TOPOGRAPHICALLY CONTROLLED DEPOSITS FROM THE EARLY STAGE OF DEEP-WATER DEPOSITION IN A FORELAND BASIN

Sea floor topography resulting from emplacement of submarine mass transport deposits can strongly influence the pathways of and deposition by subsequent turbidity currents. This study presents an example of the role of basin-scale mass transport deposits (MTDs) formed in the early stage of foreland basin evolution on subsequent processes of basin filling. We investigate deep-water sediments deposited in the Tertiary Molasse basin of Austria to understand how MTDs impacted the subsequent turbidity currents and their depositional style. We utilize multi-scale, subsurface data including cores, well logs, and 3D seismic data to understand both fine-scale sedimentology and the large-scale facies distributions. This study reveals that during the early Molasse basin development, basin-scale MTDs acted as positive topographic elements that controlled the routes and deposition of subsequent turbidity currents. We propose three stages in the Oligocene to Miocene evolution of the Molasse basin: (1) initial deposition of MTDs and local turbidites, (2) subsequent turbidity current deposition controlled by antecedent MTD topography, and (3) burial of the MTD-dominated topography and development of an organized and meandering axial channel complex. MTDs played an important role during the early evolution of the basin controlling the general distribution and facies architecture of syn- and post-MTD turbiditic sandstone deposits. Recognizing the stratigraphic architecture and geometries of MTDs in the subsurface is key to identifying the spatial distribution of these deposits as well as overlying turbidites in the Molasse basin and, we suspect, many other basins. sandstone and mudstone, and mudstone. Based on our analyses of facies and facies association, we interpret the facies assemblages of continuous seismic facies to be high- and low-density turbidity current deposits.