16. GEOCHEMISTRY OF INTERSTITIAL WATERS …GEOCHEMISTRY OF INTERSTITIAL WATERS AND SEDIMENTS, LEG 64, GULF OF CALIFORNIA 1 Joris M. Gieskes, 2 Henry Elderfield, 3 James R. Lawrence,

16. GEOCHEMISTRY OF INTERSTITIAL WATERS AND SEDIMENTS,LEG 64, GULF OF CALIFORNIA1

Joris M. Gieskes,2 Henry Elderfield,3 James R. Lawrence,4 Jeff Johnson,2 Barbara Meyers,2 and Andrew Campbell2

ABSTRACT

Studies of interstitial waters obtained from DSDP Leg 64 drill sites in the Gulf of California have revealed informa-tion both on early diagenetic processes in the sediments resulting from the breakdown of organic matter and on hydro-thermal interactions between sediments and hot doleritic sill intrusions into the sediments.

In all the sites drilled sulfate reduction occurred as a result of rapid sediment accumulation rates and of relativelyhigh organic carbon contents; in most sites methane production occurred after sulfate depletion. Associated with thismethane production are high values of alkalinity and high concentrations of dissolved ammonia, which causes ion ex-change processes with the solid phases leading to intermediate maxima in Mg+ + , K+, Rb+, and Sr + + (?). Though thisphenomenon is common in Leg 64 drill sites, these concentration reversals had been noticed previously only in Site 262(Timor Trough) and Site 440 (Japan Trench).

Penetrating, hot dolerite sills have led to substantial hydrothermal alteration in sediments at sites drilled in theGuaymas Basin. Site 477 is an active hydrothermal system in which the pore-water chemistry typically shows depletionsin sulfate and magnesium and large increases in lithium, potassium, rubidium, calcium, strontium, and chloride. Stron-tium isotope data also indicate large contributions of volcanic matter and basalt to the pore-water strontium concentra-tions. At Sites 478 and 481 dolerite sill intrusions have cooled to ambient temperatures but interstitial water concentra-tions of Li+, Rb+, Sr + + , and Cl~ show the gradual decay of a hydrothermal signal that must have been similar to theinterstitial water chemistry at Site 477 at the time of sill intrusion. Studies of oxygen isotopes of the interstitial waters atSite 481 indicate positive values of δ 1 8 θ (SMOW) as a result of high-temperature alteration reactions occurring in thesills and the surrounding sediments.

A minimum in dissolved chloride at about 100-125 meters sub-bottom at Sites 478, 481, and particularly Site 479records a possible paleosalinity signal, associated with an event that substantially lowered salinities in the inner parts ofthe Gulf of California during Quaternary time.

INTRODUCTION

Drilling by Glomar Challenger in the Gulf of Califor-nia (Fig. 1) presented a unique opportunity to study indetail the geochemical processes affecting sediments andinterstitial waters in an area of rapid sediment accumu-lation, relatively high heat flow, and ocean floor gene-sis. Because of the nearness of the Gulf to terrigenoussediment sources as well as the high productivity in thesurface waters, sedimentation rates are high throughout(van Andel and Shor, 1964). In sediments of this nature,diagenetic processes involving the bacterial decomposi-tion of organic carbon generally leave characteristic im-prints on the chemical composition of the interstitialwaters (Berner, 1980; Gieskes, 1975, 1981). Elevated heatflow, characteristic of extensional basins, can be expect-ed to affect the diagenetic processes occurring in thesediments, in particular the diagenesis of biogenic silicato more stable silica phases (Kastner et al., 1977). Final-ly, drilling on or near the observed high heat flow anom-alies found in the Guaymas Basin (Lawver et al., 1975)would provide an opportunity to test theories of hydro-thermal circulation associated with basaltic magma gen-eration in an extensional basin characterized by very high

Curray, J. R., Moore, D. G., et al., Init. Repts. DSDP, 64: Washington (U.S. Govt.Printing Office).

2 Scripps Institution of Oceanography, La Jolla, California.3 Department of Earth Sciences, The University, Leeds, England LS2 9JT.^ Lamont-Doherty Geological Observatory, Palisades, New York.

115°

110° 109° 108° 10S°

Figure 1. The Gulf of California and Leg 64 site locations.

rates of sediment accumulation (Moore, 1973; Williamset al., 1979; Einsele et al., 1980).

In this paper we present the results of the study ofthe chemical composition of the interstitial waters and

675

J. M.GIESKES ET AL.

of sediments obtained during Leg 64. Interpretationsare necessarily preliminary in nature, but the data willbe used to delineate some general, observable trendsthat will help in understanding the geochemical pro-cesses affecting sediments in the Gulf of California.

METHODS

Interstitial Waters

In these studies interstitial waters were obtained by routine ship-board squeezing of sediment samples (Manheim and Sayles, 1974),usually effected within a very short time after retrieval of the cores.No special attention was given to temperature-of-squeezing effects(Sayles et al., 1973; Gieskes, 1973, 1974; Sayles and Manheim, 1975),though such effects may be of importance in sediments such as thoseobtained at Site 477, where temperatures at the bottom of the holemay exceed 200°C in situ. Samples obtained at this site, particularly inthe deeper sections, have suffered to greater or lesser extents from sea-water contamination, which would again have complicated attemptsto simulate in situ conditions (200°C, 200-250 atmospheres of pres-sure). In order to correct for this contamination we have assumed thatmagnesium would be absent from the pore waters below 150 meterssub-bottom depth.

In order to check on the validity of the routine interstitial waterprogram, in situ samples (Barnes et al., 1979) were taken at Site 477(one sample), Site 479 (three samples), and Site 481 (one sample).These data will be compared with shipboard samples in the discussionof observations at each drill site.

The shipboard program included p H , alkalinity, salinity, chloride,calcium, magnesium, silica, phosphate, and ammonia (J.M.G.). Allsubsequent analyses were carried out in our shore laboratories.

Methods are documented in Table 1. For rubidium a new methodwas developed; it is described in the Appendix to this chapter.

Bulk Sediments

For the chemical analysis of the bulk sediments we utilized wetchemical methods similar to those described by Donnelly and Wallace(1976). Sediment standards were those prepared by E. R. Sholkovitz,which were then standardized against U.S.G.S. standard rocks. In ad-dition we analyzed U.S.G.S. Standard AGV-1 as an unknown. Gen-erally, quantities of 20 mg or less of ground-up material were used inthese analyses. Though weighing errors, particularly when smallerquantities of material are involved, may not be trivial, atomic ratios ofthe elements with aluminum as the referent will be little affected. Acomparison of the atomic ratios for AGV-1 (Table 5) indicates thatwith the exception of Mg/Al a good agreement is generally obtainedwith the reported values of Flanagan (1972).

For the determination of manganese and lithium and the solid8 7Sr/ 8 6Sr ratio, we digested 0.5 g samples in hydrogen fluoride in Tef-lon bombs using a modification of the method of Shapiro and Bran-nock (1962). Determinations were carried out by atomic absorption

Table 1. Methods used in interstitial water analyses.

Component Method Reference

pAlkalinitySalinityChlorideCalciumMagnesiumSilicaPhosphateAmmoniaLithiumRubidiumPotassiumStrontiumManganese87 S r /86 S r

18O/16O

TitrationRefractometerTitrationTitrationTitrationColorimetricColorimetricColorimetricAtomic absorptionFlameless A.A.Atomic absorptionAtomic absorptionAtomic absorptionMass spectrometryMass spectrometry

Gieskes, 1973, 1974Gieskes, 1974Manheim and Sayles, 1974Gieskes, 1974Gieskes and Lawrence, 1976Gieskes and Lawrence, 1976Mann and Gieskes, 1975Gieskes, 1973, 1974Gieskes, 1973, 1974Gieskes and Johnson, 1981aAppendixGieskes, 1974Gieskes, 1974Gieskes, 1974Hawkesworth and Elderfield, 1978Epstein and Mayeda, 1953

techniques using the method of internal addition for the Li data.8 7Sr/ 8 6Sr measurements were made by mass spectrometry.

Interstitial water data are presented in Tables 2, 3, and 10 (Site 477data corrected for sea-water contamination); data on the solids arepresented in Tables 4-8.

As yet, no salt corrections have been made to the bulk sedimentdata, but these corrections will be small ( < 5 % ) even for constituentssuch as K and Mg. Further work on this is in progress, but elementalatomic ratios presented in this paper will be little affected.

DISCUSSION

In our discussion, we will first address the observa-tions made at each site and will follow with a more gen-eral discussion of particular problems.

Since sedimentation rates are of great importance inall these discussions, a generalized sedimentation ratediagram is presented in Figure 2.

Site 474 (Figs. 3 and 4)

Quaternary sedimentation rates at this site have beenvery high (>260 m/m.y.) and thus it is not surprisingthat sulfate reduction is completed below 10 metersdepth into the sediments. Below this depth methane pro-duction is common (Simoneit, this volume, Pt. 2). Asso-ciated with these processes of bacterial degeneration oforganic matter are large increases in alkalinity, ammo-nia, and dissolved phosphate. As a result of the large in-crease in dissolved ammonia, significant ion exchangeoccurs with the clay minerals of the sediments, leadingto maxima in dissolved magnesium at about 90 meters.Slight increases in dissolved rubidium and potassiumand in strontium are also related to these ion exchangeprocesses. Similar maxima have been observed previ-ously at Site 262 in the Timor Trough (Cook, 1974) andat Site 440 in the Japan Trench (Moore and Gieskes,1980).

Dissolved silica values show a gradual increase withdepth in the upper 270 meters of sediments. Below thispoint a sharp decrease in dissolved silica coincides witha lithologic change in the sediments that results from thereconstitution of biogenic opal-A to opal-CT in theform of silicified claystones. This break in lithology iscomparable to that associated with the silicificationfront discussed by Kastner and Gieskes (1976) for Site323 in the Bellingshausen Abyssal Plain. Important tonote here are the dissolved calcium, magnesium, andpotassium profiles, which are again similar to those ob-served at Site 323. Kastner and Gieskes (1976) showedthat in the latter site the silicification reactions wereassociated with the alteration of Plagioclase (source ofCa) and the formation of smectites (sink for Mg) and ofK-feldspar (sink for K). We suggest that similar reac-tions also occur at Site 474. A possible volcanic sourcefor Ca is indicated by the parallel decrease in the 87Sr/86Sr ratio in dissolved strontium to values well belowthose of contemporaneous sea water (Hawkesworth andElderfield, 1978). In addition, a minimum occurs inδ 1 8 θ (Fig. 16), indicating involvement of volcanic mat-ter alteration (Gieskes and Lawrence, in press).

Dissolved lithium appears unaffected by the ion ex-change processes that have just been noted for other cat-ions. A rather major source of lithium is located below

676

GEOCHEMISTRY OF INTERSTITIAL WATERS AND SEDIMENTS, LEG 64

Table 2. Interstitial water data, Leg 64.

