DEEP SEA DRILLING PROJECT SITE 532, WALVIS RIDGE, …

26. CARBONATE AND ORGANIC-CARBON CYCLES AND THE HISTORY OF UPWELLING ATDEEP SEA DRILLING PROJECT SITE 532, WALVIS RIDGE, SOUTH ATLANTIC OCEAN1

James V. Gardner, U.S. Geological Survey, Menlo Park, CaliforniaWalter E. Dean, U.S. Geological Survey, Denver, Colorado

andChristine R. Wilson, U.S. Geological Survey, Menlo Park, California

ABSTRACT

Detailed carbonate and organic-carbon stratigraphies were constructed from samples collected every 20 cm in a250-m hydraulic piston core recovered at DSDP Site 532 on Walvis Ridge. This sampling interval represents about onesample every 5000 yr., based on sediment accumulation rates calculated from nannofossil biostratigraphic zones. Allsamples were analyzed for percent CaCO3, resulting in a detailed carbonate stratigraphy for the past 5.0 m.y. Thesamples for the top 110 m of section were also analyzed for organic carbon in order to construct a detailed organic-carbon stratigraphy for the last 2.5 m.y.

The recovered section has distinct dark-light color cycles with average periodicities of 55, 58, and 30 k.y. for theQuaternary, upper Pliocene, and lower Pliocene, respectively. Periodicities of carbonate cycles are similar to the colorcycles; most carbonate minima correspond to the dark parts of color cycles. The average periodicity for carbonate cy-cles is about 36 k.y. Darker parts of color cycles usually contain higher concentrations of organic carbon, but the organ-ic-carbon record does not follow the cyclicity of the color cycles in detail, at least for the last 2.5 m.y. Organic-carboncycles have an average periodicity of about 34 k.y. for the Quaternary and upper Pliocene.

The cycles of CaCO3 and color have periodicities similar to those reported from carbonate stratigraphies from thenortheast Atlantic, Caribbean, and eastern equatorial Pacific. The carbonate cycles at Site 532 are the result of externalforcing, probably related to global climate, that affected fluctuations in both sediment supply from the African con-tinental margin and productivity of siliceous organisms. The organic-carbon cycles have similar periodicities and simi-lar changes in periodicities to those of the CaCO3 cycles.

Semiquantitative estimates of diatom abundance from smear slides and concentrations of biogenic SiO2 calculatedfrom chemical analyses suggest that upwelling at Site 532 was minor until about 3 m.y. ago. The Benguela-Current up-welling system either began at that time or, more likely, migrated into the area of Site 532, where it prevailed until sometime between about 1.2 and 0.5 m.y. ago. The increase and decline of upwelling in the area of Site 532, however, did notdisturb the trend of cyclicities of carbonate and organic carbon. The latest change in conditions at Site 532 was an in-crease in intensity of bottom currents during the past 0.5 m.y. that winnowed nannofossils, diatoms, and clay and left alag deposit represented by a foraminifer-rich fades.

INTRODUCTION

Walvis Ridge is a structural spur that projects south-westward from the continental margin of South Africaoff Namibia and is beneath the cold, nutrient-rich, Ben-guela-Current upwelling system (Fig. 1). DSDP Site 532is located on the eastern part of Walvis Ridge at a waterdepth of 1331 m in a trough with a relatively thick sedi-ment section. The site is about 2 km from DSDP Site362 (Bolli, Ryan, et al., 1978) which was rotary drilled,but unfortunately the upper 200 m of the section is bad-ly disturbed. The data from Site 362, however, suggestthat increases in abundances of diatoms and organiccarbon may be linked to the onset and development ofthe Benguela-Current upwelling system (Bolli, Ryan, etal., 1978; Diester-Haass and Schrader, 1979; Siesser,1980). The Benguela-Current upwelling system appar-ently began about 10 m.y. ago in the early late-Miocene,with progressively more intense upwelling in the Plio-cene and Pleistocene. Seisser (1980) concluded that in-creases in diatoms and organic carbon reflect the estab- 3 0 ° -

10 15°

1 Hay, W. W., Sibuet, J.-C, et al., Init. Repts. DSDP, 75: Washington (U.S. Govt.Printing Office).

Figure 1. Map showing general bathymetry of the continental marginoff southwest Africa and locations of DSDP Sites 362 and 532.

905

J. V. GARDNER, W. E. DEAN, C. R. WILSON

lishment of the strong southeast trade winds that drivethe up welling system today.

Hydraulic piston coring at Site 532 recovered a nearlycontinuous section of late Neogene and Quaternary age.Biostratigraphic data from Site 532 indicate that all nan-nofossil zones of Ellis (1981) are present (Site 532 sum-mary chapter, this volume). The section from Site 532was divided into three lithostratigraphic subunits basedon relative proportions of siliceous and calcareous micro-fossils and nonbiogenic material (clay) (Fig. 2; see alsoSite 532 summary chapter, this volume). The amount ofclay steadily decreases from the bottom to the top of thesection. The section from 290 m (bottom of Hole 532B)to 114 m sub-bottom consists of nannofossil marl withrare (< 5%) planktonic foraminifers and rare (< 1 °7o) dia-toms. The section from 114 to 50 m sub-bottom consistsof nannofossil diatom marl that contains about equalamounts of diatoms, nannofossils, and clay (Fig. 2).The abundance of diatoms decreases and the abundanceof nannofossils increases above 50 m sub-bottom. Dia-

toms are rare above 20 m sub-bottom, and foraminifersincrease in abundance and make up more than 50% ofthe sediment at the top of the section (Fig. 2).

Preliminary shipboard descriptions of the section atSite 532 noted cycles of dark- and light-colored sedi-ment that contain abrupt changes in abundances of for-aminifers and diatoms (Site 532 chapter, this volume),but these changes in microfossil abundance are not sys-tematic within the color cycles. The concentration ofCaCO3, however, does change systematically within in-dividual color cycles and is highest in the lightest col-ored part of a cycle. The changes in color and abun-dances of siliceous and calcareous microfossils may re-flect changes in productivity associated with the intensi-ty of the Benguela Current up welling system. We there-fore chose this site to construct detailed carbonate andorganic-carbon stratigraphies to detect any cyclic varia-tions in CaCO3 and organic carbon that can be corre-lated with cyclic variations in other sediment parame-ters.

532 + 532B

I 1 5 0

• j Clay Nannofossils Foraminifers Diatoms Biogenic SiO2 SiO2:AI2O3 CaCO3 Organic carbon< E 0 30 60 90 0 40 80 0 40 80 0 20 40 60 0 8 16 24 2 4 6 8 10 0 25 50 75 100 0 2 4 6 8~ 0-

30 60 90 0 40 80 0 40 80 0 20 40 60 0 8 16 24 2 4 6 8 10 0 25 50 75 100 0 2 4 6 8Clay Nannofossils Foraminifers Diatoms Biogenic SiO2 SiO2:AI2O3 CaCO3 Organic carbon

Magnetic polarity

300

Nannofossil Nannofossil- Dolomiteooze or chalk foraminifer

ooze or chalk

Figure 2. Lithology, age, magnetics, percentages of nonbiogenic material (clay), nannofossils, foraminifers, diatoms, biogenic silica, CaCO3, andorganic carbon, and SiO2: A12O3 ratio, at DSDP Site 532. Percentages of clay, nannofossils, foraminifers, and diatoms are from smear-slide esti-mates (Site 532 summary chapter, this volume). Percent biogenic silica and the SiO2: A12O3 ratio are from Dean and Parduhn (this volume). Per-centages of CaCO3 and organic carbon are from Table 1. Smoothed curves through the smear-slide data were computed using a 5-point weightedmoving average. Smoothed curves through the CaCO3 and organic-carbon data were computed using a 15-point weighted moving average.

906

CARBONATE AND ORGANIC CARBON CYCLES

DESCRIPTION OF THE CYCLES

Color Cycles

The most noticeable characteristic of the sediment atSite 532 is the cyclic dark and light variations in sedi-ment color (Fig. 3). The upper 160 m of the section hasdark-light alternations mostly of yellow brown (hue5Y); the section below 160 m has cycles of light and darkchromas mostly of greenish olive (hue 10Y). The con-tacts between light and dark interbeds usually are grada-tional over about 10 to 20 cm. The overall color of thesection is lightest in the lower Pliocene, but becomesdarker in the middle Pliocene. The intensity and fre-quency of darker colored layers are highest in the earlyPliocene. The overall color again becomes lighter in theuppermost Quaternary. We determined the periodicitiesof the color cycles by counting the number of cycles be-tween time datums established by nannofossil zones.

9-1 9-2 9-3 9,CC 10-1 10-2 10-3 10-4

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150 L-

Figure 3. Photograph of Core 10, Hole 532.

The cycles have periodicities of 55, 58, and 30 k.y. forthe Quaternary, upper Pliocene, and lower Pliocene sec-tions, respectively.

Carbonate and Organic-Carbon CyclesThe entire section in Hole 532 was sampled at 20 cm

intervals for analyses of CaCO3. This sampling resultedin 1057 samples with an average sampling interval ofabout 5000 yr./sample. All samples were analyzed forCaCO3 using the gasometric technique of Hulsemann(1966). One-hundred fifty-three shipboard analyses ofCaCO3 by the carbonate-bomb method (Muller andGastner, 1971) from Holes 532 and 532B were mergedwith the larger gasometric data set (Table 1). Four-hundred and twenty of the 20-cm carbonate samples be-tween 0 and 109 m sub-bottom were also analyzed fororganic carbon by the LECO method (Table 2). An ad-ditional 50 analyses of organic carbon by Meyers, Bras-sell, and Hue, et al. (this volume) from the samestratigraphic interval were merged with the LECO data.The only analyses of organic carbon that we have forthe interval between 109 and 250 m sub-bottom arefrom Meyers, Brassell, and Hue (this volume).

The results of analyses of CaCO3 and organic car-bon, listed in Tables 1 and 2 and plotted in Figure 2,show that the average concentration of CaCO3 tends todecrease from about 60% at the bottom of the section toabout 25% at 55 m, and then to increase to almost 70%at the top of the section. Stratigraphic variations in or-ganic-carbon concentration are roughly opposite to thoseof CaCO3. Organic carbon increases from about 2% atthe bottom of the section, to a maximum of almost 4%at about 55 m sub-bottom. The most striking feature ofthe records, however, is the high-frequency fluctuationsof both CaCO3 and organic carbon.

