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Influence of Mass Failure Deposit Topography on Post-Emplacement Sediment Gravity Flows and Fills: Offshore Eastern Trinidad


Mass transport deposits (MTDs) form complex post-emplacement accommodation that are filled with a variety of deep-water gravity flow deposits. These post-emplacement deposits, here termed healing-phase top fills, form reservoir-quality sedimentary rocks in a variety of setting (i.e., offshore Nigeria, North Slope Alaska, Gulf of Mexico), and have been documented both in subsurface and in outcrops. The MTDs’ surface topography which creates accommodation for post-emplacement deposits is controlled by many factors including sheer spatial size, material composition, flow rheology, deformation styles, and many variables that influence the distribution of these factors in the mass failures (e.g., pre-emplacement bathymetry along the flow path). A combination of these contributes to the difficulty in predicting mass failures’ surface accommodation and its influence on post-emplacement deep-water sedimentation.

To evaluate the manner in which post-emplacement sediments fill such complex accommodation, a near-surface Pleistocene-age MTDs in the slope and basin floor of offshore eastern Trinidad, West Indies was mapped in extreme detail using high-quality 3D seismic data and stratigraphically shallow well data. This shelf-attached mass failure has a muddy composition and exhibits a high plasticity of flow, moving around randomly-distributed, isolated mud diapirs, and exhibiting a very parallel flow fabric. The basal and top surfaces of the MTDs were mapped and the nature of the MTDs’ internal fabric was analyzed using a series of interval attributes to map the tectonomorphic characteristics of the deposit. We compute and assess a series of primary and secondary topographic attributes as well as employ spatial classification algorithms to document accommodation trends on the MTDs top surface, and to evaluate the thickness and distribution of healing-phase deposits filling the surface accommodation. Relationships between post-emplacement accommodation on MTDs and overlying deposits are quantified for a better understanding of topographic influence on healing-phase deposits. This study has resulted in a template for distribution of healing-phase deep-water reservoirs over muddy MTDs.