Sample(interval in cm)

Hole 474

1-1,90-942-1, 140-1503-2, 140-1505-2, 140-1507-3, 0-1011-2, 81-8713-1, 41-4716-2, 95-10617-5, 140-150

Hole 474A

1-2, 140-1504-5, 140-1507-2, 140-15010-1, 140-15013-3, 140-15016-4, 140-15019-1, 140-15023-3, 140-15027-4, 14CM5030-2, 140-15033-3, 140-15036-1, 140-15039-1, 140-15040-4, 20-3041-4, 140-150

Hole 475

1-1, 140-1502-4, 140-1503 ^ , 140-1505-3, 140-1507-1, 140-1509-3, 140-15011-5, 140-15013-3, 140-15015-4, 140-15017-1, 140-150

Hole 475A

1-5, 140-150

Hole 476

1-3, 140-1502-2, 140-1503-5, 140-1505-3, 140-1507-6, 140-1509-4, 140-15011-4, 140-15012-4, 140-15013-5, 140-15015-2, 140-15017-2, 140-15018-4, 140-15020-5, 140-15021-4, 0-1026-1, 18-22

Hole 477

2-3, 140-1503-1, 140-1504-1, 133-1405-1, 140-150In situ7-1, 142-1507-2, 27-3215-1, 126-13116-4, 140-15017-2, 140-15019-1, 140-15020-1, 140-15020-2, 71-7622-1, 140-15023, CC

Hole 477A

5-1, 114-1205-1, 114-1206.CC7-1, 3-78.CC9-1,69-7110-1, 110-12010-1, 110-120

Z

14

13334490

108138150

165197224250280310330368405431462490516.5530539

2122139557599

116135153

6

61227.542.56180

100110120135152167186193238

61221.532.54851.552

10612012614615.5156173185

195195210212229231240240

pH

7.657.387.407.317.21

7.71

7.237.227.02

6.99IM7.067.147.337.327.33

7.587.487.387.407.247.307.147.016.98

7.47

7.467.357.457.397.207.297.197.287.197.177.176.947.217.34

7.587.577.337.28

6.976.006.056.486.23

6.74

Alk(meq/1)

3.9317.434.933.637.571.5

59.652.5

54.250.043.935.923.416.312.9510.84.654.855.20

6.1211.815.516.718.316.614.911.29.2

5.3

15.622.226.726.822.521.819.418.116.216.29.99.06.974.64

38.346.660.156.5

6.211.3

6.86.38.99.6

13.8

11.1

SO4(mM)

28.116.00.00.20.20000

0

0

0

0

26.8

18.515.512.513.115.319.520.3

28.7

18.3

3.91.61.63.27.59.1

11.616.622.422.624.427.7

14.510.09.3

11.314.621.9

23.717.04.60.64.1

8.5

NH 4

(mM)

0.943.554.156.50

12.8013.913.8

(18.5)

15.014.514.112.710.67.86.55.74.253.603.052.92.71.9

0.070.360.791.141.311.411.411.321.251.08

1.111.582.062.402.582.392.061.861.731.281.040.910.670.49

2.033.608.40

10.901.572.802.030.93

11.311.04.3

10.88.90.3

10.26.6

PO4(µM)

41119104(25)1151028144

4028.5124.5

12.511.54.5

16214.58

121.57

421323124199674.5

21

59987568352516115.522210

185158186188

00

2000000000

SiO2

(µM)

830925885

10651020

10951030

11901105127013007804805205403203703601959595

130

628700865850840

1035970

109011701440

835840950900985980

105511201075965

127513201110360

970980

13201300570

13101420740

1780181525001905168020501200

Ca(mM)

7.454.674.864.633.262.984.755.10

5.807.229.49

12.216.219.119.6524.924.827.827.228.832.544.840.9

10.0610.129.088.759.12

10.0011.2412.7114.9016.04

10.35

7.555.964.834.775.706.89

10.2811.7215.4218.1819.1120.7920.822.723.8

5.884.285.635.119.93

10.079.60

16.2922.630.850.239.044.526.730.9

36.435.525.035.938.312.535.128.2

Mg(mM)

48.745.144.140.651.346.739.238.2

35.735.133.230.526.822.825.019.514.112.613.612.29.54.18.5

52.750.748.949.247.646.544.845.143.343.7

51.1

50.650.246.744.940.442.242.843.643.845.044.944.846.446.446.7

48.549.554.756.446.339.638.751.223.4

2.80.7

17.71.4

30.726.3

2.24.95

25.44.76.3

45.148.34

21.09

Sr(µM)

8796

127125148196

205203

199194185190191207193219246309281

86100819596

104108111109

86

871008888939397

104109122119109107113

9610290

108112167

121154186312204

143

152

193

Mn(µM)

29.20.60000

00

8127.4

11.213.315.525.030.8

5.48.6

14.0

30.225.920.220.233.623.220.013.19.4

24.3

9.46.2006.32.59.7

12.615.418.424.124.017.422.9

42.335.917.138.218.913.5

72.8313295

92122

119

Li(µM)

2729464545

104123

144186268329464527551606614666456417428273270

27

77

118128

27

464340

121

193

226

15.6131823

159(147)

192273413693424

851

495

K(mM)

11.411.010.410.510.915.0

14.814.6

13.412.611.09.75.82.72.41.41.71.31.9

11.210.510.19.39.78.77.88.07.2

9.6

10.411.111.410.39.59.89.18.38.78.17.26.96.15.3

10.210.010.610.313.18.4

7.419.120.830.626.0

22.7

89

23.5

36.534.0

Rb(µM)

2.72.42.02.43.4

2.82.4

2.52.21.31.51.40.950.951.41.251.41.251.3

1.31.4

1.8

1.3

1.31.3

1.8

1.92.51.352.253.5

3.512163827.3

25.327.3

56.520.5

3.74733

8 7Sr/8 6Sr

0.70916

0.70910

0.70879

0.708400.708230.707960.707890.707920.70788

0.70765

0.70793

0.70915

0.70886

0.70872

0.70866

0.70891

0.70859

0.707710.707050.706350.70658

0.70655

0.7064:

0.70560

Cl(‰)

19.219.219.119.219.219.218.919.0

19.019.319.319.219.519.419.419.419.419.319.319.019.118.919.4

(18.9)19.119.219.319.219.319.319.319.319.2

19.1

19.0619.2519.2519.1919.2819.3119.2219.1619.2219.1519.2519.1919.2519.2219.04

19.0519.0519.2319.1719.4219.74

20.2420.7421.1521.1820.5821.2420.1820.74

20.9621.2420.2121.12

—17.5320.9320.21

S(‰)

34.634.134.134.136.336.335.234.9

35.234.634.434.133.833.633.633.333.033.033.032.731.932.233.3

34.934.934.935.234.934.934.934.934.935.2

35.234.934.134.033.833.834.434.434.435.235.536.035.836.035.8

34.134.336.336.235.234.134.137.136.635.536.836.6

36.636.6

677

J. M. GIESKES ET AL.

Table 2. (Continued).


Hole 478

1-3, 135-1502-4, 140-1503-4, 140-1504-5, 140-1505-4, 140-1506-4, 140-1507-5, 140-1508-4, 140-1509-3, 140-15011-4, 110-12013-3, 140-15015-2, 140-15017-3, 140-15019-5, 140-15021-2, 140-15022-2, 140-15028-3, 140-15029-2, 140-15030-2, 0-1033-1, 140-15036-2, 140-15039-2, 140-15040-1, 140-150

Hole 479

1-1, 140-1503-1, 135-1455-3, 110-1207-5, 140-1508-3, 140-1509-2, 140-15011-2, 140-150In situ I13-1, 140-15015-5, 140-15017-5, 140-150In situ II19-4, 140-15021-4, 140-15024-4, 140-150In situ III2 7 A 140-15032-4, 140-15036-4, 140-15039-4, 140-15043-1, 140-15044-4, 140-15047-4, 140-150

Hole 481 (HPC)

1-1, 131-1352-1, 145-1503-1, 145-1504.CC6,CC7-2, 144-1508-2, 145-1509-1, 145-15010-2, 145-15011-2, 145-150In situ

Hole 481A

1-1, 140-1503-1, 116-1164-2, 140-1505-5, 140-1506-4, 140-1508-5, 140-15010-4, 140-15012-1, 140-15014-3, 140-15014-3, 140-15018-1, 14-1820-1, 145-15022-6, 140-15023,CC24-5, 140-15025-6, 140-15026-6, 140-15027-7, 140-15028-5, 140-15030-5, 140-150

Z

31019.53139.54860687697

114131.5150164178187248253259.5280310328338

214345563729099

110130149165170188212231.5245283330360395409438

1.36.3

11.015.825.031.53639.545.550.042

43.564748694

116134148168168203224248260268278288298305325

pH

8.157.837.587.637.637.647.667.547.487.627.367.397.387.25

7.617.507.84

7.92

7.45

7.567.65

7.01

6.966.92

6.856.866.80

6.916.956.84

6.83

6.796.79

7.747.46

(7.51)

7.77

7.577.647.71

7.617.407.407.457.44

7.50

Alk(meq/1)

11.1513.5417.3320.721.520.723.931.043.851.756.644.961.560.650.142.0

9.67.88.4

10.89.3

6.2

46.081.176.575.371.370.172.3

66.762.056.4

52.348.444.7

38.133.730.227.7

23.917.3

17.130.776.292.674.956.547.948.747.850.449.3

49.545.826.556.453.245.736.429.813.6

33.936.7

29.231.636.634.541.514.4

SO4

(mM)

25.326.6

7.917.817.416.613.08.31.4011111

3.54.54.0

3.3

3.2

1.42.8

3.4

2.8

15.37.33.7

3.6

3.03.0

2.8(15.9)

3.6

NH4(mM)

0.91.82.22.452.72.73.354.46.18.99.79.58.99.8

10.810.55.95.35.13.353.3

>3.56.1

2.810.09.6

14.515.617.217.713.120.923.323.419.424.626.026.2

7.625.624.422.423.6

18.614.5

1.02.56.49.0

11.28.38.35.76.46.06.5

6.49.58.5

16.115.314.112.511.87.47.8

10.817.017.815.014.515.016.816.715.910.5

PO 4

(µM)

48728481847881

128228216204195219198115634.5000000

1862882751118647380

302851535624456621202424151320

11398

222236280212135162171116168

19726018527026360

7.50000000000000

SiO2

(µM)

830740840860910960870

10101050101511901220116513701225135516501350147515601525780475

970920

1180890

11601200125010301270139013901120140015201620

15551700156019301375970820

825875

950855935

1300120010201000840

8401100830

1400990

11001000805180

600168015501375121013401280114014601320

Ca(mM)

10.079.008.278.147.957.896.855.324.123.983.563.413.894.373.815.65

16.1217.2717.1919.2220.83

(18.67)17.23

6.075.055.595.234.375.447.778.088.399.57

10.1110.8010.1910.7611.0710.4410.8811.9412.0211.2815.3015.8514.81

9.695.994.153.663.891.792.594.132.302.592.49

2.232.894.942.843.085.357.696.19

13.2012.8011.828.888.918.29

13.5112.8110.9810.8614.0515.92

Mg(mM)

52.450.951.552.451.351.851.851.951.950.753.458.357.455.148.041.423.718.721.421.821.2

(23.5)19.3

50.453.854.939.634.333.934.335.228.023.720.0

19.017.419.117.516.716.714.512.712.514.915.5

50.352.159.665.163.751.849.648.947.647.150.5

48.851.752.848.847.244.443.632.332.431.229.827.425.825.226.727.726.026.127.022.8

Sr(µM)

83868184929294736496

11811090

1019599

142132146162190

150

115112142181159

180155209

202214221

219204223226

285275

11682

1001081211001101038384

111

94929799

100119128267332

232201

177160183197206171

Mn(µM)

166.52715.112.56.29.96.2

10.210.616.230.215.58.28.2

12.311.740.721.321.327.427.1

26.4

14.814.514.216.58.7

3.413.212.7

7.8

0

0000

00

02.9000000000

000000000

0000000000

Li(µM)

19.2

23

20

3039527189

120118151118234202145120126

7676

404525

602500705

718900

1040990800990

10001080107512261040

42

29

22

45585996

3701240870

12101817146613491400546

1038

K(mM)

11.412.111.59.5

10.210.29.18.59.6

10.011.49.67.97.26.86.86.85.87.15.95.9

7.5

10.410.111.213.911.4

11.611.712.4

12.111.512.5

11.810.99.18.6

7.75.7

10.210.210.112.010.710.810.710.111.710.910.5

12.59.29.7

11.110.110.88.6

(5.2)7.0

5.27.4

8.07.38.68.48.88.0

Rb(µM)

1.31.31.32.12.12.62.31.32.052.41.35

2.01.31.251.631.231.31.31.38.5

4.85.0

3.30.550.651.31.31.3

8 7Sr/8 6Sr

0.70875

0.70873

0.70877

0.70828

0.70822

0.70920

0.70907

0.70912

0.70905

0.709100.70894

0.70905

0.70905

0.70878

0.70858

0.70816

0.70830

0.70849

Cl(‰)

19.1219.1919.0919.0919.1618.9619.0018.9619.0918.9619.0919.1619.2819.3219.30

(18.50)19.2219.2819.3419.1919.41

(19.62)19.31

19.1218.9719.0918.6818.7218.8118.7818.6518.72

18.81

18.6218.8118.84

19.1219.0619.0319.1819.0319.0319.12

18.9718.9719.0619.0319.0618.9718.9418.9719.0618.9718.97

18.8718.9419.0018.8718.8719.0019.0319.0919.2519.2520.1920.1319.5319.2219.5919.6619.5019.7819.4719.59

S(‰)

35.535.234.934.734.935.235.034.934.935.035.235.234.9

34.93331.9

32.732.433.033.031.9

35.236.336.635.834.935.534.934.934.734.434.3

33.633.333.3

33.2

32.7

35.234.936.637.537.535.234.634.234.434.934.9

34.634.935.235.235.235.235.234.134.3

34.6

Note: Blank spaces indicate that no data were obtained. Data in parentheses are considered to be uncertain.