Calcium carbonate cycles were defined as a section ofthe record between successive CaCO3 minima. These cy-cles correspond to the C cycles of Gardner (1982). Wedefine an organic-carbon cycle as the interval betweensuccessive maxima on the organic-carbon profile from 0to 109 m sub-bottom (0 to 2.4 m.y.) (Fig. 2).

We constructed profiles of CaCO3 and organic car-bon versus time using the ages assigned to nannofossilzones (Ellis, 1981; Site 532 summary chapter, this vol-ume). However, even though all late Neogene and Qua-ternary nannofossil zones were identified (Steinmetz andStradner, this volume), the nannofossil zonation usedis based on western equatorial Pacific floras (Ellis,1981), and they may not be strictly applicable to theeastern South Atlantic. We encountered problems whenwe plotted age as determined by the nannofossil zona-tion versus depth for Site 532. An apparent expandedsection with a sedimentation rate of iO6 m/m.y. was im-mediately preceded by an apparent abbreviated sectionwith a sedimentation rate of 5 m/m.y. (Fig. 4). WhenCaCO3 is plotted versus age using this time scale, artifi-cial expansions and compressions of parts of the sectionbecome apparent (Fig. 5A). We modified the zonationby using a correlation with the zonation of Martini(1971) (Fig. 6). The plot of age versus depth using theMartini zonation (Fig. 4) shows that the expanded andcompressed sections were not eliminated, but only

907


Table 1. Calcium carbonate data, Site 532.

Depth-m

. 20

.40

.60

.801.00

1.201.401.571.701.90

2.102.303.203.403.60

3.723.804.004.204.20

4.404.604.805.005.20

5.405.705.906.106.30

6.506.706.907.067.20

7.407.607.607.808.00

8.208.608.809.009.20

X CaC03

75.262.573.667.954.6

61.359.268. O64.964.2

58.164.552.256.363.6

67.061.460.558.262.3

62.659.858.354.957.7

61.562.865.967.958.1

64.752.944.038.O57.2

62.164.262.062.156.1

58.149.651.856.156.3

Depth-m

9.409.609.80

10.1010.19

10.3010.5010.7010.9011.10

11.3011.6011.8012.0012.20

12.4012.4612.6012.8013.00

13.0413.2013.4013.6013.80

14.0014.2014.4714.5014.70

14.9015.1015.3015.3015.50

15.7016.0016.2016.4016.60

17.0017.1817.4017.6017.80

% CaC03

64.669.466.071.273.0

76.869.974.963.856.1

64.961.861.660.866.8

65.558.O58.770.674.5

61.958.766.664.565.5

55.364.968.067.678.8

69.363.064.168.166.7

66.561.663.456.142.2

42.942.549.239,439.1

Depth-m

18.0018.1618.2018.4018.60

18.9019.1019.3019.5019.70

19.9020.1020.4020.6020.80

21.0021.1621.2021.4021.60

21.8022.0022.2022.4022.60

22.8023.0023.3023.5023.65

23.7023.9024.1024.3024.50

24.5424.8025.0025.2025.40

25.6025.8026.0026.2026.40

X CaC03

44.241.O39.436.730.8

61.641.446.942.344.7

42.532.657.363.372.6

78.970.O73.669.568.6

50.255.364.062.158.5

67.057.054.252.134.O

43.144.155.757.059.6

62.O56.253.256.160.4

71.668.055.045.546.3

Depth-m

26.6026.7526.8027.0027.20

27.4027.7027.9028.1028.30

28.5028.7028.9029.2029.40

29.6029.8030.6030.6030.75

30.8031.0031.2031.4031.60

31.8032.1032.3032.5032.60

32.7032.9033.1033.3033.60

33.8034.0034.2034.4034.96

35.0035.2035.4035.6035.80

X CaC03

48.640.O38.758.346.7

41.325.936.237.139.6

35.144.040.246.645.2

57.554.237.541.624.8

46.441.232.535.036.6

47.551.543.455.239.O

40.140.843.641.840.6

41.643.334.236.362.0

43.554.650.353.259.4

Depth-m

36.0036.2036.5036.7036.90

37.1037.3037.3837.5037.70

38.0038.2038.4038.6038.80

39.0039.0339.2039.4039.46

39.6039.8040.0040.2040.40

40.6040.9041.1041.3041.34

41.5041.7041.7541.9042.10

42.4042.6042.6442.8043.00

43.2043.9044.0044.2044.40

X CaC03

58.354.553.756.055.4

57.465.142.O63.861.5

61.663.354.159.763.0

58.058.O49.150.750.4

56.354.351.750.248.5

42.138.853.657.658.0

43.849.950.O57.859.6

50.648.150.051.344.9

32.031.639.044.534.6

Depth-m

44.6044.8045.0045.3045.50

45.7045.7945.9046.1046.30

46.5046.8047.0147.1347.20

47.4047.6047.8048.0048.09

48.2048.3048.4048.4448.60

48.7948.8049.0049.2049.40

49.6049.8150.0050.1950.21

50.4050.6050.8051.1051.30

51.5052.6052.8053.0053.09

X CaC03

28.639.236.236.128.8

41.853.058.548.431.0

36.545.454.041.O51.8

61.657.237.937.655.0

35.946.640.734.742.3

42.041.345.655.456.0

53.553.732.633.034.3

20.116.922.333.927.8

31.530.828.527.925.0

Depth-m

53.2053.4053.6053.8054.10

54.3054.4354.5054.7055.60

55.8056.0056.2056.2956.40

56.6056.7757.0057.2057.40

57.6057.8058.0058.2058.51

58.6858.7058.9059.1059.30

59.5059.7060.1060.2860.30

60.5060.7060.9061.4061.60

61.8062.0062.2062.4062.60

X CaC03

26.326.224.722.726.6

23.527.032.523.238.5

31.922.235.941.034.0

40.651.923.034.825.1

34.533.526.315.311.6

15.019.425.312.838.6

44.331.243.444.046.4

47.344.839.436.027.8

26.831.619.423.130.3

moved from the lower Pliocene to the upper Pliocene.Because all of the nannofossil zones and sub-zones ofEllis (1981) were identified, and because we found nosedimentological evidence for a greatly expanded sec-tion, nor any indication of an unconformity, we devel-oped a preferred zonation for Site 532, based mainly onthe Martini (1971) time-scale (Fig. 6).

Successive age datums from our preferred zonationwere used to calculate an average sedimentation rate be-tween datums. Each sample was then assigned an ageby linear interpolation. The resulting plots of percentCaCO3 and organic carbon versus age are shown inFigures 5B and 5C. We subdivided the age axes of theCaCO3 and organic carbon versus age plots into 0.5m.y. intervals and counted the number of cycles in each0.5 m.y. segment. We calculated the average percent-ages of CaCO3, organic carbon, and biogenic silica foreach 0.5 m.y. interval (Table 3). We also calculated theperiodicities of CaCO3, organic carbon, and dark beds(Table 4).

The periodicities of the CaCO3 cycles (Table 4) rangefrom a low of 26 k.y. to a maximum of 49 k.y. and aver-

age about 36 k.y. Most of the CaCO3 minima corre-spond to the dark parts of color cycles (Figs. 3 and 5B),and most of the maxima correspond to the lightest partsof color cycles.

The periodicities of the organic-carbon cycles (Table4) range from 28 k.y. to about 36 k.y., with an averageof about 34 k.y. for the interval 0 to 2.5 my. Althoughall dark-colored beds correspond to an organic-carbonmaximum, the relationship between organic-carbon con-centration and dark and light beds is not so clear as forCaCO3. Many of the organic-carbon maxima do not ap-pear to correspond to a dark bed. As a result, the organ-ic-carbon cycles have a higher frequency (shorter peri-od) than those of the dark beds (Table 4).

The CaCO3 and organic-carbon profiles (Fig. 2) alsoshow lower frequency cycles on a scale of 5 to 10 mthick, which corresponds to an average periodicity ofabout 150 k.y. These longer cycles are best seen in thesmoothed curves for parts of the profiles between 40and 80 m sub-bottom (Figs. 2 and 10).

A color cycle just over 2 m long from Core 10, Sec-tion 2, to Core 11, Section 1 (mid-Pleistocene) was

908


Table 1. (Continued.)

