14. geochemistry of sediments in the western central … · 2007. 5. 11. · carbonates are mainly...
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14. GEOCHEMISTRY OF SEDIMENTS IN THE WESTERN CENTRAL ATLANTIC,DSDP LEG 39
E.M. Emelyanov, P.P. Shirshov Institute of Oceanology, USSR Academy of Sciences, Kaliningrad, USSR
INTRODUCTION
Twenty chemical elements were studied and CaCθ3,CO2, and C (organic) were determined by the modifiedvolumetric chemical method (Sokolov and Sokolova,1975). Other samples were decomposed to determine Fe,Mn, Ti, Na, O, K2O, Zn, Cu, Ni, Co, Cr, and Cd.Decomposition of the sample (0.25 gr) was accom-plished with acid (with the application of HC1, HNO3,and HF) in platinum crucibles. The concentrations ofNa2θ and K2O were measured by flame photometry(M-3, FRG), Ti was measured by the photoelectro-colorimeter (FEK-56, U.S.S.R.), and all other elementswere analyzed using the atomic-absorption spectro-photometer "Saturn" (U.S.S.R.). Phosphorus wasanalyzed in a separate sample (0.5 gr), decomposed inaqua regia, i.e. a mixture of HC1 (3 parts) and HNO3 (1part). The concentration of P was determined photo-colorimetrically by FEK-56. Ba, Zr, V, Sn, Mo, Be, Ge,Ni, and Cr were analyzed by the quantitative spectralmethod (Meyshtas, 1970) using the ISP-28 (U.S.S.R.).All samples were analyzed twice. Control of analysisquality was carried out by means of the Sovietgeological standards SGD-1, SG-1, and ST-1, andstandards of the German Democratic Republic. Intra-laboratory geological standards were also used.Accuracy and quality of the analyses are thought to begood. Analyses were performed in the Laboratory ofAtlantic Geology, Atlantic Branch, P.P. ShirshovInstitute of Oceanology, Academy of Sciences of theU.S.S.R., under the author's guidance (analysts Yu. O.Shaydurov, G.S. Khandros, Z. Yablunovskaya, T.I.Khomina, and N.G. Kudryavtsev).
Silicate analyses were carried out by conventionalchemical methods in the laboratory of the GeologicalSurvey of Western Siberia (Novokuznetsk).
The comparative data on Recent and late Quaternarysediments near Leg 39 drill sites (Figure 1) is alsoincluded.
CARBONATES
CaCθ3 content varies considerably, ranging from 0.0up to 92.52% (Tables 1, 2, 3).
Site 353
The carbonate content in sediments from the VemaFracture Zone is low. This is due to two reasons: (1)dilution of carbonate by terrigenous sediment from theAmazon River (Bader et al., 1970); and (2) depth of thesite at or near the level of carbonate compensationdepth (the compensation depth in the Guiana Basin is5500 meters [Lisitzin, 1971; Emelyanov et al., 1975]).
Carbonates are mainly biogenic remains. Low-magnesian calcite is the dominant mineral. Authigeniccarbonates occur as single grains (Tables 4, 5).
Site 354
CaCO3 content varies from 8.75 to 85.05%. Theminimum content of CaCθ3 (8.75%) was found inthe sediments of Pleistocene age as a result of strongdilution by terrigenous input from the Amazon River;carbonate content is considerably higher in the oldersediments (37.02-85.05%). Variations of CaCOs contentover such a wide range may be caused by one or moreof the following: (1) variations of the rate of supply ofbiogenic carbonates to bottom sediments; (2) irregularsupply of terrigenous material from the Amazon Riverdrainage; (3) variations of the depth carbonate dissolu-tion. The Ceará Rise site was presumably situatedbelow the lysocline between late Eocene and middleOligocene, a time when the lysocline might have beenshallower than at present. After middle Oligocene, thecontent of CaCθ3 increased slightly, which could berelated to a subsidence of the lysocline or shoaling ofthe site. The high content of CaC03 indicates that thesite was above the carbonate compensation depth formost or all of the Tertiary.
wJ 355J +400-2
\ 1 J t 3 5 6 1
\ r ^ ) \ *357 1
\ ^ C ^ ^ \ *358 1
<-V-———-—" 1 "^ I
X
]
fX
/
X
1
20"
40°
60° 40°
Figure 1. Location of DSDP and other sites. 1 = Leg 39sites, 2 other sites, 3 = Mid Atlantic Ridge.
All
E. M. EMELYANOV
TABLE 1Range of Contents of Elements in the Sediments from Leg 39
Type of Sediments
Sites 353-358
All types
Site 359
All types
CaCO3
0.00-92.52
3.25-90.96
Corg
0.03-1.35a
0.15-0.66
Fe
0.30-7.32(1.58-28.58)
0.12-6.07
Content, (%)
Mn Ti
0.003-0.70 0.01-1.05(0.02-2.39) (0.05-2.00)
0.01-0.15 0.006-1.58
P
0.01-0.65(0.01-2.17)
0.01-0.26
0
0
Na2O
.37-3.10
.86-4.73
K 2 O
0.30-3.77
0.07-4.38
Zn
<4-231(<l 7-554)
<2-223
Note: Content given for dry sediment and for carbonate-free sediment (in brackets).aIn one sample 9.81%.
The carbonate consists mostly of coccoliths, withlesser foraminifers. Low magnesian calcite is thedominant mineral (Table 4). About 2% dolomite isfound in sediments of Eocene, Oligocene, and Mioceneage and 15 to 20% authigenic carbonate is present. Upto 6% dolomite and 4% siderite (Table 4) occur in theferruginous marly nannofossil oozes.
Site 355
The site is below the present carbonate compensationdepth (4600-4800 m) and is located in the zone ofRecent red clays deposition in the Brazil Basin. There-fore, carbonate content is very low in the upper part ofthe core (lower Eocene-Pleistocene), which is char-acterized by terrigenous muds (and red clays) and byzeolitic pelagic muds. In the lower part of the core, innannofossil oozes of Late Cretaceous age, the contentof CaCCh is high, being up to 60.79 to 89.12%. On thebasis of the smear slides study, the carbonate isrepresented by the remains of coccoliths (40% on theaverage) and authigenic calcite (50% on the average).Calcite occasionally forms hydrothermal veins with athickness of 3-13 mm. These veins are associated withthe brown-reddish ferruginous nannofossil muds. Thedegree of iron enrichment (oxidized form of Feprevails; Table 3) increases with depth. Grains ofdolomite were found in the upper part of the coccolithmuds. On the basis of X-ray analyses calcite (onlyauthigenic?) in the Cretaceous sediments contains 4-6mol. % MgCθ3 in its lattice.
The carbonate data indicate that in the LateCretaceous the bottom of the Brazil Basin (Site 355)was much shallower and was situated above thecompensation depth. Site 355 in the Cretaceous wasprobably located within the limits of the Mid-AtlanticRidge. In the early Maestrichtian the site subsidedbelow the compensation depth (Sclater et al., 1971),and carbonate dissolution began.
Site 356
The content of CaCθ3 varies in the range of 1.75 to85.80% (40% on the average). The highest carbonatecontent was found in the sediments of early Miocene-Pleistocene age, from 48.78% up to 85.80%. Carbonatesare represented by coccoliths and foraminifers. In UnitsII and III (Core 16, Section 1 up to Core 6, Section 4),represented by siliceous-calcareous muds (coccolithsand foraminifers, mainly), the content of CaCO< is21.76 to 37.74% and 19.02 to 41.78%, respectively. The
dominant carbonate mineral is biogenic low-magnesiancalcite. Dolomite is detected in the sediments of earlyEocene age and authigenic calcite is present.
Unit IV (Core 26, Section 2 up to Core 19, Section 4)is represented by nannofossil muds (marly mud) with aCaCO3 content from 41.78 to 57.54%. Interbeds ofterrigenous and terrigenous-siliceous (?) muds with alow content of CaC03 (14.76 and 18.51%) are present intwo cores of this unit (Core 17, Section 4 and Core 29,Section 2). Carbonates are represented by coccoliths,foraminifers, and authigenic calcite which containsabout 5 mol. % MgCOa.
Unit V is represented by marly nannofossil muds(chalk), slightly cemented by authigenic calcite. It con-tains 39.02 to 45.28% CaCO3. There is a considerableadmixture of dolomite, increasing downward.
Unit VI (Core 40, Section 6 and Core 39, Section 5,clayey conglomerates and mudstones) contains lowquantities of CaCθ3, from 1.75 to 6.25%. Carbonatesare represented by coccoliths and authigenic calcite.
Unit VII (Core 44, Section 3 and Core 41, Section 3)consists of marly dolomitized limestones (32.02-37.27%of CaCθ3). The limestones are recrystallizedcarbonates (calcite) and are dolomitized. Coccolithsand foraminifers are in neglibible quantities.
Thus, judging from the carbonate studies, allsediments at Site 356 accumulated under pelagicconditions, but above the carbonate compensationdepth. Active biogenic pelagic accumulation ofcarbonates took place (deposition of coccoliths,foraminifers) followed by the consequent recrystal-lization of these biogenic carbonates and diageneticformation of calcite and dolomite.