678

GEOCHEMISTRY OF INTERSTITIAL WATERS AND SEDIMENTS, LEG (54

Table 3. Interstitial water data, Site 477 (corrected for sea-water contamination).


Hole 477

2-3, 140-1503-1, 140-1504-1, 133-1405-1, 140-150In situ7-1, 142-1507-2, 27-3215-1, 126-13116-4, 140-15017-2, 140-15019-1, 140-15020-1, 140-15020-2, 71-7622-1, 140-15023,CC

Hole 477A

5-1, 114-1206.CC7-1, 3-78,CC10-1, 110-120

Depth(m)

61221.532.54851.552

106120126146155156173185

195210212229240

pH

7.587.577.337.28

6.976.006.056.48

Alk(meq/1)

38.346.660.156.56.20

11.25

6.846.278.879.58

S O 4

(mM)

14.510.0

9.311.314.621.9

23.717.04.60.60?

0?

NH4(mM)

2.03.68.4

10.91.62.82.00.92.44.19.2

10.512.211.211.3

11.98.3

11.910.111.5

PO4(µM)

185158186186

00

200000

SiO2

(µM)

970980

13201300

13101420740

1780181525002860487216802380

Ca(mM)

5.94.35.65.19.9

10.19.6

16.322.630.850.253.345.449.150.9

37.838.538.442.139.9

Mg

(mM)

48.549.554.756.446.339.638.751.223.4

2.80.70.0a

0.0a

0.0a

0.0a

0 a

oa

oa

oa

o3

Sr

(µM)

9610290

108112167

121154186312261

213

207

212

Mn(µM)

423617381914

73313294

92182

277

Li

(µM)

16131823

159147

192273413693625

927

851

886

K

(mM)

10.210.010.610.313.18.4

7.419.120.830.633.6

38.9

9235.1

45

Rb

(µM)

1.92.51.42.23.5

3.512163841

5753

6139

54

8 7Sr/8 6Sr

0.70891

0.70859

0.70771

0.707050.706350.7061

0.7049

0.7052

0.7053

Cl

(‰)

19.0519.0519.2319.1719.4219.74

20.2420.7421.1521.1821.3221.3021.6722.3

21.2521.2321.32

21.11

Note: Blanks indicate that no data were obtained.a Mg assumed to be zero.

270 meters in the zone of silicification. Lithium concen-trations in the solid phases (Fig. 4) suggest higher valuesbelow 300 meters. If a substantial portion of this lithiumis associated with biogenic silica, the reconstitution ofopal-A may cause this lithium to be released to the inter-stitial waters. At lithium concentrations of 45-68 ppmin the solids, less than 5% release would be able to ac-count for the dissolved lithium increases. Below 400 me-ters, dissolved lithium shows a large drop that may beassociated with uptake reactions in clay minerals duringalteration of basalts.

Dolerite sills occur in this site, often showing wide,vertical, calcite veins, especially in the upper sills. Wedecided to carry out oxygen and carbon isotopic studieson these carbonates (M. Kastner, pers. comm.); the re-sults are presented in Table 9. The data imply "normal"values for the calcites recovered in Sections 474A-42-5and 474A-44-5—that is, they were formed at relativelylow temperatures and with carbonate ions with oceanicδ13C values. However, the carbonate veins recovered inSections 474A-40-2 and 474A-41-5 indicate formation atslightly higher temperatures, with carbon dioxide de-rived from the decomposition of organic matter. Thiscan be understood in terms of alteration reactions oc-curring after burial underneath a sediment in which sul-fate reduction has led to the production of isotopicallylight (δ13C) carbon dioxide. Temperatures of formationare lower than presently prevailing temperatures, indi-cating, presumably, that the calcite veins formed afterthe cooling of the sill intrusions and the subsequent frac-turing. Pore waters containing biogenically producedbicarbonate must then have penetrated these veins andcaused the alteration of the basalts, which provided cal-cium for carbonate precipitation. Typically the inter-stitial waters below the sills are enriched in dissolved cal-

cium and depleted in magnesium as a result of continu-ing basalt alteration processes.

The chemical composition of the sediments (Fig. 4)shows little systematic changes with depth, so that reac-tions involving the uptake of magnesium and potassiumin these sediments do not appear to be of major impor-tance to that composition. Of course, at sedimentationrates of 260 m/m.y. the sediment becomes isolated fromthe overlying ocean below 40-50 meters sub-bottom(Gieskes, 1975), so that a significant influx of potassiumand magnesium from the ocean cannot be expected.

Site 475 (Fig. 5)

At this site sedimentation rates have averaged -40m/m.y. (Fig. 2). Because of these high accumulationrates and the relatively high organic carbon contents(1-2%, Simoneit, this volume, Pt. 2), sulfate reductionoccurs at this site. A minimum in sulfate is observed atabout 100 meters and appears to be the result of in-creased sulfate reduction in the upper sediment column.Similar minima in dissolved sulfate have been observedat several other sites, for instance, Sites 241, 242 (Gies-kes, 1974), and 336 (Gieskes et al., 1979). The decreasesin dissolved sulfate are accompanied by the usually ob-served increases in alkalinity, ammonia, and phosphate,and by a minimum in calcium. Decreases in dissolvedmagnesium are only minor, and dissolved potassium ap-pears to have a sink in the deeper sections of the site.Dissolved lithium clearly has a source in the sediments,probably in the siliceous materials of the site. Dissolvedsilica shows a gradual increase with depth, which isprobably a result of increased solubilities of opalinesilica as a result of the higher temperatures with depth(heat flow = 4 HFU).

679

J. M.GIESKES ET AL.

Table 4. Chemical composition bulk solids, in wt.%, Sites 474, 477, and 479.


Hole 474

3-2, 140-15016-2, 95-106

Hole 474A

4-5, 140-15016-*, 140-15023-3, 140-15030-2, 140-15039-1, 140-150

Hole 477

2-3, 140-1503-14-15-17-17-29-1

140-150133-140140-150142-15027-32Piece 6

15-1, 126-13116-4, 140-15017-2, 140-15019-1, 140-15020-1, 140-15022-1, 140-15023.CC

Hole 477A

5-1, 114-1206.CC7-1, 3-78.CC9-1, 69-7110-1, 110-120

Hole 479

1-1, 140-1503-1, 135-1455-3, 110-1207-5, 140-1508-3, 140-1509-2, 140-15011-2, 140-15013-1, 140-15015-5, 140-15017-5, 140-15019-4, 140-1502 1 A 140-15024-4, 140-15027-4, 140-15032-4, 140-15036-4, 140-15039-4, 140-15043-1, 140-15044-4, 140-15047-4, 140-150

Depth

(m)

13138

197310368431517

61221.532.551.55260

106120126146155173185

195210212229231240

2143455637290

110130149170188212245283330360395409438

Siθ2

44.445.2

54.153.155.557.252.2

55.756.453.058.053.148.358.434.836.964.260.376.458.044.2

59.641.064.362.163.062.2

59.054.053.661.851.953.567.762.565.066.059.464.963.460.561.163.364.856.350.155.3

Tiθ2

0.430.53

0.630.620.620.580.57

0.760.780.450.610.550.752.030.730.490.790.800.920.680.56

0.720.910.690.550.740.67

0.430.510.500.450.530.430.300.370.360.450.510.440.460.470.540.490.510.500.450.58

A12O3

11.1212.32

15.0914.4615.3414.0314.22

13.1512.919.25

11.0311.1612.9514.5514.609.76

14.6513.1119.9314.0710.97

13.5717.5613.7012.5314.3913.15

6.4410.73

8.168.04

10.527.815.556.517.46

10.4211.919.59

10.4110.6111.4611.8310.0311.5010.2415.44

Fe 2 O 3

3.924.86

5.306.034.734.874.84

4.984.563.314.134.524.83

11.395.616.285.264.256.755.564.69

4.8617.673.696.003.694.62

2.864.123.563.074.203.882.362.912.873.153.983.402.963.343.473.373.123.623.624.59

MgO

1.592.23

2.342.322.032.022.83

2.712.352.312.243.946.147.25

11.11

3.481.643.132.812.01

2.82

1.293.231.982.58

2.362.102.001.642.04

.81

.14

.26

.50

.18

.55

.39

.42

.58

.41

.52

.302.634.822.81

CaO 1

12.8311.26

2.214.672.024.771.48

3.544.355.514.425.913.81

12.51 (0.48

13.540.523.96 :3.47 <3.482.17

4.11 (3.46 (3.14 (5.18 (4.35 (4.77 (

1.273.023.370.875.96 :8.240.653.761.710.87 :3.22 ;0.961.762.301.020.951.005.147.924.86

<2O

2.532.60

S.261.375.45).2OS.88

2.801.10.10.90.40.10

).10S.40.61

1.302.951.612.222.39

).39).4O).34).28).28).28

.552.23.92.86

'.282.42.26.64.74

2.162.47.96.91

'.012.612.34.97

2.30.93

U 2

Site 476 (Fig. 6)

At this site sedimentation rates have averaged —42m/m.y. (Fig. 2), rates similar to those observed at Site475.

Again a distinct minimum in dissolved sulfate is ob-served in the upper sediment column, with almost com-plete depletion of sulfate at about 50 meters (<2mM).At the bottom of the sediment column, just above theunit containing metamorphic cobbles and illitic clays,dissolved sulfate concentrations are equal to normalsea-water concentrations. This poses an interesting prob-lem: It is almost certain that even in the lower sedimentsection, below 66 meters sub-bottom, sulfate reductionprocesses have been operative. If this is so, it is difficultto understand why dissolved sulfate values at the bot-

tom of the sediment section would be like those in seawater. There is little doubt that the sulfate minimum isinduced by the relative increase in importance of sulfatereduction in the upper sediment column. However, theconcentrations at the bottom of the sediment column dosuggest that perhaps sea water penetrates advectivelythrough the cobble zone, which may outcrop at theedges of the sediment terrace. If the latter is indeed thecase, of course, the penetrating sea water must haveinteracted with the sediments or cobbles to cause a slightincrease in dissolved calcium, a decrease in magnesium,and a decrease in the 87Sr/86Sr ratio of the dissolvedstrontium. This, of course, could also explain the sul-fate minimum at Site 475. Though the possibility of sea-water penetration is intriguing, we cannot actually proveit. However, a similar penetration of sea water through

680


Table 5. Bulk sediment atomic elemental ratios to aluminum,Sites 474, 477, and 479.

Table 6. Trace element chemistry in sediments, Sites 474, 477, and481.


