The influence of complex palaeobathymetry on development of deep-lacustrine fan systems

Pre-existing complex palaeobathymetry often plays a key role in the spatial-temporal distribution and character of deepwater sedimentary systems. Particularly in deep-marine fan systems where their spatial-temporal association with complex syn-depositional palaeobathymetry have been widely investigated. When present in deep-marine settings, complex palaeobathymetry is known to affect flow-type, flow direction, and resultant fan distribution, which ultimately leads to atypical reservoir rock distribution. By contrast, far fewer studies explore the influencing controls of palaeobathymetry on deep-lacustrine sedimentary systems. This is important to investigate as deep-lacustrine basins have quite different allogenic and autogenic controls on flow types and resultant fan systems and fan lobes, which varies through different stages of basin configuration. To address this knowledge gap, this study documents and characterises a suite of deep-lacustrine sedimentary systems imaged in high-quality 3D seismic data from the rift-sag transitional and early post-rift phases of the North Falkland Basin, Falkland Islands. A range of multi-scalar seismo-geomorphological features are identified, including super systems, fan systems, fan lobes, and channel elements. The influence of palaeobathymetry on flows and resultant sedimentary features is evidenced by frontal and lateral structural confinement at the super system scale, and lateral confinement plus fan/flow deflection at the fan system, fan, and lobe scale. Offset stacking and compensational lobe-scale stacking geometries are developed in response to the type and scale of confinement. Palaeobathymetry, created as depositional relief by preceding fan deposits, is shown to progressively influence flow types and resultant spatial distribution of ensuing sedimentary systems. During periods of basin-fill where encircling palaeobathymetry ultimately controlled super system scale distribution, the ponding of flows and resultant fan features against intra-basinal highs formed thick packages of potentially coarse-grained sediments. As the basin filled-up and encircling topography exerted less control on super system scale distribution, flows were able to surmount the intra-basinal highs, leading to flow stripping processes. The combination of ponding and flow stripping processes resulted in the deposition and preservation of coarse-grained sediments immediately behind or on top of intra-basin structures. The results of this study provide key insights into the interaction of deep-lacustrine sedimentary systems and complex palaeobathymetry, which ultimately influences reservoir distribution