Chapter 5 Deep-water Bottom Currents and their Deposits

Abstract

This chapter discusses deep-water bottom currents and their deposits from oceanographical and sedimentological standpoints. Deep-water bottom currents operate in deep waters of both marine and lacustrine environments. Bottom current covers a variety of bottom currents of different origins, flow directions, and velocities. Five types of bottom currents are recognized at the shelf break based on their origin. These currents are generated by: (1) thermohaline differences, (2) wind forces, (3) tidal forces, (4) internal waves, and (5) surface waves. Four basic types of deep-water bottom currents and their deposits are discussed: (1) thermohaline-induced geostrophic bottom currents, (2) wind-driven bottom currents, (3) deep-water tidal bottom currents, and (4) internal waves and tides (baroclinic currents). Sand or mud rhythmites, double-mud layers, climbing ripples, mud-draped ripples, sigmoidal cross-bedding with mud drapes, and flaser bedding are deposits of deep-marine tidal bottom currents. These features represent alternating events of traction and suspension deposition. Sedimentary structures of bottom-current deposits occur in discrete units. Selected examples of studies that dealt with tidal processes and their deposits in modern and ancient deep-water environments are also reviewed. Traction features interpreted as indicative of deep-water bottom current reworking are also diagrammatically represented.