Hole 474

3-2, 140-15016-2, 95-106

Hole 474A

4-5, 140-15016-4, 140-15023-3, 140-15030-2, 140-15039-1, 140-150

Hole 477

2-3, 140-1503-1, 140-1504^1, 133-1405-1, 140-1507-1, 142-1507-2, 27-329-1, Piece 615-1, 126-13116-4, 140-15017-2, 140-15019-1, 140-15020-1, 140-15022-1, 140-15023,CC

Hole 477A

5-1, 114-1206,CC7-1, 3-78,CC9-1, 69-7110-1, 110-120

Hole 479

1-1, 140-1503-1, 135-1455-3, 110-1207-5, 140-1508-3, 140-1509-2, 140-15011-2, 140-15013-1, 140-15015-5, 140-15017-5, 140-15019-4, 140-15021-4, 140-15024-4, 140-15027-4, 140-15032-4, 140-15036-4, 140-15039-4, 140-15043-1, 140-15044-1, 140-15047-4, 140-150

AVG-1 (Exp.)AGV-1 (Flanagan)

Si/Al

3.393.11

3.043.123.073.463.11

3.593.714.864.464.043.163.412.383.783.723.903.253.503.42

3.731.983.984.213.714.01

7.774.275.576.524.185.81

10.358.147.405.384.245.745.174.844.524.545.484.154.153.042.842.90

Ti/Al

0.0250.027

0.0270.0270.0260.0260.026

0.0370.0390.0310.0350.0310.0370.0890.0320.0320.0340.0390.0290.0310.033

0.0340.0330.0320.0280.0330.033

0.0430.0280.0390.0360.0320.0350.0350.0360.0310.0270.0270.0290.0280.0280.0300.0260.0320.0280.0280.024

0.0390.039

Fe/Al

0.2250.252

0.2240.2260.1970.2220.217

0.2420.2260.2280.2390.2590.2380.5000.2450.4110.2290.2070.2160.2520.273

0.2290.6420.1720.3060.1640.224

0.2840.2450.2780.2440.2550.3170.2720.2850.2460.1930.2130.1970.2080.2010.1930.1820.1990.2010.1990.190

0.2460.251

Mg/Al

0.1810.229

0.1960.2030.1670.1820.252

0.2610.2300.3160.2570.4470.6000.6300.963

—0.3010.1580.1990.2530.232

0.263—

0.1190.3260.1740.248

0.4630.2480.3100.2580.2450.2930.2600.2450.2540.1430.1650.1690.1870.1900.1560.1620.1640.2890.5950.230

0.1450.112

K/Al

0.2460.228

0.2340.3270.2430.2470.295

0.2300.2600.1290.1860.1360.0920.0070.2520.1790.3180.2440.2500.1710.236

0.0310.0250.0270.0240.0210.023

0.2600.2250.2550.2500.2350.3350.2460.2730.2520.2240.2240.2040.2160.2070.2460.2130.2130.2160.2040.219

a metamorphic conglomerate was invoked by Gieskesand Johnson (1981b) for Site 453 in the MarianaTrough.

Of some interest is also the minimum in dissolvedmagnesium, which again may be induced by a relative


Depth(m)

Li(ppm)

Mn Rb Sr(ppm) (ppm) (ppm)

87Sr/86Sr

Hole 474

5-2, 140-150

Hole 474A

1-2* 140-15016-4, 140-15030-2, 140-15033-3, 140-15039-1, 140-15041-4, 140-150

Hole 477

2-3, 140-1503-1,4-1,5-1,7-1,7-2,9-1,

140-150133-140140-150142-15027-32Piece 6

15-1, 126-13116^17-219-120-122-1

, 140-150, 140-150, 140-150, 140-150, 140-150

23,CC

Hole 477A

5-1, 114-1206.CC7-1, 3-78.CC9-1, 69-7110-1, 110-120

Hole 481

7-2, 144-150

Hole 481A

6 ^ , 140-15010-4, 140-15012-1, 140-15014-3, 140-15018-1, 14-1820-1, 145-15022-6, 140-15023,CC24-5, 140-15025-6, 140-15026-6, 140-15027-7, 140-15028-5, 140-15030-1 , 140-150

33

165310431462517539

61221.532.551.55260

106120126146155173185

195210212229231240

31.5

94134148168203224248260268278288298305325

48

456367476858

5137373623

97

24545728112827

83751

536

51

5837-523131413345624858496934

340

4701100820

1800770650

450650490

12601010660

1250 1.09230510490450 93.0460770810 69.5

8901670540

1690740 2.08950

\\

2300

470650560590720

2400950600540530570600600450

211 0.70274 ±4

296

243

0.70750 ±4

0.70715 ±3

559 0.70611 ±6

change in accumulation rates, or by the influx of seawater from below the sediment section.

Site 477 (Figs. 7, 8, and 9)

Site 477 is located very close to the heat flow anomalyfirst detected by Lawver et al. (1975). A temperaturemeasurement at 48 meters sub-bottom indicates a tem-perature of 45 °C, for a temperature gradient of - 88 °C/100 m. The configuration of the heat probe used at thattime would probably lead to an underestimate of thetemperature, so that temperatures at the bottom of thehole must have exceeded 200°C.

681

J. M.GIESKES ET AL.

Table 7. Protodolomite and dolomite samples, in wt.%, Leg 64.


Hole 479

10,CC,1210-6, 92-9413.CC23-1, 58-5927.CC29-1, 1-429-1, 13-1429-1, 26-26.532.CC "light"32.CC "dark"34-5, 148-14941.CC44.CC45.CC47-2, 124-12647-2, 134-15647-2, 145-147

Hole 478

22.CC

Hole 480

21,1

Depth(m)

87.488.4

110.8203.1250259.5259.6259.8290.2290.2314.2375411414.6433.2433.3433.4

188.3

100

Siθ2

24.2629.6720.2828.809.85

20.209.67

30.6056.159.0510.1033.7219.5913.4210.3711.1810.96

19.71

12.03

TiO 2

0.190.450.160.200.140.190.130.320.540.090.120.300.200.190.140.140.14

0.18

0.12

A12O3

4.565.763.555.792.444.822.586.77

13.502.202.037.425.454.643.573.883.82

4.66

0.92

Fe 2 O 3

1.732.151.092.530.824.201.444.244.231.153.182.795.148.372.752.202.97

2.14

0.70

MgO

8.7010.3214.0910.2815.8912.5016.0110.20

17.2016.1310.4212.2012.5617.6117.8917.09

14.70

14.48

CaO

20.2620.7623.7317.9829.8724.6424.8617.64

1.3929.3128.4416.2523.8427.1327.6426.9729.52

25.06

32.36

K 2 O

1.160.870.420.980.221.400.571.302.490.280.321.280.720.720.400.510.50

0.76

0.20

A major phenomenon at this site is the occurrence ofsills in an apparently cooled-off state in Holes 477 (58-105.5 m) and 477A (32.5-62.5 m). The sills must be rela-tively old, probably 20,000 years or more, to have cooledoff so completely (Vacquier, this volume, Pt. 2). Withsedimentation rates estimated to be as high as 2000 m/m.y., the sediment thickness at the time of intrusion ofthe sills was probably 25 meters or less in this site. Theheat source leading to the observed high heat flow must

be located deeper in the site, as is also clear from thecontinuous increase in temperature with depth observedduring the logging of this hole.

Interstitial water concentration profiles show greatcomplexity at this site (Fig. 7). The upper 30 meters,which probably have been deposited after the cooling ofthe upper sills, indicate concentration changes typicallyobserved in rapidly accumulating sediments with highorganic carbon contents. A sharp increase in alkalinityis accompanied by a rapid lowering of dissolved sulfate,increases in ammonia and phosphate, a decrease in dis-solved calcium, and finally a reversal in magnesium con-centrations, observations similar to those made at Site474.

Below 30 meters toward the sill in Hole 477 as well asjust below the sill, the influence of the doleritic sillintrusion is clearly observable in the interstitial waterconcentrations. Alkalinity and dissolved ammonia val-ues rapidly decrease and dissolved silica, at least directlybelow the sill, also appears strongly affected. Dissolvedsulfate and dissolved magnesium appear especially in-fluenced by the sill intrusion, with the dissolved sulfateconcentrations being relatively high both above and be-low the sill. The latter increase is also accompanied byhigh magnesium concentrations. These observations canbe explained in two ways: (1) relatively unaltered seawater has been trapped in the sill and is diffusing intothe surrounding sediments, or (2) sulfates, precipitatedduring the hydrothermal interaction between the pene-trating dolerite sills and sea water/pore water, are pres-ently dissolving, and the resultant sulfate ions will dif-fuse into the sediments. We consider the first possibility

Table 8. Elemental atomic ratios to Al and calculated protodolomite compositiona

protodolomite samples, Holes 479, 480, and 478.


Hole 479

10-6, 92-9410.CC.1213.CC23-1,58-5927.CC29-1, 1.5-429-1, 13-1429-1, 26-26.532.CC (dark)32.CC (light)34-5, 148-14941,CC44.CC45.CC47-2, 124-12647-2, 134-13647-2, 145-147

Hole 480

21-1

Hole 478

22.CC

Depth(m)

87.488.4

110.8203.1250

259.5259.6259.8290.2290.2314.2375411414.6433.2433.3433.4

100

188.3

Ti/Al

0.0500.0270.0290.0220.0370.0250.0320.0300.0260.0260.0380.0260.0230.0260.0250.0230.023

0.083

0.025

Fe/Al

0.2380.2420.1%0.2790.2150.5560.3560.4000.3340.2001.000.2400.6021.150.4920.3620.4%

0.486

0.293

Ca/Al

3.24.16.12.8

11.14.68.82.4

12.10.09

12.72.04.05.37.06.37.0

32.0

4.9

Mg/Al

1.92.95.02.2

8.23.37.81.99.9

10.01.82.83.46.25.85.7

19.9

4.0

K/Al

0.2180.2060.1280.1830.0980.3140.2390.2080.1380.2000.1710.1870.1430.1680.1210.1420.142

0.235

0.176

Si/Al

4.374.514.854.223.423.563.183.843.493.534.223.863.052.452.462.442.43

11.10

3.49

CaCO3

(<Vo)

64595556

5856535555

54545656525254

MgCO3

(%)

364145424239464044

42453834464743

FeCO3

(%)

204.5150.6

31

610212

a The composition of the protodolomites was calculated as follows: The Ca/Al, Mg/Al, and Fe/Al ratios werecorrected for background values calculated for the nondolomite sediments (Ca/Al = 0.4 upper 150 m, Ca/Al= 0.1 below 150 m; Mg/Al = 0.3 upper 150 m, Mg/Al = 0.2 below 150 m; Fe/Al = 0.2 below 150 m). Thepercentage of CaCθ3, MgCC>3, and FeCθ3 was then calculated from the corrected ratios. It was assumed thatall other constituents of the protodolomites were < 1%.

The estimated errors were ± 3% of the CaCC>3 value, ± 4 % of the MgCθ3 value, and ± 10% of the FeCθ3value. These estimated errors were obtained by taking a low and a high correction for Ca/Al, Mg/Al, andFe/Al and calculating the spread for the corrected values of several samples containing high Al.

682


Age (m.y.)

3

400

(DebrisI Flow

N ? d

\

0 m/m.y.

4N42 m/m.y.

475

>260m/m.y.

m/m.y.

0.5

474

1.0

200

400

>200 cm/ky

476

N = Nannofossild = Diatom• = 475O = 476Θ = coincidentA = glauconite N and dO = ash

1.5

1.8-2.4

Figure 2. Sedimentation rate diagram, Leg 64.

rather improbable and prefer the second. Edmond et al.(1979) and Bischoff and Seyfried (1978) indicate that amagnesium-hydroxy sulfate forms rapidly during hy-drothermal interaction between sea water and basalts,or by heating sea water itself. It is, therefore, possiblethat small quantities of this material (as well as gypsumand anhydrite) have formed during the penetration ofthe sills. Quantitatively these minerals may be un-important but would nevertheless leave an imprint onthe pore fluids. No magnesium-hydroxy sulfate hasbeen detected (M. Kastner, pers. comm.), but the dis-solution of such material would explain the observedmagnesium and sulfate anomalies most satisfactorily.No precise stoichiometry would be expected because ofthe different reactivities of sulfate and magnesium in thebasalt-pöre-water-sediment system. Indeed the doleritesill appears to serve as a sink for ammonia, potassium,and perhaps magnesium as a result of relatively coldtemperature alteration reactions.

