Signal Preservation in Pulsing Turbidity Currents

Abstract

Recent debate has focused on the potential preservation of the signal of seismic events in the sedimentary record via the initiation of large-scale turbidity current flows. It has been postulated that details of seismic activity may be recorded in turbidites. For example, given the long run out time of turbidity currents, secondary turbidity currents events, initiated by seismic aftershocks, are likely to interact with the primary events creating a “pulsing” flow. Such pulsing flow may also be generated if the failure of a seismic fault lies across an interconnected series of submarine channel systems, where a seismic trigger may generate multiple linked flows. With variation in feeder channel length causing variation in the time taken for individual flows to reach channel confluences, the resultant turbidity current is also expected to be pulsed. Thus, cyclical waxing to waning behavior preserved in graded flow deposits may be a key indicator of secondary seismic activity or a seismic trigger acting over an interconnected channel system. Dependent on the ability for signal preservation in pulsing flows, deposit grading may provide a novel means of assessing proximity to source and/or system architecture. Novel experimental research is presented that explores the dynamics of pulsed turbidity currents. The experimental study is used to quantitatively examine controls on the time and length scale of signal preservation. Parameters investigated include volumes of material released, effective flow density and viscosity (as a proxy of flow mud content). Full flow field visualization was made using an array of interlinked HD cameras. Dyeing separate components of the flow different colors enabled detailed analysis of flow dynamic behavior occurring between head and tail. The secondary pulsing flow was seen to rapidly overtake the first flow. Observations of flow velocity and density suggested that due to stratification the secondary flow was travelling along the density interface between the main body of the primary flow and its turbulent wake. As the pulsing flows created in the laboratory experiments rapidly merged, it suggests that it is difficult to preserve pulsing signals of interacting turbidity currents over long run out distance or times. However, these initial experiments have been carried out with solute currents on flat slopes. Particulate currents travelling over a pronounced gradient may have a significantly different signal preservation behavior.

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