16. GRAIN-SIZE ANALYSIS

Stan M. White, California State University, Fresno, Fresno, California

PROCEDURES

The grain-size samples taken from opened sections of thecores consisted of 10 cc of sediment. Project directions forthe actual sampling procedure were followed; however,personal judgment, in most cases, governed the decision asto where in the core the actual sample was taken. Moreoften than not, specific coarse-grained silt or sand units(turbidite layers), or ash-bearing units were sampled.Therefore, the data presented in the accompanying chartsand tables should not be considered as derived from arandom sampling program. It is also highly probable thatsome of the sand units sampled had been subjected towashing during core-barrel retrieval. The data presented forthese sand units should be interpreted carefully. Coresections that were highly deformed were sampled only if adistinct coarse-grained lithology was present.

The shore laboratory method of grain-size analysisfollowed standard methods as outlined in the DSDP projectmanual. In general, the methods consisted of sedimentdispersal in a Calgon solution, or other suitable dispersant,using an ultrasonic bath. Sand and any coarser fractionswere sieved, while the silt and clay fractions were analyzedby pipette methods. There were 113 samples taken forgrain-size analysis, and 23 of these samples were furtheranalyzed for detailed size determinations in the sand- andsilt-size fractions (Tables 1 and 2 and Figures 1 and 2).

NOMENCLATURE

The size analyses are plotted on a triangular diagram(Figure 1) which has sand, silt, and clay as end members(Shepard, 1954). The nomenclature used (Table 1) is also inaccordance with that of Shepard (1954). The nomenclaturesand, silt, and clay do not imply any compositionalcharacteristics. Specific discussion of the compositionalnature of the size fractions are considered in the followingsection for each site.

RESULTS

Triangular diagrams, based on the results of grain-sizeanalyses from each site, are given in Figure 1. A completelisting of grain-size results is presented as Tables 1 and 2.Cumulative curves of the 23 detailed analyses are presentedas Figure 2.

Site 239

Site 239 is in the western Mascarene Basin, 180 mileseast of Madagascar, in water 4971 meters deep. Corerecovery totaled 106.1 meters from a total penetration of326 meters. At Site 239, silty clays are dominant,comprising 75 percent of the 16 grain-size samples. Theremaining samples are equally divided among clays andclayey silts, at a little over 6 percent each. Two samples, or

12 percent, were classified as sandy silts. Of the 16 samplestaken, 14 came from cores whose dominant lithology wasthat of interbeds of clays, clayey or sandy silts, and siltyclays within nannofossil oozes. Two samples, from Cores 13and 14, came from brown silty clay and clayey silt unitsthat were the dominant lithology. Many of the interbedsfrom which samples were obtained did exhibit a gradingdescribed as vague to obvious. The silt-size componentgenerally includes quartz, feldspars, and trace amounts ofheavy minerals, including augite, hornblende, biotite,zircon, garnet, and rare staurolite. For all samples, the sandcomponent contains on the average 4.4 percent (lo=0%,hi=33.7%); the süts, 40.9 percent (lo=15.1%, hi=58.2%);and the clay component contains on the average54.7 percent, with a low of 13.6 percent to a high of84.9 percent.

One sample from a sandy silt unit (Core 1, Section 1) wasanalyzed for detailed grain size in the sand-silt-clay fractions.The sample shows 28.2, 58.2, and 13.2 percent inthe sand-silt-clay fractions, respectively, with the bulk ofthe sand fraction in the very fine sand range (26.5%). X-rayanalyses, (Cook and Zemmels, this volume) correspond indepth to two grain-size samples. Both samples arenanno-bearing silty clays (Cores 3 and 8). The bulk analysesare strikingly different; the sample in Core 8 has a highercalcite-aragonite content (79.9%), a lower potassiumfeldspar (2.2%) and Plagioclase (4.7%) content, and a lowermontmorillonite content (3.0%). These trends are not truefor the 2 to 20µ or less than 2µ analyses.

