region causes an apparent decrease in over-all carbonate content. GLAUCONITE General Glauconite; a hydrous iron, potassium, magnesium, aluminum silicate, is a green authigenic marine mineral. It Is found In recent sediments of the continental shelf and on bank tops and has been reported in rocks of every geologic period. X-ray studies show that its internal structure resembles the hydrous micas, which in the form of illite compose a high percentage of the marine muds (Grim, Dietz, and Bradley, 19^4-9) • Physically, however, it is quite different from, the marine clays. Glauconite is found in two forms; a green stain on marine clays and rocks, and as Individual grains of approximately sand size. The shape of the sand sized granules ranges from ovoid, 54 polylobate to cylindrical. Commonly the grains are covered with a fine network of fractures that show alteration to a light brown micaceous material. Alteration to limonite is common along some of these fractures. An increase in the number and the size of these fractures can be brought about by treating the grains with hydrogen peroxide. This sug gests that they form by the oxidation of the glauconitic material. Environmental Evidence from Analysis of the Chemical Formula An analysis of the formula for glauconite indicates some of the chemical conditions necessary for the formation of glauconite. The chemical formula for glauconite reported by Hendrix and Ross (1941) is: (K, Cai,Ha,).84 (Al & • n r / Fs ".191£S.40^ <Si3.65 A1.35)010 (0H2> This formula is similar to the chemical composition of illite. (Grim, Bray, and Bradley, 1937) which is as follows K .5Q (Al1.38 Fe.37 Fe".04 MS#34^ (Si5.41 A1.59^ 0 10 (0H)2 In the development of any theory a working hypothesis is desirable; therefore, the writer has chosen to assume that glauconite forms from a diagenetic change of marine clays. Potassium and magnesium are needed in trie production of glauconite from marine clay. Takahashi and Yagi (1939) 55 have shown by experiments that silica-gel will remove potassium and magnesium from sea water by selective absorp tion. This experiment may, In part, explain the increase In potassium and magnesium content reported by Grim, Dietz and Bradley (1949). Their data Indicates that there is an increase In potassium and magnesium with distance from shore, and in the nearshore samples, with an increase in depth, suggesting that the increase of these elements is brought about during diagenesis of the sediments. The presence of ferrous iron in glauconite has been used as evidence to indicate that glauconite forms in a reducing condition. (Kendricks and Ross, 1941; Galilher, 1955, Clark, 1915; Murray and Reynolds, 1891). This assumption is not entirely correct because there Is from five to twenty times as much ferric iron as there Is ferrous iron in glauconite (Table 3). Alteration of glauconite to limonite and the variability of the amounts of ferric iron indicate that glauconite Is an intermediate member of sub marine weathering of Iron silicates. Pyrite has been found associated with glauconite and % j o from this association it has been inferred that glauconite forms in a reducing environment. The reports of this association are usually from consolidated rocks, and there is certainly a possibility that the pyrite may be secondary. The samples examined by the author and studed by 56 Investigators at the University of Southern California have shown no such relationship in the glauconite that is now forming on continental terrace and bank tops. Calliher (1935) reports samples containing glauconite which reek with hydrogen aulfide. The presence of this material Is certainly positive evidence of reducing condi tions, but it is difficult to explain the presence of Eg3 on the continental shelf in a region where there Is no depression in which water can become stagnated as is the case in the area where Galliher conducted his studies. It is evident from the preceding discussion that the validity of the assumptions of past writers who speculated on the environmental conditions necessary for formation of glauconite is questionable. Field Evidence of Environmental Conditions In five samples containing glauconite, which were taken from the continental shelf near Point Arguello, all had a positive oxidation-reduction potential and thus were in an 5 oxidizing condition. Table 4 3 1 /hows the relation between depth and the oxidation-reduction potential of these samples. These measurements were made with a Beckman pH meter by using a calomel and platinum electrode series. Other samples which contained glauconite, from Tanner and Cortez Bank, taken by Eolzman (194-9) show that a similar oxidizing condition exists. The continental 57 Percentage Si02 55.95 51.90 ; a12°3 11.56 1.52 p©2^3 9-99 27.98 FeO 2.02 1.26 Mg 0 6.77 i t -.67 CaO 3-95 0.89 Na20 -0.61 0.53 k2o i t -.12 4.90 H20 i t - . 