THE INFLUENCE OF SEDIMENTARY GRAVITY FLOW CONFINEMENT, CONTAINMENT AND BASIN SIZE UPON DEPOSITIONAL CHARACTER AND DISTRIBUTION IN DEEP-WATER CONFINED SYSTEMS

The confinement and containment of sedimentary gravity currents, and the depositional systems that they emplace, by sea floor topography is commonplace in deep-water topographically complex settings (e.g., salt mini-basins, intra-cratonic basins, passive slopes with gravity tectonic systems). A distinct type of gravity current deposit containing a mud-clast-rich or clay-rich sandstone interval sandwiched within an otherwise clean sandstone bed are termed hybrid event beds (HEB) and can both develop and show systematic variation in depositional character towards confining topographic features. Such deposits present baffles to hydrocarbon fluid flow and can be indicators of proximity to topographic confinement.

New research on outcrop from the Castagnola Basin (Miocene, Northern Italy) and the Pennine Basin (Pennsylvanian, Northern England) has highlighted the contrasts between sedimentary systems that are confined and contained to those which are only contained. Specifically HEBs in the former systems are less likely to be localised to topographic confinement and show no systematic variation in depositional character in respect to palaeoflow direction or proximity to confining topography. Confined systems are more likely to have HEBs localised to bathymetry but this is also determined by permitted flow run-out distance which is a function of basin size. Such contrasts are considered to arise due to flow containment restricting flow expansion and energy dissipation to promote a number of factors. Specifically, 1) significant erosion of muddy substrate; 2) high sedimentation rates; 3) strong and complex 3D flow following interaction with multiple basin margins. This research provides insight for predicting depositional character, thus hydrocarbon reservoir quality, in topographically complex settings and for reconstructing the geometry and evolution of basins utilizing the character of their sedimentary infill.