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Salt Tectonic Controls on Fluvio-Lacustrine Stratigraphy: Outcrop and Subsurface Examples


Matthews, Wendy1, Gary Hampson1, Bruce Trudgill2, John Underhill3, Lutz Seiffert4 (1) Imperial College London, London, United Kingdom (2) Colorado School of Mines,Golden, CO (3) University of Edinburgh, Edinburgh, UK (4) Total Exploration UK PLC, Aberdeen, United Kingdom


Salt-sediment interaction occurs at a range of scales with a variety of different manifes­tations including, structural controls in the subsurface, geomorphological processes at the surface, formation-scale thickness changes, and intra-formational facies variability. An under­standing of this interaction is critical to the evaluation and prediction of depositional facies in both outcrop- and subsurface-based studies. Large-scale stratal geometries and thickness changes resulting from salt movement are often apparent on 3D seismic data, but to date there are few predictive models for facies architecture at sub-seismic, reservoir scale.

This study uses a high-quality outcrop dataset of fluvio-lacustrine strata in an exhumed salt basin (late Triassic Chinle Formation, Paradox Basin, Utah) as an analogue for improved understanding of a subsurface dataset of similar structural and sedimentological setting (Triassic Skagerrak Formation, Central North Sea, UK). Salt-sediment interaction in the Chinle Formation is expressed by localised (km-scale) stratigraphic thickness variations, angular stratal relationships and changes in facies architecture. Based on these criteria, there is evidence for salt-sediment interaction across a range of syn-depositional salt struc­tures, including an anticline above a buried salt pillow (Cane Creek anticline), a salt wall exposed at surface (Moab Valley salt wall), and a salt-withdrawal mini-basin (Big Bend mini­basin). Stratigraphy and facies architecture across these structures reflect the following con­trols: regional subsidence, localised differential accommodation space, and localised palaeogeomorphology. Both localised controls were driven by syn-depositional salt move­ment. The results of this outcrop study are being applied to predicting stratigraphic relation­ships, facies architecture and reservoir distribution in the subsurface.