Depth-m

62.8863.0663.1063.3063.50

63.7063.9064.1064.3964.54

64.6164.8065.0065.2065.40

65.6065.7565.8065.9066.00

66.2066.3966.6066.7866.80

67.0067.3067.5067.7067.90

68.1068.3068.3268.5068.80

69.0069.0169.2069.4069.60

69.8070.0070.2070.4070.60

X CaCO3

35.527.028.220.914.4

20.931.430.140.442.0

42.534.728.735.639.4

38.239.827.239.127.7

43.252.353.748.049.4

50.046.134.446.735.0

28.623.419.O38.128.4

25.029.833.527.231.3

48.228.422.833.845.8

Depth-m

70.8171.0071.2071.4071.70

71.9072.1072.3072.3172.50

72.7072.9073.2073.4073.60

73.8073.8173.9174.0074.20

74.6074.8075.0075.2075.31

75.4075.6075.8076.1076.30

76.5076.7076.8176.9077.10

77.3077.6077.8078.0078.20

78.4078.6078.8079.0079.18

X CaCü3

43.045.743.741.134.0

35.538.336.632.036.8

38.339.647.246.247.3

52.847.O32.043.637.2

30.328.114.013.521.O

30.138.940.132.134.3

26.327.520.O26.428.3

37.841.620.629.934.8

38.740.739.543.542.5

Depth-m

79.4079.6079.8080.0080.20

80.5080.7080.9081.1281.30

81.4981.6881.8082.0082.20

82.4082.6082.6982.8083.00

83.4083.6083.8083.9084.00

84.2184.4084.6084.9085.10

85.3085.5186.4086.6086.80

86.9187.0087.2087.4187.60

87.8088.0088.2088.4088.60

X CaC03

38.934.037.340.339.8

45.954.649.239.029.4

19.126.239.339.138.7

37.732.828.O34.534.3

38.835.533.031.O35.8

28.329.935.436.340.1

40.741.526.528.636.9

31.036.738.536.940.0

42.640.141.741.542.3

Depth-m

88.8089.0089.3089.3989.50

89.7089.9090.1090.3090.50

90.8091.0091.2091.4091.48

91.6091.8092.0092.2092.30

92.4092.6092.8093.0093.20

93.3693.4093.7093.9094.10

94.3094.5094.7094.8694.90

95.2095.4095.6095.9796.00

96.2096.3096.4096.4096.60

% CaC03

32.133.116.48.0

41.3

42.138.036.338.136.8

49.849.049.753.248.0

52.258.753.043.150.8

46.142.543.741.643.2

40.O40.837.935.939.4

46.453.345.941.O44.3

31.319.428.429.435.8

34.332.O41.541.543.6

Depth-m

96.8096.9997.0297.2097.40

97.6097.8098.1098.3098.50

98.7098.9099.1099.3099.60

99.7499.80

100.00100.20101.00

101.20101.40101.60101.80101.89

102.00102.20102.50102.70102.90

103.10103.30103.50103.57103.70

104.00104.20104.40104.60104.73

104.80105.40105.60105.71105.80

% CaC03

56.645.O46.351.952.6

59.463.852.051.047.8

53.854.059.458.262.0

58.O61.862.263.057.6

56.255.761.457.555.O

58.356.752.654.651.4

48.749.348.750.O56.9

50.750.748.544.723.038.939.826.011.O10.2

Depth-m

105.98106.20106.40106.60106.90

107.10107.21107.30107.50107.70

107.90108.10108.30108.43109.80

110.00110.09110.20110.40110.60

110.80111.00111.15111.30111.50

111.70111.90112.10112.30112.50

112.80113.00114.20114.40114.60

114.80114.86115.00115.20115.41

115.70115.90116.10116.16116.30

X CaC03

24.041.752.347.051.2

42.831.O25.3

8.723.0

47.654.746.156.546.0

46.540.O41.534.231.0

28.139.745.047.342.2

34.942.641.940.735.9

32.633.343.444.142.6

42.732.038.943.738.6

47.437.810.113.O40.6

Depth-m

116.36116.50116.70116.91117.20

117.40117.60117.80117.92118.40

118.60118.78119.08119.12119.30

119.50119.70119.90120.00120.10

120.29120.56120.80121.00121.20

121.40121.60121.80122.00122.20

122.40122.50122.70122.90123.10

123.90124.05124.23124.43127.60

128.00128.20128.41128.60128.80

% CaC03

34.035.131.525.431.8

26.844.933.136.92b\2

32.025.527.029.533.2

29.026.434.655.138.2

29.932.236.936.736.6

28.334.334.533.131.4

45.O47.150.148.l35.0

25.027.738.950.767.4

54.955.252.242.339.4

studied in detail. Figure 7 is a composite of data for thisinterval (Site 532, Meyers, Brassell, and Hue, this vol-ume and this chapter).

The color changes from moderately light values at41.5 and 44 m sub-bottom to very dark values at 41.3and 43.5 m sub-bottom (Fig. 7). The lower dark sectionat 43.5 m has moderate concentrations of CaCO3 andlow Rock-Eval S2 values (see discussion below for ex-planation of Rock-Eval). The section from 43.5 m to41.5 m sub-bottom shows a steady trend to lighter col-ors and an increase in CaCO3 from a low of 23% at43.4 m to more than 50% between 42.9 m and the top ofthe cycle. For some reason there is no decrease in per-cent CaCO3 that corresponds to the sharp upper colorchange that marks the boundary with the overlying cy-cle. In most other cycles, a marked color change is ac-companied by a sharp change in percent CaCO3.

The concentration of organic carbon decreases fromover 4% in the dark beds to about 1% at 41.3 m. Forthis cycle, there is a good correspondence between colorand organic-carbon concentration. As mentioned above,however, not all organic-carbon maxima correspond todark beds. Figure 7 shows that, in general, there is agood correspondence between CaCO3 and organic car-

bon, which recapitulates the general inverse relationshipbetween these two variables over the entire section atSite 532 (see Figs. 10 and 11).

The Rock-Eval S2 values (in mg of hydrocarbons perg of sediment) is a rough estimate of the amount oflipid-rich marine organic matter. When normalized tothe amount of organic carbon in the sediment, the S2values give the hydrogen index in mg hydrocarbons perg organic carbon (Tissot, et al., 1974). The decrease inS2 values from the darker base to the lighter top of thecycle, therefore, suggests a change from more to lesslipid-rich organic matter upward in the cycle. Althoughthere appears to be differences in type of organic matterwithin individual cycles, shipboard and shorebased Rock-Eval studies and the shorebased studies of humic acidsshow that most of the organic matter at Site 532 is de-rived from marine sources (Meyers, Brassell, and Hue,this volume).

Mass Accumulation Rates

We calculated mass accumulation rates (MAR; g/cmVm.y.) for each 0.5 m.y. interval in order to elimi-nate the effects of compaction and to examine the influxrates of bulk sediment, CaCO3, biogenic silica, organic

909



Depth-m

128.84129.10129.30129.50129.54

129.70129.90130.10130.29130.58

130.60130.80131.00131.20131.40

131.91132.00132.20132.20132.40

132.60132.80133.00133.20133.50

133.70133.76133.90134.10134.30

134.50134.70134.77135.00135.20

135.40135.60135.80136.00136.20

136.40136.60136.90137.10137.30

% CaCO3

21. O28.831.216.112.O

24.939.944.038.946.0

48.045.127.336.239.5

20.O9.2

27.460.025.4

33.042.250.944.434.5

33.926.037.736.350.5

46.059.362.O60;445.1

56.755.150.458.755.8

55.949.046.639.639.6

De pt h-m

137.31137.50137.70137.90138.10

138.40138.60138.61138.80139.00

139.20139.40139.40139.60139.80

140.00140.20140.39140.41140.60

140.90141.10141.19141.30141.41

141.50141.70141.90142.10142.29

142.44142.80143.00143.20143.40

143.60143.80144.00144.30144.50

144.70144.90145.04145.10145.30

X CaC03

39.043.652.857.060.5

55.560.159.057.351.1

42.448.050.452.338.3

36.446.955.453.054.6

50.837.433.039.425.0

45.446.842.644.351.8

61.857.254.137.537.8

40.429.432.236.751.0

57.756.355.053.247.2

Depth-m

145.49145.80146.00146.20146.30

146.40146.60146.80147.00147.20

147.31147.40147.60147.80148.00

148.30148.50148.70148.90149.10

149.30149.50149.80150.00150.20

150.44150.60150.80151.00151.20

151.42151.60151.69151.80152.00

152.30152.49152.50152.70152.90

153.63153.76154.00154.20154.40

X CaC03

50.137.345.137.843.0

46.254.942.053.051.8

53.051.954.055.554.3

55.049.142.928.944.6

38.732.641.643.351.3

53.354.144.654.061.9

51.959.354.053.648.5

43.140.O41.644.853.8

37.837.444.648.856.6

Depth-m

154.45154.60154.80155.00155.20

155.49155.70155.80155.90156.10

156.30156.50156.71156.94157.00

157.20157.60157.80158.00158.20

158.50158.70158.90158.91159.10

159.30159.50159.68160.00160.20

160.40160.60160.80161.00161.00

161.20161.20161.40161.55161.60

161.80162.00162.20162.50162.70

X CaC03

57.057.653.452.848.1

47.635.429.O45.646.2

47.2hi .148.155.752.8

52.348.347.557.155.6 *

56.745.145.047.151.4

56.463.257.963.158.1

57.760.268.556.169.9

56.566.843.137.O41.5

53.954.251.649.546.2

Depth-m

162.90163.10163.30163.50163.70

164.00164.20164.40164.55164.60

164.80165.00165.20165.40165.60

165.80166.00166.20166.40166.60

166.84167.10167.30167.50167.70

167.90168.10168.24168.40168.60

168.80169.00169.20169.43169.43

169.80170.00170.20170.40170.60

170.80171.00171.30171.50171.70

% CaC03

36.944.347.941.548.9

45.139.853.851.O53.2

51.144.442.443.550.1

45.747.145.544.344.5

34.249.851.052.545.4

39.728.727.O39.949.4

46.048.345.048.853.2

53.652.058.452.954.4

51.839.646.449.251.9

Depth-m

171.81171.89171.90172.10172.30

172.48172.50172.80173.00173.21

173.40173.60173.80174.20174.40

174.60174.71174.80175.00175.17

175.20175.40175.70175.90176.10

176.33177.20177.40177.60177.82

178.00178.20178.40178.60178.80

179.00179.20179.40179.60179.80

180.10180.30180.50180.70180.90

% CaC03

58.054.055.948.548.1

40.034.054.654.547.7

43.137.848.044.946.4

47.850.O48.743.338.0

37.448.653.961.054.3

52.243.048.645.445.5

43.844.234.736.642.1

38.144.949.544.542.2

40.036.136.652.346.4

Depth—m

181.10181.30181.60181.76181.80

182.00182.20182.40182.50182.60

182.80183.00183.20183.40183.60

183.80183.96184.00184.20184.50

184.70184.72184.90187.00187.20

187.40187.58187.80187.81188.00

188.20188.50188.70188.90189.10

189.30189.31189.50189.67190.00

190.20190.40190.60190.76190.80

X CaC03

47.247.744.830.O29.4

42.852.952.953.052.5

55.063.262.761.660.7

53.355.048.456.767.4

71.168.071.263.252.3

61.068.573.O72.973.0

61.460.948.452.937.9

44.048.048.453.253.2

49.654.857.055.O55.9

carbon, and clay (Table 5). Average accumulation rateswere calculated for each time interval (length of sectionin m/0.5 m.y.), and the average dry bulk density foreach interval was calculated from porosity data (Site532, this volume) according to the equation:

Dry bulk density (DBD) = (1 - porosity /100)2.7, (1)

where 2.7 is the assumed average grain density (Rea andJanecek, 1981). Values of DBD are in g/cm3, and ifmultiplied by 100 are in units of g/cmVm of section.Values of DBD/m of section, when multiplied by theaverage accumulation rates in m/m.y. give MAR valuesfor bulk sediment in units of g/cm2/m.y. (Table 5). Theoverall equation, therefore, for calculating bulk sedi-ment MAR is:

ma-ray attenuation porosity evaluator (GRAPE) rela-tionship between DBD and WBD is:

DBD = WBD - (0.01025 × porosity) (3)

Bulk sediment MAR (g/cm2/m.y.) =(accumulation rate) × 100 ×

(1-porosity/100) × 2.7 (2)

An alternate method of obtaining DBD is to use thewet-bulk density (WBD) obtained from shipboard gam-

(van Andel et al., 1975). Both methods involve assump-tions: Equation (1) assumes a grain density of 2.7 g/cm3

and Equation (3) relies on GRAPE data. Because of theuncertainties in GRAPE data, we chose to use MARvalues calculated by Equation (1).

