CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF THE BRAZOS RIVER AREA, FALLS COUNTY, TEXAS

The Brazos River area is located at the entrance of the former Western Interior Seaway on the shallow northern Gulf of Mexico shelf. Marine sediments in the region were deposited in a middle to outer shelf environment. Outcrops on the Brazos River in the Falls County area of Texas record nearly continuous and predominantly siliciclastic sedimentation during the Late Cretaceous and early Paleogene. The Cretaceous-Paleogene (K-P) boundary there, as well as the Upper Cretaceous and Paleogene sediments around it, are clay-rich marls with excellent preservation. The main goal of this study is to document the well-preserved Upper Cretaceous (Campanian-Maastrichtian) nannofossils with a low resolution look across the K-P boundary into the lowest Paleocene sediments.

In this study, eight outcrop sections from the Upper Cretaceous Marlboro, Neylandville and Corsicana Formations and the lower part of the Danian Kincaid Formation from the Brazos River area have been examined for calcareous nannofossils. The nannofossil assemblages are abundant and diverse in the Campanian and Maastrichtian sections, and abundant with low diversity in the lower Danian. The samples have yielded 7 biozones defined by 8 nannofossil datums. Of these datums, six first occurrences (FO), one last occurrence (LO) and one first occurrence acme were observed. Based on quantitative analysis 58 genera and 114 species have been identified in this study.