82 6.15 p2°5 0.18 0.11 organic matter trace 99*97 trace 99*91 Table I 4 .. Relationship of ferric and glauconite and their relationship to the mineral. (Galliher, 1939)* ferrous iron in other elements in Depth 300 fathoms Oxidation-Reduction Potential ll6 mv. Amount of Glauconite present 500 fathoms 315 mv. abundant 1000 fathoms 102 mv. present 1300 fathoms 260 mv. abundant Table 5* Relationship of glauconite to depth and oxidation reduction potential of sediments. Amount of glauconite is shown to bear a direct relationship to strength of the oxi- dation-reduction potential. shelves and banks are areas of hiah oxygen content, and glauconite is found almost exclusively in these areas. Therefore, it is the author’s belief that glauconite forms in an oxidizing rather than a reducing environment. Relationship to Rate of Sedimentation The rate of deposition is another important environ mental factor. Glauconite is found only on the continental shelves and topographic highs which are, in general, areas of erosion or extremely slow sedimentation (Shepard and Revelle, 1939)* Its common occurrence with phosphorite which is known to form only in areas of retarded deposition (Dietz, Emery, and Shepard, 19h.2.) (Emery, 19^8), is another proof of slow sedimentation. In addition, ancient sediments which contain glauconite are commonly associated with uncon formities or breaks in sedimentation (Goldman, 1922). Such an association might be expected in rocks that had been deposited in areas of slow sedimentation, like the contin ental terraces and shallow banks. Origin of Glauconite It is not the Intent of this paper to consider the mode of origin of glauconite. However, the examination of some of the samples obtained by the writer, off Point Conception, suggests an origin that should be presented In conduction with environmental conditions. 59 A sequence of stages showing what seemed to be the alteration of clay to glauconite was observed in one of the samples. This gradation was shown by a change of color and shape. The sample was recovered from a topo graphic high on the continental shelf and contained clay and glauconite. Some of the clay was similar to the usual greenish gray clay found on the shelf which does not contain glauconite. The remainder of the sample, however, showed the transition of clay to glauconite. This transition was indicated by green stained clay associated with clay containing partially formed glauconite grains, and finally completely altered clay grains in the form of glauconite. Chemical and X-ray data were not ob tained and this transition was observed only by color and shape variations of the Individual grains. This transi tion has also been observed by Gould (1951) in the tests of foraminifera, where he noted foraminifera containing clay and ones containing glauconite existing side by side. It Is fully realized that the evidence presented for the origin of glauconite is not conclusive. However, the measured values of E^, pH, oxidized, or reduced states of iron, rates of deposition and location on the continental terrace do give the environment in which glauconite forms. The fact that glauconite was not found in reducing but in oxidizing conditions refutes beliefs that a reducing environment is essential for the formation of glauconite. The preponderance of ferrous iron over ferric iron in the continental terrace sediments indicates that the sediment must he oxidized and not reduced in order to account for the ferric iron in glauconite. The presence of some fossil and many recent foraminiferal tests coupled with a pre dominance of benthonic over pelagic forms in areas of glauconite formation indicates slow rates of deposition. The organic content of the sediments in the area of glauconite formation was low and indicates that it has been oxidized to a highly stable compound or to water and carbon dioxide before or shortly after deposition. In summary glauconite probably forms from green muds (probably illite) during early diagenesis in areas of slow deposition, fairly low organic content, and in an oxidizing environment. All four of the above conditions are found in a zone which lies approximately half way across the conti nental terrace in the vicinity of Point Arguello,California. SUMMARY OP OBSERVATIONS AND CONCLUSIONS The following observations and conclusions were drawn from, the study of the sediments off Point Arguello; 1. The median grain size and abundance of the detrital sediments decreases with distance from shore. 