The next step was to determine the MARs for in-dividual sediment components using average measuredpercentages of CaCO3, organic carbon, and biogenicsilica (opal) for each interval in Table 5. Average con-centrations of CaCO3 and organic carbon for each0.5 m.y. interval were taken from Table 3.

Data for percent biogenic silica (percent opal) wereobtained by two different methods. First, the total per-centages of siliceous biogenic components were takenfrom smear-slide estimates (Fig. 2; Site 532 summarychapter, this volume) and averaged for each interval.The second estimation of biogenic silica was obtainedfrom analyses of SiO2 and A12O3 by X-ray fluorescence

910



Depth-m

191.25191.40191.60191.80192.10

192.30192.50192.59192.70192.90

193.10193.30193.60193.80194.00

194.20194.39194.50194.59194.80

195.10195.30195.50195.80196.00

196.20196.24196.40196.60196.80

197.00197.30197.50197.68197.90

198.10198.30198.50198.52198.65

198.80199.00199.20199.40199.60

Z CaCü3

53.950.753.164.061.0

55.654.956.O56.554.0

54.757.161.162.357.2

56.353.941.O49.750.2

54.360.961.736.251.3

62.062.O62.561.255.3

52.347.250.059.666.7

59.959.542.034.033.0

46.8

55.6

52.6

59.9

51.5

Dept h-m

199.80

200.00

200.20

2UO.3O

200.40

200.60

200.81

201.00

201.30

201.50

201.70

201.90

201.96

202.80

203.00

203.20

203.40203.60

203.80203.80

204.00

204.20204.42

204.43

204.60

207.80

208.00

208.20

208.40

208.60

208.80

209.00209.04

209.30

209.50

209.70

209.85209.90

210.10

210.30

210.49

210.80

210.99

211.20

211.80

% CaCO3

53.6

56.4

53. J

55.052.4

52.050.450.654.061.9

b2.655.755.O59.454.5

59.252.651.740.551.3

56.746.946.021.018.2

57.343.642.545.945.0

46.447.061.O48.455.7

64.263.O64.162.768.2

65.360.036.032.466.4

Depth-m

212.00212.20212.24212.40212.60

212.80213.00213.30213.50213.70

213.90214.10214.30214.51214.80

215.00215.20215.40215.60215.78

220.20220.40220.60220.80220.81

221.00221.20221.40221.70221.90

222.10222.30222.50222.70222.90

223.20223.40223.60223.80224.00

224.20224.40224.60224.80225.00

% CaC(J3

71.165.244.056.260.6

58.266.562.959.258.1

63.554.450.148.558.7

51.454.158.056.455.7

67.469.771.170.247.O

70.562.769.865.959.9

67.970.174.973.468.4

70.067.666.766.165.3

65.568.266.569.667.4

Depth-m

225.09225.20225.40225.70225.90

226.10226.30226.50226.59226.71

226.90227.20227.40227.60228.20

228.40228.60228.80229.00229.20

229.40229.70229.84229.90230.10

230.30230.50230.70230.90231.20

231.40231.60231.79232.00232.20

232.40232.49232.60232.82233.10

233.30233.50233.69233.71234.60

X CaC03

64.O64.466.366.266.7

63.266.854.148.O46.6

53.154.553.257.254.6

51.862.861.462.465.1

65.552.947.O48.961.4

63.860.360.868.369.4

71.964.464.265.562.6

58.949.046.159.863.5

60.865.162.060.965.6

Depth-m

234.802 35.00235.00235.17235.20

235.40235.472 35.60235.81236.00

236.20236.50236.70236.90236.97

237.12237.31238.06238.25238.60

238.80239.00239.20239.48243.00

243.20243.40243.60243.80244.00

244.20244.51244.67244.72244.90

245.10245.30245.50245.70246.00

246.07246.20246.43246.60246.97

% CaC03

61.363.064.758.255.9

63.260.O60.566.968.4

66.661.757.140.932.0

37.043.645.749.055.0

54.558.356.353.540.1

41.747.246.948.043.4

43.445.048.648.049.1

51.248.645.446.949.1

49.051.549.649.251.4

Depth-m

247.30247.49

% CaC03

50.448.9

• = Shipboard CaCO3 Bomb Analysis

(XRF) (Dean and Parduhn, this volume). A plot of theSiO2:Al2O3 ratio (Fig. 2) shows that there is a baselinelow of about 3.3 in those parts of the section where nosiliceous biogenic debris was detected in smear slides(Fig. 2). We assumed therefore that an average SiO2:A12O3 ratio of 3.3 is representative of nonbiogenicalumniosilicates that were deposited at Site 532. Non-biogenic SiO2 was then calculated according to the equa-tion:

Nonbiogenic SiO2 = (% A12O3) × 3.3 (4)

Biogenic SiO2 was calculated according to the equation:

Biogenic SiO2 = (total SiO2) - (nonbiogenic SiO2). (5)

Bostrom et al. (1972) used the same method for calcu-lating opaline silica in sediments from the South At-lantic, but assumed a SiO2:Al2O3 ratio of 3.1, that ofaverage continental crust. Both smear-slide data andXRF-derived biogenic silica show similar trends (Fig. 2),

but the smear-slide estimates usually are higher. We pre-fer the estimates calculated from the XRF data becausesmear-slide data are volume estimates that are semi-quantitative at best and usually tend to overestimatepercentages of siliceous biogenic components, particu-larly if volume estimates of this high-porosity compo-nent are then used for weight-percent calculations.

The component MARs were calculated according tothe equation:

Component MAR = (bulk sediment component MAR)× (fraction of component) (6)

The clay MAR for each interval was calculated by thedifference between the bulk-sediment MAR for the in-terval minus the sum of MARs for CaCO3, biogenicSiO2, and organic carbon. Component MARs are tabu-lated for each 0.5 m.y. interval in Table 5. The MARsare plotted versus time in Figure 8 in order to show gen-eral trends in MAR for each component with time. Theindividual MARs will be discussed in the section on up-welling intensity and organic productivity.

911


Table 2. Organic carbon data, Site 532.

Depth-m

.20

.40

.60

.801.00

1.201.401.571.701.90

2.102.303.203.403.60

3.804.004.204.404.60

4.805.005.205.405.70

5.906.106.306.506.70

6.907.107.207.407.60

7.808.008.208.608.80

9.009.209.409.609.80

2 C-org.

1.633.382.102.774.70

3.784.103.663.674.82

5.254.294.023.272.94

3.223.263.403.133.18

3.233.543.283.123.84

3.132.773.742.394.02

5.172.7O3.412.612.73

2.70O3.283.524.044.03

3.202.843.222.973.69

Depth-m

10.1010.2010.3010.5010.70

10.9011.1011.3011.4011.60

11.8012.0012.2012.4012.46

12.6012.8013.0013.0413.20

13.4013.6013.8014.0014.20

14.5014.7014.9015.1015.30

15.5015.7016.0016.2016.40

16.6016.8017.0017.1817.20

17.4017.6017.8018.0018.20

% C-org.

2.57.99*

1.522.131.73

2.123.402.393.282.93

2.643.002.252.463.28

4.322.401.662.453.78

2.302.272.223.242.42

1.951.482.632.852.58

2.552.623.212.753.08

5.023.346.415.324.883.945.305.666.085.85

Deptti-m

18.4018.6018.9019.1019.30

19.5019.7019.9020.1020.40

20.6020.8021.0021.1621.20

21.4021.6021.8022.0022.20

22.4022.6022.8023.0023.30

23.5023.7023.9024.1024.30

24.5024.8025.0025.2025.40

25.6025.8026.0026.2026.40

26.8027.0027.2027.7027.90

X C-org.

4.9h7.433.705.484.99

5.895.394.666.054.42

2.861.681.301.982.05

2.632.824.013.592.75

3.353.212.774.385.90

5.686.064.573.453.05

2.362.744.344.083.65

2.553.183.833.913.26

2.882.232.564.954.22

Depth-m

28.1028.3028.5028.7028.90

29.2029.4029.6029.8030.60

30.7530.8031.0031.2031.40

31.6031.8032.1032.3032.50

32.6032.7032.9033.1033.30

33.3533.6033.8034.0034.20

34.4034.9635.0035.2035.40

35.6035.8036.0036.2036.50

36.7036.9037.1037.3037.38

X C-org.

4.394.615.063.915.32

3.483.823.585.164.42

5.664.724.114.894.48

4.103.264.465.152.03

1.703.072.923.613.80

3.64*5.025.144.185.33

4.482.013.652.792.30

2.422.041.722.342.84

2.613.682.911.963.57

üepth-m

37.5037.7038.0038.2038.40

38.6038.8039.0039.0339.20

39.4039.4639.6039.8040.00

40.2040.4040.6040.9041.10

41.3041.3441.5041.7041.80

41.9042.1042.4042.6042.80

43.0043.2043.6043.9044.00

44.2044.4044.6044.8045.00

45.3045.5045.7045.8045.90

2 C-org.

1.721.902.251.722.88

2.201.751.201.162.28

3.502.591.751.792.20

2.222.662.984.182.05

1.381.261.971.902.20

1.931.822.633.143.13

3.354.044.304.062.63

2.564.063.903.182.99

3.895.012.891.80O2.15

Depth-m

46.1046.3046.5046.7046.80

47.0147.1347.2047.4047.60

47.8048.0048.0948.2048.30

48.4048.4448.6048.8049.20

49.4049.6049.8150.0050.20

50.3050.4050.6050.8051.10

51.3051.5052.6052.8053.00

53.0953.2053.4053.6053.80

54.1054.3054.4354.5054.70

X C-org.

3.385.825.306.51O3.64

2.195.522.472.633.65

6.046.421.883.942.48

3.266.592.672.981.69

1.462.602.474.673.91

5.045.465.254.833.59

4.314.284.454.374.22

3.483.633.913.563.75

2.963.402.742.243.12

Deµth-m

55.6055.8056.0056.2056.30

56.4056.6056.7756.8057.00

57.2057.4057.6057.8058.00

58.2058.5158.6858.7058.90

59.1059.3059.5059.7060.10

60.2860.3060.5060.7060.90

61.4061.6061.8062.0062.20

62.4062.6062.8863.0063.10

63.3063.5063.7063.9064.10

X C-or/.

