Controls on Fluvial Sedimentary Architecture in Salt-Walled Mini-Basins
Banham, Steven G.; Venus, Joanne H.; Mountney, Nigel
The distribution of accumulations of fluvial architectural elements in salt-walled mini-basins is controlled by factors related to: (i) halokinesis, including rate and style of salt-wall growth and adjacent mini-basin subsidence, and lateral continuity and orientation of growing salt-wall structures; (ii) independent external factors, such as the rate and direction of sediment delivery, sediment caliber and climatic regime. Together these factors influence the intrinsic behavior of fluvial systems, for example by governing plan-form channel pattern, by dictating avulsion style and frequency, and by controlling the timing and location of episodes of erosion and deposition.
Sediment delivery in directions perpendicular to elongate salt walls tend to favor: (i) repeated fluvial incision, localized reworking and sediment bypass over growing salt highs; (ii) rapid rates of aggradation in locally subsiding mini-basins or in rim-synclines on the upstream sides of salt walls; (iii) local deflection and diversion of fluvial drainage pathways to directions parallel to salt walls; (iv) proximal-to-distal changes in drainage style whereby accumulations become progressively finer-grained in mini-basins more distal to the source; (v) the increased likelihood of the preservation of eolian deposits in the downstream lee of uplifted salt walls in arid settings.
By contrast, sediment delivery in directions parallel to elongate salt walls tends to favor: (i) the accumulation of markedly different successions between adjacent mini-basins where salt-wall uplift lead to basin isolation; (ii) the coeval development of sand-prone and sand-poor neighboring basin fills where fluvial systems experience different rates and sources of sediment supply; (iii) increased fluvial activity adjacent to one salt wall due to differential subsidence, which allows one part of the basin to become distinctly sand prone.
Examples of fluvial successions influenced by halokinetic activity include: (i) the Permian Cutler Group, Salt Anticline Region, SE Utah, in which fluvial systems flowed predominantly perpendicular to growing salt-walls; (ii) the Triassic Moenkopi and Chinle formations, also of the Salt Anticline Region, in which fluvial systems flowed predominantly parallel to the axes of elongate salt walls; (iii) the Triassic Judy and Joanne sandstones, J-Block, Central North Sea, in which salt structures formed polygonal patterns, giving rise to complex drainage pathways.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013