Heavy mineral studies on samples at this site, althoughnot necessarily at grain-size sample depths, show amphi-boles > orthopyroxenes or clinopyroxenes, along withepidote, garnet, zircon, apatite, and tourmaline.

Site 240 (Holes 240 and 240A)

Two complementary holes were drilled in the centralabyssal plain of the west Somali Basin, in water depth of5082 meters. For Hole 240, 25.1 meters of sediment wasrecovered from 195 meters penetration, and for Hole 240A,3.2 meters was recovered from 202 meters of penetration.At Hole 240, eleven grain-size samples were taken of whichseven were examined for detailed grain-size determinations.All samples contain on an average 55 percent sand,17 percent clay, and 27 percent silt. The two samples forHole 240A show an average of 55 percent sand, 40 percentclay, and 5 percent silt. Further size nomenclature for thesamples of the sites are as follows: Thei l samples ofSite 240 were recorded as silty clays (9%), clayey silts(18%), silty sand (9%), sand (54%), and silts (9%), and thetwo samples of Hole 240A were recorded as a sand and as aclay.

For the most part, the samples taken from the cores ofthese two sites came from silty clay or clayey silt interbeds

417

S. WHITE

TABLE 1Grain-size Determinations, Leg 25

TABLE 1 - Continued

Sample Sand(Top of Interval in cm) (%)

Silt Clay(%) (%) Classification

Sample Sand Silt Clay(Top of Interval in cm) (%) (%) (%) Classification

239-1-1,49239-1-1,96239-1-1, 99a

239-3-1, 132239-3-2, 30239-3-3, 60239-4-2, 1452394-3,30239-4-4, 60239-7-4, 135239-8-1,45239-8-2, 138239-8-5, 90239-9-2, 85239-13-2, 108239-14-2, 145240-1-1,74240-1-2,129240-1-3, 15a

240-1-4, 49a

240-3-1, 272404-2, 21 a

240-4-2, 79a

240-4-2, 123a

240-5-2, 111240-5-6, 121a

240-5-6, 136a

240A-1-1, 94240A-2-1, 99241-2-1,42241-3-2, 19241-3-3,972414-3,932414-5,23241-5-3, 90241-10-3, 87241-104, 75241-104,78241-104,81241-104, 85241-104, 88a

241-11-2, 18241-11-3, 77a

241-114, 30a

241-114, 39a

241-15-1, 144241-16-2,63241-19-1, 124241-19-2, 87241-23-3,47241-25-3, 12324M7-1, 124241-27-2, 32a

241-24-3, 110a

241-27-3, 126241-27-4, 62a

241-274, 68a

241-28-1, 101241-28-1, 141a

241-28-2, 71a

241-28-3, 18a

241-28-3, 95a

241-29-1, 140241-29-2, 39242-7-6, 65242-8-1,107242-19-3, 136243-1-1, 127a

245-1-2, 100

0.233.728.2

0.10.00.00.80.40.20.00.20.60.60.15.30.18.83.85.14.6

65.566.196.497.193.085.483.312.896.6

3.010.952.627.123.937.426.167.166.069.169.236.415.136.465.240.526.829.2

0.01.0

22.50.00.11.50.10.10.00.0

36.340.519.20.62.00.30.00.60.10.5

100.00.0

36.854.658.236.933.245.744.242.535.648.744.441.538.728.550.315.129.250.986.074.519.319.80.70.71.27.19.7

10.70.5

17.558.028.436.826.440.335.620.221.720.220.136.433.043.519.237.432.142.4

7.480.645.811.817.354.551.923.420.623.749.643.051.862.758.9

8.713.826.323.935.1

0.029.7

63.011.713.663.066.854.255.057.164.351.355.557.960.871.444.484.962.045.3

8.921.015.114.1

2.92.25.87.47.0

76.52.9

79.531.219.036.149.722.438.312.812.310.710.727.351.820.115.522.141.128.492.518.431.788.282.743.948.076.579.376.314.116.528.936.739.191.086.273.076.064.5