Site 357
This site is on the Rio Grande Rise and the CaCθ3content in the sediments is high, up to 92.56%.Although there are interlayers with very low content,from 1 to 3% (Table 2), at this site the depth was alwaysmoderate (1000 m in the Cretaceous and 2100 m atpresent).
Unit I (foraminiferal-coccolith muds) is richest inCaCO3 being from 84.10 to 92.56%. Planktonicforaminifers and coccoliths are dominant and ptero-pods and benthic foraminifers are found in negligiblequantities.
The sediments of Unit II consist mainly of coccolithooze and contain from 70.04 to 92.56% CaCOs. Itdiffers from the first unit by: (1) the presence of
478
GEOCHEMISTRY OF SEDIMENTS
TABLE 1 - Continued
Cu Ni Co Cr
Content (10"4%)
Ba Zr Mo Be Ge Cd
6-232(20-543)
<6-354(< 13-864)
<4-65(<4-159)
7-513(7-796)
<2OO-13OO«200-3589)
<40-600(66-1138)
13-870(46-883)
<5-13K5-120)
<l-4« l -8 )
<50(<50-334)
<6<6
<6-18 <6-20 <6-26 4-28 <6
TABLE 2Chemical Composition of Sediments From Leg 39
Sample(Interval in cm)
Hole 353
2-2, 30-32
Hole 35 3A
1-1, 102-105
Site 354
1-1, 1151-2, 1193-1, 1204-1, 40-424-2, 40-425-2, 71-736-3, 916-2, 1077-1, 1377-3, 168-2, 309-3, 11210-2, 9811-5,2512-4, 1113-6, 12514-1, 10615-2, 4515-3, 8417-2, 11718-1, 13018-4, 128
Site 355
1-2,69-711-6, 80-822-3, 130-1322-5, 135-1373-2, 88-903-5, 58-604-3, 110-1125-1, 40-425-4, 98-1006-2, 100-1027-2, 90-927-3, 100-1028-2, 140-1419-2, 50-5211-2,91-9212-4, 60-6213-3, 52-5414-3, 93-94
CaCO3
4.75
4.25
19.518.75
46.5343.7861.0440.7867.0256.5473.0547.2851.2854.7885.0567.5455.0367.5471.5563.7964.2953.7852.7837.02
0.251.001.250.758.500.750.000.500.245.002.504.500.000.000.000.000.000.00
org
0.36
0.48
0.180.360.120.060.060.060.060.030.030.030.150.150.180.150.180.150.120.120.150.150.210.27
0.240.270.300.210.510.540.360.390.450.630.300.510.480.390.210.420.330.27
Fe
4.65
5.30
4.634.952.532.951.973.501.251.901.202.732.372.401.083.172.902.772.020.991.833.321.541.90
5.475.335.546.014.915.556.075.324.655.635.146.263.543.624.524.654.735.37
{%
Mn
0.087
0.070
0.6750.1070.0650.0700.0940.0840.0870.0770.1600.0920.0710.0510.0410.0320.0320.0500.0510.1000.0730.0690.0730.040
0.270.670.300.100.130.240.090.080.150.070.050.180.370.020.040.020.040.04
)
Ti
0.50
0.47
0.400.500.240.280.160.290.190.190.080.240.210.170.160.120.110.120.080.020.080.210.190.29
0.630.560.590.520.480.590.670.590.560.590.590.630.460.520.500.480.520.59
P
0.05
0.05
0.050.050.030.030.030.030.020.030.030.050.040.030.030.030.020.030.020.030.020.040.040.06
0.050.040.050.060.050.050.060.060.040.050.050.060.060.030.040.030.030.05
Na20
1.75
1.76
2.022.301.431.381.031.180.881.091.301.041.050.970.830.800.900.580.710.440.680.540.830.42
2.322.542.061.882.112.141.531.882.112.121.901.702.131.611.441.401.441.36
K2O
2.62
2.84
2.252.501.561.641.171.760.761.300.601.070.830.900.521.050.860.810.470.340.741.081.000.91
2.652.542.823.342.262.352.242.212.352.212.402.181.841.761.671.521.812.24
Zn
108
120
951027688647342463890668044646023162519273756
14138132146130152166135111123122145106104125138134157
Cu
37
19
536030682239
11030283046926054
200362817
194581234
88858476569473463342403332
23224268550
( I0" 4
Ni
50
48
65614441315343513560384627227610101266
158
75725684758678565745
10.7567252668682
100
%)
Co
22
<20
.3622222222.22
<20<20<20<20<20
28<20
1021
88
1088
148
352025201531251515153115252123252337
Cr
66
42
70763852465838423262585426362730242126503852
535452505444695455546364616087798288
Cd
4.0
<4.0
4.0<4.0
4.5<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0<4.0
<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6
479
E. M. EMELYANOV
TABLE 2 - Continued
Sample(Interval in cm)
14-5, 87-8915-1, 8415-1, 12717-3, 140-14217-4, 15-1717-6, 61-6318-1, 115-11718-3, 36-3819-2, 127-12920-2, 115-117
Hole 356
2-1, 28-313-2, 71-734-3, 43-455-4, 120-1236-4, 80-837-4, 30-338-2, 70-739-2, 130-13210-3, 59-6111-3, 113-11512-1,9-1114-1, 20-2316-1, 127-12917-4, 60-6319-4,42-4423-2, 60-6224-5, 121-12325-2, 40-4226-2, 26-2829-2, 120-12229-6, 40-4231-5, 54-5633-2, 88-9035-3, 70-7238-3, 107-10939-5, 95-9740-6, 44-4641-4,56-5844-3, 109-111
Hole 356A
1-4, 74-762-5, 73-75
Site 357
1-3, 93-963-2, 97-995-3, 90-926-4, 70-738-2, 80-839-2, 60-6310-1, 70-7210-2, 70-7211-2, 108-11113-5, 65-6815-2, 100-10317-2, 70-7220-3, 91-9422-3, 84-8723-3, 42-4524-1, 96-9924-5, 75-78
CaCO3
0.001.500.00
69.8075.0581.3075.7864.7960.7989.12
85.8057.5448.7860.0425.5221.7630.0237.7729.5241.7819.0131.5222.2614.7641.7842.5345.5457.5452.3118.5155.0342.0339.0242.0345.28
6.251.75
32.0237-77
33.0240.02
92.5689.5684.1085.3087-8192.5684.3081.0689-0680.3081.5576.3086.0581.3073-8785.5664.29
Corg
0.300.630.510.300.360.390.510.150.660.48
1.080.511.081.020.510.660.750.541.140.810.480.540.720.600.780.900.601.201.200.600.690.660.601.050.750.721.359.810.87
0.361.35
0.450.420.840.750.360.300.240.690.600.540.600.540.270.540.300.330.39
Fe
6.774.537.321.211.761.181.232.053.081.40
0.702.052.291.522.953.183.243.002.463.002.571.812.643.862.002.783.252.523.013.882.122.603.502.573.275.664.343.413.32
2.862.14
0.400.340.950.780.470.350.490.300.370.740.810.880.980.981.360.601.50
(9
Mn
0.070.700.130.060.120.100.150.180.760.26
0.030.050.050.060.060.040.040.080.120.130.080.130.120.040.090.100.120.130.140.040.160.070.070.100.090.0320.0210.030.10
0.030.04
0.030.030.030.040.020.0030.020.020.030.030.030.020.020.040.050.050.05
o)
Ti
0.610.630.650.140.120.030.080.160.230.08
0.050.230.230.180.270.310.420.270.370.270.310.200.270.520.250.370.290.270.300.500.230.310.350.340.480.790.651.010.40
0.340.29
0.0060.010.080.050.010.010.030.010.010.040.080.100.080.100.310.080.61
P
0.060.050.060.030.030.020.020.030.060.04
0.030.050.040.040.030.050.030.040.030.050.030.030.030.030.030.030.060.030.030.030.030.040.030.050.050.050.050.020.05
0.050.05
0.020.010.020.030.030.030.030.030.030.050.060.050.050.040.070.040.12
Na20
1.331.301.190.600.580.520.620.580.820.49
1.022.082.222.10.2.182.081.951.702.361.621.621.411.361.951.271.551.311.241.211.801.151.171.201.350.901.301.391.011.21
2.482.16
0.941.161.500.951.100.850.861.040.991.290.961.140.380.870.850.861.36
K2O
2.352.862.641.080.960.730.651.301.530.68
0.341.151.331.011.571.601.711.402.041.371.330.981.142.221.681.711.731.501.742.681.57'2.002.201.792.013.662.621.572.06
1.601.44
0.190.220.530.540.330.210.770.270.360.660.660.830.570.590.490.620.64
Zn
15617116045261822526624
18567059717485529856566296
116386482717593575670776586
13010952
6149
44
1415
72524
68
161425
835238066
Cu
30113
27698
21304423
2020204425272823341323503373343120184532232322232978859533
2734
1714141611171413141515185
16171460
(I0"4?
