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Processes |
Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741, USA
Fine-grained sediments and sedimentary rocks make up as much as 75% of the present and past sedimentary records. River discharge is the largest single source of fine-grained material, followed by biological, volcanic and aeolian sources. The composition, texture and bulk properties that characterize different sediment facies are controlled primarily by climate, tectonics, sediment supply, oceanic dispersal systems and biological activity.
Fine sediments are transported into deep water by low-concentration nepheloid plumes, turbidity currents of a range of concentrations, flows and mass-movements. Mass-movement may be the major process delivering fine-grained sediment to the deep-sea floor over long time periods. Abyssal plains, the end of the passive margin transport system, are more affected by turbidity currents. Much bottom current reworking of sediments occurs at all depths in the ocean with results that may be very subtle. In shallower waters, balances between supply and dispersal may allow for the accumulation of mud belts on shelves and much fine sediments passes through such systems. Organic matter concentrations in fine sediment may be more a function of accumulation rates of organic versus terrigenous matter than local biological productivity.
Fine-grained sediments require the application of methodology and results of a broad range of scientific disciplines. Effective understanding of the fine record will require interaction between several sciences.
