The effect that basin floor topography and flow efficiency have upon turbidity flows, and the way they control turbidite deposition, is poorly understood. The applications of new flume-based and theoretical depositional models in this study have improved our understanding of these effects and thus the prediction of depositional sites within topographically influenced turbidite systems.

Flume experiments were performed in which turbidity currents were released via a lock exchange mechanism and then allowed to interact with obstacles, which modelled diapirs. The range of depositional possibilities around diapirs can be shown to be controlled by the ratio between the obstacle height to the flow height (H*). The deposit of flows where the dimensionless obstacle height (obstacle height/flow thickness) is less than 0.1 resembles the deposit geometries of unobstructed standard flows. However, the lower the dimensionless obstacle height (H* < 0.1), the more sediment is deposited in the lee of the obstacle, suggesting that more of the suspended sediment moved over the area of the obstacle than in the case of the unobstructed flow. Higher dimensionless obstacle heights (H* > 0.1) result in thicker sediment accumulation upstream of the obstacle and reduced sedimentation immediately in the obstacle lee. This reflects the fact that the flow has been deflected elsewhere.

In another set of experiments, the factors influencing flow efficiency and their effect on the geometries of turbidites were investigated. Flow efficiency gives a relative measure of the distance a flow may travel. In flows of higher efficiency, the transport phase is prolonged. Early workers stressed the importance of the fine-grained component of the sediment budget and flow volume on flow efficiency. The work outlined here confirms the existence of a number of linked controls, which include: (a) the suspended sediment grain-size distribution, (b) flow volume and also the (c) suspension density. The presence of a significant fine-tail to the sediment budget is interpreted to control flow efficiency through the mechanisms of buoyancy enhancement for the coarser-grained suspended sediment component, reduced rates of momentum loss due to low mud deposition rates and friction reduction; suspension density is interpreted to affect flow efficiency principally through its impact upon the flow momentum, whilst suspension volume is interpreted to control flow efficiency principally by affecting shear velocities. The experiments have illustrated that each of the controls outlined above has a characteristically different effect upon the volume, geometry and the stacking patterns of resultant deposits.

Studies of the distribution of turbidites around salt diapirs in the subsurface have shown the occurrence of sediment accumulations at specific sites comparable to those found in the experiments. Through comparison of the experiments detailing the control of H* upon deposit geometry, it was possible to infer the values of H* in the subsurface. In seismic, if H* can be quantified from the observed sediment distribution patterns around diapirs, it may be possible to add value to the existing depositional geometries around topography (e.g. diapirs) and also make predictions about the extent and nature of depositional geometries in areas where seismic quality/coverage are poor.