Ni
9686
11219312126246928
129
11111619196
221124132658751322192245
9161316244225
20814
913
<8<8
99
<8<8<8<8<8
88
<8<8
899
58
Co
32333711101010163610
10<IO<IO<IO<IO<IO<IO<IO<IO<IO
13<IO<IO
1320
<IO<IO<IO<IO
25<IO<IO<IO<IO<IO
1213
<IO<IO
<IO<IO
<IO<IO<IO<IO<IO
569
12<4
8<4<4
4<IO<IO
13
Cr
93939323211818243013
1529331844473735574547355570294542333263293150465592
1116037
4126
10111317121414121617191917359024
154
Cd
<6<6<6<6<6<6<6<6<6<6
<6<6<6<6<6<6<6<6<6<6<6<6<6<-"-<-"-<6<6<6<6<6<6<6<-"-<6<6<6<615<6
<6<6
<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6
480
GEOCHEMISTRY OF SEDIMENTS
TABLE 2 - Continued
Sample(Interval in cm)
24-5, 84-8724-5, 91-9424-6, 101-10424-6, 131-13426-3, 148-15127-3, 107-11028-1, 92-9529-1, 6-930-1, 13-1631-2, 122-12533-3, 140-14334-4, 34-3736-1, 65-6840-1, 76-7940-4, 44-4541-2,76-7941-2, 81-8242-3, 37-4043-3, 82-8544-3, 30-3346-3, 72-7547-2, 60-6348-1, 42-4350-2, 126-12851-3. 34-36
Site 358
1-6, 82-842-4, 94-963-2, 68-703-5, 68-704-1, 98-1005-1, 56-586-3, 71-737-1, 69-718-1, 112-1149-3, 28-3010-4, 68-7011-3,9-1111-4, 82-8412-3, 77-7912-4, 61-6313-4, 105-10714-2, 138-14015-1, 65-6716-2, 101-103
Hole 359
1-3, 72-742-6, 132-1343-4, 66-683-5,49-514-2, 17-19
Hole 35 9A
1-4, 110-1122-2, 80-82
CaCO3
35.5259.0489.5690.3170.8070.0424.2787.0583.3080.8063.0451.2844.0355.79
1.0015.013.00
40.7856.0447.2855.5459.5467.2948.5340.27
0.000.000.000.000.000.000.000.000.000.000.000.00
61.2971.0440.0222.0140.02
1.7510.26
89.3171.80
3.2556.297.90
87.8190.06
Corg
0.600.720.540.510.300.600.390.240.330.630.360.480.240.360.390.240.390.420.360.570.510.360.390.720.45
0.480.450.240.540.180.180.240.180.330.240.390.300.240.300.240.450.300.360.33
0.150.180.240.240.39
0.450.66
Fe
2.082.682.232.771.191.453.480.590.920.622.001.793.122.383.413.594.673.021.823.823.052.331.301.451.34
4.864.435.485.284.264.044.064.434.044.094.004.581.601.102.454.443.625.404.63
0.122.523.982.646.07
0.140.19
(%
Mn
0.020.070.050.070.040.060.040.060.040.050.640.060.060.060.020.020.0030.050.050.050.050.060.060.060.05
0.060.090.060.180.060.040.060.040.040.080.030.070.030.300.190.120.180.100.12
0.010.120.060.110.15
0.020.02
)
Ti
1.050.800.100.160.220.350.790.050.080.080.230.230.300.310.340.340.310.400.270.410.340.290.160.140.16
0.520.500.530.520.420.450.470.480.500.500.470.500.160.120.220.380.380.560.46
0.0060.230.250.521.58
0.090.09
P
0.20
0.030.030.060.650.190.030.030.010.030.030.030.030.010.020.030.030.030.030.040.050.030.03
-
0.030.020.020.110.070.030.030.030.030.030.050.080.030.030.050.070.080.050.05
0.010.180.020.080.26
0.020.01
Na20
1.961.480.370.620.651.541.921.230.740.701.051.14
—_
2.061.811.921.120.741.020.850.90
_0.650.76
2.763.102.412.352.993.132.902.752.071.851.822.040.960.851.141.401.361.671.51
1.111.454.732.191.95
0.861.30
K2O
0.850.860.320.450.520.971.150.830.720.901.792.10
-1.910.671.110.472.481.572.302.041.94
_0.880.88
2.742.483.002.782.462.742.432.562.763.233.221.941.080.831.383.102.453.773.09
0.070.724.381.531.01
0.120.12
Zn
2933142714167226149
35506876
16011123110151
1278065253410
122108108102
8894
14097
196111118113563769
12310812895
<230
22352
133
2<2
(I0"4
Cu
2045118
151620141716182320281816193727323233201819
10782
11974326583547870493923157664428240
12176
187
<8<8
%)
Ni
37354
3129
91833152112232324203485
5203826613331157
13
38466846503848333327445235283046445732
<820101026
<8<6
Co
<IO65
<IO<IO<IO
812
547656
<4501875116
<4<4
8<4
5<4
222430222213101113
54
1311
61118<62218
<6<6<6<626
<6<6
Cr
513224
163235192022161928283932
919
74732513432262220
43453838313633335044473120254445453842
1027
628
4
117
Cd
<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6
<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6<6
<6<6<6<6<6
<6<6
authigenic calcite, the quantity of which increasesdownward; (2) lesser quantity of foraminifer shells; and(3) the absence of pteropods. The oozes are locallycemented, grading into limestones. Nannofossil oozeswith a decreased content of CaCCh from 35.52 to64.29% (Core 24, Section 5) are typical of the second
unit. These sediments are enriched by silica (spicules,diatoms, radiolaria) and volcanic material (weatheredash). An interlayer at the very bottom of the unit (Core28, Section 1) contains 24.27% of CaCCh. These aresilico-terrigenous sediments.
Unit III was not studied, but is similar to Unit II.
481
E. M. EMELYANOV
TABLE 3Total Chemical Composition of the Sediments in the Central Atlantic, Leg 39 (in %)
Sample(Interval in cm)
353-2-2, 30-32353-3-2, 120-122354-8-2, 30354-14-1, 106354-18-4, 127355-1-2, 72-74355-3-5, 60-62355-5-1, 38-40355-5-4, 100-102355-12-5, 86-88355-13-3, 75-77355-17-4, 20-22356-5-4, 101-103356-6-4, 50-53356-14-1, 25-27
SiO2
52.7278.7626.1914.9440.7549.9052.8655.0756.0960.6955.0112.3623.6343.8249.64
356-24-5, 120-122 31.56356-39-5, 75-77357-40-1, 76-79357-51-3, 34-36357-9-2, 60-63358-1-6, 70-72358-3-2, 71-73358-3-5,71-73358-5-2, 62-64358-10-3,73-75358-15-1, 66-68359-3-5,49-51359-2-6, 139-141
51.4626.2448.85
2.2354.6955.5155.9156.9261.0056.7023.0110.05
TiO2
0.920.480.500.300.581.071.111.071.081.021.040.340.450.720.440.621.430.650.390.161.021.081.090.991.041.010.970.41
A12O3
19.367.35
11.424.48
12.1919.2419.2417.8717.6915.9217.974.306.289.346.919.24
13.557.174.121.08
17.7617.7617.4415.9214.9017.446.632.33
FeO
1.734.030.290.431.730.430.430.290.431.150.430.140.210.430.360.432.011.150.540.431.130.940.580.580.860.290.860.36
Fe2°3
5.351.513.771.791.968.268.827.647.106.639.463.242.194.152.644.646.772.771.500.186.426.697.256.126.527.643.092.67
MnO
0.060.040.030.030.050.060.060.060.060.060.060.030.030.050.050.040.070.040.050.020.060.060.060.060.050.060.040.03
CaO
3.111.41
22.4441.1618.93
1.131.130.580.580.580.58
41.2732.2315.4617.1624.120.85
28.6421.2052.010.850.850.851.131.130.85
31.7342.24
MgO
2.841.021.221.221.223.453.652.943.452.843.251.421.632.842.032.444.273.252.240.813.643.753.754.063.253.551.221.22
K2O
2.691.500.980.311.002.822.582.462.502.122.321.131.131.771.131.883.422.000.880.262.953.202.902.663.064.051.370.71
Na2O
1.691.361.271.020.412.822.422.322.141.321.331.022.722.401.621.691.521.270.881.442.352.602.702.901.901.602.902.01
P2°5
0.2170.0680.1420.0930.2350.2230.2470.2230.1670.1610.1240.0930.1980.1730.1980.2660.2660.1480.1480.1790.1370.1050.3340.1550.1920.2100.3840.711