2.442.974.693.202.65O

3.152.42

.991.52O4.68

3.844.723.272.824.20

7.617.615.916.475.76

7.233.683.925.574.00

2.682.622.893.234.29

3.564.334.384.106.39

4.574.252.633.45O3.57

6.337.616.274.324.72

DISCUSSION

Origin of the CaCO3 and Color Cycles

Carbonate cycles can result from CaCO3 dissolution,dilution of CaCO3 by noncarbonate material, or changesin carbonate productivity. Carbonate dissolution is notan important cause of the cycles at Site 532 because thesite is only 1331 m deep, and the calcareous nannofossilsare moderate to well preserved with no apparent signs ofdissolution (Site 532 summary chapter, this volume).The magnitudes and trends of the periodicities of theCaCO3 cycles at Site 532 are similar to those from thewestern Caribbean and eastern equatorial Pacific (Gard-ner, 1982). The similarities of CaCO3 periodicities fromsuch widespread areas suggest that productivity, prob-ably a local effect, is not a controlling factor in theCaCO3 cycles. Dilution of CaCO3 by fine-grained ter-rigenous material is a possibility for control of theCaCO3 cycles at Site 532 because the area is on the con-tinental margin of Africa. However, dilution by noncar-bonate terrigenous material implies fluctuations of eu-static sea level as the probable primary mechanism.

The fact that the darker layers contain more clay thanthe lighter layers suggests that there was at least somedilution by terrigenous elastics. Also, even though thedark layers usually contain the highest concentrations ofbiogenic silica, this is not true for all cycles, and smear-slide data usually do not show systematic variations insiliceous biogenic debris within cycles. Semiquantitativeestimates of clay abundance from smear slides show thatclay content of dark interbeds is about 25% comparedwith about 10% in the lightest parts of light-colored,high-CaCO3 interbeds. This difference represents a 150%increase in clay content between lighter and darker in-terbeds. A 175% increase in noncarbonate dilution isneeded to reduce the higher concentrations of CaCO3 indark-colored interbeds. This 175% calculated dilutionof CaCO3 is reasonably close to the semiquantitativesmear-slide estimate of clay increase, which suggeststhat dilution by terrigenous elastics alone could accountfor the dark interbeds of the CaCO3 cycles.

The range of periodicities of the CaCO3 at Site 532(26 k.y. to 49 k.y.) is similar to that of CaCO3 cyclesfrom Neogene and Quaternary sections from the eastern

912



Depth-m

64.3964.5064.6164.8065.00

65.2065.4065.6065.7565.90

66.0066.8067.0067.5067.70

68.3068.3068.8069.0069.01

69.4069.8070.0070.8071.40

71.9072.3072.3172.5072.70

72.9073.6073.8073.9074.00

74.2074.6074.8075.0075.20

75.3075.6075.8076.3076.50

X C-org.

3.482.01O3.584.835.50

4.053.934.234.113.86

4.282.46O2.013.022.27

2.655.004.982.97O4.02

6.132.695.343.15O3.13

3.802.783.202.772.48

2.472.602.083.06O4.44

4.274.304.255.964.78

4.12O2.933.053.974.56

Depth-m

76.7076.8176.9077.1077.80

78.0078.2078.4078.6080.00

80.2080.5080.7080.9081.10

81.3081.4981.6882.0082.20

82.4082.6082.8083.0083.60

83.8083.9084.0084.2184.40

84.6084.9085.1085.3085.51

86.6086.8086.9087.0087.41

87.6087.8088.6088.8089.30

Z C-org.

4.90

4.303.394.195.61

4.543.573.003.092.49

2.482.882.872.294.02O

2.473.342.502.042.22

2.572.552.703.324.56

4.413.15O3.824.313.78

3.113.092.622.342.59

4.392.684.91O3.012.93

2.754.354.294.965.85

Depth-m

89.3989.4089.5089.9090.10

90.3090.5090.8091.0091.20

91.4091.5091.6091.8092.00

92.3093.2093.4094.1094.30

94.5094.7094.8694.9095.20

95.4095.6095.9796.3096.40

96.8097.0297.6098.1098.50

98.9099.6099.7099.80

100.00

101.00101.40101.60101.80101.90

Z C-org.

6.355.90O3.073.243.44

3.063.612.211.962.10

1.601.36O1.781.771.68

2.051.692.56O2.052.12

1.583.43

4.124.564.91

6.193.30

2.542.76O2.75

1.552.771.822.261.87

2.161.474.05O1.291.60

1.822.411.41

• 1.582.31O

Depth-m

102.00102.50102.90103.10103.30

103.57103.70104.00104.20104.40

104.60104.73105.40105.60105.71

105.80105.98106.60106.90107.10

107.21107.50107.70108.10108.30

108.43110.09111.20114.86116.10

116.16116.40119.10119.90120.10

120.29122.40122.70123.90128.00

128.80129.50129.54129.60129.70

Z C-org.

1.26.96

1.231.951.92

2.651.632.382.263.21

2.91

3.403.696.02

6.04

5.836.222.82Il882.24

3.037.656.171.251.77

1.472.471.56O

3.876.08

4.481.99O2.26O2.531.78

3.082.51O2.444.442.47

5.175.845.873.71O4.89

üepth-m

130.60131.20131.91132.00133.80

135.40136.00136.60137.30137.50

138.60139.40140.40140.60141.20

141.41145.00146.00146.30147.30

147.60148.70149.10150.44150.60

152.60154.50154.80155.49155.80

158.90159.40161.55167.50168.24

171.80171.89172.50174.70175.20

175.30175.70180.80182.50184.00

% C-org.

2.26O3.32

5.867.001.8UO

1.241.042.022.98O1.98

.8001.50

.91O1.31O2.13O

5.542.17O2.363.27*2.47O

2.003.872.501.781.94

2.31O.94O

2.022.63

3.12

1.31O3.56O

2.992.37O

4.11

1 . 9 1 O

1.542.901.16O3.22O

3.92O2.394.24O

1.692.20O

Depth-m

184.70189.30190.80195.30196.30

198.50200.30202.00203.60204.42

204.60209.04209.85211.20212.24

214.50220.81229.00229.84232.49

236.97237.20242.10242.30244.72

250.30250.80254.00257.70258.50

260.20262.00262.30267.10269.10

270.60272.00273.50277.20277.90

281.50284.60285.60287.10290.00

Z C-or«.

.55O2.04O1.75O

2.59.93*

3.75O1.65O

.45O2.02O2.24

3.99

2.021.034.092.86

2.24O

3.95• 68O

1.99*2.20

3.112.06O1.69O2.66O1.23*

1.66O1.43

.57O2.17O2.92O

1.84O1.44O

• 21O3.27O2.15O

2.61O.68O.38O

2.HO2.85O

.14O

.500

.98O

.1002.no

• = Shipboard CHN Analysis

O - Shorebased CHN Analysis

equatorial Atlantic (Dean et al., 1981), Western Carib-bean (Gardner, 1982), and eastern equatorial Pacific(Gardner, 1982). Carbonate cycles with periods of about41 k.y. are common in late Quaternary deep-sea sedi-ment and are almost certainly related in some way to theEarth's orbital cycle of obliquity (tilt of the Earth'saxis), which has been suggested as one of the main driv-ing forces behind long-term climatic change (Broeckerand van Donk, 1970; Hays, et al., 1976). One of themanifestations of global climate change is variations inglobal ice volume and, therefore, in changes in globalsea level. Studies of fluctuations in the composition ofoxygen isotopes in benthic foraminifers from Quater-nary deep-sea sediment have related them to fluctua-tions in global ice volume and hence global sea level(Shackleton, 1967). These studies have been extendedinto the Pliocene (Prell, 1982), and arguments have beenpresented that oxygen-isotope fluctuations throughoutthe Tertiary are related to fluctuations in global ice vol-umes (Matthews and Poore, 1980; Matthews, in press).Climate-related sedimentary cycles are not unique tothe Quaternary, but extend well back into the Tertiary

(Dean et al., 1977 and 1981; Clifton, 1980) Mesozoic(Fischer, 1964; Dean et al., 1977; Arthur and Fischer,1977; McCave, 1979; Arthur, 1979), and even the Paleo-zoic (Anderson, 1982). These sedimentary cycles fromdifferent geologic periods and from widely scatteredareas, but all with somewhat similar periodicities, aremost likely coincident with, if not the result of, changesin eustatic sea level.

Furthermore, the CaCO3 cycles at Site 532 are pres-ent at the base of the recovered section and continuethroughout the section. Changes in periodicity of CaCO3cycles at Site 532 (Table 4) at first appear to correspondto other changes in sediment character, such as the largepulse of siliceous biogenic debris in the upper Pliocenesection or the large decreases in clay and CaCO3 MARsin the mid-Pliocene section (Fig. 8). However, the peri-odicities of the CaCO3 and organic-carbon cycles at Site532 are similar in magnitude to the CaCO3 cycles atSites 502 and 503 in the western Caribbean and easternequatorial Pacific (Fig. 9). In addition, trends ofchanges in periodicity with time are also similar at allthree sites. The similarities of magnitudes and trends of

913


50-

100-

•à 150CO

200^

250

Site 532

- - Ellis zones and time scale

• Martini zones and time scale

D—D Martini time scale andselected zones

0 1 2 3 4Age (m.y.)

Figure 4. Plots of depth vs. age using the biostratigraphy of Stein-metz (this volume), a modified biostratigraphy with Martini (1980)datums, and our preferred age vs. depth scheme. (See text for ex-planation.)

Table 3. Statistics for the concentrations of CaCC>3, organic carbon,and biogenic Siθ2 in Hole 532 for 0.5-m.y. intervals between 0 and5.0 m.y. Data for biogenic Siθ2 are from Dean and Parduhn (thisvolume).

0.5 m.y.intervals

0.0-0.50.5-1.01.0-1.51.5-2.02.0-2.52.5-3.03.0-3.53.5-4.04.0-4.54.5-5.0

Numberof

analyses

8511311011711189

117160140130

CaCO3

Mean(%)

62.450.038.935.044.036.444.648.254.358.0

Standarddeviation

(%)

7.111.211.99.0

10.910.611.27.49.78.9

Organic carbon

Numberof

analyses

8110811084782729201710

Mean(%)

3.053.723.563.732.823.543.042.522.112.19

Standarddeviation

W

0.841.371.431.181.301.861.751.001.100.93

Biogenic

Numberof

analyses

36934276

1414

Siθ2

Mean(%)

0.186.62

12.809.17

13.3011.203.242.430.463.15

periodicities of CaCO3 cycles from widely separatedareas suggest that the CaCO3 cycles are produced by aglobal, not local, forcing mechanism. The MAR data(Fig. 8) show responses to local conditions such as up-welling and climate on the African continent, but eventhere local processes probably were triggered by globalclimatic changes.

