SEDIMENTOLOGY OF THE UPPER PENNSYLVANIAN BIGHEART SANDSTONE MEMBER, TALLANT FORMATION, PAWNEE AND OSAGE COUNTIES, OKLAHOMA

During the later part of the Pennsylvanian Period about 305 million years ago the southeastern shoreline of the Midcontinent Seaway fluctuated across northeastern Oklahoma as polar ice waxed and waned. The Bigheart Sandstone in northeastern Oklahoma was deposited in a major fluvial-estuarine system that headed in the recently uplifted Ouachita Mountains. Its basal contact with the underlying Barnsdall Formation is a previously unrecognized unconformity. This study adds to the knowledge of the processes that deposited a succession of thick sandstones that thin and even pinch out northward onto the Kansas Shelf. Southward these sandstone bodies grade into multistory siliciclastic deposits in the trough formed by the uplift of the Ouachita Mountains. So these sandbodies play an important role in understanding the overall paleogeography and how deposition changed from the early Pennsylvanian tectonic activity to the more quiet later Pennsylvanian post- uplift time.

Field observations indicate that the Bigheart Sandstone was a fluvial deposit. In Osage County, flaser bedding in the upper part of the sandstone suggests that it might transition from fluvial to estuarine environment. Paleocurrent indicators in the Bigheart Sandstone facies show that transport was mainly northwest. Petrographic analyses indicate that the Bigheart Sandstone is a quartz-rich sublitheranite with a high concentration of sedimentary lithic fragments, but with a limited concentration and diversity of heavy minerals. XRD Clay minerals analyses show a high proportion of illite, which suggests that the Bigheart Sandstone was likely influenced by intense chemical weathering. Both paleocurrent direction and petrographic data suggest that Ouachita Mountains were the source of the Bigheart Sandstone.