DINOFLAGELLATE CYST PALYNOFACIES AND PALEOENVIRONMENTAL ANALYSIS OF THE MAASTRICHTIAN AND BASAL DANIAN, BRAZOS RIVER SECTION, TEXAS

Palynologic study of the Maastrichtian Neylandville and Corsicana Formations and the Danian Kincaid Formation exposed along the Brazos River revealed abundant well preserved marine and terrestrial palynomorphs, and kerogen. These sediments were deposited on the latest Cretaceous middle shelf on northwest margin of the Gulf of Mexico. Biostratigraphically useful species for Maastrichtian and Danian ages are Xenascus ceratioides, Alterbidinium acutulum, Cerodinium diebelii, Deflandrea galeata, Cyclonephelium distinctum, Palynodinium grallator, Disphaerogena carposphaeropsis, Damassidinium californicum and Carpetalla cornuta. The overall marine/terrestrial ratio is low, but shows two peaks of high marine input: one peak is 17 m below the K-Pg boundary and correlates with the first high abundance of Glaphyrocysta spp., and the other is 0.16 m below the boundary and correlates with the another high occurrence of Glaphyrocysta spp, and highest abundances of Yolkinigymnium lanceolatum and Achomosphaera ramulifera. Three dinoflagellate assemblage intervals are described. Interval-1 is defined as early Maastrichtian in age, Interval-2 is of late Maastrichtian age, and Interval-3 is of Danian age. The ages defined by the dinoflagellate cysts are supported by calcareous nannofossils - the highest occurrence of Aspidolithus parcus constrictus and the lowest occurrence of the nannofossil Micula prinsii - as well as by the K-Pg Boundary. Dinoflagellate cyst assemblages are also supplemented by δ¹⁸O and δ¹³C (benthic foraminifera) stable isotopes and TEX₈₆ sea-surface temperature proxy. TEX₈₆ determinations of sea surface temperatures indicate a decrease in water temperature in the middle of the late Maastrichtian.