Palynology and Paleoenvironment of Paleocene-Eocene Wilcox Group Sedimente in Bastrop, Texas

摘要

The Wilcox Group is an intensely studied group of sediments deposited primarily during the Laramide orogeny in the western United States and is important in paleocli-matological and paleoenvironmental studies, as it pertains to the Paleocene-Eocene Thermal Maximum (PETM). This particular stratigraphic section in the northwestern part of the Gulf of Mexico region has limited documentation of the changes in microbiota, despite the high level of interest in the interval. The organic acids produced by the decay of plant tissue have resulted in the diagenetic loss of nearly all carbonate remains. Therefore, palynology provides the best means of documenting age determination and environmental change for these deposits. Calvert Bluff strata consist of shoaling-upwards, fine-grained shallow marine deposits; the sequence boundary is marked by a paleosol and incised channel fill; the Carrizo is a transgressive marine sand deposit (Fig. 1). Palynological sampling within a 20 m (66 ft) section of Calvert Bluff and Carrizo Formation strata and a nearby 10 m (33 ft) section of upper Calvert Bluff and lower Carrizo contain a rich assemblage of well-preserved palynomorphs and occasional dinoflagellates (Figs. 2 and 3) in outcrops containing a major sequence boundary. The channel assemblage is composed primarily of freshwater algal cysts. The palynomorphs and dinoflagellates present in these sections are essential in reconstructing paleoenvironmental conditions present at the time of deposition.