PALEOLIMNOLOGY OF UPPERMOST CRETACEOUS LACUSTRINE DEPOSITS IN WESTERN TEXAS

Abstract

The association of vertebrate, invertebrate, plant, and ichnofossils from two Upper Cretaceous lacustrine environments in West Texas permits interpretation of the paleolimnology of part of the Javelina Formation. The relatively rich fossil assemblages permit studies of paleoenvironments and food web complexities, as well as provide paleohydrological information. In Big Bend National Park, at least three juvenile Alamosaurus sauropods were preserved in situ in anoxic mud among shallow-water lacustrine charophytes. Alamosaur remains in the Moon Valley section are both in situ and transported. Mussels, gastropods, gar, and crayfish trace fossils largely define the paleoecology, as well as reveal details of specific biological relationships, especially at several intervals in Moon Valley. The modern larval-host reproduction system of mussels may have existed in the possible case of an ectoparasitic relationship in the co-occurrence of fossil Unio and Lepisosteus. Relatively fine time-frame resolution is present based on investigations of the mussel, Unio, and the presence of crayfish burrows. Unio sclerochronology indicates continuous inundation for at least seven years at two different stratigraphic intervals. Horizons of fossil crayfish burrows record both periods of nondeposition and the level of the water table at those times. Viviparus gastropods suggest subtleties of water movement and oxygen concentration. Studies of the dinosaur bones and the presence of probable footprint impressions suggest dinosaurs visited these types of water bodies.