BENTHIC FORAMINIFERAL PALEOECOLOGY OF THE STONE CITY AND WHEELOCK MEMBERS OF THE CROCKETT FORMATION (EOCENE; BARTONIAN) OF THE TEXAS GULF COASTAL PLAIN

The late middle Eocene Crockett Formation of the Texas Gulf Coastal Plain consists of a series of marine sands, clays, and glauconitic shell beds deposited on a storm dominated shelf. The Crockett Formation represents the Transgressive Systems Tract of Gulf Coast depositional sequence TE 2.4 in the Texas Gulf Coastal Plain. Planktonic foraminifera and calcareous nannofossils present suggest correlation with the Cook Mountain Formation of Louisiana and Mississippi and the upper Lisbon Formation of Alabama.

Benthic foraminifera were collected from 51 samples from the Stone City Member and the lower Wheelock Member of the Crockett Formation in the Conover #1 Stone City core, Burleson County, Texas and from outcrops along the Little Brazos River, Brazos County, Texas. A diverse benthic foraminiferal fauna was obtained from all but 5 of the samples.

The benthic foraminiferal fauna of the lower Stone City Member is characterized by an assemblage dominated by species of Quinqueloculina and Triloculina and is considered to represent water depths of 0-10 m. Above this interval an assemblage of agglutinated foraminifera dominated by Ammobaculites and Textularia is associated with a 1 m thick bed of silt and clay. This interval may be associated with a sudden increase in sedimentation rate. Above this bed, The Quinqueloculina-Triloculina assemblage is present and gradually is replaced by an assemblage dominated by Discorbis, Cibicidoides, Alabamina, and Cibicidina among others. The Discorbis-Cibicidoides is present elsewhere in the Gulf Coastal Plain and is associated with depths of 10-20m. Virtually all of the Wheelock Member is characterized by the Discorbis-Cibicidoides assemblage. Only one sample in the lower Wheelock Member contained the Discorbis-Siphonina assemblage indicating depths of 20-50 m. This assemblage characterizes the upper Lisbon Formation in Alabama.

The benthic foraminiferal record collected in this study is consistent with the Crockett Formation forming as a part of the transgressive systems tract. Based on the benthic foraminiferal assemblages collected in this study, the Crockett Formation formed in a shallower setting than the correlative upper Lisbon Formation of Alabama.