Deep-Sea Drilling Interstitial Water Studies: Implications for Chemical Alteration of the Oceanic Crust, Layers I and II
Joris M. Gieskes, 1981. "Deep-Sea Drilling Interstitial Water Studies: Implications for Chemical Alteration of the Oceanic Crust, Layers I and II", The Deep Sea Drilling Project: A Decade of Progress, John E. Warme, Robert G. Douglas, Edward L. Winterer
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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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At the present the Glomar Challenger has drilled over 500 holes over the world ocean, involving hundreds of scientists from dozens of countries. This volume is intended as a review of some of theimportant results from the most comprehensive, ambitious and successful earth-bound geologic project ever undertaken. The symposium upon which this volume originated was held April 4, 1979 at the SEPM/AAPG Annual Meeting in Houston. No comprehensive synthesis of all aspects of the DSDP has appeared, and the topic coverage in this volume is biased towards the sediments and fossils, and their significance for certain aspects of earth history – paleogeography, bathymetry, climatology, oceanography, ecology, environments – all in keeping with the audience of sedimentary geologists.