co2
2.980.61
21.4731.6416.500.452.320.000.000.910.00
32.7726.8912.8813.4118.762.71
23.7316.1641.81
trtrtr
2.261.630.00
25.2835.26
L. o. i.
9.451.90
26.5034.0320.49
9.248.109.058.256.938.02
34.5229.1718.4717.4023.0010.3426.3518.9141.09
8.247.006.508.005.746.40
26.7036.82
s0.150.170.170.140.221.280.200.160.230.290.080.060.140.270.110.121.690.190.350.070.310.170.070.300.120.050.100.23
F
0.090.020.060.040.050.060.090.090.080.060.080.050.060.080.080.070.090.080.070.040.050.090.080.090.070.090.100.09
H2°6.641.745.021.804.228.347.209.108.206.098.001.982.745.494.004.127.742.762.800.498.306.986.585.704.246.441.661.41
TABLE 4Contents of Carbonate Minerals in Bottom Sediments From Leg 39 (in %)
Depth(m)
Sample(Intervalin cm)
Hole 353
126.5263.7263.9
2-3, 50-523-2, 120-1223-2, 142-144
Hole 35 3A
181.0
Site 35-
4.85.4
54.559.6
140.6142.1145.3147.6148.5195.5243.0243.4243.9285.9345.5397.7455.8522.3611.9612.4699.7
1-2, 91-941,CC
t1-1, 751-1, 1402, CC3-1, 1104-1, 60-624-2, 60-624-4, 754-6, 104-6, 1025-2, 91-936-3, 846-3, 946-3, 1387-3, 438-2,59-1, 11710-2, 12611-2, 7912-5,4012-5, 9113-6, 124
Calcite
<l.O<l.O<2.0
tr<l.O
13.023.018.031.038.053.033.030.055.035.030.054.026.047.017.041.041.035.048.042.047.0
Aragonite
0.00.00.0
0.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Dolomite
0.00.00.0
tr0.0
0.00.00.00.0
<2.0<2.0<l.O<2.0
0.00.00.0
<l.O<l.O<l.O
0.0<l.O
0.0<l.O<l.O<l.O
0.0
Siderite
0.00.00.0
tr0.0
0.00.02.0
<2.00.00.00.0LO0.00.00.00.0LO0.00.00.00.00.00.00.00.0
Magnesite Manganocalcite
0.00.00.0
0.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
482
GEOCHEMISTRY OF SEDIMENTS
TABLE 4 - Continued
Depth(m)
705.4820.9823.4835.5842.2858.3872.8877.3Site 35f
55.2113.5117.3169.4173.6223.1243.4248.5264.2287.9289.5308.7321.1349.9363.9374.8386.4386.5408.9409.2412.7419.7421.9430.8442.0
Sample(Intervalin cm)
14-4, 35-4015-2, 3515-3, 13816-2, 4716-6, 12417-1, 12718-1, 13018-4, 127
1-2, 72-742-3, 50-522-5, 130-1323-2, 90-923-5, 60-624-3, 110-1125-1, 38-405-4, 100-1026-2, 66-687-2, 90-927-3, 100-1028-2, 120-1219-2, 58-6011-2, 86-8812-5, 86-8813-3, 75-7715-1, 8615-1, 10117-3, 142-14517-4, 20-2217-6, 65-6718-1, 120-12218-3, 41-4319-2, 131-13320-2, 148-150
Hole 356
10.339.860.691.0
119.0138.0169.6198.5225.0244.8253.1273.8292.0299.5318.4353.7365.0365.9368.2372.8381.7408.8411,1416.7443.7487.0545.0654.3681.3701.4705.0734.1
2-1, 82-853-2, 28-304-3, 55-575-4, 101-1036-4, 50-537-4, 50-538-2, 60-639-2, 98-10010-3, 48-5011-2, 129-13112-1, 11-1314-1, 25-2716-1, 100-10217-4,50-5319-4, 40-4223-2, 70-7224-3, 101-10324-4, 35-3724-5, 120-12225-2, 30-3326-2, 23-2529-1, 30-3229-2, 110-11229-6, 30-3231-5, 68-7033-2, 94-9735-3, 50-5238-3, 82-8439-5, 75-7740-6, 42-4441-2, 48-5044-2, 110-112
Calcite
51.047.031.036.037.034.042.027.0
0.00.00.0
33.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
87.079.089.082.072.061.086.0
67.052.042.052.030.024.030.036.029.016.021.031.017.044.016.038.021.070.042.050.046.0
8.024.050.063.045.046.045.0
0.02.00.0
26.0
Aragonite
0.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Dolomite
0.00.00.00.00.06.0
<l.O0.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.03.0(?)0.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0tr
0.00.00.00.0
Siderite
0.00.00.00.00.04.00.00.0
0.00.0tr
0.00.00.0
<2.0<l.O<l.O<2.0<l.O<2.0
0.0tr
0.00.00.00.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.0trtr
0.00.0tr
0.00.00.00.00.00.00.0trtr
0.00.00.00.00.00.0tr
0.00.00.00.0
Magnesite
0.00.00.00.00.00.00.00.0
__—_——_
—————
—
——
___-
_—_—__—_—__——____________—_____-
Manganocalcite
_
_—____-
0.00.0tr0.0trtr3.02.01.03.02.04.01.02.0trtrtrtr0.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
483
E. M. EMELYANOV
TABLE 4 - Continued
Depth(m)
Sample(Intervalin cm) Calcite Aragonite Dolomite Siderite Magnesite Mangano calcite
Hole 356A24.235.1
1-4, 72-742-5, 55-57
Hole 359
6.436.958.262.062.891.2
1-3, 91-1412-6, 139-1413-1, 15-173-3, 96-983-4, 26-284-2, 19-21
Hole 35 9A
17.617.621.5
1-6, 108-1101-6, 112-1142-2, 104-106
34.043.0
74.058.047.040.0
0.03.0
73.072.072.0
0.00.0
0.00.00.00.00.00.0
0.00.00.0
0.00.0
0.00.00.00.00.00.0
0.00.00.0
0.00.0
0.00.00.00.0
<l.O0.0
0.00.00.0
0.00.0
0.00.00.00.00.00.0
0.00.00.0
Unit IV is represented by slightly cemented nanno-fossil oozes (chalk) and limestones containing CaCChin the range of 44.03 to 87.05%, with carbonate decreas-ing from top to bottom. In addition to coccoliths andforaminifers, dolomite is found locally (up to 10-15% ofthe sediment).
Unit V consists of marly muds and siliceous lime-stones; the content of CaCOa is 40.27 to 67.29%. Thebasic components are authigenic calcite, coccoliths, andplanktonic foraminifers. At the very bottom of the unita calcareous concretion of 10 cm was found. In theupper part of Unit V (Core 40, Section 4 and Core 41,Section 2) are found interlayers of terrigenous(siliceous) sediments, containing 1 to 15.01% of CaCCh,enriched by Zn, Ni, Co, and very low in potassium.
Thus, the quantity of CaCC>3 decreases from top tobottom. The role of foraminifers decreases in the samedirection, and authigenic calcite and biogenic siliceousremains increase.
Site 357 presents a classical example of transitionfrom loose foraminiferal-coccolith ooze of Plio-Pleistocene age into chalk and limestones of Cretaceousage.
Site 358The content of CaCCh varies in the range from 0.00
to 61.29%. In Unit I CaCOa is completely absent. It ispossibly related to: (1) unfavorable (cold) conditionsfor organisms with calcareous skeletons; (2) withposition of the site below the present compensationdepth (4600-5000 m for the Argentine Basin); or (3)with intrusion of cold Antarctic bottom waters into thebasin.
The lower unit of sediments is represented by marlychalks and terrigenous muds (mudstones). The calcare-ous material consists mostly of coccoliths, withforaminifers occurring more rarely. This materialconsists exclusively of low-magnesian calcite (Table 5).The content of CaCCh decreases to 1.75% inmudstones.
The high CaCCh content indicates that the depth hadbeen either close to the compensation depth or above it
during the period of accumulation of the sediments ofthe lower unit. Large amounts of barite are in the chalkand Paleogene sediments of Site 358 (Figure 2).
After the deposition of Unit II sediments (lateEocene?), the conditions of sedimentation abruptlychanged. This change represents not only a possiblevariation (rise) of the compensation depth (orsubsidence of the bottom below it), but also a time ofgeneral drop of temperature in the southern hemi-sphere, beginning in the Eocene when local glaciers
Figure 2. Microphotograph of barite at the Site 358 (Sam-ple 11-4, 91-93 cm). Heavy coarse aleurite fraction (0.1-0.05 mm).
