--> Stratigraphic Evolution of Confined Deep-Water Basins: Insights From Physical Models and Outcrop Analogs

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Stratigraphic Evolution of Confined Deep-Water Basins: Insights From Physical Models and Outcrop Analogs

Abstract

Turbidity currents in confined basins generate deposits which may pinch-out abruptly or over longer distances, depending on the character of the flows and the basin margin topography. These sub-seismic pinch-outs are critical for the understanding of stratigraphic trap potential and reservoir quality distribution. Here, physical models of turbidity currents are used to better understand the processes that govern the architecture of submarine lobe deposits adjacent to topography. The seafloor topography is formed by a 10 cm high, 40 cm wide and 25o dipping symmetrical and erodible ridge that is rotated around a common point to be 1) parallel, 2) oblique and 3) perpendicular to the incoming flow. Flow-parallel confinement on one side causes the deposit to extend 20 % further into the basin compared with an unconfined lobe, with the flow eroding and running up the lateral topography, forming a lateral fringe that onlaps the confining relief. This fringe thickens away from the topography toward the axis of the deposit, resulting in the creation of accommodation space adjacent to the topographic barrier. Flow-oblique confinement generates a lobe with a run-out length similar to the unconfined lobe. The oblique confinement, however, causes the deposition of a secondary lobe that was deflected by the confining ridge, resulting in two lobes deposited by one sediment influx to the basin. Each of these lobes have a lower volume than the unconfined deposit. Perpendicular confinement results in initial up-dip ponding and lateral spreading at the barrier, followed by axial erosion and down-dip overspill that forms a lobe deeper in the basin. The results of these experiments are compared to field observations from the well-exposed and confined Cenozoic Annot Basin of SE France and the Mesozoic Basque-Cantabrian Basin of northern Spain. Many stratigraphic relationships within these outcropping basins have previously been interpreted as the result of allogenic processes, however the findings of this study indicate that many of the relationships seen can be explained by autogenic processes. These findings have implications for the paleogeographic reconstructions of structurally complex deep-marine basins, the interpretation of stacking patterns within confined basins and, therefore, the prediction of reservoir and stratigraphic traps within these highly prospective settings.