Obstacles and sinks: effects on turbidite flow and deposition on deep water continental margins

Waltham, David, Department of Geology, Royal Holloway, University of London, Egham, Surrey, United Kingdom; Ian Davison, Earthmoves, Virginia Water, Surrey, United Kingdom

Abstract

Faults and salt diapirs control turbidity currents in deep water on continental margins. Counter regional faults create obstacles to flow. We use 3D numerical models to investigate the critical height and length of fault scarps, which impede flows of different momentum. Seaward-dipping fault scarps accelerate flow, and a series of fault scarps will ensure that the turbidite deposition takes place much farther downslope. Models predict the effects of different scarp heights, and combinations of parallel scarps.

Salt diapirs create positive bathymetric relief due buoyancy and compression. On deepwater margins where a downslope gravitational push is present (e.g., Gulf Coast of Mexico or the Brazilian Atlantic margin) diapirs can create a freeboard up to 375 metres above the regional. We investigate the effects of diapir shape and freeboard height on turbidity flow and show how these affect flow direction, speed, and thickness. Where salt diapirs are actively dissolving, this creates a sea bed depression above the diapir. The effects of these on turbidite flow can be dramatic and our model allows us to quantify critical depression widths and depths for arresting flows.