484
GEOCHEMISTRY OF SEDIMENTS
TABLE 5X-ray Diffraction Analysis of Bulk Samples From Sites 357, 358, Leg 39
(in % from total crystalline componnets)
Depth(m)
4.020.441.051.867.777.288.389.8
112.1137.1178.3193.0196.0262.7309.2333.6351.0357.4359.0359.3383.5411.6436.9471.5474.3498.7525.9554.8607.7693.3697.4697.5705.3705.3705.3718.0726.4733.2746.3753.1759.5781.4790.9796.2Site 358
55.7128.9201.7206.2282.5359.6426.9493.0552.2595.6640.2706.1708.4752.6754.3781.8791.4804.7825.5
Sample(Intervalin cm)
1-3, 100-1033-2, 90-925-3, 100-1026-4, 80-838-2, 70-739-2, 70-7310-1, 80-8210-2, 80-8211-2,103-10613-4,62-6515-2, 78-8117-3, 100-10217-5, 100-10220-2, 117-12022-4, 13-1623-2, 61-6424-1, 45-4824-5, 84-8724-6, 101-10424-6, 132-13526-3, 148-15127-3, 108-11128-1, 9129-1, 98-10130-1, 31-3431-2, 123-12633-3, 142-14584-4, 32-3536-1, 68-7140-1, 74-7740-4, 44-4540-4, 45-4641-2, 76-7941-2, 79-8041-2, 81-8242-3, 96-9943-3, 140-14344-2, 18-2146-3, 31-3447-3, 56-5948-1, 47-4850-3, 42-4451-3, 34-3651-6, 125-126
1-6, 70-722-4, 94-963-2, 71-733-5, 71-734-1, 96-985-2, 62-646-3, 139-1417-2, 99-1018-1, 117-1199-2, 63-6510-3, 73-7511-3, 7-911-4, 86-8812-2, 59-6112-3, 75-7713-2, 130-13214-2, 137-13915-1, 66-6816-2, 103-105
Calcite
95.293.590.591.381.096.294.392.896.681.890.689.280.888.488.191.286.182.30.00.0
100.087.957.688.594.891.668.071.952.861.017.4tr
51.417.919.549.750.367.277.859.682.280.762.164.5
0.00.00.00.00.00.00.00.00.00.00.00.0
86.764.389.186.670.8
8.922.6
Dolomite
0.03.90.00.00.00.00.00.00.00.00.00.00.00.00.00.03.4
10.2100.0100.0
0.00.00.00.00.00.09.5
tr7.0
15.40.00.0
tr0.00.0
11.11.8
10.30.0
18.00.06.80.00.0
trtr0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
Siderite
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.02.01.40.0tr
0.00.00.00.00.0
4.44.30.00.03.63.12.90.00.04.00.00.00.00.00.00.00.00.00.0
Total
95.297.490.591.381.096.294.392.896.681.890.689.280.888.488.191.289.592.5
100.0100.0100.087.957.688.594.891.677.571.959.876.417.4tr
51.417.919.562.853.677.577.877.682.087.562.164.5
4.44.30.00.03.63.12.90.00.04.00.00.0
86.764.389.186.670.8
3.922.6
Pyrite
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0tr
0.06.38.60.00.00.00.00.00.00.00.00.0
0.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.0
485
E. M. EMELYANOV
TABLE 6Comparative Data on the Chemical Composition of the Recent and
Upper Quaternary Sediments in Areas Near Leg 39 Sites (see Figure 1 for locations)
Horizon,(in cm)
0-10
30-40
80-90
110-120
140-149
170-180
210-220
240-250
260-270
290-302
313-320
Type of Sediment
Guiana Basin, Site 53. Depth 5080m, 12°59'N, 53°
Pelitic terrigenous low-calcareous brown mud
Pelitic terrigenous low-ferrugenous, low-man-ganese brown mudPelitic terrigenous low-ferrugenous, low-man-ganese brown mudPelitic terrigenous, low-ferrugenous brown mud
Pelitic terrigenous dark-gray mud
Pelitic terrigenous low-calcareous, low-man-ganese brownish gray mudPelitic terrigenous low-ferrugenous grayish brownmudAleuritic-pelitic, low-ferrugenous,bluish gray mudAleuritic-pelitic, ethmodiseus,low-siliceous, bluish gray mudPelitic terrigenous, low ferrugenous, bluishgray mudThe same
Guiana Basin, Site 375. Depth 4330m, 03°00'N, 39° 5 8 ^
0-3 Aleuritic-pelitic coccolith-foraminiferal ooze
Brasilian Basin, Site 400-2. Depth 4670m, 17°50'S, 31°35'W.
0-7
20-25
41-46
74-79
103-108
131-136
155-160
178-183
217-222
233-238
Pelitic terrigenous, low-ferrugenous-low-man-ganese, grayish brown mud (red clay)Pelitic terrigenous, low-ferrugenous-low-man-ganese, brown mud (red clay)Pelitic terrigenous, low-ferrugenous-low-man-ganese, brown mud (red clay)
The same
Pelitic terrigenous low-manganese, brown mud(red clay)Pelitic terrigenous, low-ferrugenous low-man-ganese, brown mud (red clay)The same
Pelitic terrigenous, low-ferrugenous low-man-ganese, grayish brown mud (red clay)The same
The same
Argentine Basin, Site 16. Depth 5100m, 40°39'S, 36°27'W.
0-25
25-30
50-70
75-100
100-125
Pelitic terrigenous, low-calcareous, with diatoms,greenish gray mudPelitic terrigenous, with manganese nodulas,greenish gray mudPelitic terrigenous, low-ferrugenous, greenishgray mudPelitic terrigenous, greenish gray mud
Pelitic terrigenous, low-ferrugenous, greenishgray mud
CaCO3
01'W.
26.22
0.64
3.75
1.64
0.00
0.50
0.50
0.00
0.00
0.50
0.00
56.06
0.75
1.57
2.64
0.50
0.75
0.50
0.00
0.26
0.25
0.00
11.14
4.94
7.04
4.88
7.27
SiC^-Amorph
1.31(1.85)1.28
(1.29)1.35
(1.41)1.00
(1.02)0.74
(0.74)0.94
(1.12)2.20
(2.24)
8.44(8.44)12.84
(12.84)1.38
(1.39)1.27
(1.27)
0.84(1-93)
0.98(1.00)1.51
(1.56)
1.50(1.57)1.65
(1.69)1.72
(1.77)1.66
(1.70)1.53
(1.53)1.61
(1.64)1.81
(1.95)1.75
(1-75)
5.14(6.31)1.64
(1.69)2.08
(2.24)1.55
(1.63)1.15
(1-24)
Content (%)Corg
0.36(0.50)0.26
(0.27)0.38
(0.40)0.23
(0.24)0.50
(0.50)0.35
(0.42)0.23
(0.24)
0.27(0.30)0.33
(0.39)0.25
(0.25)0.25
(0.25)
0.33(0.77)
0.38(0.39)0.31
(0.32)
0.32(0.33)0.50
(0.51)0.29
(0.29)0.26
(0.26)0.24
(0.24)0.26
(0.26)0.18
(0.18)0.16
(0.16)
_
—
-
—
—
Fe
4.01(5.56)6.12
(6.26)5.37
(5.68)6.31
(6.50)4.19
(4.24)4.42
(5.34)5.37
(5.53)
5.45(6.11)3.44
(4.09)5.65
(5.77)5.98
(6.07)
2.54(5.93)
5.84(5.96)5.65
(5.84)
5.09(5.32)5.37
(5.52)4.80
(4.94)5.37
(5.50)5.47
(5.47)5.56
(5.68)5-56
(5.69)5.18
(5.18)
3.82(4.81)4.94
(5.21)5.05
(5.61)4.91
(5.27)6.75
(7.47)
Mn
0.14(0.19)1.01
(1.03)0.25
(0.26)0.10
(0.13)0.08
(0.08)0.21
(0.23)0.05
(0.05)
0.05(0.06)0.02
(0.02)0.12(0.12)0.05
(0.05)
0.08(0.19)
0.25(0.26)0.32
(0.33)
0.32(0.33)0.24
(0.24)0.26
(0.26)0.32
(0.32)0.33
(0.33)0.38
(0.38)0.35
(0.36)0.30
(0.30)
0.20(0.24)0.05
(0.05)0.06
(0.06)0.05
(0.05)0.04
(0.04)
Ti
0.33(0.46)0.49
(0.50)0.46
(0.47)0.46
(0-47)0.51
(0.52)0.33
(0.40)0.46
(0.47)
0.42(0.47)0.39
(0.46)0.46(0.47)0.48
(0.49)
0.24(0.56)
0.51(0.52)0.43
(0.44)
0.43(0.45)0.45
(0.46)0.46
(0.47)0.45
(0.46)0.45
(0.45)0.46
(0.47)0.46
(0.46)0.51
(0.51)
_
-
-
-
-
P
0.03(0.04)0.04
(0.04)0.04(0.04)0.04
(0.04)0.02
(0.02)0.02
(0.02)0.03
(0.03)
0.02(0.02)0.03
(0.04)0.03(0.03)0.05
(0.05)
0.04(0.09)
0.05(0.05)0.04
(0.04)
0.05(0.05)0.04
(0.04)0.04
(0.04)0.05
(0.05)0.05
(0.05)0.05
(0.05)0.06
(0.06)0.06
(0.06)
_
-
-
-
-
486
TABLE 6 - Continued
GEOCHEMISTRY OF SEDIMENTS
Horizon(in cm) Type of Sediment
Argentine Basin - Continued
125-150
150-175
175-200
200-225
225-250
Pelitic terrigenous, greenish gray mud
Pelitic terrigenous, low-ferrugenous, greenishgray mudPelitic terrigenous, low- ferrugenous, greenishgray mudPelitic terrigenous, low-ferrugenous, low-Cal-careous, light-green mudThe same
CaCC
6.59
4.32
9.66
16.94
14.34
Content (%)
o r g
Ee Mn Ti
1.13(1.21)1.12
(1.17)1.32
(1,46)1.08
(1.30)1.21
4.88(5.36)5.22
(6.435.64
(6.43)5.66
(6.98)5.71
0.05(0.05)0.05
(0.05)0.07
(0.08)0.05
(0.06)0.04
Content of elements in dry sediment and on a carbonate-free basis (in brackets).
