Implementing Orbital Climate Control on Alluvial Stratigraphy in Subsurface Predictive Models

Summary Low net-to-gross alluvial stratigraphy is characterized by floodbasin sediments with sparse intercalating channel sandbodies. Better predicting the occurrence of sweet spots depends on our ability to determine the controlling mechanisms of sedimentation. Control on alluvial deposition by orbital climate cycles would include a rich predictive value for intercalating sandbody geometry and their stratigraphic positions. However, in subsurface work-flows orbital-forcing models are hardly used. Here, we present results of our study into implementing orbital forcing of alluvial sedimentation into subsurface workflows. First, we analyse floodplain avulsion-overbank sedimentary cycles in the early Eocene Bighorn basin, Wyoming, providing additional evidence that these cycles are driven by orbital climate forcing. High lateral variability is found on the floodplains by tracing individual beds in UAV-based photogrammetry panels. Our data further suggest compensational stacking patterns of thick cycles following thin cycles and vice versa. Next, numerical model runs are used to demonstrate that upstream cyclic forcing is indeed well able to produce cyclic alluvial stratigraphy. At long and short cyclic wavelengths and with low forcing amplitudes autogenic processes start to dominate. Future work includes analysing geometry and stratigraphic position of incorporated sandstone bodies in our field-based and numerical alluvial stratigraphies.