Dinocyst biostratigraphy of Santonian-Maastrichtian formations of the Western Gulf Coastal Plain, southern United States

Abstract

This palynological investigation of Santonian-Maastrichtian formations of Texas, U.S.A. consists of an examination of 82 outcrop samples from 19 stratigraphic sections exposed in 9 countries in a north-south trend from about Dallas to Kinney. The Austin Chalk Formation, the Taylor Group, and the lower Navarro Group are examined for palynological data. Most of the samples are rich in dinocysts assemblages. In a total assemblage of 163 palynomorphs species in 95 genera, 111 dinocyst species of 60 genera, 6 acritarch species of 5 genera, and 46 spore pollen species of 33 genera are recognized and their stratigraphic distribution documented. Systematic descriptions and illustrations of all dinocysts and acritarch taxa are given. Spore-pollen taxa occur sporadically in the studied sections and thus are only listed, illustrated and their occurrences noted in the text.

The stratigraphic distribution of dinocysts species indicating the Santonian age can be recognized by the presence of Chatangiella granulifera, C. robusta, C. spectabilis, Phelodinium gaduatum and Spinidinium lanturnum. The characteristic species of Campanian assemblage are Cannosphaeropsis hyperacantha, C. utinensis, Ceratiopsis subquadra, Chattangiella armata, C. williamsii, Diconodinium martianum, Dinogymnium denticulatum, D. enclaense, D. nelsonense, Impagidinium cristatum, I. microarmum, Rottnestia borusstca, Triblastula utinensis and Xenascus gochtii.

The appearance of the following dinocysts species viz., Andalusiella acicornula, Areoligera senonensis, Ceratiopsis navarriana, Glaphyrocysta retiintexia, Lejeunecysta decorinassa, L. byalina, Litosphaeridium fenestreconum, Palaeocystodinium australinum, Phelodinium tricuspe and Thalassiphora bononiensis in the Maastrichtian is significant.

Pollen occurrences indicate that the land area, west of the Senonian epeiric sea, was terrigenous source in the Santonian and the Late Maastrichtian whereas the land on the east of the eperic sea was the source in the Campanian.