Micropaleontology of the upper eagle ford and lower austin groups, Big Bend National Park, Texas
Bostik, Wayne Charles
The Upper Eagle Ford and Lower Austin Groups in the Big Bend National Park contain an abundant for a mini feral population characterized by a large number of individuals, a small number of species, and a predominance of pelagic forms. The Upper Boquillas Member (Upper Eagle Ford Group) contains a marine foraminifera fauna of 7 families, 13 genera and 21 species. The Order Ostracoda is represented by one family, 2 genera and 3 species. The Austin Chalk Member (Lower Austin Group) embodies a marine foraminifera fauna of 14 families, 42 genera and 69 species. One new species is described. The Order Ostracoda comprises 3 families, 5 genera and 7 species. The Upper Boquillas Member was deposited in a fluctuating and deepening sea. The fossil evidence indicates deposition occurred in an infraneritic bathymetric zone. The sea withdrew rapidly from the area at the termination of Boquillas time. The Austin Chalk Member is representative of a neritic to infraneritic bathymetric zone characterized by two sea fluctuations. The sea fluctuations are recognized in the area by paleontologic and lithic properties. The Upper Boquillas Member is a stratigraphic correlative of the Arcadia Park Formation in Central Texas and the â€œDry Tankâ€ Member of the Boquillas Formation in the Kent area. The stratigraphic correlative of the Austin Chalk Member in Central Texas is the Austin Chalk (without Exogyra ponderosa). The Austin Chalk Member is equivalent to the lower portion of the â€œStocksâ€ Formation in the Kent area.