The organic-carbon cycles do not appear to be closelyrelated to CaCO3 and color cycles and have a range ofperiodicities between 28 k.y. and 44 k.y./cycle. Theseperiodicities are considerably different from organic-carbon cycles described from the late Neogene and Qua-ternary from the western Caribbean and eastern equato-rial Pacific (Gradner, 1982). The difference in organic-carbon periodicities from widely scattered localitiessuggests that the forcing mechanism for organic-carboncycles is a local phenomena and may be diagenetic. Therelationships between the trends of average organic car-bon and CaCO3 are not entirely independent, however,because the two variables are negatively correlated onscales ranging from individual cycles (Fig. 7) to the en-tire sequence at Site 532. The correlation coefficient forCaCO3 and organic carbon averaged for 0.5 m.y. inter-vals (Table 4) is -0.62. Figure 10 shows the smoothedcurves of CaCO3 and organic-carbon redrawn fromFigure 2, and illustrates the striking negative correlationbetween CaCO3 and organic carbon at the scale of the150 k.y. cycles for the past 2.5 m.y. Another way of ex-amining the relationship between CaCO3 and organic-carbon is by using a moving correlation coefficient(Dean and Anderson, 1974) the results of which areplotted in Figure 11. Note that there is usually a strongnegative correlation between CaCO3 and organic car-bon except during periods of strongest upwelling asevidenced by abundance of biogenic SiO2 (comparemaximum pulses of biogenic SiO2 in Fig. 2 with zones ofnonsignificant correlation coefficients in Fig. 11).

Upwelling Intensity and Organic Productivity

One of the principal objectives of drilling Site 532was to recover a detailed late Neogene and Quaternaryrecord of the Benguela-Current upwelling system. Be-cause upwelling intensity, and hence organic productiv-ity, is sensitive to seasonal as well as long-term climaticfluctuations, we first thought that the cycles of CaCO3

and color might be reflections of biogenic silica fluctu-ations resulting from variations in upwelling intensity.We do not think that this is true, however, for the fol-lowing reasons. First, diatoms are the dominant bio-genic component in sediment from most mid-latitude,open-ocean upwelling areas (Diester-Haass and Schra-der, 1979; Schuette and Schrader, 1981; deVries andSchrader, 1981). Siliceous biogenic debris is negligible inthe lower Pliocene and upper Quaternary sections atSite 532, and only equal in abundance with nannofossilsin the upper Pliocene and lower Quaternary sections

Table 4. Number of cycles and periodicities of CaCC>3 and organic carbon for 0.5 m.y. intervals,Hole 532.

Timeinterval(m.y.)

0-0.50.5-1.01.0-1.51.5-2.02.0-2.52.5-3.03.0-3.53.5-4.04.0-4.54.5-5.0

CaCO3

Numberof cycles

14.5014.0015.7513.0010.2510.5/425 k.y.10.5019.0016.0/410 k.y.9.0/300 k.y.

Periodicity(k.y./cycle)

34.535.731.738.548.840.547.626.325.633.3

Numberof cycles

1818151411.5—

—

—

Corg


27.827.833.335.743.5

—

—

—

Number ofdark beds

611121085/425 k.y.

181814/410 k.y.9/300 k.y.


83.345.441.750.062.585.027.827.829.333.3

CaCO 3

35 1

45.6

28.4

Mean values

Dark bedsC o r g (k.y./cycle)

31 2 55 1

43.5 58.4

— 29.9

914

100

I I I I I I I I I I I ' I I I I I ' I I I I I I I < I • I

ii •i mi I I I • • • I inn 111 ill imu ii i ii 111 m II•I miniI ' I • I ' I ' I I • I

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4Age (m.y.)

Figure 5. A. Plot of CaCO3 vs. age using the Ellis (1981) nannofossil zonation (Steinmetz and Stradner, this volume). B. Plot of CaCO3 vs. age for Site 532 using our preferred age model.Black bars along age scale indicate position and thickness of dark-colored sediment. C. Plot of organic carbon vs. age for Site 532 using our preferred age model. (See text for explanation.)

£


Age

Martini, 1971

Sedim.rate

(m/m.y.)Time(m.y.)

Nannozone

NN12throughNN1S

Ellis, 1981

Sedim.rate

(m/m.y.)Time(m.y.)

Nannozone

This paper

Sedim.rate

(m/m.y.)

Time(m.y.)

-0 .2—

-0.6—

Figure 6. Comparison of zonation and time scale of Martini (1971)with those of Ellis (1981) and the resulting sedimentation rates atSite 532. The zonation, time scale, and sedimentation rates used inthis chapter are on the far right. (See text for explanation.)

(Figs. 2 and 8). Also, smear-slide data for the cycle inCore 10 (Fig. 7) and for other cycles (see lithology sec-tion in Site 532 summary chapter, this volume) do notshow any trends or cyclic changes in diatom abundancethat correspond to trends in abundance of CaCO3. In-stead, the diatom abundances and biogenic SiO2 MARabruptly increase in the late Pliocene and early Quater-nary (Figs. 2 and 8). This pulse of siliceous biogenicdebris, with some relatively high frequency fluctuations,is the strongest evidence in the section to suggest thatthere were marked changes in the upwelling history atSite 532.

c a c o 3 (%) c o r g (%)

20 30 40 50 60 0 1 2 3 4

4 1 -

4 2 -

4 3 -

44 J

S2 (mg HC/g sed.) Color

4 8 12 16 20 light dark

10Y5/2

\5Y 6/4

5Y6/41

5Y4/4

5Y3/4

10Y 4/2

Figure 7. Plots of the data for the dark-light cycle in Hole 532, Core10, Sections 2 and 3.

To investigate the broad scale record of upwelling atSite 532 more closely, the curves of MAR (Fig. 8) can beviewed as three segments that represent the pre-upwell-ing, upwelling, and post-upwelüng intervals. The bio-genic silica MAR curve was used to define the boun-daries between the intervals. Sediment that accumulatedduring the pre-upwelling interval (>3 m.y. old) was anannofossil marl; CaCO3 and clay both predominatedover biogenic silica, each by more than an order of mag-nitude, and sedimentation rates were relatively high (63m/m.y.). This is not to say, however, that intense up-welling associated with the Benguela Current system didnot occur elsewhere during the late Miocene and earlyPliocene, perhaps north or south of Site 532 or closer tothe south African coast. The center of southwest Afri-can coastal upwelling will migrate in response to the lo-cation of the main core of the southeast Trade Winds. Ifthe position of the intertropical convergence zone didfluctuate with global climate changes during the late

Table 5. Mass accumulation rates (MAR) for sediment components at Hole 532, using our preferred time scale and zonation. (See text for explana-tion.)

Timeinterval(m.y.)

0-0.50.5-1.01.0-1.51.5-2.02.0-2.52.5-3.03.0-3.53.5-4.04.0-4.54.5-5.0

Depthinterval

(m)

0-16.916.9-39.239.2-61.261.2-83.283.2-105.2

105.2-127.6127.6-149.6149.6-181.3181.3-213.1213.1-244.8

Averagebulk density

(g/cπr)

.44

.47

.43

.42

.49

.50

.64

.70

.71

.74

Averageporosity

(%)

73737679757468656261

Averagewater

content(%)

52515557525142393736

Averagesediment

rate(m/m.y.)

33.844.644.044.044.044.044.063.463.463.4

MARbulk

sediment

2491325128512495297030893802599165056676

AverageCaCθ3

w62.450.038.935.044.036.444.648.254.358.0

MARCaCθ3

155416261109873

130711241696289435323872

Average

Corg(*)

3.03.73.63.72.83.53.02.52.12.2

MARCOrg

751201039283

108114150137147

Averagebio-Siθ2

<*)

0.186.62

12.89.2

13.311.23.242.430.463.15

MARbio-Siθ2

4.521536523039534612314630

210

MAR"clay"

858129012741300118515111869280128062447

Note: Wet-bulk density, porosity, and water content are from Site 532 chapter, this volume. Bulk-sediment MAR = [(1 - poros./lOO) × 2.7] × 100 × (sed.rate). MAR's for CaCC>3, Co rg, and biogenic Siθ2 = bulk-sediment MAR × (W>/100) of CaCθ3, C o r g, and biogenic SiC>2, respectively. Percent CaCC>3and % C o r g f ° r e a c h 0.5-m.y. interval are from Table 3. Percent biogenic Siθ2 for each 0.5-m.y. interval were obtained from Dean and Parduhn, this vol-ume. MAR s 'c lay" is the difference between bulk-sed. MAR and the sum of MAR's for CaCC^, C o r g, and biogenic Siθ2

916


7000-j A iviass accumulation rate (MAR)

Age (m.y.)

Biogenic SiO_

30

j Quaternary late Pliocene | early Pliocene |

Post-upwelling Upwelling Pre-upwelling

Figure 8. A. Plots of mass accumulation rates (MAR) of bulk sedi-ment, CaCO3, organic carbon Corg, biogenic silica, and clay vs.time for Hole 532. B. Plots of average weight percent CaCO3,organic carbon, and biogenic silica for each 0.5 m.y. interval forHole 532. Data are from Table 5.

Neogene and Quaternary, as suggested by Gardner andHays (1976), then the position of the core of the south-east Trades also would have fluctuated.

When upwelling migrated into the area of Site 532 be-tween 3 and 2 m.y. ago, CaCO3 and clay MAR de-creased by 60% and 47% respectively, and biogenic sili-ca MAR increased by 144%. However, because CaCO3and clay had been accumulating in such large volumesduring the pre-upwelling interval, the reduction in thesecomponents during the upwelling period was not offsetby the increase of initially low biogenic silica, and thebulk MAR was reduced by 49% and the sedimentationrate dropped to 44 m/m.y. The cause of the reductionof CaCO3 and clay is problematical. One possibility forthe reduction of CaCO3 is that the initiation of up-welling cooled the surface and near-surface waters to a

80

7 0 -

- 60-

:s 50

4 0 -

3 0 -

20

0 CaCO3 cycle. Site 532A Color cycle. Site 532a Corg cycle. Site 532<J> C cycles. Site 502• C cycles. Site 503

B B

2 3Age (m.y.)

