THE INFLUENCE OF SALT WITHDRAWAL SUBSIDENCE ON PALEOSOL MATURITY AND SEDIMENTATION RATES IN THE TRIASSIC CHINLE FORMATION: THE SALT ANTICLINE REGION OF EASTERN UTAH

This study evaluates paleosol expression and sedimentation rates within a rapidly subsiding salt withdrawal minibasin in the Triassic Chinle Formation. The sedimentary response to salt withdrawal may be better preserved in fossil soils than depositional structures or lithology. The Chinle was divided into seven fluvial aggradational cycle sets (FACSET), based on stacking patterns and paleosol development. Twelve pedotypes are characterized, including paleosols similar to modern entisols, inceptisols, aridisols, vertisols and alfisols. A maturity index (1 to 5) is assigned to each pedotype. An estimated amount of time to develop each pedotype and uncompacted stratigraphic thicknesses are used to calculate sedimentation rates. Paleosol maturity is indirectly proportional to FACSET thickness, and decreases towards the minibasin axis. There tends to be more paleosols near the minibasin axis, usually limited to entisols and inceptisols with maturity indexes of one or two. Areas marginal to the minibasin are characterized by fewer, more mature (Bk horizons, alfisols) paleosols with maturity indexes of four or five. Pedogenically estimated sedimentation rates can be an order of magnitude greater in the minibasin than in marginal areas. Paleosol expression significantly contributes to the paleogeographic interpretation of salt withdrawal minibasins.