Below 140 meters the influence of hydrothermal reac-tions taking place in the sediments and underlying ba-salts(?) leaves a clear imprint on the interstitial waters.Typically sulfate becomes depleted and magnesium dis-appears quantitatively from the interstitial waters. In-creases in dissolved calcium, lithium, potassium, ru-bidium, and ammonia are evident, much in accord withobservations made on hydrothermal fluids emanatingfrom ridge crests (e.g., Edmond et al., 1979). A quanti-

meq/l

mM0 5 10 15 mM

60

200

400

6 8 20 40 60 0 10 20 30 SO4 40 80 120 0 400 800 1200 0 20 40

Calcium and Magnesium

µM µM µM mM0 100 200 300 .708 .709 0 200 400 600 0 2 4 6 0 4 8 12 16

E§ 200

•S 400

V

Strontium

/

i / i - •

87Sr/86Sr Lithium

t

Rubidium Potassium

µM 30 34

200

Chloride and Salinity

Figure 3. Interstitial water chemistry, Site 474. Lithology: I, diatomaceous oozes, muds, and turbidites; II, siltyclaystone and clayey siltstone-graded mud turbidites; III, dolerite sills and claystones.

683

J. M.GIESKES ET AL.

0.02 0.03 0.0 0.2 0.4 2 3 4 0.0 0.2 0.4

200

400

\

Ti/Al Mg/AI Si/Al K/Al

= 0.0 0.1 0.2 0.3 20 40 60 80 0 1000 2000

™ o

2 0 0 -

400 -

/ "

<

! 1 1

»

\ :

\ •

i i i i >

: \rY

•Fe/AI Lithium (ppm) Manganese (ppm)

Figure 4. Elemental atomic ratios to aluminum of bulk sediment atSite 474; Li and Mn in concentrations (ppm).

tative comparison, however, is not possible because oursamples were obtained under conditions different fromthose prevailing in situ. The concentrations for K + ,Li + , Rb+ and NH 4

+ may be underestimates, especiallyin view of the well-known temperature-of-squeezing ef-fects (Sayles and Manheim, 1975). Among these effects,that on K+ is probably the best documented: an increase

Table 9. δ I 8 0 and δ 1 3 C of calcites in basalts at Site 474.

Sample Depth δ18O(PDB) δ13C(PDB) δ18O(SMOW) Temp,(interval in cm) (m) (‰) (%) (‰) (°Q

474A-40-2, 55-57 526.56 -4.16 -19.84 26.57 34.0474A-41-5, 129-133 541.31 -5.23 -27.37 25.47 40.0474A-42-5, 10-12 549.61 2.72 0.30 33.89 1.8474A-44-5, 112-114 569.63 1.17 0.36 32.07 8.9

in K+ concentrations of 15-20% has been estimated fora 20 °C rise in temperature (4-24 °C). This temperatureeffect appears confirmed from our only in situ sample,which indicates an effect of 30% for a 40 °C tempera-ture change (Table 2). This implies that K+ concentra-tions in situ may be as high as 125 mM in the deeperparts of this site. Clearly it is unfortunate that no in situsamples could be obtained in these deeper parts. In ad-dition since sample sizes were small and sea-water con-tamination always present, a meaningful temperature-of-squeezing program would have been very difficult toperform. Thus, though our observations are necessarilyqualitative, there is little doubt that large increases inthe concentrations of the alkali metals result from hy-drothermal interactions between sediments or basalts.These changes are larger than those estimated by Ed-mond et al. (1979), but, of course, the parent sedimentsin the Guaymas Basin are much more enriched in Li+,K+, and Rb+ than are ridge crest basalts. This, for ex-ample, is clear from the data in Tables 4-6. Indeed, theconcentrations of K+ in the solids (Table 4, Fig. 9) showthat the K2O is almost quantitatively removed from thesediments in Hole 477A.

The increase in dissolved chloride is about 15%; itindicates a substantial removal of water, presumably aswater of hydration, during the formation of hydrother-mal minerals.

6 7 8meq/l10 20

0-51 0

mMLO 1.5 N H 42 0 3 0 S O 4 0

1 0 2 0 40

100 - - - A - -

Phosphate

10 20mM

30 40 50

100

µM100

mM4 8 12 0

400 800 1200 1600

"V. ' ' ' '

µM2

Silica

\

\

*\Ca

Calcium and Magnesiumi

7}AlVlπ

Lithium Potassium Rubidium

Figure 5. Interstitial water chemistry, Site 475. Lithology: IA, nannofossil diatomaceous silty clay to clayey silt;IB, clayey silt to silty clay; II, diatomaceous silty clay; III, zeolite-bearing clay, dolomitic mudstone; IV,metavolcanic conglomerate.

684


µM0 400 800 1200

100 - I I - - ' - –

2 0 0

~ v T p H T Alkalinity

mM20 40

100

200

µM 87Sr/86Sr100 .708 .709 0 100

V

/ V

\ - -

7Strontium 87Sr/86Sr Lithium Potassium

Figure 6. Interstitial water chemistry, Site 476. Lithology: I, nannofossil and diatomaceous oozes to muds; II, siltyclay; III, muddy diatomaceous oozes, turbidites, glauconitic sands; IV, glauconite sands, zeolitic silty clays,phosphorite, pyritic organic claystone; V, metamorphic cobbles and sandy clay.

mM

100

200

300

m e q / | 0 5 10 NH4 µ M

5 6 7 8 20 40 60 ° 1 0 2 0 S 0 4 1000 2000 0

F7

pH

I I ^+^à‰ •H•T i i i

mM

20 40 60

„ K ^ so4 - *

Su If ate andAlkalinity f Ammonia ' Silica

1•S 0

100

200

% µM mM18 19 20 21 22 0 400 800 0 20 40 0

µM µM

20 40 60 0 100 200 300i i i i i i i π i i I i i i i r

3 0 0 r Chloride

\ "

Lithium

i i i i i i i c i i i i i r

-R/vvvvvvvvv^

V-

Potassium

~ K

Rubidium

I I I

vvvvvvvvvvv

Manganese

Figure 7. Interstitial water chemistry, Site 477. Lithology: I, diatomaceous ooze, sandy silts, and silty clay (tur-bidites); II, dolerite sill; III, hydrothermally altered clay and claystone, sandy siltstone. (Data with arrowsare corrected for sea-water contamination. Open symbols are corrected data for Hole 477A.)

Of importance in this site are the results of the studiesof the oxygen and strontium isotopes of the waters anddissolved strontium. The δ 1 8 θ of the interstitial watersbelow the sill increases to values as high as + 1.37%O (M.Kastner, pers. cornm.). The values of δ 1 8 θ of the bulksolid silicates show a gradual decrease (Kastner, this vol-

ume, Pt. 2), testifying to the importance of hydrother-mal alteration of the sediments in this site. The data ob-tained for the 87Sr/86Sr ratio in the interstitial waters, aswell as for some selected solids, are presented in Figure8. Though the lowermost two of the interstitial-water87Sr/86Sr values have been corrected for sea-water con-

685

J. M. GIESKES ET AL.

0.7020

0.704100

0.706200

8 7 Sr/ 8 6 Sr

300

100

200-

/l4 A

-

Δ//

// Δ

A

,„„„„„„

~- • _A ^

1 oA

J®

8 7Sr/86Sr/(water) /

VVV^VVVVVViyVVlLVVVV.

1

(solids)

Figure 8. Dissolved strontium and 8 7Sr/ 8 6Sr of interstitial water stron-tium and solid phases, Site 477. Open circles: Sr+ + in 477A; opentriangles: 8 7Sr/ 8 6Sr in 477A.

tamination in a manner similar to that described in themethods section, it is evident that very low values arereached in Holes 477 and 477A. The interstitial watervalues are lower than those in the bulk solids. This canbe interpreted in two ways: (I) the sediments, consistingmainly of detrital material of volcanic origin and of bio-genic silica, lose their strontium preferentially from theirvolcanic sources during hydrothermal alteration, or (2)a large basaltic imprint on the strontium isotopic com-position of the dissolved strontium occurs. We propose

to perform leaching experiments to determine whetherthe first hypothesis is viable, but at present we prefer thehypothesis of a basalt Sr-isotope signal. John Lupton(pers. comm.) has, indeed, shown excess δ3He values incap gases in this site (3He/4He [sample/air] = 6.3 at 144m). Such values elsewhere have been shown to reflecthydrothermal processes (Lupton, 1979). Furthermorethe 87Sr/86Sr results are similar to those found by Alba-rede et al. (1980) in hydrothermal waters of the East Pa-cific Rise at 21 °N as well as geothermal sea-water sys-tems in Iceland, where Sr-isotope exchange has led tovery low values in the circulating sea water (Elderfieldand Greaves, pers. comm.). Of some interest here is thedissolved strontium profile, which shows a maximum atabout 140 meters depth. This may indicate that stron-tium is removed from the pore fluids in the deeper partsof the site. Humphris and Thompson (1978) also de-scribe strontium enrichments in epidotes, indicative ofbasalt-sea-water alteration at low water/rock ratios(Menzies and Seyfried, 1979). If this is indeed the case, abasaltic contribution to the dissolved 87Sr/86Sr profilesseems evident, and our data may be part of a generalphenomenon.

The analysis of the bulk chemical composition of thesolid phases (Tables 4 and 6, Fig. 9) clearly indicates theinfluence of the sill intrusion on the surrounding sedi-ments (elevated Mg/Al, depressed Si/Al, K/Al, andlowered Li concentrations). In the deeper parts of thesite, especially in Hole 477A, the influence of hydrother-mal alteration is mostly evident from the very low K/Alin the bulk solids below 190 meters. Ratios of Mg/Al,

0.04 0 0.2 0.4 0.6 0.8 1.0 6 0 0.1 0.2 0.3 0.4

I I

100

. Λ Λ Λ Λ Λ Λ Λ Λ Λ /

. Λ Λ Λ Λ Λ Λ Λ Λ Λ

. Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ

Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ ΛΛ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ -Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ

Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ

Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ•Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ ΛΛ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ

200

- Ti/Al -– Mg/Al

0.0 0.2 0.4 0.6 0.0 20 400

-– Si/Al

80 0 1000 2000 3000

-– K/Al

ΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛ

ΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛ/ΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛ Λ

KΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛΛ100

200

Fe/AI T Lithium (ppm) T~ Manganese (ppm)

Figure 9. Elemental atomic ratios to aluminum of sediments at Site 477. Li and Mn in concentrations (ppm).

Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ• Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ ΛΛ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ

686


Si/Al, and Fe/Al appear little affected. The lack of in-crease in the Mg/Al ratio is probably the result of com-plete removal of Mg + + from the pore fluids prior toreaching the zones of alteration in this site. Only thoseelements that are efficiently removed during hydrother-mal interaction—K+ and Li +—would show depletionsin the solids; here this is clearly the case, especially forK+.

Site 478 (Fig. 10)

Interstitial water profiles obtained in this site showgreat complexity. Concentration-depth profiles of alka-linity, sulfate, ammonia, phosphate, and calcium allshow breaks at about 60 meters sub-bottom depth. Am-monia production between 60-170 meters again appearsto induce a maximum in dissolved magnesium and per-haps in potassium. All these data imply non-steady-stateconditions at this site, with biogenic activity involvingthe degradation of organic matter being more importantbelow than above 60 meters. WhetheF this situation is aresult of differential sedimentation rates, of differentreactivities of organic carbon, of the deposition of largesections of turbidites with lesser bacterial activity, or ofa combination of these factors cannot be determined atthis stage. It is clear, however, that as a result of thevery high accumulation rates concentration changes oc-cur in the interstitial waters that reflect non-steady-stateconditions.

Within 20 meters above and below the limestone-chert-dolerite complex between 190-230 meters, the in-fluence of this complex is noticeable in the pore fluids.For instance, a rapid change occurs in dissolved magne-sium, potassium, strontium (below sill), and lithium.

This appears to be related mostly to the sill intrusions,which must have had an influence on the surroundingsediments during the penetration at high temperaturesand subsequently may have undergone low-temperaturealteration reactions. The latter would lead to the up-take of magnesium (though magnesium may also beconsumed during dolomitization of the limestones) andpotassium. Below the sills the 87Sr/86Sr ratio of dis-solved strontium is significantly lower than above thesills. Dissolved lithium shows a more complex distribu-tion, especially below the sill complex. Below the sillsthere occurs a maximum in Li+ which may be explainedbest in terms of a decaying dissolved-lithium profile:during the high-temperature stage dissolved lithium val-ues may have been very high, but since that period up-take reactions during low-temperature alteration of thesills and diffusion into the overlying and underlying sed-iments have led to the gradual disappearance of the veryhigh lithium concentrations. Measurements of the 18O/16O composition of interstitial waters obtained belowthe sill indicate values that may be slightly higher in δ 1 8 θthan sea water is (M. Kastner, pers. comm.).