01070.3

Silty claySandy siltSandy siltSilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty clayClayey siltClaySilty clayClayey siltSiltClayey siltSilty sandSandSandSandSandSandSandClaySandClayClayey siltSilty sandSand-silt-elaySand-silt-claySand-silt-claySand-silt-claySilty sandSilty sandSilty sandSilty sandSand-silt-claySilty claySand-silt-claySandSand-silt-claySand-silt-claySand-silt-clayClaySütSand-silt-clayClayClayClayey siltClayey siltClaySilty claySilty claySandy siltSandy siltClayey siltClayey siltClayey siltClayClaySilty clayClaySilty claySandSilty clay

245-1-4, 29245-14-5, 7245A-2-5, 120245A-4-2, 134245A-5-1, 89245A-54, 129246-5-1, 94246-5-3, 99246-5-3, 146246-5-4, 44246-5-5, 89246-9-1,119246-9-2, 139246-9-6, 29246-11-1,99246-11-2, 1246-11-2, 19246-11-2,49246-11-2, 72246-11-2, 100246-11-2, 100248-2-2, 90248-2-3, 542484-5,50248-6-1, 146a

248-8-1,40248-8-1, 90248-8-1, 143248-9-1, 67a

248-9-2, 80248-11-1, 127249-8-1, 134249-9-3, 79249-23-2, 58249-234, 129249-23-5, 70249-24-1, 75249-25-1, 82249-25-2, 82249-25-3, 17249-27-2, 90249-30-7, 0249-31-3,36249-32-7, 0

0.03.50.10.10.00.0

88.171.276.067.973.283.667.764.693.193.792.892.993.165.467.6

3.83.60.4

67.098.598.5

3.494.998.4

0.31.73.71.56.80.10.05.84.0

13.03.74.25.50.1

23.655.322.626.214.616.67.0

18.315.620.716.59.9

18.522.1

3.42.63.63.43.7

20.018.933.038.330.816.00.40.3

12.51.00.2

30.531.431.326.240.032.728.941.434.720.645.938.143.113.8

76.441.277.373.885.483.4

5.010.58.4

11.310.46.5

13.813.33.53.73.63.73.1

14.613.563.258.168.817.11.11.2

84.14.11.4

69.166.965.072.253.167.271.152.961.366.450.457.751.586.1

ClayClayey siltClaySilty clayClayClaySandSilty sandSandSilty sandSilty sandSandSilty sandSilty sandSandSandSandSandSandSilty sandSilty sandSilty claySilty claySilty claySandSandSandClaySandSandSilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty claySilty clayClay

aDetailed analysis is shown in Table 2.

within dominant nannofossil-radiolarian ooze lithologies. Inthree instances, the samples came from well-defined sandysilt or silty sand interbeds within a dominant silty clay orsilt-rich nannofossil ooze lithology. Compositionally, thesand-and silt-size fractions consist of' fossiliferous compo-nents or fragments as well as terrigenous or detritalminerals, including quartz, feldspar, heavy minerals, andopaques. The heavy minerals include clinopyroxenes,orthopyroxenes, amphiboles, garnet, and epidote. Fainttraces of graded bedding were observed in the interbedssampled; however, most of the coarser units tend to besoupy and infiltration and in-core mixing is common.

Detailed grain-size determinations were preformed onseven samples representing silt or sand units in Cores 1, 4,and 5 of Site 240 (Table 2). The samples are classified(Table 1, Figure 2) as sands (five samples or 71%), silts, andclayey silts. The sand samples contain on an average87.7 percent sand, with 53 percent of this sand fractionequally divided into the medium and fine sand sizes. About

418

CLAY CLAY CLAY

Site 239(16 Samples)

Site 242(3 Samples)Site 243(1 Sample)

Site 248(10 Samples)

Site 240(11 Samples)Site 240A(2 Samples)

Site 245(3 Samples)Site 245A(4 Samples)

Site 249(13 Samples)

SAND SILT SAND SILT

Figure 1. Results of grain size analyses of samples from cores collected on Leg 25.

