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Deep-Sea Drilling Interstitial Water Studies: Implications for Chemical Alteration of the Oceanic Crust, Layers I and II

By
Joris M. Gieskes
Joris M. Gieskes
Science and Public Policy, University of California
San Diego, California 92093 U.S.A
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Published:
January 01, 1981

Abstract

This paper represents a review of observations made on the composition of interstitial waters of sediments recovered during the Deep Sea Drilling Project.

In pelagic sediments with relatively slow rates of deposition (< 50 m/106 yr) increases commonly are measured in dissolved calcium and decreases in dissolved magnesium and potassium as well as H218O. These changes, to a large extent, can be understood in terms of alteration reactions occurring in the basalts of Layer II of the oceanic crust, and, to a lesser extent, in terms of alteration of volcanic matter dispersed in the sediment column (Layer I).

Dissolved silica concentrations are generally enhanced in sediments containing opaline biogenic silica. Such enhanced silica activities in turn provide an environment in which reactions involving the alteration of volcanic matter in the sediments may occur. These reactions are particularly evident in zones of silicification, in which opal-A is transformed to opaJ-CT and quartz.

Dissolved strontium concentrations in carbonate sediments are affected by carbonate recrystallization processes, which release strontium to the interstitial waters. These increases imply that Sr/Ca distribution coefficients in calcites must be smaller than generally accepted. In carbonate-free sediments increased strontium is often the result of reactions involving volcanic matter in the sediments and/or the underlying basalts. This relationship is particularly evident from observations on the 87Sr/86Sr ratio of dissolved strontium.

Dissolved manganese and lithium appear to be released by biogenic silica. For Mn such sediments contain relatively more reactive organic carbon, which appears to act as the reducing agent in marine sediments.

In rapidly-deposited hemipelagic sediments complex concentration-depth gradients result, particularly as a result of processes involving sulfate reduction and methane gas generation. High alkalinities (bicarbonate) result, as well as high dissolved ammonia values. Carbonate precipitation (calcite, ankerite, dolomite) can be important in such sediments.

Freshwater acquifers near salt deposits can result in saline brines being advected into the sediment column in areas on the continental shelves and slopes.

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Contents

SEPM Special Publication

The Deep Sea Drilling Project: A Decade of Progress

John E. Warme
John E. Warme
Colorado School of Mines, Golden Colorado.
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Robert G. Douglas
Robert G. Douglas
University of Southern California, Los Angeles California
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Edward L. Winterer
Edward L. Winterer
Scripps Institution of Oceanography, La Jolla California
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SEPM Society for Sedimentary Geology
Volume
32
ISBN electronic:
9781565761629
Publication date:
January 01, 1981

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