TABLE 7Average Contents of Elements in Extended Genetic Types of Sediments in Sites 353 to 358 (see Table 2)
Type of Sediment
Terrigenoussediments« 3 0 % CaCO3)
Siliceous muds(<30% CaCO3)
Calcareous
(>60%CaCO3)
Marly carbona-
ceous sediments(30-60% CaCO3)Pelagic muds(ancient clays)
Sites
35 3 a, 354a, 356a,357 a,358 a
353b,354b, 356b,357 b ,358 b
356a
356b
3 5 8 a ' b
356 + 358a
356 + 3 5 8 a ' b
354a to 15-3C
3 5 4 a ' b t o 15-3C
357 a to28-l c
357 b to28- l c
354, 355a, 356a,357a, 358a
354b, 355b, 356b
357 b ,358 b
354a, 356a, 357a
TotalSamples
13
13
999
1818
99
2121
45
45
35354 a ' b,356 a ' b,357 a ' b 35
355a
355b
2121
CaCO3
9.43
_
28.79_
0.0028.79
-
68.98_
82.68-
76.94
_
49.32
1.27-
org
0.46
_
0.68_
0.280.48
0.11_
0.48-
0.41
_
0.77
0.39-
Fe
4.55
5.04
2.763.924.463.614.19
1.715.970.986.351.27
6.04
2.665.16
5.285.34
Content (in %)
Mn
0.11
0.13
0.090.130.060.070.09
0.080.250.030.27
0.09
0.40
0.070.14
0.180.18
Ti
0.50
0.56
0.300.420.490.390.45
0.110.400.120.610.12
0.52
0.340.54
0.570.58
P
0.06
0.06
_
_0.04
_- •
0.030.09
_-
0.03
0.12
0.040.07
0.050.05
Na2O
2.09
2.29
1.812.532.683.03
-
0.81_
0.98-
0.91
1.14
1.84
-
K 2 O
2.30
2.54
1.462.052.572.43
-
0.71_
0.58-
0.73
_
1.58
2.30-
Zn
120
132
72101118
95110
37130
18136
27
132
66126
132133
Content in lO~'
Cu
45
50
2840745257
61207
16105
27
119
4280
6266
Ni
84
91
1825473336
22781587
19
90
4689
7677
Co
26
28
101018—-
_
---
-
_
_
-
2525
Cr
49
54
4763384250
31104
28154
26
122
60114
6767
Cd
<5
<6
<6<9<6<6<7
<4<14
<6<46
<6
<33
<5< l l
<6<6
Natural (dry) sediment.
Evaluated in carbonate free basis.cFrom surface to noted depth.
began appearing in the Antarctic (Geitzenauer et al.,1968). More intensive glaciation occurred in the Oligo-cene and an ice surface, similar to that of the present,was formed in the Miocene. The fall of temperature inthe Antarctic resulted in formation of cold watermasses, which as near-bottom currents (Neumann andPierson, 1966; Bulatov, 1971; Ewing et al., 1971)penetrated far to the north and probably crossed theEquator. This resulted in (1) the rise of thecompensation depth level: (2) a sharp increase of coldAntarctic water productivity and mass development ofphytoplankton with siliceous skeletons, leading to theaccumulation of siliceous muds in the Argentine Basin.
Oligocene-Pleistocene sedimentation took placemainly in a reducing environment, evidenced by graysediment color and the presence of pyrite and siderite(Table 5). In late Quaternary time, the climaticcondition of the Argentine Basin had evidently becomemore moderate (warm), as a result of which the content
of CaCθ3 increases locally to 16.94%, whereas Siθ2drops to 1.08% (Table 6).
Site 359
The upper sediment unit (Core 2, Section 6 and Core1, Section 3) consists of foraminiferal-coccolithic ooze,the content of CaCXh being respectively 71.8% and89.31%. Considerable authigenic magnesian calcite (5-6mol. % of MgCθ3) occurs.
Unit II (from Core 4, Section 2 up to Core 3, Section4) consists of foraminiferal (Core 3, Section 5),terrigenous (Core 3, Section 4), and volcanogenic (Core4, Section 2) sediments with the content of CaCθ3being low (up to 3.25%). Authigenic magnesian calciteand dolomite occur in negligible quantities there.
Organic Carbon
The content of Crin the sediments of the western
part of the central Atlantic varies from 0.03 up to 9.81%
487
E. M. EMELYANOV
TABLE 8Average Contents of Elements in the Recent Sediments (0.5 cm layer) of the Atlantic Ocean
(Emelyanov, Shurko, 1973, Emelyanov, 1974a, b, 1975; Emelyanov et al., 1975)
Type ofSediments
Terrigenous sedi-ments (<10% CaCO3)
(and terrigenouspelitic muds)Mixed biogenic-terrig.(30-50% CaCO3)Foram-sands nanno-foram oozes«50% CaCO3)
Diatom ooze(>30% SiO2) amorph.
VolcanogenicsedimentsIceland areaRed clays«10%CaCO3)All types ofsediments
QuantitySamples
ab
ab
ab
ab
ab
ab
ab
ab
169168
5352
1818
7163
4
3131
1414
452435
orgLimits ofContents
0.04-8.100.04-8.90
0.10-12.200.15-20.62
0.37-8.100.41-8.90
0.17-6.570.38-20.08
0.18-0.60
0.12-1.900.12-2.54
0.11-0.440.11-0.45
0.04-12.500.04-20.62
Average
0.920.98
0.841.42
1.841.94
0.933.60
0.34
0.921.09
0.320.33
1.091.67
QuantitySamples
284270
5554
123120
265263
55
6666
814
959947
Fe
Limits ofContents
fr.-9.97tr.-7.35
0.74-7.000.80-7.35
0.75-6.710.92-10.400.06-4.940.50-16.24
0.58-1.621.58-4.14
5.04-11.855.47-12.88
5.28-6.594.92-13.52
tr.-16.05tr.-19.94
Average
3.183.22
5.015.34
2.965.161.465.71
0.972.85
7.078.23
5.856.43
3.054.88
QuantitySamples
13.1128
2828
6450
135110
22
3630
1814
494428
Mn
Limits ofContents
tr.-1.88tr.-2.00
0.02-1.880.03-2.00
tr.-0.39tr.-0.74tr.-1.12tr.-2.98
0.06-0.610.14-1.67
0.05-0.240.06-0.36
0.08-1.150.23-3.62
tr.-3.14tr.-3.62
Average
0.090.10
0.190.200.100.200.080.29
0.330.90
0.150.17
0.400.710.100.19
or 0.4 to 0.5% on the average. It is lower than in theRecent sediments of the Atlantic Ocean, but approxi-mately the same as reported from Cenozoic sedimentsat sites drilled on Legs 3 and 4 (Pimm, A.C., 1970;Pimm, A.C., 1970).
The lowest contents of COTg (from 0.03-0.27%) occurin biogenic calcareous sediments at Site 354. They areslightly lower than in pelagic terrigenous muds of lateQuaternary age in the Guiana Basin (Table 2). This is aresult of low biological productivity of this area in theLate Cretaceous and Cenozoic, and of low rates ofsedimentation and rapid oxidation of organic material.In the Miocene the sedimentation rate was as low as0.004 cm/1000 years (probably representing importanthiatuses). In the Eocene-Oligocene-Miocene the ratewas 1.7-2.2 cm/1000 years, compared to 10 cm/1000years in the Pleistocene.
The content of COTg at Site 355 varies in the range of0.15 to 0.66%; i.e., it is very close to the average contentin Recent red clays (Table 8). Approximately the samequantities of Corg occur in the pelagic muds at Site 358.Thus, despite the high productivity of phytoplankton inAntarctic waters and waters of the Argentine Basin inthe Oligocene-Pleistocene, the intensive accumulationof the remains of diatoms there, the rapid rates ofsedimentation and, presumably, reducing environmentsof sedimentation, as little organic substance occursthere as in pelagic diatom muds from near Antarctica.Probably this is a result of rapid rates of decompositionof organic substances.
The Corg in the sediments of the Rio Grande Rise(Site 357) contain from 0.24 to 0.84%, with an averageof 0.50%, which is approximately the same as in Recentcoccolith-foraminiferal oozes of the west Atlantic(Emelyanov, 1975).