A clear minimum in dissolved chloride occurs atabout 80 meters sub-bottom. Below this minimum thechlorinities increase to slightly higher than present-daybottom water values (19.3% chlorinity). The occurrenceof the chlorinity minimum will be discussed for Site 479,where a more pronounced minimum has been observed.


Site 479 is located on the slope of the Guaymas Basinat a water depth of 747 meters. The sediment accumula-tion rates are rapid in the upper section of this site

mM

meq/l 0 5 10

7 8 9 . 2 0 40 60 ° 1 0 20Jil l I

SO4 o 100 200 0 400 80012001600 18.5 19.0' M^f=sn—i—i—

19.5

πzr~rr

" p H T Alkalinity T Sulfate and Ammonia

- Calcium and Magnesium - Strontium "" Potassium

Figure 10. Interstitial water chemistry, Site 478. Lithology: IA, diatomaceous ooze with frequent turbidites; IB, diatomaceoussilty mud; II, dolomitic siltstones, two dolerite sills, diatomaceous mudstone; IIIA, diatomaceous mudstone, laminated dia-tomaceous mudstone with dolomite; IIIB, siltstone and contact zone to basaltic intrusion.

687

J. M.GIESKES ET AL.

100

200

300

400

meq/l6 8 20 40 60 80 0

'7H_ M i l 1• I - | I - U710

mM20 30 0

µM100 200 300 0

µM1000

100

200

300

400

i

;

• Alkalinity

mM20 40

A

" • Sulfate and Ammonia

19.5

r- • Phosphate

60 0µM

100 200

- Calcium and Magnesium • • Strontium

I I I I I I300 0.708, 0.709 0

-• Silica

µM400 800

mM1200 0 4 8 12

\.i ÷\.-–

M I

-– 8 7Sr/8 6Sr -– Lithiu

i I i I i | I I I

-–

Potassium

Figure 11. Interstitial water chemistry, Site 479. Lithology: I, soft unconsolidated diatomaceous oozes and muds, 4 calcareouslimestone (dolomitic) beds; II, increased induration; limestone beds; III, claystones; limestone beds. (Open circles and tri-angles are in situ data.)

100

200

300

400

8 10 .025 .030 .035 .040 0.15 0.20 0.25 0.30π—i—r

Si/Al Ti/Al

vI

Fe/AI

Figure 12. Elemental atomic ratios to aluminum of bulk sediments atSite 479.

(-600 m/m.y.), which implies that below about 15 me-ters sub-bottom the sediment acts as a closed system(Gieskes, 1975). Sulfate reduction is essentially com-plete below 10 meters, that is, constant sulfate concen-trations of 3 mM ± 1 are reached. It is not certain whynonzero sulfate values are obtained, but sea-water con-tamination ( 10%) cannot be ruled out completely inthese disturbed, gaseous sediments. Generally methaneproduction occurs only when sulfate reduction pro-cesses are completed. However, it is possible that theseprocesses will occur when sulfate reduction processeshave ceased, even at nonzero sulfate concentrations. Be-

low 10 meters depth the production of methane andhigher hydrocarbons become increasingly important (Si-moneit, this volume, Pt. 2). Alkalinity values reach lev-els higher than 80 meq/1 and dissolved ammonia valuesincrease gradually to reach concentrations as high as 26mM at 250 meters depth. Again, as at all other Leg 64sites, dissolved phosphate rapidly increases below thesediment surface, with a maximum occurring at about25 meters depth.

As a result of the production of ammonia by the de-composition of organic carbon, a subsurface maximumin dissolved magnesium again occurs. The rapid de-crease in Mg + + below 50 meters is probably related tothe formation of dolomite in these sediments. The firstwell-defined layer of dolomite occurs at about 88.5 me-ters. Dissolved calcium typically shows a minimum as aresult of carbonate precipitation reactions, but only inthe deeper sections are concentrations slightly abovethat of sea water observed. Agreement between dis-solved calcium data obtained from routine squeezingtechniques and by means of the in situ samples is excel-lent, as is the agreement for dissolved magnesium, in-dicating the essential validity of the shipboard squeezingprocedure.

Dissolved strontium concentrations increase rapidlywith depth, which may in part be due to ion exchangeprocesses as well as to carbonate recrystallization pro-cesses. The carbonate contents in the sediments, how-ever, are generally very low (Simoneit, this volume, Pt.2). The data on the strontium isotope composition indi-cate little or no contribution of volcanic material.

688


Data on dissolved lithium indicate a very rapid in-crease to very high concentrations, with the in situ con-centrations being slightly less than the concentrationsobtained from routine samples. This phenomenon clear-ly shows that high lithium concentrations are not neces-sarily caused by hydrothermal reactions alone. Thesource of lithium is most likely located in the siliceousphases (opal-A, diatoms), which can contain substantialamounts of lithium (B. Fenical, pers. comm.). Dissolvedsilica concentrations in interstitial water appear close tosaturation with respect to opaline silica, but it is diffi-cult to estimate how much opal dissolution and subse-quent removal of silica to other mineral phases has oc-curred. Further work on the lithium concentrations inthe solid phases is planned to assess this problem.

Again dissolved chloride indicates a distinct mini-mum at 125 meters, more pronounced than at Sites 478and 481. We do not think the minima can be related tothe occurrence of aquifers in these sediments, particu-larly not at Site 481. It is doubtful that the increases inchloride are due to dilution effects resulting from or-ganic carbon decomposition. Organic carbon contentsthroughout the site vary between 2 and 4% C, and weestimate that only a relatively small part of this organiccarbon is decomposed in the upper 200 meters. Simplemass balance calculations then indicate that the ob-served dilution effect is difficult to understand in termsof organic matter diagenesis. We are left with the specu-lation that the minima represent a paleosalinity signal,recording an event of substantially reduced salinities inthe Gulf of California. Careful work on the distributionof 18O/16O and D/H isotopes of the interstitial watersmay elucidate this problem. The idea that the minimumrepresents a paleosalinity signal is reinforced by themore pronounced minimum occurring at the shallowestsite (Site 479). Unfortunately, at this stage no preciseage is available for the minimum at these sites, and suchinformation is necessary to determine whether such apostulated event occurred simultaneously at both.

The data on the bulk sediment composition (Fig. 12)indicate a distinct change in the regime of sedimentationat Site 479, with the sediments between 0 and 150 metersshowing much higher ratios of Ti/Al and Fe/Al, similarto the ratios observed in the Guaymas Basin. If the ac-cumulation rates are calculated from diatom data (op-tion 479[b] in Fig. 2), a break in the sedimentation pat-tern is indeed observed at —150 meters depth. Thus alarge change in the sedimentation pattern has occurredat about the same level that the chloride minimum is re-corded. At this stage we cannot state whether there iscausal relation between these observations.

In Table 8 the atomic elemental ratios of a series ofspecial samples taken from the dolomite layers of Site479 are presented. In these samples, Ti/Al, K/Al, andSi/Al ratios are generally lower than in the remainder ofthe sediments (cf. Table 5 and Fig. 12). This may indi-cate slight changes in the mineralogy of associated clayminerals or that in addition to the formation of pro-todolomites diagenetic changes in the aluminosilicateshave also occurred. We have made an attempt to esti-mate the composition of the dolomites from the ele-

mental ratios in Table 8 as follows: First, the "averagenoncarbonate" Fe/Al, Mg/Al, and Ca/Al ratios are de-termined from the data in Tables 5 and 6 at low Ca/Alratios; second, these ratios are subtracted from the ele-mental ratios in Table 8, and these corrected ratios arethen considered to be the result of the protodolomites.This procedure then results in the computation of thecarbonate composition given in Table 8. Whereas the(yoCaC03 remains relatively constant, it appears thatMgCO3 and FeCO3 are interchangeable. No consistentdownhole trend in the MgCO3/FeCO3 ratio is apparent.From the general lack of calcium gradients in the inter-stitial water column we suggest that calcium carbonatehas undergone in situ alteration to protodolomite, withthe Mg + + and Fe + + being generated from the sur-rounding sediments during diagenesis. As suggested be-fore, mobilization of Mg++ from ion exchange posi-tions would have caused the Mg + + migration, whereasFe + + would be produced by diagenetic processes in-volving organic matter decomposition in these reducingsediments. The increase in dissolved strontium (constant87Sr/86Sr) is probably due to release of Sr + + from cal-cite during the formation of protodolomite.


Site 481 was drilled in the Northern Trough of theGuaymas Basin. Again the sediments are characterizedby rapidly accumulated, siliceous, terrigenous sedimentswith several megaturbidite deposits at 50 meters and 100meters depth. At 170-195 meters sub-bottom a series ofsill intrusions occurs.

The interstitial water data in the upper 150 metersshow a clear non-steady-state distribution with minima inalkalinity, ammonia, and phosphate occurring around45-50 meters. These minima may be related to reducedbiogenic activity in the zones of megaturbidites. Valuesof alkalinity in the upper section are among the highestrecorded hitherto in DSDP cores (cf. Cook, 1974; Mooreand Gieskes, 1980). Again the production of ammoniahas led to the occurrence of one or two maxima in dis-solved magnesium, with possible maxima in strontium,potassium, and rubidium.

Below 125 meters the influence of the dolomite-doleritic sill complex becomes most evident. A sharprise in dissolved strontium occurs just above and belowthe sill complex. In addition, sharp decreases in the87Sr/86Sr ratio are observed. The increases in dissolvedchloride and rubidium also testify for the influence ofhydrothermal processes on the surrounding sediments.A study of the carbon and oxygen isotopic compositionof carbonates above the sill indicate that temperaturesas high as 170°C may have occurred just above the sill(Kastner, this volume, Pt. 2). During the period thatsuch elevated temperatures occurred the sediment andbasalts underwent hydrothermal alteration, as is alsoevident from the low opaline silica contents (low dis-solved silica) and the recrystallization of clay minerals(Kastner, this volume, Pt. 2). The temperatures prevail-ing must have been elevated enough to cause increases inboth dissolved lithium and rubidium. Decreases both indissolved lithium and potassium toward the sill imply

689

J. M.GIESKES ET AL.

meq/l6 8 20 40 60 80 100

mM10 20 30

µM100 200 300

mΦ

µM

400 800 1200 1600

" Calcium and Magnesium T Strontium

200

300 -

Figure 13. Interstitial water chemistry, Site 481. Lithology: I, alterations between muddy diatomaceous ooze, tur-bidites, and diatomaceous muds; II, dolerite and basalt sills; III, diatomaceous muds and turbidites; IV, twomass flows, laminated ooze and sill; V, basalt sills in muddy oozes. (Open circles and triangles are in situ data.)

20 1000 2000 30001 1 1 1 1 1 1

3 0 0 -

Lithium (ppm) Manganese (ppm)

Figure 14. Lithium and manganese in bulk sediments at Site 481.

uptake into the sill during subsequent low-temperaturealteration reactions. The distribution of δ 1 8 θ in the in-terstitial waters shows high values below the sill complex(Fig. 15). These elevated values must be the result of hy-drothermal alteration of the sills and/or the sedimentssurrounding the sills (M. Kastner, pers. comm.). The

data do not allow us to speculate on a possible decreasein δ 1 8 θ near the sill; this would be expected from low-temperature alteration reactions.

GENERAL DISCUSSION

Early Diagenetic Processes

In all of the sites drilled in the Gulf of California,sediment accumulation rates and organic carbon con-tents are higher than found in more open ocean environ-ments. For these reasons the bacterial processes of sul-fate reduction and of methane formation, which gen-erally occur after cessation of the sulfate reduction pro-cesses, are of great importance. Only at Sites 475 and476, which are characterized by much slower accumula-tion rates, does the sulfate reduction process nevercease, and typically no significant production of meth-ane is observed. Chemical changes caused in the inter-stitial waters by these processes of bacterial degradationof organic matter will be considered as "early diage-netic" in accord with similar changes observed in muchshorter cores in the near-shore environment.

