Some thoughts on fine-grained sediment transport and deposition

Abstract

Fine sediments are receiving greater emphasis due to economic significance as source rocks for petroleum, the often nearly continuous record of depositional histories, and the volumetric importance in the geologic record. Distribution of these particulates is driven primarily by ocean circulation. Deposition is primarily controlled by planktic biologic filtering, aggregation, and reworking; early diagenesis is controlled by bacterial processes with consequent changes in bulk and chemical properties. Most fine particulates are initially deposited in the continental margins and then move to deep-ocean floors by mass wasting and high-concentration flows. Stability of these fine deposits even on slopes of gentle gradient is controlled primarily by water content which, in turn, is a function of sedimentation rate and texture of the supply. Mass transport can occur in a variety of forms from slow creep to catastrophic failures of large scale. A sequence of morphologies can result from the various forms of movement. Most of the fine-grained stratigraphic record urgently needs reevaluation and restudy. Models of paleogeographic reconstructions on a large scale need to include the results of physical and biological oceanographers since the older simpler scenarios of locations of zones of high bioproductivity and of the patterns of major ocean currents have been greatly modified in recent years. Biological oceanographers have contributed models for contemporary upwelling systems that have changed the thinking of paleobiologists and biostratigraphers working with biogenically dominated fine sedimentary rocks.