Abnormally high quantities of C ^ (from 0.48-9.81%)occur in older sediments at Site 356, being 0.80 to 1.0%
on the average. Interlayers of sediments with sapropelsand pyrite accumulated there during Coniacian andTuronian time. Similar interlayers with sapropels weredescribed in holes drilled during Leg 14 (Berger andvon Rad, 1972), and also in the Caribbean Sea. Thehigh quantities of organic substance are thought tohave accumulated in situ under reducing conditions.High contents of Corg are independent of genetic type ofsediment and depth of subbottom. The high contents ofCorg are caused mainly by high constant biologicproductivity, favorable conditions for burial andpossible supply of organic material from outside thebasin. The area of the ocean now occupied by the SàoPaulo Plateau was a semi-isolated (shallow) basin,supplied by terrigenous material from South Americaduring the Late Cretaceous and Early Cenozoic. Ratesof sedimentation were usually high (2-6 cm/1000years), and reducing conditions (pyrite is frequentlypresent in sediments) were prevalent. Redeposition ofsediment occurred, with the formation ofconglomerates and turbidites.
DISCUSSION AND CONCLUSIONSTables 1 to 5, 7, and 9 show the relative abundance of
a series of selected elements determined to be in cores ofsediments from DSDP Leg 39. Tables 6, 8, and 10 showtheir comparative abundance in a variety of ancient andmodern marine lithofacies elsewhere in the AtlanticOcean. Examination of this data shows that, in general,sediments of any one genetic type have a chemicalcomposition that varies only slightly through space andtime which suggests, in turn, that there has beenessentially no geochemical "evolution" in the centralAtlantic from Late Cretaceous to the present. Incontrast, the geographic distribution of the lithofaciesin that area has changed markedly during the same time
488
GEOCHEMISTRY OF SEDIMENTS
TABLE 8 - Continued
QuantitySamples
188177
5346
9493
206204
65
3632
1510
700682
Ti
Limits ofContents
tr.-0.82tr.-0.85
0.04-0.660.11-0.71
0.05-0.810.08-1.49
tr.-0.44tr.-1.30
0.07-0.100.11-0.31
0.52-1.960.70-2.36
0.11-0.660.41-0.57
tr.-1.96te-2.36
Average
0.340.38
0.400.47
0.270.47
0.120.48
0.080.21
1.131.35
0.440.50
0.310.50
QuantitySamples
177177
4747
8181
184183
65
3127
1414
623615
P
Limits ofContents
tr.-0.46tr.-0.48
tr.-0.460.02-0.48
0.01-0.700.02-1.16
tr.-4.360.01-9.13
0.02-0.030.03-0.06
0.06-0.180.07-0.20
0.05-0.110.05-0.12
tr.-4.36tr.-9.13
Average
0.070.08
0.080.08
0.090.14
0.110.42
0.020.05
0.110.13
0.080.08
0.100.21
QuantitySamples
100100
2222
4242
8080
88
2929
-
352352
Ba.10' 4
Limits ofContents
130-3750130-4260
130-3750130-4260
100-1200160-2100
<200-1830<200-7870
210-1040220-1090
<200-1300<200-1870
-
90-7870110-7870
Average
470500
690740
450740
350460
570590
410460
-
450780
QuantitySamples
103103
2222
4242
8080
7
2727
:
354354
Zr.10 ' 4
Limits ofContents
300-850300-860
80-27090-290
<50-500<70-1180
<20-670<40-2220
40-130
<40-360<40-370
- .
<20-850<40-1630
Average
210220
150160
150240
90340
70
180190
160240
interval, influenced by paleoenvironmental conditionsand diagenesis.
CaCCh data indicate that the conditions of carbonateaccumulation changed sharply near the Paleocene-Eocene boundary. This is particularly true of areas thatwere deep or distant from the continent of SouthAmerica (i.e., Sites 355, 357, and 358).
In the Argentine Basin terrigenous sediment hadbeen primarily accumulating in the Late Cretaceous;carbonates were meager. The conditions of sedimenta-tion in Cretaceous time suggest the site was shallowerthan at present. During Paleocene and the beginning ofEocene time, biogenic calcareous material accumulatedin greater quantities, producing chalk. Conditions thenchanged sharply with the onset of glaciation in the Ant-arctic and the generation of cold, near-bottom current,which penetrated into the Argentine Basin. Thecompensation depth became shallower, leading todissolution of carbonates and accumulation of siliceousand silico-terrigenous sediments. This sedimentationregime lasted into the Pleistocene. In late Pleistocene-Holocene time conditions appear to have moderated,favoring biogenic calcareous material as witnessed byan increase of CaCθ3, up to 16% in Holocenesediments.
At the Rio Grande Rise site, in the Cretaceous,conditions for accumulation of CaCCh were variable,perhaps because of the changing distance of the sitefrom the continent and variations in rates of supply ofterrigenous material. The depth of the Rio Grande Risesite itself may also have been changing. From lateMaestrichtian to the present, the conditions ofaccumulation of CaCθ3 were rather stable andfavorable, resulting in a thick section (about 550 m) offoraminiferal-nannofossil oozes. These oozes(beginning in the Miocene, at least) underwent
diagenetic transformation (consolidation, cementation)and, down section, were converted into chalk and lime-stones. In addition, in the middle Eocene, dolomiteoccurs with limestones and marls.
Conditions for accumulation of biogenic carbonatesin the Brazil Basin, during Late Cretaceous, were evenmore favorable than those in the Argentine Basin or onthe Rio Grande Rise. The consistently high content ofCaCCh in the form of pelagic nannofossil oozes andchalk give evidence to this. In the Eocene an abruptchange occurred and conditions became unfavorablefor CaCCh accumulation. This was caused by eithersubsidence of the bottom, and/or intrusion of coldbottom waters from the Antarctic into the basin withconsequent shoaling of the compensation depth. Theseconditions have remained essentially unchanged to thepresent and resulted in accumulation of noncarbonatepelagic muds and terrigenous sediments. The rates ofsedimentation during this interval has been low,permitting extensive formation of zeolites.
In cases where sites were situated close to thecontinent (i.e., Sites 354, 350) and where depths weremoderate (above compensation), terrigenous materialdiluted the biogenic carbonate. At certain times (LateCretaceous especially) the accumulation of carbonateswas affected not only by dilution by terrigenous matter,but also by partial dissolution of carbonate, resultingfrom either subsidence of the bottom belowcompensation level or a rise in the compensation levelitself.
The paucity of volcanogenic (pyroclastic) material isnoteworthy (except at Site 359). In the Cretaceousperiod volcanic activity is evidenced but became muchless active in Tertiary time; in only a few cases are therepyroclastics in the post-Cretaceous sediments. Anexample is the middle Eocene at Site 357 (Core 24,
489
E. M. EMELYANOV
TABLE 8 - Continued
Type ofSediment
Terrigenous sediments(<10%CaCO3)(and terrigenouspelitic muds)Mixed biogenic-terrig.(30-50% CaCO3)Foram-sandsnanno-foram oozes(<50% CaCO3)Diatom ooze(>30%SiO2amorph
VolcanogenicsedimentsIceland areaRed Clays(<10%CaCO3
All types ofsediments
QuantitySamples
ab
ab
ab
ab
ab
ab
ab
ab
103103
2222
4343
8181
88
2727
_-
359359
Cr.10"4
Limits ofContents
<20-850<20-850
43-16647-173
9-25018-403
<10-25041-793
55-11056-117
23->100029-> 1000
_-
<9-100013->1000
Average
7881
101106
5388
47193
7376
145155
_-
71114
Ni. I0"4
QuantitySamples
103103
2222
4242
8080
88
2626
-
354354
Limits ofContents
2->5002-> 511
2-> 5002-> 511
10-11016-177
<5-10121-381
8-1079-111
<10-67<15-74
_-
2-> 5002-> 511
Average
4648
7881
2850
26109
8285
3538
—-
3539
V.K
QuantitySamples
100100
2222
4141
8281
88
2626
—
-
353353
r4
Limits ofContents
< 10-400< 10-494100-400100-494<20-160
32-260
5-18016-866
113-570118-590
< 20-40023-420
_-
5-57010-590
Average
97102
180191
67111
43182
323337
212228
_-
89133
Note: C - Cotm Fe, Mn, Ti, and P for deep water muds of the preantarctic zone of the ocean (Emelyanov and others., - Ba, Zr, Cr, Ni,V, and Cu for shallow water muds of the southwest coast of Africa (Emelyanov, 1973)
Section 5) where limestones and marls, enriched inpyroclastics accumulated. The carbonates are char-acterized by a peculiar chemical composition, withproperties in common with volcanoclastic sediments ofbasaltic composition. Ti (1.63-2.00%)' and Cr (431-796ppm) contents are high, as are Ni, Co, P, Mn, and Mo.Like volcanoclastic sediments, they are characterizedby low concentrations of Fe (3.22-6.54%).
In some cases, the chemical composition of sedimentwas affected by endogenic (hydrothermal) processes.Chalk deposits at the bottom of Site 355 (Core 19,Section 2 and Core 20, Section 2) overlie basaltsubstrate (Core 21, Section 1). The sediments,influenced by the products of hydrothermal activity,contain high quantities of Fe, Zn, Cu, Ni, and Co andlow quantities of Ti, Na2U3, K2O, and Cr. Suchferruginous sediments, formed by means of endogenicsources, have been described from surface samples inthe South Atlantic Ridge area (Boström et al., 1969;Boström et al., 1972), and in certain other recentsediments (Emelyanov, 1975).