2. Sorting decreases with distance from shore. 3. Foraminiferal tests aid in increasing the median grain size of fine grained clay sediments on the outer edge of the continental terrace# ip. Grain size decreases with depth in all cores# 5# Sediments are zoned across the terrace; the inner most portion is characterized by an abundance of detrital sediments, the middle portion by authigenic minerals, and the outermost portion by clay and foraminiferal tests# 6. Water content of the sediments increases with distance from shore and is closely related to grain size. The water content decreases with depth in the core as a result of compaction. 7# A possible origin of glauconite is the oxidation of marine clay, in areas of high oxidation# An observed transition from clay to glauconite was found in one of the cores (core 6). The presence of ferric iron in glauconite (which forms from sediments in which the iron is predomin antly in the ferrous state) indicates that the glauconite forms in oxidizing rather than reducing conditions. The measurements bear out this observation. 8. The abundance of glauconite decreases with depth in the core. 9# Glauconite and phosphorite are most abundant in the size grades above 0.062 mm. 10. Phosphorite was found only on a small topographic high (station 7) in an environment of high oxidation and slow deposition. 11# Organic matter is greatly altered in the top few inches of sediment# 12# Organic nitrogen increases with distance from shore and decreases with depth in the sediments. The greatest change in the percentage of nitrogen is in the top few inches of sediment# 13. The percentage of nitrogen in the sediments can be correlated with the grain size and the rate of deposi tion. l l } _ . Activities of organisms in the presence of oxygenated sea water are the main agents in the oxidation of material in the sediments. 15• The oxidation-reduction potentials (E^) indicates that the sediments become more oxidized with distance from shore, and become more reduced with depth in the sediment# All values for the are positive, indicating that oxi dizing conditions prevail over the entire terrace# l6« The increase in the on the outer edge of the terrace indicates that the sediments are approaching the found in red clays, which have a large positive oxida tion potential. 17* The oxidizing conditions indicate that sediments deposited on the continental terrace are undergoing an entirely different diagenesis than those in the basins to 63 the south on the continental borderland where reducing conditions prevail, l8. The pH varies over the continental terrace de pending on the organic activity. It increases with depth in the sediment showing that with age the sediments be come more alkaline, 19* The pH of the sediment is largely determined by the break down of organic material by organisms. In creases In pH are probably due to the breakdown of organic material by micro-organisms to ammonia, the consumption of carbon dioxide and phosphates, and the destruction of acids which are the by-products of many organic functions# Decreases in pH result from the production of carbon dioxide by organisms during respiration and the oxidation of organic matter, 20. The iron content of the sediment off Point Arguello Increases with distance from shore and decreases with depth in the core. 21. Iron is kept In its reduced state by the organic material in the sediments. The state of iron is also dependent on the state of oxidation of the organic material. The iron on the continental terrace is predominantly in its ferrous state because of the abundant organic material de posited there. 