Stratigraphy of the Paluxy River Tracksites in and around Dinosaur Valley State Park, Lower Cretaceous Glen Rose Formation, Somervell County, Texas.

摘要

The dinosaur tracks of the Glen Rose Formation in the Paluxy River at Dinosaur Valley State Park are among the best preserved and most abundant in the world. Although many tracksites are easily correlated to the Main Tracksite, others, especially those at the extreme ends of the park, are differently preserved and not obviously correlated. To count track horizons, several stratigraphic sections were measured along the river from upstream at the McFall Ledge Site to 7.6 km downstream at the County Road 1001 crossing (3.1 km linear distance). High-resolution correlation of these sections reveals that 6 meters of strata separate two track-bearing intervals exposed in the river. Seven distinctive beds can be correlated: 1) the lowest, the main track layer, a dolomitic mud with Arenicolites burrows and finely preserved footprints, 2) a hardground bed with oyster-encrusted bored cobbles, 3) the “steinkern marl,” a fining upward shaly-concretionary unit containing a diverse fauna including clams and serpulid mounds in life position, 4) the “Corbula bed,” a few cm of grainstone consisting almost exclusively of mm-size, diagenetically-altered articulated clam steinkerns, 5) the serpulid bed, a fine-grained packstone riddled with Thalassinoides burrow networks and occupied by sparsely-scattered metersized serpulid mounds, 6) the Taylor track layer, containing variably-preserved footprints and mudcracks and 7) the highest, the Diplocraterion bed, a wackestone ledge characterized by the U-shaped burrow Diplocraterion. High-resolution geologic maps showing the outcrop distribution of these stratigraphic units in the Paluxy Riverbed reveal patterns of local structural relief that expose the main track layer in the northern Park Central park area, and expose the higher Taylor track layer at the eastern and western/southern part of the park. These maps also serve as a guide to resource management in the Park, showing where erosion is destroying track layers and where the same erosion is uncovering new tracksites.