Influence of basin physiography upon the character and distribution of hybrid event beds

Confinement of sedimentary gravity currents and the deep-water depositional systems they emplace by sea-floor topography is commonplace in a number of settings (e.g., salt mini-basins, intra cratonic basins, passive margins with gravity-driven tectonic systems). Distinct sedimentary gravity flow deposits, containing co-genetic matrix- mud-clastrich and matrix-poor sandstone, are recognised in a range of deep-water depositional systems, including topographically complex settings where gravity flows can be confined and or contained (ponded) by sea floor topography. In the latter settings HEBs can exhibit systematic development and variation in their depositional character with increasing proximity towards their confining topography. New research from the Castagnola Basin (Miocene, Northern Italy) and the Pennine Basin (Namurian, Northern England) has begun to highlight contrasts between sedimentary systems that are confined and contained (CC) and those which are confined but uncontained (CU). In CC settings HEBs are less likely to be localised to their topographic confinement and exhibit no systematic variation in depositional character in respect to palaeoflow direction or proximity towards the confining slope. Compared to CC settings, HEBs in CU settings are more likely to be localised to confining topography and exhibit systematic variation in depositional character over short length-scales; however systematic variation in depositional character can occur over longer length-scales where HEB extend further upstream and are not locally restricted to the confining basin margin. These contrasts are considered to arise due to flow containment which restricts flow expansion and promotes a number of factors. Specifically significant erosion of muddy substrate, high sedimentation rates and the extensive complex 3D flow dynamics following interaction with multiple basin margins. This work highlights a range of boundary conditions which influence the character and distribution of HEBs, and thus that of depositional reservoir quality, in topographically complex settings. Awareness of these boundary conditions may provide insight when attempting to reconstruct basin geometries and evolutions using the character of their sedimentary infill.