Influence of Bottom Currents on Gravity-Induced Deposits as Potential Triggers for Slope Instability and as Sediment-Redistribution Agents

Abstract

Gravity-induced processes and associated deposits in deepwater settings have been investigated for decades. However, the magnitude of the influence exerted by deepwater bottom currents as a destabilizing agent for mass transport deposits (MTDs), as well as their capacity to redistribute sediments, is poorly understood. MTDs form an important component of the stratigraphic column, but these units are often found in association with contourites and sediment wave fields. We undertook a survey of contourites and deepwater sediment waves so as to better understand the location, sedimentology, and morphology of these deposits. This survey also improved our understanding of the nature of the bathymetry in and around known modern and ancient contourites and sediment wave fields. Examination of the survey indicates that the presence of contourites and sediment waves underlying MTDs is not uncommon in most continental margins. In this study we integrate elements of the geologic context (nature of the bathymetry, physiography of the shelf break, velocity and direction of known currents, sediment sources) in which these units are deposited with their corresponding morphometric parameters, in order to try to establish a relationship between environmental conditions and final architecture of the deposits. Plausible scenarios that link the coupling of MTDs and bottom-current deposits include: 1) contourites acting as shear basal surfaces promoting mass wasting events; and 2) alongslope bottom currents destabilizing the base of the slope and promoting gravitational instabilities that can influence the onset of mass-wasting events. This paper will review a variety of settings where contourites and sediment waves are found beneath, and often on top, of MTDs. We hope this study will provide a better understanding of the association between bottom currents and gravity-induced deposits.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015