Both the sulfate reduction processes and the methanefermentation processes produce large increases in the bi-carbonate (alkalinity) concentrations as well as largeamounts of ammonium ions. In the upper 50 meters or

690


Table 10. Oxygen isotope composition of inter-stitial waters, Sites 474 and 481.

Hole/Core/Section

474-1-1474-2-1474-3-2474-5-2474-7-3474-16-2474-17-5

474A-1-2474A-4-4474A-7-2474A-10-1474A-13-3474A-16-4474A-19-1474A-23-3474A-27-4474A-30-2474A-33-3474A-36-1474A-39-1474A-41-4

481-2-1481-3-1481-4,CC481-7-2481-9-1481-11-2

481A-1-1481A-3-1481A-4-2481A-5-5481A-6-4481A-8-5481A-10-4481A-12-1481 A-14-3481A-20-1481A-22-6481A-24-5481A-25-6481A-27-7481A-28-5481A-30-5

Depth(m)

13143354138152

166198223250282312328367407432461488516540

51016303950

4362818795115133147169223250267279298305324

δ1 8θ ( S M O W )

-0.4±0.2

-0.1-0.7-0.6-0.5-1.1 ±0.1-0.5±0.1

-1.5-0.9±0.1-1.2±0.2-1.7±0.1-2.0±0.1-1.9±0.1-1.5 ±0.2-1.7-l.O±O.l-1.3±0.1-l.O±O.l-o.δ±o.i-1.2-0.9

-0.2±0.1-0.1-0.30.0

-0.4-0.3

0.0O.O±O.l

-0.3-0.3±0.1-0.2-OJ±O.l0.2±0.10.7±0.10.41.92.02.0±0.11.3+0.11.31.00.5

less of the sediment column, large increases in dissolvedphosphate also occur, but these concentrations dissipaterapidly with depth, presumably as a result of precipi-tation as phosphates. The amounts of phosphates pro-duced are probably small (organic carbon contents areonly 5% or less) and, therefore, these phosphates will bedifficult to detect. As a result of the very high values ofalkalinity, carbonate precipitation processes in the formof calcite and perhaps of dolomite (Site 479) can explainthe lower values of dissolved calcium and magnesium atgreater depths. We do not intend here to expand on stoi-chiometric calculations of organic matter diagenesis,but we do wish to stress the large-scale production ofdissolved ammonia in these sediments.

Previous workers (e.g., Rosenfeld, 1979) have shownthat ammonia produced in sediments with high organiccarbon contents will affect the concentrations of bothexchangeable and nonexchangeable ammonia in the solid

phase. In very recent sediments the exchangeable am-monia concentrations are especially affected (Rosen-feld, 1979), but in older sediments the nonexchangeableammonia concentrations may change appreciably (Ste-venson and Tilo, 1970). These sediments, especially atSite 479, may lend themselves particularly well to thestudy of exchangeable versus nonexchangeable ammo-nia, but such studies have not yet been carried out.

Walton (1949) gives the following orders for the ab-sorption of monovalent and divalent cations on cationexchangers: Cs+ > Rb+ > K+ > NH4+ > Na+ > Li +

and Ba+ + > Sr++ > Ca + + > Mg+ + . Typically, in sea-water-equilibrated clay mixtures (80% illite, 20% mont-morillonite), the exchange complements found for ma-jor constituents are 0.52 Na, 0.28 Mg, 0.11 Ca, and 0.10K (Sayles and Mangelsdorf, 1977). These complementswill change with interstitial water composition and cer-tainly when NH 4

+ ions are introduced in large amounts.Unfortunately, no information is available on the ex-change complements of Li + , Rb + , and Sr + + . Thoughthese ions are only minor constituents of sea water, ex-change reactions may still be important. Thus, introduc-tion of relatively large quantities of dissolved ammonia(> 10 mM in Leg 64 sites) is likely to result in ion ex-change reactions with the solid phases. Until Leg 64only two sites have ever shown reversals in the concen-trations of dissolved constituents in their concentration-depth profiles: Site 262 (Timor Trough; Cook, 1974) in-dicated intermediate maxima in Mg + + and lessequivocally in K+ and Ba+ + , and Site 440 (JapanTrench; Moore and Gieskes, 1980) showed a clear maxi-mum in dissolved magnesium associated with very highNH 4

+ values. Most sites drilled during Leg 64 showintermediate maxima in K+, Rb + , Mg + + and perhapsSr + + ; the effect on dissolved magnesium and potassiumis the most discernible. These phenomena are especiallyclear at Site 474, where maxima in K + , Rb + , and Mg + +are well defined (Fig. 3). No apparent ion exchange ef-fect on dissolved lithium has been observed, suggestinga relatively small exchange complement of this ion onthe clays.

Why do only relatively few sites show these maximain cations? At DSDP sites characterized by sedimenta-tion rates of >200 m/m.y., the sediment column be-comes essentially a closed system at sub-bottom depthsof less than 45 meters (Gieskes, 1975). Such sedimentsare often characterized by high organic carbon contentswith associated high rates of chemical decompositionreactions involving organic matter. When such reactionrates are relatively high, diffusion processes cannotsmooth out any concentration gradients caused in theinterstitial waters by such reactions (Lasaga and Hol-land, 1976). This, therefore, appears to be the case atthe sites at which these concentration reversals in cat-ions have been observed. The maxima occur in the up-per part of the methane production zone, where concen-trations and rates of production of dissolved ammoniaare very high. In the Leg 64 sediments the observedmaxima occur below depths of 20 meters. In principle,these concentration reversals should also be observablein near-shore sediments with very high accumulation

691

J. M.GIESKES ET AL.

—u

100

200

300

1 0 +111 J,+2

i i i I i i

vvvvvvvvvvvvvvvvvvvvvv

~**^**

Site 481

Site 474

Figure 15. 18O/16O in interstitial waters at Sites 474 and 481. Dotted line represents trend line.

rates, within the normal "piston coring range" at depthsof less than 20 meters.

Of some interest is the occurrence of a salinity maxi-mum, mostly caused by the high alkalinity (HCO3)values, in the zone of the observed concentration rever-sals. Below this salinity maximum, salinities decreaserapidly to values typical of interstitial waters depleted insulfate and alkalinity (Gieskes, 1974).

Hydrothermal Alteration of Sediments and/or Basalts

The drilling of Sites 477, 478, and 481 in the GuaymasBasin afforded a unique opportunity to study the effectsof doleritic sill intrusions on hydrothermal processes inthe sediments of the Guaymas Basin (Einsele et al.,1980). Site 477 in the Southern Trough represents a sys-tem in which hydrothermal activity is presently occur-ring in the sediment column below the dolerite sill intru-sions between 30 and 100 meters sub-bottom. The heatsource must be located below the cored section. Site478, located near the transform fault connecting theSouthern Trough and the Northern Trough, does showthe presence of sills, but these intrusions are presumablyold; because of the location of the site no new intrusionsare to be expected there. Site 481 is situated in the North-ern Trough, but at some distance from the heat flowanomaly described by Williams et al. (1979). At this sitethe interstitial water data (Fig. 13) clearly indicate thatthe uppermost sill complex represents the most recentintrusion.

Work on the hydrothermal alteration occurring dur-ing high-temperature interaction between basalts andsea water (Bischoff and Dickson, 1975; Bischoff andSeyfried, 1978; Hajash, 1975; Mottl and Holland, 1978;Seyfried and Bischoff, 1979; Edmond et al., 1979) hasindicated that, at temperatures above 200°C, mag-nesium and sulfate are generally removed quantitativelyfrom sea water, whereas elements such as Li + , K + ,Ca++ are released. Evidence from altered basalts (Hum-

phris and Thompson, 1978) indicates that some of theseelements, for example Li+ and particularly Sr + + , areprecipitated in hydrothermal phases, such as epidote. Atlower temperatures some of these trends reverse. For in-stance, Seyfried and Bischoff (1978) showed that be-tween 75° and 150°C a reversal occurs for dissolved po-tassium, which at lower temperatures is removed fromsea water. J. L. Bischoff and W. Seyfried kindly madeavailable some samples from their hydrothermal experi-ments, and we carried out analyses for dissolved lithiumand rubidium (Table 11). These data suggest that attemperatures between 150° and 200 °C a reversal occursfor lithium—that is, at lower temperatures uptake oflithium occurs into the basalts. The data for rubidiumsuggest release of Rb + to sea water even at temperaturesas low as 150°C. The quenched samples suggest rapiduptake of Rb+ upon cooling. Finally, at low tempera-tures, reaction rates are so slow that no significantchange in Li+ or Rb + occurs even after 27 months.Water /rock ratios in sediments are generally much low-er than in experimental systems, and thus much larger

Table 11. L i + and R b + concentration, sea-water-ba-salt experiments.a

Temperature(°C)

25°

150°

200°C

300°C

Sample

Sea-water25-5-20 mo.25-6-27 mo.GL-150-10-QuenchGL-150-10-6 1968 hr.GL-200-10 QuenchGL-200-10-3 192 hr.GL-300-10 QuenchGL-3OO-1O-3 240 hr.GL-3OO-1O-5 1296 hr.

Li(µM)

27.027.027.022.821.644.346.8

17394.292.7

Rb(µM)

1.51.51.51.32.31.42.851.32.23.0

a Samples provided by J. L. Bischoff and W. Seyfried.

692


changes occur in the concentration of Sites 477-481 andin oceanic hot springs (Edmond et al., 1979; Menziesand Sey fried, 1979).

The interstitial water chemistry in the Guaymas Basinsites is in qualitative agreement with these observations.At Site 477, where temperatures in excess of 200°C oc-cur at the bottom of the site, enrichments are typicallyobserved in Li + , K + , Rb + , Ca + + , and Sr + + . As dis-cussed later, these concentration changes are differentfrom those observed in the Galapagos hot springs (Ed-mond et al., 1979), not only because of different water-rock ratios but also because concentrations of Li, K,and Rb are much higher in sediments than in basalts. AtSite 481, where the sills presently have temperatures be-tween 30 and 35°C, uptake of K+ and Li+ occurs in thedolerite, as is indicated by the interstitial water profiles.However, evidence from recrystallized calcites (M. Kast-ner, pers. comm.) indicates that temperatures higherthan 167°C must have prevailed in the sediments duringthe period that the sill intrusions occurred. These pro-cesses would have caused increases in Li + , Rb + , andK+ in the interstitial waters surrounding the sills. Afterthe sills cooled, however, reversals in these concentra-tions would occur as a result of "retrograde" reactions.Thus the anomalies caused by the high-temperature in-teractions between basalts-sediment-pore waters are ina state of decay at this site. At Site 478 the only profilethat still shows the hydrothermal signal is the Li+ con-centration profile. In addition to these alkali cations,the hydrothermal interaction is also noticeable in thedissolved chloride and the 18O/16O profiles (Kastner,this volume, Pt. 2).

Chemical evidence on the solid phases of Site 477 in-dicates that the sediments are to a large extent thesources of dissolved Li + , K + , and Rb + . Data on δ 1 8θof the bulk silicates (Kastner, this volume) support thiscontention. Data on the 87Sr/86Sr composition of dis-solved strontium and of the solid phases indicate a pos-sible basaltic contribution to the dissolved strontium.The 87Sr/86Sr data of the strontium dissolved in theinterstitial water are summarized in Figure 16, in whichthe data for Site 479 serve as reference values.

That the interstitial waters also record a signal causedby hydrothermal interactions with basalts is confirmedby the finding of an excess 3He/4He ratio in a gas sam-ple collected from Site 477, at 144 meters sub-bottomdepth.

ACKNOWLEDGMENTS

We wish to thank the scientific staff and technicians on boardGlomar Challenger for their cooperation in this geochemical program.We thank Mr. Jim Pine, the shipboard chemist, whose tolerance ofJ.M.G.'s presence in the ship's laboratory is appreciated.

This research was generously supported by NSF Grant OCE 77-24102 (J.M.G) as well as by the National Environmental ResearchCouncil of Great Britain (H.E.).

Dr. R. E. McDuff critically reviewed the manuscript.

REFERENCES

Albarede, F., Vitrac-Michard, A., Minster, J. F., and Michard, G.,1980. Strontium isotope composition in hydrothermal systems.Trans. Am. Geophys. Union (Eos), 61:994-995.