Ferruginous sediments were found in the cores anddredge material recovered from the Iceland Plateau andNorwegian Sea during cruises on the R/V AcademicKurchatov. The age of these sediments ranges fromearly Miocene to Pleistocene. They are represented bytuffoargillites, tuffosandstones, sandstones, terrigenous(glacial) clays, and ferromanganese crusts. Thefollowing contents are characteristic of these ore-bearing sediments: Fe, up to 19%; Mn, up to 17.36%;Ti, up to 0.83%; P, up to 0.35%; Ni, up to 1000 ppm;Co, up to 500 ppm; Cu, up to 440 ppm; V, up to 240
'Here and hereafter evaluated on carbonate-free basis.
ppm; Zn, up to 525 ppm; Ba, up to 720 ppm; Mo, up to100 ppm; Cr, up to 74 ppm; Zr, up to 160 ppm; CaCChis absent. As a rule, the ratio (Fe + Mn)/Ti (Strahov,1974), a good indicator of endogenic processes for areasof the open ocean and the Mid-Atlantic Ridge, is over25. Although the value is not over 25 in the sedimentsof Site 355 (Core 19, Section 2 and Core 20, Section 2),it is close to it (ranging from Core 17, Section 21). Theupper chalk deposits at Site 355 (Core 18, Section 3 upto Core 17, Section 3) were also enriched in iron andmanganese by hydrothermal activity (Fe, 4.01-7.05%;and Mn, 0.20-0.62%). This enrichment is less pro-nounced up the section. The influence of hydrothermalaction on the chemical composition of sediments in theCretaceous is further indicated by the presence ofcalcite veins associated with reddish-brown ferruginousnannofossil ooze. By early Eocene hydrothermalactivity had completely ceased.
A second zone enriched in ore matter as a result ofvolcanic activity is the layer of dolomites, occurring inconjunction with a volcanic breccia at Site 357 (Core24, Section 6). These dolomites are overlain andunderlain by limestones, are associated withpyroclastics, and contain the highest quantities of Fe(21.36-28.58%) of all studied samples. They alsocontain high quantities of Mn, Zn, and Ni. However, Tiand Cr, which are characteristic of pyroclastics andvolcanoclastic sediments of basaltic composition, occurvery rarely in the dolomites. Therefore we mayconclude that the dolomites were formed as the resultof a combination of several factors: (1) supply ofpyroclastics (found in quantity up to 5%; seedescription of the smear slide of Sample 357-24-6, 140cm; (2) emanation of ore matter by means of hydro-thermal action, associated with subjacent volcanic
490
GEOCHEMISTRY OF SEDIMENTS
TABLE 8 - Continued
QuantitySamples
2626
77
1010
3232
1111
Cu.lO~4
Limits ofContents
14-23415-25350-13551-15031-8250-152
11-8816-640
29-8030-99
Average
758086905493
31178
5562
TABLE 9Content of Some Elements in Bottom Sediments From Leg 39
105105
11-26415-640
54108
breccias; (3) possible chemical precipitation of dolomiteand authigenic calcite from sea water. The range of theratio (Fe + Mn)/Ti, being 17 to 23, is less than inferruginous sediments of endogenic origin (where itusually exceeds 25), but greater than in pyroclasticsediments (where it usually equals 5-10, Emelyanov,1975). This suggests that both fluid and solid volcanicsource products supplied the Fe, Mn, and Zn and alsoTi and Co.
Leg 39 shipboard scientists concluded that mud-stones and marly chalk of Late Cretaceous age(Maestrichtian) are also enriched in ore matter.Laboratory study shows clearly that these sedimentscontain neither high contents of Fe, Mn, Zn, Ni, or Conor low contents of Ti, Cr, or AI2O3. (Fe + Mn)/Tiratio is very low in these sediments (10-11), and is moretypical of normal terrigenous or biogenic calcareoussediments (Emelyanov, 1975). A hydrothermalinfluence is evidenced by relatively high contents of Fe(7.10%) and Mn (0.15%) in sediments of Cretaceous ageat Site 354 (Core 17, Section 2).
Some of the chalk sediments are enriched in organicmatter and contain sapropelic interlayers (Site 356,Core 41, Section 4). In addition to the high Cw g content(up to 9.8%) they are also characterized by high valuesof Ni and Zn and low concentrations of Mn. Ni, andZn, probably precipitated in the form of organo-metallic compounds. The low content of Mn isgenerally characteristic of shallow reduced muds(Emelyanov, 1973; Emelyanov et al, 1975).
The chemical composition of marly limestones ofSantonian age at Site 357 (Core 48, Section 1 up toCore 51, Section 3) is rather unusual in that thesediments contain very low concentrations of Fe, Zn,Ni, and Co, and low concentrations of Ti, Cu, Cr, andother elements. Most likely this has been caused byadmixture of considerable biogenic siliceous material,since the sediments are high in Siθ2 and low in AI2O3(Site 357, Core 51, Section 3).
Sample(Intervalin cm)
Site 3543-1, 1204-1, 40-424-2, 40-425-2, 71-736-2, 1076-3, 917-1, 1377-3, 168-2, 309-3, 11210-2, 9811-5, 2512-4, 1113-6, 12514-1, 10615-2, 4515-3, 8417-2, 11718-1, 130Site 3551-2, 69-711-6, 80-822-3, 130-1322-5, 135-1373-2, 88-903-5, 58-604-3, 110-1125-1, 40-425-4, 98-1006-2, 100-1027-3, 100-1028-2, 140-1419-2, 50-5211-2, 91-9212-4, 60-6213-3,52-5414-3, 93-9414-5, 87-8915-1, 8415-1, 127
Ba
<200<200<200<200<200<200<200<200<200
840830970960960990
1300980980
1000
350350320220300300250
<200<200
300<200<200<200<200
320<200<200<200<200<200
Zr
8060347060
<40<40
60<40<40<40
50<40
50<40
60<40<40<40
110130907060
1009070907060
130200130120140170140250100
V
70805182593229534862303537311319273738
180150180140110130140130150110170120110100110160280220870120
Sn Mo
6.5<5.011.0
<5.010.013.012.010.0
5.76.4
1810.0
7.88.07.88.77.96.3
<5.0
<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0<5.0
Be
3.73.62.54.03.12.5
<l.O2.6
<l.O<l.O<l.O
2.62.53.22.12.52.22.31.2
<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O<l.O
Ge
<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5
<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5<5
The composition of pelagic zeolithic claystones andmudstones of Eocene age (Site 355), with low contentsof Mn, Fe, P, and several other elements, is quitedifferent from mid-Pleistocene muds and red clays ofthe Brazil Basin. It is proposed that they may not bepaleo red clays, but pelagic terrigenous muds,accumulated at the depths below the compensationlevel.
ACKNOWLEDGMENTSThe author expresses gratitude to Dr. P. Supko, Co-chief
scientist, Leg 39, for providing samples and for considerableassistance in preparation of this report and improving theEnglish. The author also expresses gratitude to Dr. Yu.Neprochnov for performing shipboard sampling and forassistance in preparation of this work. I am very muchobliged to colleagues and assistants, who conducted thechemical analyses.
REFERENCESBader, R.G. et al., 1970. Site 23. In Bader, R.G., Gerard,
R.D., et al., Initial Reports of the Deep Sea Drilling
491
E. M. EMELYANOV
TABLE 10Content of Rate Elements in the Recent Sediments of the Atlantic
Ocean near Leg 39 Sites, (10" 4%)
Station
375
400-2
Horizon(in cm)
0-3
0-7
Ba
200(460)
<200«200)
Cr
66(150)102
(103)
Zr
180(410)
90(90)
Ni
46(105)
65(66)
V
820(1870)1910
(1920)
Mo
<50
<50«50)
Ge
<50K114)<50
«50)
Be
<l.O«2.3)<l.O
(<l.O)
Sn
<β.O
<β.O(<β.O)
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Boström, K., Peterson, M.N.A., Joensuu, O., and Fisher,D.E., 1969. Aluminium-poor ferromagnesian sedimentson active oceanic ridges: J. Geophys. Res., v. 74, p. 3261-3270.
Boström, K., Joensuu, O., Valdes, S., and Riera, M., 1972.Geochemical history of South Atlantic ocean sedimentssince Late Cretaceous: Marine Geol., v. 12, p. 85-121.
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, 1973. Ooze distribution and composition on thesouthwestern African shelf. In Formation of biologicproductivity and bottom sediments in respect withpeculiarities of water circulation in the southeast part ofthe Atlantic Ocean, IOAN Reports, v. 95, Kaliningrad(Publishing House of Kaliningrad), p. 211-238.
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Sclater, J.G., Anderson, R.N., and Bell, M.L., 1971. Eleva-tion of ridges and evolution of the central eastern Pacific:J. Geophys. Res., v. 76, p. 7888-7915.
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492