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.