SAND

Site 241(35 Samples)

Site 246(15 Samples)

CompositeAll Sites

SILT

o

TABLE 2Detailed Grain Size Determinations, Leg 25

Sample(top of interval

in cm)

239-1-1,99240-1-3, 15240-1-4, 49240-4-2, 21240-4-2, 79240-4-2, 123240-5-6, 121240-5-6, 136241-10-4, 88241-11-3, 77241-11-4,30241-11-4, 39241-27-2, 32241-27-3,110241-27-4, 62241-27-4,68241-28-1, 141241-28-2,71241-28-3, 18241-28-3, 95243-1-1, 127248-6-1, 146248-9-1,67

0

0.00.00.00.00.10.77.06.30.00.00.00.00.00.00.00.00.00.00.00.0

74.50.00.0

0-1

0.00.00.00.05.5

19.921.618.9

0.00.01.13.00.00.00.00.00.00.20.00.0

25.40.20.0

1-2

0.00.00.10.5

39.547.424.425.2

0.10.0

13.912.40.00.00.00.00.90.50.00.00.16.51.8

2-3

1.70.10.2

20.646.026.822.322.3

8.55.3

40.618.2

0.30.00.00.0

15.62.60.00.10.0

35.983.2

3-4

26.55.04.3

45.05.32.3

10.210.527.731.2

9.67.01.20.00.00.0

24.016.00.61.80.0

24.49.9

Percent at

4-5

35.357.239.214.90.70.53.74.6

15.127.0

5.113.511.7

2.50.70.6

27.228.216.616.10.1

10.20.5

Phi Units

5-6

12.422.125.12.70.00.11.52.3

10.57.34.84.0

25.425.4

5.91.88.9

12.631.628.2

0.02.60.1

6-7

6.74.87.21.60.40.11.01.56.45.35.15.9

12.515.46.9

10.04.37.29.2

10.70.11.80.2

7-8

3.81.93.00.60.50.10.91.34.43.94.2

13.94.98.67.2

12.52.63.85.23.90.11.40.3

8-9

2.11.03.40.90.30.10.71.03.73.63.19.79.28.59.0

14.42.75.78.08.70.01.40.5

9-10

2.21.23.80.80.20.10.70.93.16.22.86.7

10.111.214.416.82.94.6

10.011.30.11.40.4

10

9.26.6

13.712.42.40.16.05.0

20.510.39.65.6

24.628.256.045.110.818.618.719.10.2

14.23.2

Sand(%)

28.25.14.6

66.196.497.185.483.336.436.465.240.5

1.50.10.00.0

40.519.20.62.0

100.067.094.9

Silt(%)

58.286.074.519.80.70.77.19.7

36.443.519.237.454.551.920.623.743.051.862.758.9

0.016.0

1.0

Clay(%)

13.68.9

21.014.12.92.27.47.0

27.320.115.522.143.948.079.376.316.528.936.739.1

0.017.14.1

1

s-

SITE 239

Core I, Section I

0 1 2 3 4 5 6 7 8 9 I0PHI SIZES

SITE 241 I I I )

A: Core 27, Section 4 (62 cm)B: Core 27, Section 4 (68 cm)C: Core 28, Section ID: Core 28, Section 2E: Core 28, Section 3 (18 cm)F: Core 28, Section 3 (95 cm)

SS

o

Core I, Section 3Core I, Section 4Core 4, Section 2 (21 cm)Core 4, Section 2 (79 cm)Core 4, Section 2 (123 cm)Core 5, Section 6 (121 cmCore 5, Section 6 (136 cm

SITE 241 ( I )

A: Core I0, Section 4B: Core II, Section 3C: Core II, Section 4 (30 cm)D: Core I I , Section 4 (39 cm)E: Core 27, Section 2F: Core 27, Section 3

4 5 6 7PHI SIZES

SITE 243

Core I, Section I

4 5 6PHI SIZES

I0 II

Figure 2. Cumulative curves from detailed grain size analyses of samples from cores collected on Leg 25.

