Controls on Fluvial Stratigraphy in Actively Subsiding Salt-Walled Mini-Basins
Differential rates and styles of salt-wall uplift and associated mini-basin subsidence exert a primary control on the distribution of fluvial channels and their resultant preserved stratal architectures in salt basin provinces developed in continental settings, both spatially across mini-basins and temporally throughout the accumulating succession. The surface expression of salt-wall growth can be manifest as topography that can act to divert and partition fluvial systems passing across regions experiencing halokenesis. This results in significant variation in the preserved distribution of channel elements both within a single mini-basin and between adjoining basins, such variation being primarily dependent on the balance between rates of salt withdrawal beneath evolving mini-basins, rates of salt-wall uplift and sedimentation, which together determine the fill-state of evolving basins. Within individual mini-basins, differential rates of subsidence/uplift both across a mini-basin and along its strike can control fluvial system distribution, through complex spatio-temporal changes in depocenter position.
The Salt Anticline Province in the foredeep of the Paradox Basin (SE Utah) is a region where several salt-walled mini-basins developed in response to loading of Pennsylvanian-age salt during Permian through to Jurassic times. Within this region, the Triassic Moenkopi Formation represents the preserved succession of a braidplain and overbank fluvial system developed in a dryland setting. The preserved thickness of Moenkopi sediments across the region varies from absent where salt-wall uplift resulted in non-deposition and erosion, to over 200 m in mini-basin depocenters. Preserved fluvial architecture varies in a predictable manner and records a systematic response to salt movement and basin evolution that is governed by proximity to adjacent salt-walls, and the balance between rates of subsidence and sedimentation.
Models that enable the prediction of the proportion and distribution of sand bodies in these types of salt mini-basins are important for hydrocarbon exploration and reservoir prediction, where the stacking patterns of channel elements governs connectivity of hydrocarbon-bearing packages. Field-derived architectural data are being used to constrain a range of attributes used for the stochastic modeling of sand-body connectivity and prediction of net-to-gross in several Triassic plays and reservoirs of the Central North Sea.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California