Quaternary I. Pliocene e. Pliocene

Figure 9. Plot of periodicities of 0.5 m.y. intervals of CaCO3 andorganic carbon from Site 532, and from Site 502 in the eastern Ca-ribbean and Site 503 in the eastern equatorial Pacific. Data for Site532 are from Table 4; data for Sites 502 and 503 are from Gardner(1982).

degree that biogenic carbonate productivity was slowed.The increased flux of biogenic silica at this time wouldreflect the response of increased diatom productivitythat took advantage of the cool, nutrient-rich, upwell-ing zone. But this does not account for the coeval reduc-tion in the flux of clay. The timing of the beginning ofupwelling, 2.5 m.y. to 3.0 m.y. ago, is coincident withthe inferred age for the initiation of glaciation in theNorthern Hemisphere (Dalrymple, 1963; Curry, 1966;McDougall and Wensink, 1966; Kent et al., 1971; Berg-gren, 1972; Backman, 1979; Poore, 1978; 1981, amongothers). Northern Hemisphere glaciation had to havecaused a drop in sea level as water was transferred fromthe oceans to land. Consequently, one would intuitivelyexpect an increase, not a decrease, in the MAR of clay atthis time. Perhaps the climate of southwest Africa be-came drier at this time, which would have reduced theflow of the Orange River and thus reduced sediment in-put to the continental margin. We have no data to sub-stantiate this, and the reduction of clay at the beginningof upwelling in the area of Site 532 remains an unex-plained enigma.

The upwelling interval is characterized by rather con-stant values of MAR for all components (Fig. 8), but therecord of biogenic silica (Fig. 2) shows a series of large

917


CaCO3 (%)

0 25 50 75 100i i . I • i i i I i i i i I i i i i I

0i—i—i—i—r

50 —

100 —

•o

E 150

200 —

250 —

300

i I i i i I i i i |

2 4 6Organic carbon (%

— 1

^ _ O

11 111 I I 11 11111111

25 50 75 100CaCO, (%)

r—3

— 4

— 5

Figure 10. Smoothed curves of CaCO3 and organic-carbon percen-tages from Figure 2.

-1.0 -0.5 0.0Correlation coefficient

1.0

Figure 11. Moving correlation cefficients between CaCO3 and or-ganic carbon using a 21-point window which represents about 100k.y. The vertical line at a correlation coefficient of -0.43 rep-resents the 95% confidence limit for correlation coefficients forN = 21.

fluctuations (cycles) that suggest upwelling intensity orposition was not steady. An event occurred some timebetween 1.2 m.y. and 2.2 m.y. ago which reduced totalbiogenic production but did not affect the flux of clay(Fig. 8). This event was probably a major fluctuation ineither the strength or position of the center of upwell-ing; erosion can be discounted because the flux of claywas unaffected. Upwelling was reinstated in the area ofSite 532 after the event, and continued until some timebetween 0.5 m.y. and 1.0 m.y. ago. It should be em-phasized that during the upwelling interval, the fluxes ofCaCO3 and clay were still three to four times the flux ofbiogenic silica.

Mass accumulation rates for the post-upwelling inter-val (< 1.0 m.y. ago) reflect a 99% reduction in biogenicsilica relative to values during the upwelling period anda reduction of 35% in clay. The flux of CaCO3 duringthe post-upwelling period increased by 28% over thevalues during the upwelling interval, but the averagesedimentation rate was only 34 m/m.y.

The post-upwelling interval is complicated by a peri-od of winnowing by bottom currents that affects sedi-

918


ment from 0.5 m.y. old to the present. Apparently, cur-rents as deep as 1300 m were intensified in the lateQuaternary and have continued to winnow or inhibitdeposition of fine-grained sediment since then. Win-nowing has altered the composition of the sediment inthis interval (Fig. 2) and consequently the MAR valuesin this interval may be misleading. The 99% reductionof biogenic silica and 35% reduction in clay MAR is cer-tainly the result in part of the effect of erosion or non-deposition of fine-grained components. The apparentincrease in CaCO3 MAR is a reflection of the lag offoraminifers left. It may be that the entire post-upwell-ing period is, in fact, not post-upwelling, but rather acontinuation of the upwelling record that has been al-tered by erosion and/or nondeposition. However, thebiogenic silica and diatom data (Fig. 2) suggest that up-welling in the area of Site 532 was losing intensity ormigrating out of the area from about 1.2 m.y. to0.5 m.y. ago (before the pronounced effects of winnow-ing).

One of our goals was to find whether any componentin the sediment could be used as a recorder of organicproductivity. The Benguela Current upwelling systemtoday produces massive upwelling of cold, nutrient-richwaters that result in high biological productivity (Bron-gersma-Sanders, 1957; Diester-Haass and Schrader,1979; Brongersma-Sanders, et al., 1980; Siesser, 1980).In the open ocean at middle latitudes, diatoms take ad-vantage of the upwelled supply of nutrients and theirabundances in the underlying sediment overwhelm theother biogenic components (foraminifers, nannoplank-ton, and radiolarians). We do see increases in abun-dances of both diatoms and organic carbon in upperPliocene and lower Quaternary sediment at Site 532(Figs. 2 and 8), but not in the overwhelming proportionsimplied by the above citations. Either the plot of percentsiliceous biogenic debris (mostly diatoms) or the plot ofpercent biogenic silica by XRF in Figure 2 can be used toobtain a semiquantitative measure of diatom productivityat Site 532, and presumably of upwelling intensity at Site532.

Seisser (1980) suggested that Benguela Current up-welling began in early late Miocene (ca. 10 m.y. ago).Our data do not extend back that far, but percentages ofdiatoms and biogenic silica both show that diatom pro-ductivity was lower during the late Miocene and earlyPliocene, reached a maximum in the late Pliocene andearly Quaternary, and again diminished in the late Qua-ternary. The amount of organic carbon (Fig. 2) does notshow a strong correlation with amount of clay, but doescorrelate with biogenic silica (Figs. 2 and 8) in that theaverage concentration of organic carbon is highest inthe upper Pliocene to lower Quaternary. The overallcorrelation coefficient between organic carbon and bio-genic silica, averaged over 0.5-m.y. intervals, is 0.60.

Organic-carbon content has been correlated with sed-imentation rate (Muller and Suess, 1979; Ibach, 1982),but, more interestingly, the data of Muller and Suesssuggest that the combination of sedimentation rate andamount of organic carbon can be used to infer primaryproductivity, particularly for sedimentation rates great-

er than about 40 m/m.y. When the data for Site 532 areplotted along with those of Muller and Suess on a sedi-mentation rate-organic-carbon diagram (Fig. 12), theSite 532 values are similar to those from the CanaryCurrent upwelling system off northwest Africa. We canalso project from Figure 12 that, as a very rough ap-proximation, primary productivity at Site 532 rangedbetween 100 and 150 gC/mVy.

CONCLUSIONS

The entire section recovered at Site 532 on WalvisRidge shows distinct cycles in amount of CaCO3 thatgenerally correlate with cycles of sediment color. Aver-age periodicities of the CaCO3 cycles range from 28.4k.y./cycle in the lower Pliocene, to 45.6 k.y./cycle inthe upper Pliocene, to 35.1 k.y./cycle in the Quater-nary, with an overall average of about 36 k.y./cycle.Most minima of the carbonate cycles correspond todarker-colored beds, and most maxima of the carbonatecycles correspond to lighter-colored beds. These cyclesin amount of carbonate persist even through periods ofincreased upwelling when there were large changes inthe relative proportions of different sediment compo-nents.

Cycles in amount of organic carbon are not so dis-tinct as those for CaCO3; maxima in organic-carbonconcentration have an average periodicity of about34 k.y./cycle for the last 2.5 m.y. All dark-colored bedscorrespond to organic-carbon maxima, but many max-ima do not appear to correspond to a dark bed. Theprofiles of both CaCO3 and organic carbon show longer-period cycles with average periodicities of about 150k.y./cycle. In general, concentrations of organic carbonand CaCO3 are inversely related, both on a short-term

5!6

1"̂3 CM

I εα o&" —

iL

irb

on

(%

;

oo

§1

O

3 0 0 -

-

2 0 0 -

_

1 0 0 -

-

0 -

-

1 0 -

-

1 _

-

I I I II

B

•• ••A

0 / •

I [ M l

III I I

C~LOCP

Site 532 .

^× α^ o

" I ' '10

I I I

o

I III I

oo

oIA

O

I° ç

o

Φ

°o /

I I 11 111 I100

j I I

D

•

o•

•

i l l i i i i 11 n

• •

D

W. Baltic

PeruOregon

N.W. AFrica

Argentine Basin

Central Pacific

I M M I I M I II1000 10,000

Sedimentation rate (m/m.y.)

Figure 12. Relations among sedimentation rate, organic-carbon con-tent, and primary productivity for recent marine sediments (modi-fied from Muller and Suess, 1979).

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basis within individual cycles and on a long-term basisover the entire recovered section.

The carbonate cycles are not the result of carbonatedissolution, but rather some complex combination ofinflux of terrigenous elastics and carbonate produc-tivity. Because of the similarity of the periodicities ofthe Site 532 cycles to those of carbonate cycles in thenortheast Atlantic, Caribbean, and eastern equatorialPacific oceans, these cycles probably are responses toglobal events. Fluctuations in global sea level is one pos-sible forcing mechanism for the CaCO3 cyclicity at Site532 because of the correlation of the carbonate cycles toclay input.

The carbonate record shows no apparent response tothe Benguela-Current up welling history in this region.Organic carbon does show a gross correlation to in-ferred upwelling in that there is a positive correlationbetween organic carbon and biogenic silica. The best in-dicators of upwelling intensity are semiquantitative esti-mates of diatom abundances from smear slides, calcu-lated concentrations of biogenic SiO2, and the ratioSiO2:Al2θ3. These indicators all suggest that upwellingat Site 532 was minor until about 2.5 m.y. ago Qate Plio-cene). Diatom abundances, biogenic SiO2, and organiccarbon increase in the upper Pliocene section, and theaverage values remain high, but with fluctuations untilmid-Quaternary. This period, 2.5 m.y. to 0.5 m.y., ap-pears to be a time of relatively intense upwelling at Site532. Upwelling may have occurred before 2.5 m.y. alongother segments of the southwest African continentalmargin, as it does today. The center of upwelling mayhave migrated in response to the location of the maincore of the southeast Trade Winds.