S. WHITE

2 percent is very coarse sand, with 14 percent each of thecoarse and very fine sand sizes.

X-ray and carbon-carbonate samples were not takensufficiently close to the grain-size sample depths to warrantdiscussion here.

Site 241

Site 241 was drilled on the east African continental risein 4054 meters of water. The site, 170 miles from the coast,was drilled to a depth of 1174 meters, with 136.7 meters ofsediment recovered.

For the 35 samples from Site 241, of which 12 weresubjected to detailed grain-size analyses, 30 percent are inthe sand-silt-clay classification, 22 percent are clays, and14 percent are silty sands. The remaining samples aredistributed among silts (2%), clayey silts (17%), sandy silts(2%), silty clays (8%), sand-silt-clays (28%), and one sample(2%) each for silt and sand. The averages for sand, silt, andclay for all 35 samples show 23.6, 34.1, and 42.3 percent,respectively. The samples were taken basically from twomajor lithologies present in the cored interval. Twenty-three, samples were taken from streaks or interbeds ofclayey silts, or silty clays within nannofossil oozes. Twelvesamples were taken from clay stone, clayey siltstone, andfine sandstone units. Compositionally, the high silt or sandunits, especially in the upper portion of the cored interval(Cores 1-11), show a high percentage of fossiliferousfragments (benthic foraminifer a), with accompanyingpercentages of quartz and feldspar, and with traces ofpyrite and volcanic glass. The samples from the lowerportion of the cored interval (Cores 12-29) consist ofdetrital quartz (25%-65%), feldspar (2%-5%), detrital (?) ormicrocarbonate (5%-15%), foraminiferal tests (l%-2%),dolomite rhombs (2%-4%), and with minor percentages ofrock fragments and accessory minerals.

Graded beds are common and generally well defined inthe basal portions, with the tops of the beds frequentlyindistinct. Twelve samples were subjected to detailedgrain-size determinations (Figure 2, Table 2). The samplesare dominantly clayey silts (five samples or 41.8%), withsand-silt-clay classifications containing on the average25 percent and silty clays, 16.8 percent. Others reported,include sand (8.4%) and sandy silt (8.4%). The averagesand, silt, and clay content for all 12 samples is 20.2, 42.0,and 37.8 percent, respectively. The majority of the sandfraction is fine to very fine sand.

It appears that about five carbon-carbonate samplesrepresent similar depths as the grain-size samples. Theseoccur in Cores 11, 16, 27, and 28. Two samples representsand-silt-clay units and show 7.2-9.7 percent total carbon,0.1-0.2 percent organic carbon, and 58-80 percent calcium-carbonate. One sample, a clay, shows 0.3, 0.2 and1.0 percent for total carbon, organic carbon, andcalcium-carbonate, respectively. The final two samples aresandy and clayey silts with 2.5-4.0 percent total carbon,0.3-2.0 percent organic carbon, and 17-19 percent calcium-carbonate.

Heavy mineral studies of the sand-silt units illustrate aheavy mineralogy of orthopyroxenes = amphiboles >clinopyroxenes. Garnet, epidote, apatite, monazite, tourma-line, and staurolite are also present.

Site 242

Site 242, in a water depth of 2275 meters, is on the eastflank of the weakly seismic Davie Ridge in the northernMozambique Channel. At the site, 676 meters were drilledwith 103.1 meters of core recovered. Three grain-sizesamples were taken and contain on the average less than1 percent sand, 28 percent silt, and 72 percent clay. Twosamples, or 66 percent, were classified as silty clays, andone sample, or 33 percent, as a clay. All three samples weretaken from clay or silt interbeds within a dominantlithology of a nannofossil chalk. Composition of the siltfraction includes authigenic(?) carbonate grains as well asdetrital quartz, micro-carbonate, and heavy minerals.

