Coastal Sabkha and Salt Pan Deposition of the Lower Clear Fork Formation (Permian), Texas

Abstract

ABSTRACT Middle Permian (Leonard Series) evaporites, carbonates, and red beds of the lower Clear Fork Formation in the Texas Panhandle display many features common to modern coastal and continental sabkha facies. Similarities among lithofacies patterns and sequences, sedimentary structures, and anhydrite-halite textures and fabrics of both the lower Clear Fork Formation and modern sabkha facies permit construction of a model of halite deposition in coastal-sabkha salt pan environments which may be generally applicable to other ancient sabkha facies in intracratonic basins and around stable or rifted continental margins. Inferred coastal sabkha and marine inner-shelf environments and lithofacies recognized in the lower Clear Fork Formation are largely based upon analogous modern depositional se tings and include the following: 1) red siltstone to mudstone deposited in a wadi or desert alluvial-eolian plain and inner-sabkha mud flats, both passing basinward into 2) chaotic mudstone-halite of an inner-sabkha saline mud flat, which flanked 3) inner-sabkha salt pans bearing banded to massive halite and laminated anhydrite, and 4) nodular, nodular-mosaic, and massive anhydrite and dolomite deposited in marginal sabkha and inner shelf environments. Salt pans may have formed in the inner sabkha as a result of displacive gypsum-anhydrite growth and jacking up of the marginal sabkha surface, which impeded seaward drainage of floodwater off the sabkha. Modern process-sediment analogs include alluvial fans, saline mud flats, and salt pans of the coastal sabkhas in Baja, Mexico, the Trucial Coast, and Kutch, India. Evaporites and terrigenous clastics in Bristol Dry Lake, California, exhibit many features analogous with the Permian, suggesting that this setting, though strictly continental, serves as a process analog. Bromide values in lower Clear Fork halite average 40 ppm, which is less than an unaltered marine halite but still within the range of marine halite that has undergone diagenesis. Upward decreasing values in the lower Clear Fork upper-cycle may indicate a decrease in salinity during deposition or that the younger halite beds suffered more diagenesis than the underlying halite.