Transversely-sourced mass-transport deposits and stratigraphic evolution of a foreland submarine channel system: Deep-water tertiary strata of the Austrian Molasse Basin

Abstract

Abstract Mass-transport deposits (MTDs) generate seafloor topography that can strongly influence the stratigraphic architecture of submarine channels. In deep-water depositional environments, both MTDs and turbidity currents are commonly fed into basins from a single point source, and turbidites may be observed ponding on top of, between, and beside MTDs. This study uses core data and 3D seismic reflection data to classify two major types of MTDs, 1) long-runout MTDs, which are radial in plan view and mounded, and 2) short-runout MTDs, which are elongate and weakly layered. Both MTD types deposited transversely into a deep-water axial channel belt in the lower Puchkirchen Formation in the Molasse Basin of Austria. Unlike longitudinally-emplaced MTDs previously identified in the upper Puchkirchen Formation, the surface topography of transversely-emplaced MTDs, especially those of the long-runout MTDs, provided accommodation for the ponding of sediments on a scale similar to that of large supra-MTD ponded turbidite intervals identified globally. Moreover, both types of transversely-emplaced MTDs enhanced syn-tectonic northward migration of the northern margin of the channel belt and delivered large quantities of fine-grained material that likely contributed to the mud-rich lithofacies that comprise a significant fraction of the lower Puchkirchen Formation. Our work suggests that supra-MTD ponded deposits could contain hydrocarbon reservoir units in regions previously regarded as waste zones. More broadly, this study characterizes how transversely-emplaced MTDs influence seafloor topography, submarine channel morphology, and the distribution of reservoir facies in a depositional system characterized by axial sediment transport.