A carbon-carbonate sample, equivalent in depth to agrain-size sample, shows a total carbon content of3.7 percent, organic carbon of 0.1 percent, and calcium-carbonate of 30.0 percent. The sample is a silty clayinterbed within foram-bearing clayey nannofossil chalk.Similarly, one X-ray sample corresponds to a grain-sizesample. The sample, in Core 8, shows a bulk analysis ofcalcite > mica > quartz. Palygorskite and montmorillonitewere also reported.

Sites 243-244

One grain-size sample was taken from Site 243. Bothsites (243 and 244) represented an attempt to drill withinthe Zambesi Submarine Canyon, and both were abandoneddue to technical problems of hole stability. At Site 243,0.3 meters were recovered, consisting of moderatelywell-rounded sand and fine gravel. The sample consists of95 percent quartz, 2 percent feldspar, and 2 percent rockfragments, and 1 percent shell fragments. A detailedgrain-size analysis (Table 2, Figure 2) shows the gross sizeanalysis to be 100 percent sand. The detailed analysisshowed 74.5 percent very coarse sand, and 25.4 percentcoarse sand. Minor percentages (less than 1%) were foundfrom the medium sand through the silt range.

Site 245 (Holes 245 and 245A)

Two complementary holes were drilled in the area of thesouthern Madagascar Basin. The site is 200 milesnorthwest of the axis of the Southwest Indian Ridge in4857 meters of water. Hole 245 penetrated 397 meters andHole 245A, 149 meters. Core recovery for Hole 245 was82.1 meters and 47.4 meters were recovered at Hole 245A.Three grain-size samples at Hole 245 contain on an average1 percent sand, 36 percent silt, and 63 percent clay. Theclassifications of the samples show that the three samplesare represented by a silty clay, a clayey silt, and a clay. ForHole 245A, four samples were taken and contain on theaverage 20 percent silt and 80 percent clay with, at themost, 0.1 percent sand in two samples. For these samples,three, or 75 percent, were clay and one, or 25 percent, wasa silty clay.

Two of the samples taken from the cores of Hole 245came from a dominant core lithology of brown silt-richclay. The silt composition includes quartz, feldspar, micas,and iron and manganese opaques. The one remainingsample represents a devitrified volcanic ash interbed withina dominant lithology of nannofossil chalk.

422

GRAIN SIZE ANALYSIS

The four samples at Hole 245A were all taken from siltyclay units, which tended to be the dominant lithology. Thesilt fraction consists of quartz, feldspar, micas, opaques,and heavy minerals, which included epidote and rutile.

Only one carbon-carbonate sample from Hole 245A isclose to the depth of a grain-size sample. The values shownfor total carbon, organic carbon, and calcium carbonate are0.1, 0.2, and 0.0, respectively. The lithology is a brownsilty clay.

Site 246

Site 246, in 1030 meters of water, was located on theMadagascar Ridge. Recovery was 23.8 meters in 203 meterspenetration. A complementary hole, Site 247, wasattempted with no recovery in 26 meters penetration.

The fifteen grain-size samples show 80 percent sand,12 percent silt, and 8 percent clay. The sand percentagesrange from a low of 76 percent to a high of 93 percent.Silts have a high percentage of 22 percent and a low of2.6 percent. The clays range from 3.1 to 14.6 percent. Afurther classification showed 54 percent of the samples assands and 46 percent as silty sands.

The samples were taken from only three cores (Cores 5,9 and 11). Their dominant lithologies are shelly calcareoussands and glauconite-rich calcareous sands. The coarsefraction composition consists of 50-75 percent skeletal andcarbonate fragments, 5-20 percent glauconite pellets,5-14 percent lithic fragments, and 5-10 percent quartz,feldspar, volcanic glass, and accessory minerals, includingtourmaline.