22. The marginal region adjacent to the continents can be divided into three zones by the oxidized or reduced state of iron in the sediment. The continental terrace is characterized by iron in the ferrous state which could be related to the large production of organic material in this zone. The base of the continental terrace and seaward to the red clay zone is characterized by iron in the ferrous state. However, there is an increase in the percentage of ferric iron that may be brought about by a decrease in organic production and oxidation of organic material before reaching the bottom, and the outer most zone which is the red clay zone and characterized by little or no organic material in the sediments and predominantly ferric iron. 23• The sedimentary material on the continental terrace is subject to variable rates of deposition. The inner portion is covered with a blanket of rapidly deposite detrital material which masks all other sediment types, however, owing to its large grain size this material is dropped fairly near to the shore. Then due to the slow rates of deposition for nearly all other sedimentary types on the terrace the content of calcium carbonate and other compounds which are concentrated in the sediment increase. This increase in calcium carbonate content of the sediment is not necessarily a true increase in production of this material but may be due only to a decrease in the masking effect of the detrital material. 2Ip. Tlie permeability of sediments in general decreases with distance from shore* This decrease is brought about by an increase in the clay fraction and a decrease in the amount and size of detrital sediments* In ancient sediments this would be represented by a transition from sand to silt to shale* 25* If glauconite is encountered in ancient sediments it would be of little use to drill seaward of the glaucon ite beds in the same horizon as the sediments are mainly siltstones and shales. These rocks may contain shows of oil but will probably have insufficient permeability for production* This case will hold if there is no boarder- land type topography similar to the offshore area in southern California where the basins form excellent reser voirs for oil* 26. If glauconite and phosphorite are encountered in drilling a change In sedimentation is indicated and the sediments below such a zone may not be the same as that above this zone* 27* Some beds which contain glauconite and phos phorite may be good reservoir rocks as they are surrounded by sediments which are rich in organic material* Such beds would tend to be lenticular and grade into shales and silt- stone s at the boundry of the reservoir. 66 28. Source rock sediments would be deposited at an intermediate distance across the continental terrace be cause in this zone organic matter is not diluted by detri- tal material from the near by land masses and yet it is deposited and buried rapid enough to permit preservation of the organic matter before complete destruction by organic breakdown. In the Point Arguello region this zone lies seaward of the authegenic zone* BIBLIOGRAPHY ALLISON, L. E., 1935, Organic Soil Carbon by Reduction of Chromic Acid: Soil Science, vol. [|_0, no. q_, pp 311" 320. CLARK, F. W., 192^-5 Data of Geochemistry: U. S. Gsol. Survey Bull. 720, pp 5l9"23* CORREHS, CARL W., 19^4-1 , Beitrage zur Geochemic des Eisens und Mangans. Nachr. Akad. Wiss. Gottengen, Math.- physuk. Klasse, p. 219* ________________, I9I 4 . 2, Der Eisengehalt der Marinen Sediments und seine Entstehung. Archiv. Lagerstattenforsch. 75, P* N-7 • ________________, 1914.7 , Uber die Bildung der Sedimentaren Eisenerze. Forschungen u. Fortschr. 21-23, Nos. Ip-6. DIETZ, R. S., EMERY, K. 0., SIIEPARD, F. P., 19h2, Phos- porite Deposits on the Sea Floor Off Southern Calif.: Geol. Soc. Am., vol. 53 > PP 3l5-ipS. _________ , MENARD, IT. tf., 1951, Origin of Abrupt Change in Slope at Continental Srielf Margin: Am. Assoc. Petrol. Geol. Bull, vol. 35, no. 99 PP 199^-2016. EMERY, K. 0., I9I 4. 8, Submarine Geology of Ranger Bank, Mexico: Am. Assoc. Petrol. Geol., Bull., vol. 32, no. 5, PP 79°"80l}_. EMERY, K. 0., RITTEN3ERG, S. C., 1952, Transformation of Organic Matter in Recent Basin Sediments: Am. Assoc. Petrol. Geol., Bull. (In press). GALLIHER, E. W., 1935, Glauconite Genesis: Geol. Soc. Am., Bull., vol. ipb, pp 1351-1366. , 1935, Geology of Glauconite: Am. Assoc. Petrol Geol., Bull., vol. 19, pp 1569-I6OI. , 19399 Biotite-Glauconite Transformation and Associated Minerals: Symposium on Recent Marine Sediments, Am. Assoc. Petrol. Geol., pp 513-15* GOLDMAN, M. I., 1922, Basal Glauconite and Phosphorite Beds: Science, n.s., vol. 56, pp 171-73* GOULD, H. R., 1951* Personal Communication, University of Southern California. GRIM, R. E., BRAY, R. H., BRADLEY, W. P., 1937, The Mica in Argillaceous Sediments: Am. Mineral., vol. 22, no. 7* pp. 813-829* _________ , DI3TZ, R. S., 3RADLEY, W. P., 19h, Clay Mineral Composition of Some Sediments from the Pacific Ocean Off the California Coast and the Gulf of California: Geol. Soc. Am., Bull., vol. 60, pp 1785- 1808. GUTENBERG, B., RICHTER, C. P., 194-4-* Frequency of Earthy quakes in California: Bull. Seism. Soc. Am., vol. 34-* pp 185-188. HENDRICKS, S. 3., ROSS, C. S., 19^-1» Chemical Composition and Genesis of Glauconite and Celadonite: Am. Mineral, vol. 26, pp 683-091* HOLZMAN, J. E., 19^4-99 Geology of Cortez and Tanner Banks, unpublished thesis at University of Southern Californi MURRAY, J., REGARD, A. P., 1891, Report on Deep-Sea Deposit Based on the Specimens Collected During the Voyage of H.M.S* Challenger in the years I872-IS76: Challenger Repts., 525 PP* RANKAMA, K., SAHAMA, Th. G., 1950* Geochemistry: University of Chicago Press, p. 662. RITTENBERG, S. C., 19^4-0* Bacteriological Analysis of Some Long Cores of Marine Sediments: Jour. Marine Research, vol. Ill, no. 3* PP 191-201. SHEPARD, P. P., REVELLE, R. R., 1939* Sediments Off the California Coast: Symposium on Recent Marine Sediments Am. Assoc. Petrol. Geol., pp 24-5-281. SVERDRUP, II. U., ALLEN, W. E., 1939 * Distribution of diatons in relation to the character of water masses and currents off southern California. Jour. Marine Research, vol. 2, p. 131-lMl* TAKAHASKI J., YAGI, T., 1939* Synopsis of Glauconitization: Symposium on Recent Marine Sediments, Am. Assoc. Petrol. Geol.,pp 503“512. TWENEOFEL, W. H., TYLER, S. A., 19^1> Methods of Study of Sediments: McGraw-Hill Book Co•, Inc., New York, pp 105-120. UPSON, J. E., 19^4-9» Late Pleistocene and Recent Changes of Sea Level Along the Coast of Santa Barbara County, California: Am* Jour. Sci., vol • 2lj.7, pp 9^”H5* ZOBELL, C. E., I9I 4.B, Changes Produced by Microorganisms in Sediments After Deposition: Jour. Sed. Petrology, vol. 12, pp 127-36. ___________ , 19lj-6, Studies on Redox Potential of Marine Sediments: Am. Assoc. Petrol. Geol., Bull., vol. 30, no. i j . , pp Ip7?-5l3. C J Diversity cl Southarr. California Library
Linked assets
University of Southern California Dissertations and Theses
Conceptually similar
PDF
Cenozoic deposits of the Emigrant Canyon area, Panamint Range, California
PDF
Geology of the central portion of the Green Springs Quadrangle, Nevada
PDF
Geology of the south-central part of the Schell Peaks Quadrangle, Nevada
PDF
Distribution of Foraminifera within the Santa Barbara Basin
PDF
Oligocene - Miocene Sedimentology of the Tecolote Tunnel section of Southern California
PDF
Sedimentology of the northern half of the Laguna Salada, Baja California
PDF
Sedimentation in area of Diversion Dam, Figueredo Wash, New Mexico
PDF
Geology of the central New York Mountains, California
PDF
Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventura County, California.
PDF
Silica diagenesis in recent diatomaceous sediment from the Guaymas Basin in the Gulf of California
PDF
Geology of the northern half of the Reipetown quadrangle, Nevada
PDF
Foraminiferal biofacies off the North Asiatic Coast
PDF
Geology of the northern portions of the Seventeen Palms and Fonts Point quadrangles, Imperial and San Diego Counties, California
PDF
Solar cyclicity in the lacustrine Green River Formation (Eocene, Wyoming)
PDF
The influences of formal rhetoric on the "Aeneid" of Vergil
PDF
Sedimentary structures in Percebu Bay and vicinity, Baja California, Mexico
PDF
Economic geology of the Bullion Mining District San Bernardino County, California
PDF
Petrology and diagenesis of the early Miocene Skooner Gulch and Gallaway Formations, Point Arena, California
PDF
The use of moving pictures as a means of instruction in introductory mechanical drawing.
PDF
Duties of California school superintendents and principals of union high schools having fifteen to one hundred teachers
Asset Metadata
Creator
Dill, Robert Floyd (author)
Core Title
Environmental analysis of sediment from the sea floor off Point Arguello, California
Degree
Master of Arts
Degree Program
Geology
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
OAI-PMH Harvest,Sedimentary Geology
Language
English
Contributor
Digitized by ProQuest
(provenance)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c30-98501
Unique identifier
UC11224704
Identifier
usctheses-c30-98501 (legacy record id)
Legacy Identifier
EP58437.pdf
Dmrecord
98501
Document Type
Thesis
Rights
Dill, Robert Floyd
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA
Tags
Sedimentary Geology