Coastal Siliciclastic Sabkhas and Related Evaporative Environments of the Permian Yates Formation, North Ward-Estes Field, Ward County, Texas (1)

Abstract

During deposition of the Yates Formation (late Guadalupian, Permian), a broad, evaporative coastal plain or sabkha existed behind the Capitan reef along the Central Basin platform western margin in Ward County, Texas. Cyclic sea level fluctuations produced a succession of dolomites, evaporites, and siliciclastics as the evaporative coastal plain oscillated across the Yates shelf. Moving landward, the environments represented in this study are (1) lagoon, (2) intertidal algal flat, (3) beach ridge, (4) siliciclastic sabkha, and (5) sand sheet/playa mud flat/salina. Evaporite-based cycles, which formed on the inner shelf, grade upward from massive salina anhydrites into nodular anhydrites with increasing amounts of siliciclastic mudstone interbeds (playa mud flat). Carbonate-based cycles consist of basal lagoonal peloid and skeletal dolostones which grade upward into tidal-flat dolostones, beach-ridge sandstones, and finally into sabkha siliciclastics. The characteristic disrupted texture of the Yates siliciclastics was created by surficial and interstratal halite growth formed during seasonal flooding and subsequent desiccation in a sabkha environment. A siliciclastic accretionary complex composed of stacked beach ridges and detrital sabkhas formed behind the pisolite barrier. Local siliciclastic accumulations also occurred over sinks produced b the dissolution of bedded sulfates. Most hydrocarbon production in North Ward-Estes field comes from the beach-ridge sandstones.