0.705

87Sr/86Sr0.706 0.707 0.708 0.709

/°

Figure 16. 87Sr/86Sr of dissolved strontium at Sites 477, 478, 479, 481.

Barnes, R. O., Gieskes, J. M., Horvath, J., and Akiyama, W., 1979.Interstitial water studies, Legs 47A, B. In Sibuet, J.-C, Ryan, W.B. F., et al., Init. Repts. DSDP, 47, Pt. 2: Washington (U.S. Govt.Printing Office), 577-582.

Berner, R. A., 1980. Early Diagenesis: A Theoretical Approach.Princeton Series in Geochemistry.

Bischoff, J. L., and Dickson, F. W., 1975. Seawater-basalt interac-tion at 200°C and 500 bars: Implications for origin of seafloorheavy metal deposits and regulation of seawater chemistry. EarthPlan. Sci. Lett., 25:385-397.

Bischoff, J. L., and Seyfried, W. E., 1978. Hydrothermal chemistryof seawater from 25°C to 35O°C. Am. J. Sci., 278:838-860.

Cook, P., 1974. Geochemistry and diagenesis of interstitial fluids andassociated calcareous oozes, Deep Sea Drilling Project, Leg 27,Site 262, Timor Trough. In Veevers, J. J., Heirtzler, J. R., et al.,Init. Repts. DSDP, 27: Washington (U.S. Govt. Printing Office),463-480.

Donnelly, T. W., and Wallace, J., 1976. Major- and minor-elementchemistry of Antarctic clay-rich sediments. In Hollister, C. D.,Craddock, C , et al., Init. Repts. DSDP, 35: Washington (U.S.Govt. Printing Office), 427-446.

Edmond, J. M., Measures, C , McDuff, R. E., Chan, L. H., Collier,R., and Grant, B., 1979. Ridge crest hydrothermal activity and thebalances of the major and minor elements in the ocean: TheGalapagos data. Earth Plan. Sci. Lett., 46:1-18.

Einsele, G., Gieskes, J. M., et al., 1980. Intrusion of basaltic sills intohighly porous sediments, and resulting hydrothermal activity.Nature, 283:441-445.

Epstein, S., and Mayeda, T., 1953. Variations of O18 content of waterfrom natural sources. Geochim. Cosmochim. Acta, 4:213-224.

Flanagan, F. J., 1972. 1972 values of international geochemical refer-ences samples. Geochim. Cosmochim. Acta, 37:1189-1200.

Gieskes, J. M., 1973. Interstitial water studies, Leg 15—alkalinity,pH, Mg, Ca, Si, PO4, and NH4. In Heezen, B. C , MacGregor, I.D., et al., Init. Repts. DSDP, 20: Washington (U.S. Govt. PrintingOffice), 813-829.

, 1974. Interstitial water studies, Leg 25. In Simpson, E. S.W., Schlich, R., et al., Init. Repts. DSDP, 25: Washington (U.S.Govt. Printing Office), 361-394.

, 1975. Chemistry of interstitial waters of marine sediments.Ann. Rev. Earth Planet. Sci., 3:433-453.

., 1981a. Deep sea drilling interstitial water studies: Implica-tions for chemical alteration of the oceanic crust, Layers I andII. In Warme, J. B., Douglas, R. G., Winterer, E. L. (Eds.), TheDeep Sea Drilling Project: A Decade of Progress. Society of Eco-nomic Paleontologists and Mineralogists Special Publication 32.

, 1981b. Interstitial water studies, Deep Sea Drilling Proj-ect Leg 60. In Hussong, D. M., Uyeda, S., et al., Init. Repts.DSDP, 60: Washington (U.S. Govt. Printing Office), 749-754.

693

J. M.GIESKES ET AL.

Gieskes, J. M., and Johnson, J., 1981. Interstitial water studies, DeepSea Drilling Project Leg 59. In Kroenke, L., Scott, R., et al.,Init. Repts. DSDP, 59: Washington (U.S. Govt. Printing Office),627-630.

Gieskes, J. M., and Lawrence, J. R., 1976. Interstitial water studies,Leg 35. In Hollister, C. D., Craddock, C , et al., Init. Repts.DSDP, 35: Washington (U.S. Govt. Printing Office), 407-423.

, in press. Alteration of volcanic matter in deep sea sedi-ments: Evidence from the chemical composition of interstitialwaters from deep sea drilling cores. Gβochim. Cosmochim. Acta.

Gieskes, J. M., Lawrence, J. R., and Galleisky, G., 1979. Inter-stitial water studies, Leg 38. In Talwani, M., Udintsev, G., et al.,Init. Repts. DSDP, Suppl. to Vols. 38, 39, 40, and 41: Washington(U.S. Govt. Printing Office), 121-133.

Hajash, A., 1975. Hydrothermal processes along mid-ocean ridges:An experimental investigation. Contrib. Mineral. Petrol., 53:205-226.

Hawkesworth, C. J., and Elderfield, H., 1978. The strontium isotopecomposition of interstitial waters from Sites 245 and 336 of DSDP.Earth Plan. Sci. Lett., 40:423-432.

Humphris, S. E., and Thompson, G., 1978. Trace element mobilityduring hydrothermal alteration of oceanic basalts. Geochim. Cos-mochim. Acta, 42:127-136.

Kastner, M., and Gieskes, J. M., 1976. Interstitial water profiles andsites of diagenetic reactions, Leg 35, DSDP, Bellingshausen Abys-sal Plain. Earth Plan. Sci. Lett., 33:11-20.

Kastner, M., Keene, J. B., and Gieskes, J. M., 1977. Diagenesis ofsiliceous oozes. I. Chemical controls on the rate of opal-A to opal-CT transformation—an experimental study. Geochim. Cosmo-chim. Acta, 41:1041-1059.

Lasaga, A. C , and Holland, H. D., 1976. Mathematical aspectsof non-steady state diagenesis. Geochim. Cosmochim. Acta, 40:257-266.

Lawver, L. A., Williams, D. L., and Von Herzen, R. P., 1975. A ma-jor geothermal anomaly in the Gulf of California. Nature, 257:23-28.

Lupton, J. E., 1979. Helium-3 in the Guaymas Basin: Evidence for in-jection of mantle volatiles in the Gulf of California. J. Geophys.Res., 84:7446-7452.

Manheim, F. T., and Sayles, F. L., 1974. Composition and origin ofinterstitial waters of marine sediments based on deep sea drillcores. In Goldberg, E. D. (Ed.), The Sea (Vol. 5): New York(Wiley-Interscience), 527-568.

Mann, R., and Gieskes, J. M., 1975. Interstitial water studies, Leg 28.In Hayes, D. E., Frakes, L. A., et al., Init. Repts. DSDP, 28:Washington (U.S. Govt. Printing Office), 805-814.

Menzies, M., and Seyfried, W. E., 1979. Basalt-seawater interaction:Trace element and strontium isotopic variations in experimentallyaltered glassy basalt. Earth Plan. Sci. Lett., 44:463-472.

Moore, D. G., 1973. Plate-edge deformation and crustal growth, Gulfof California structural province. Geol. Soc. Am. Bull., 84:1883-1906.

Moore, G. W., and Gieskes, J. M., 1980. Interaction between sedi-ment and interstitial waters near the Japan Trench, Deep Sea Drill-ing Project Leg 57, In Scientific Party, Init. Repts. DSDP, 56, 57,Pt. 2: Washington (U.S. Govt. Printing Office), 1269-1275.

Mottl, M. J., and Holland, H. D., 1978. Chemical exchange duringhydrothermal alteration of basalt by seawater. I. Experimental re-sults for major and minor components of seawater. Geochim.Cosmochim. Acta, 42:1103-1115.

Rosenfeld, J. K., 1979. Ammonium adsorption in near shore anoxicsediments. Limnol. Oceanogr., 24:356-364.

Sayles, F. L., and Mangelsdorf, P. G., 1977. The equilibration of clayminerals with seawater: Exchange reactions. Geochim. Cosmo-chim. Acta, 41:951-960.

Sayles, F. L., and Manheim, F. T., 1975. Interstitial solutions anddiagenesis in deeply buried marine sediments: Results from theDeep Sea Drilling Project. Geochim. Cosmochim. Acta., 39:103-127.

Sayles, F. L., Manheim, F. T., and Waterman, L. S., 1973. Interstitialwater studies on small core samples, Leg 15. In Heezen, B. C ,MacGregor, I. D., et al., Init. Repts. DSDP, 20: Washington (U.S.Govt. Printing Office), 783-804.

Seyfried, W. E., and Bischoff, J. L., 1979. Low temperature basalt al-teration by seawater: An experimental study at 70CC and 150°C.Geochim. Cosmochim. Acta, 43:1937-1947.

Shapiro, L., and Brannock, W. W., 1962. Rapid Analysis of Silicate,Carbonate and Phosphate Rocks. U.S. Geol. Survey Bull. 1144A.

Stevenson, F. J., and Tilo, S. N., 1970. Nitrogenous constituents ofdeep sea sediments. In Hobson, G. C , and Speers, G. C. (Eds.),Advances in Organic Geochemistry: Pergamon, pp. 237-263.

van Andel, Tj. H., and Shor, G. G., 1964. Marine Geology of theGulf of California. Am. Assoc. Pet. Geol. Mem. 3.

Walton, H. F., 1949. Ion exchange equilibria. In Nachod, F. C. (Ed.),Ion Exchange, Theory and Application: New York (AcademicPress), pp. 3-28.

Williams, D. L., Becker, K., Lawver, L. A., and Von Herzen, R. P.,1979. Heat flow at the spreading centers of the Guaymas Basin,Gulf of California. J. Geophys. Res., 84:6757-6769.

APPENDIXRubidium Determinations in Interstitial Waters

Jeff Johnson

Rubidium is determined by flameless atomic absorption tech-niques. In accordance with the method of Katz (1975), sulfuric acidbackground is used to reduce interferences.

Sample Preparation

0.1 cm3 sea-water sample0.1 cm3 500 mM H2SO4

0.1 cm3 600 mM NH4NO30.2 cm3 5% ascorbic acid0.5 cm3 double-distilled water

Method

Solution is swirled thoroughly and 25 µm of sample is introducedinto the carbon furnace. A Perkin-Elmer model 403 atomic absorp-tion spectrophotometer and model HGA-2200 controller with P-Egraphite furnace are used.

Machine setting: Dry 35 s at 105°CChar 25 s at 900° CAtomize 7 s at 2700 °CFlow rate = Stop 3Wavelength = 390

The Rb-electrodeless discharge lamp is used. Data are recorded ona chart recorder.

Standards

Spiked La Jolla pier water and IAPSO standard sea water areused.

Notes

1. Good agreement was obtained with mass spectrometric data(H. Elderfield, pers. comm.).

2. H2SO4: The signal strength is strongly dependent on the sulfateconcentration below 400 mM of SO4 =. Since SO4

= varies in pore-water samples we made SO4

= 500 mM.3. NH4NO3: This mixes in sample to form NH4C1 and NaNO3. In

the latter form Na and Cl will volatilize at lower temperatures andthus they are effectively removed from the samples. The signalstrength is dependent on the Na+ concentration, so that Na+ removalis essential.

4. Ascorbic acid: It has been recommended that ascorbic acid beadded to improve reproducibility and to enhance signal strength. Theascorbic acid use does improve the signal but does have one drawback.After several burns the carbon of the ascorbic acid leaves a largeresidue in the carbon furnace, which affects the absorbance zero. Theresidue is easily removed with a pipe cleaner or Kimwipe (after 2-3burns).

5. It is very important to pipette reproducibly.

Reference:

Katz, A., 1975. The determination of rubidium and strontium in sili-cates by flameless atomic-absorption spectroscopy. Chern. Geol.,16:15-25.

694

Documents

16. GEOCHEMISTRY OF INTERSTITIAL WATERS …GEOCHEMISTRY OF INTERSTITIAL WATERS AND SEDIMENTS, LEG 64, GULF OF CALIFORNIA 1 Joris M. Gieskes, 2 Henry Elderfield, 3 James R. Lawrence,