New Model of Turbidity Current Suggested After Direct Observation of Turbidity Currents in the Congo Canyon

Abstract

Turbidity currents are efficient transporters of sediment from shallow continental shelves to deep ocean basins. Single events are capable of carrying greater sediment volumes than of all rivers in the world combined for a year, ultimately controlling the sediment forming hydrocarbon reservoirs. Despite their importance, surprisingly few direct observations of these flows are available due to the difficulties in monitoring them. Due to this, most of our knowledge of these flows relies on the analysis of outcrops, numerical modelling and the laboratory experiments. Turbidity currents in small-scale laboratory experiments typically have a three-folded structure consisting of: 1) a thick turbulent head fed by 2) a faster moving thinner body, outrunning 3) a dissipating tail. Here we compare our acoustic Doppler current profiler (ADCP) records of turbidity currents at 2,000 water depth in the Congo Canyon (Cooper et al., 2013) with the results from the small-scale flows, to determine if both flow structures are similar. The measurements from the Congo Canyon show flows with durations of 6-to-10-days and velocities of over 2 m/s for a thin frontal cell and slower for a thick body and tail. The velocity difference between the fast frontal cell and the slower body is presented as the main mechanism for the flow stretching since its generation. The analysis of the turbulence and sediment concentration, from the acoustic inversion of the ADCP echo intensity variable, within the flow points towards a frontal cell that drives the flow autosuspending sediment that feeds the more turbulent trailing body that allows for a more homogeneous sediment concentration from the top to the bottom of the flow. Cooper, C., Wood, J., Andrieux, O. (2013). Turbidity Current Measurements in the Congo Canyon. Offshore Technology Conference. doi:10.4043/23992-MS

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016