Samples taken for X-ray or carbon-carbonate do notcorrespond to grain-size sampling depths. Heavy mineralstudies of the silt-sand fractions are remarkable in their hightourmaline contents which, in some cases, exceed theamphiboles and pyroxenes.

Site 248

This site is in the northwestern Mozambique Basin closeto the eastern scarp-like slope of the Mozambique Ridge.The hole was drilled in a water depth of 4994 meters with434 meters penetration and 40.8 meters of core recovered.Size averages for 10 samples show 46.8 percent sand,16.3 percent silt, and 36.9 percent clay. Fifty percent ofthe samples are sands, 40 percent silty clays, and 10 percentclays. The sand samples (5), which have from 67 to98 percent sand, were taken from distinct sand lithologiesin Cores 6, 8, and 9. The clay (representing one sample) wasfrom a clay interbed within the sand units of Core 8. Thesilty clays represent interbeds within foraminiferal-nannofossil oozes. Grading was not overly apparent in theunits sampled; however, sharp basal contacts and burrowmottling at the tops do suggest a turbidite origin.

Compositionally, the silt units consist of quartz,feldspar, granitic rock fragments, and heavy minerals,

including hornblende, zircon, garnet, and sphene. Thesand-size composition includes 75 percent quartz, withabundant feldspar and accessory minerals, such ashornblende, garnet, tourmaline, and epidote.

Two samples had detailed grain-size determinationsperformed. The two samples contain on the average81 percent sand, 8.5 percent silt, and 10.6 percent clay. Inthe sand fraction, the dominant mode is fine sand. Onecarbon-carbonate sample corresponds to a grain-size sample.The values reported were 2.6 percent total carbon,0.3 percent organic carbon, and 19.0 percent calcium-carbonate. The sample is in a sandy silt-silty clay interbedin a nannofossil ooze.

Site 249

Site 249 is in water 2088 meters deep over a smallsediment-filled basin near the west side of MozambiqueRidge. A 412-meter penetration yielded 221.4 meters ofcore recovered.

Thirteen grain-size samples were taken and found tocontain on the average 2.8 percent sand, 32.9 percent silt,and 63.2 percent clay. Of the 13 samples, 92 percent or 12samples, are classified as silty clays and 8 percent (onesample) is a clay. Two samples came from interbeds withinforaminifera-rich nannofossil oozes (Cores 8 and 9) whilethe remaining 11 samples came from silt-rich claystones,clays, clay-rich siltstones, and volcanic ash siltstones. Thecomposition of the coarse fraction includes quartz(1%-12%), feldspar (1% 4%), opaques (5%-20%), volcanicglass (5%-40%), and glauconite (1%•5%). One sample from avolcanic ash siltstone contains 95 percent glass shards and5 percent feldspar. Nine carbon-carbonate samples areequivalent in depth to the grain-size samples. Eight of thesamples are silty clays and one is a clay. In the cores, theseunits are silty claystones or claystones. Six samples showthe organic carbon content to be greater than 0.4 percent,to a maximum of 1.6 percent, and have calcium carbonatecontents greater than 6.0 percent, to a high of 37.0 percent,with total carbon greater than 1.7 percent, to a maximumof 5.5 percent. All six samples show little or no sand (0.0%to 5.0%), a silt content of 28 to 45 percent and a claycontent of 41 to 71 percent. Generally, the higher the claycontent, the higher the content of calcium carbonate.

Six X-ray samples correspond in depth to grain-sizesamples in Cores 23, 25, 30, 31, and 32. The bulk analysisdata is variable, showing that of the six samples, onlymontmorillonite was reported in all samples.

REFERENCES

Shepard, F.P., 1954, Nomenclature based on sand-silt-clayratios: Jour. Sed.Pet., v. 24, no. 3, p. 151-158.

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