The relationships between sedimentation rate, pro-ductivity, and organic-carbon content described by Mul-ler and Suess (1979) indicate that during the period ofmaximum upwelling, the primary productivity at Site532 ranged between 100 and 150 gC/m2/yr., a valuesimilar to that occurring today of northwest Africa inthe Canary-Current upwelling system.

The top 20 m of the recovered section at Site 532 is aforaminiferal-rich facies that suggests strong currentshave occurred at this depth (1331 m) some time duringthe past 500 k.y. This increased circulation was capableof transporting and possibly eroding nannofossils anddiatoms, but not foraminifers.

ACKNOWLEDGMENTS

We thank the shipboard scientists on DSDP Leg 90 for all thestimulating discussions during the cruise. In addition, we appreciatethe thoughtful reviews by M. A. Arthur and R. Z. Poore.

REFERENCES

Anderson, R. Y., 1982. A long geoclimatic record from the Per-mian. J. Geophys. Res., 87:7285-7294.

Arthur, M. A., 1979. North Atlantic Cretaceous black shales: Therecord at Site 398 and a brief comparison with other occurrences.In Sibuet J.-C, Ryan, W. B. F., et al., Init. Repts. DSDP, 47, Pt.2: Washington (U.S. Govt. Printing Office), 719-751.

Arthur, M. A., and Fischer, A. G., 1977. Upper Cretaceous-Paleo-cene magnetic stratigraphy at Gubbio, Italy: I. Lithostratigraphyand sedimentology. Geol. Soc. Am. Bull., 88:367-389.

Backman, J., 1979. Pliocene biostratigraphy of DSDP Sites 111 and116 from the North Atlantic Ocean and the age of northernHemisphere glaciation. Stockholm Contrib. Geol., Acta Univer-sitatis Stockholmiensis, 32:115-137.

Berggren, W. A., 1972. Late Pliocene-Pleistocene glaciation. InLaughton, A. S., Berggren, W. A., et al., Init. Repts. DSDP, 12:Washington (U.S. Govt. Printing Office), 953-963.

Bolli, H. M., Ryan, W. B. F., et al., 1978. Init. Repts. DSDP, 40:Washington (U.S. Govt. Printing Office).

Boström, K., Joensuu, O., Valdes, S., and Riera, M., 1972. Geo-chemical history of South Atlantic Ocean sediments since the lateCretaceous. Mar. Geol, 12:85-122.

Broecker, W. S., and van Donk, J., 1970. Insolation changes, icevolumes and the O18 record in deep-sea cores. Rev. Geophys.Space Phys., 8:169-198.

Brongersma-Sanders, M. 1957. Mass mortality in the sea. In Hedge-peth, J. W. (Ed.), Treatise on Marine Ecology and Paleoecology(Vol. 2). Mem. Geol. Soc. Am., 67:941-1010.

Brongersma-Sanders, M., Stephan, K. M., Kwee, T. G., and de Bruin,M., 1980. Distribution of minor elements in cores from the South-west Africa shelf with notes on plankton and fish mortality. Mar.Geol., 37:91-132.

Calvert, S. E., and Price, N. B., 1970. Minor metal contents of recentorganic-rich sediments off Southwest Africa. Nature, 227:593-595.

Clifton, E., 1980. Progradational sequences in Miocene shoreline de-posits, southeastern Caliente Range, California. J. Sediment. Pet-rol., 51:166-184.

Curry, R. R., 1966. Glaciation about 3,000,000 years ago in the SierraNevada. Science, 154:770-771.

Dalrymple, G. B., 1963. Potassium-argon dates of some Cenozoicvolcanic rocks of the Sierra Nevada. Geol. Soc. Am. Bull. 14:379-390.

Dean, W. E., and Anderson, R. Y., 1974. Application of some corre-lation coefficient techniques to time-series analysis. Math. Geol.,6:363-372.

Dean, W. E., Gardner, J. V., and Cepek, P., 1981. Tertiary carbon-ate-dissolution cycles on the Sierra Leone Rise, eastern equatorialAtlantic Ocean. Mar. Geol., 39:81-101.

Dean, W. E., Gardner, J. V., Jansa, L. F., Cepek, P., and Seibold,E., 1978. Cyclic sedimentation along the continental marine ofnorthwest Africa. In Lancelot, Y., Seibold, E., et al., Init. Repts.DSDP, 41: Washington (U.S. Govt. Printing Office), 965-989.

deVries, T. J., and Schrader, H., 1981. Variation of upwelling/oce-anic conditions during the latest Pleistocene through Holocene offthe central Peruvian Coast: A diatom record. Mar. Micropaleont.,6:157-167.

Diester-Haass, L., and Schrader, H. J., 1979. Neogene coastal upwell-ing history off northwest and southwest Africa. Mar. Geol., 29:39-53.

Ellis, H., 1981. Calcareous nannoplankton biostratigraphy—DSDPLeg 60. In Hussong, D. M., Uyeda, S., et al., Init. Repts. DSDP,60: Washington (U.S. Govt. Printing Office), 507-535.

Fischer, A. G., 1964. The Lofer cyclothems of the Alpine Triassic.In Merriam, D. F. (Ed.), Symposium on Cyclic Sedimentation.Bull.-Kans., State Geol. Surv., 169, 1:107-149.

Gardner, J. V., 1982. High-resolution carbonate and organic-carbonstratigraphies for the late Neogene and Quaternary from the west-ern Caribbean and eastern equatorial Pacific. In Prell, W. L.,Gardner, J. V., et al., Init. Repts. DSDP, 68: Washington (U.S.Govt. Printing Office)., 347-364.

Gardner, J. V., and Hays, J. D., 1976. Responses of sea-surfacetemperature and circulation to global climatic change during thepast 200,000 years in the eastern equatorial Atlantic Ocean. InCline, R. M., and Hays, J. D. (Eds.), Investigations of LateQuaternary Paleoceanography and Paleoclimatology. Mem. Geol.Soc. Am., 145:221-246.

Hays, J. D., Imbrie, J., and Shackleton, N. J., 1976. Variations in theearth's orbit: Pacemaker of the ice ages. Science, 194:1121-1132.

Hülsemann, J., 1966. On the routine analysis of carbonates in uncon-solidated sediments. J. Sediment. Petrol., 36:622-625.

Ibach, L. E. J., 1982. Relationship between sedimentation rate andtotal organic-carbon content in ancient marine sediments. Am.Assoc. Petrol. Geol. Bull, 66:170-188.

920


Kent, D., Opdyke, N. D., and Ewing, M., 1971. Climate change in theNorth Pacific using ice-rafted detritus as a climatic indicator.Geol. Soc. Am. Bull., 82:2741-2759.

McCave, I. N., 1979. Depositional features of organic-rich black andgreen mudstones at DSDP Sites 386 and 387, western North At-lantic. In Tucholke, B. E. and Vogt, P. R., et al., Init. Repts.DSDP, 43: Washington (U.S. Govt. Printing Office), 411-416.

McDougall, I. and Wensink, H., 1966. Paleomagnetism and geo-chronology of the Pliocene-Pleistocene lava in Iceland. EarthPlanet. Sci. Lett., 1:232-236.

Martini, E., 1971. Standard Tertiary and Quaternary calcareousnannoplankton zonation. SecondPlankt. Conf.: Roma (Technos-cienzia), pp. 739-785.

Matthews, R. K., 1982. The oxygen isotope record of ice volume his-tory: 100 million years of glacio-eustatic sea-level fluctuations.Mem. Am. Assoc. Petrol. Geol., 66:2.

Matthews, R. K., and Poore, R. Z., 1980. Tertiary 18O record andglacio-eustatic sea-level fluctuations. Geology, 8:501-504.

Muller, G., and Gastner, M., 1971. The "karbonate bomb", a simpledevice for the determination of carbonate content in sediment,soils, and other materials. N. Jahrb. Mineral. Mh., 10:466-469.

Muller, P. S., and Suess, E., 1979. Productivity, sedimentation rate,and sedimentary organic carbon content in the oceans. Deep-SeaRes., 26:1347-1362.

Poore, R. Z., 1978. Oligocene through Quaternary planktonic fora-miniferal biostratigraphy of the North Atlantic: DSDP Leg 49. InLuyendyk, B. P., Cann, J. R., et al., Init. Repts. DSDP, 49:Washington (U.S. Govt. Printing Office), 447-518.

, 1981. Temporal and spatial distribution of ice-rafted min-eral grains in Pliocene sediments of the North Atlantic: Implica-tions for Late Cenozoic climatic history. SEPM Spec. Pubi, 32:505-515.

Prell, W. L., 1982. Oxygen and carbon isotope stratigraphy for theQuaternary of Hole 502B: Evidence for two modes of isotopicvariability. In Prell, W. L., Gardner, J. V., et al., Init Repts.DSDP, 68: Washington (U.S. Govt. Printing Office).

Rea, D. K., and Janecek, T. R., 1981. Mass-accumulation rates ofthe non-authigenic inorganic crystalline (eolian) component ofdeep-sea sediments from the western Mid-Pacific Mountains,Deep Sea Drilling Project Site 463. In Thiede, J., Valuer, T. L., etal., Init. Repts. DSDP, 62: Washington (U.S. Govt. Printing Of-fice), 653-659.

Schuette, G., and Schrader, H., 1981. Diatom taphocoenoses in thecoastal upwelling area off southwest Africa. Mar. Micropaleont.6:133-155.

Seisser, W. G., 1980. Late Miocene origin of the Benguela UpwellingSystem off northern Namibia. Science, 208:283-285.

Shackleton, N. J., 1967. Oxygen isotope analyses and Pleistocenetemperatures reassessed. Nature, 215:15-17.

Tissot, B., Durand, B., Espitalié, J., and Combaz, A., 1974. Influ-ence of nature and diagenesis of organic matter information ofpetroleum. Amer. Assoc. Petroleum Geol. Bull., 58:499-506.

van Andel, Tj. H., Heath, G. R., and Moore, T. C , Jr., 1975. Ceno-zoic history and paleoceanography of the central equatorial Pa-cific Ocean. Men. Geol. Soc. Am., 143.

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DEEP SEA DRILLING PROJECT SITE 532, WALVIS RIDGE, …