HOW MANY TRACK HORIZONS ARE EXPOSED AT DINOSAUR VALLEY STATE PARK? STRATIGRAPHY OF THE CRETACEOUS GLEN ROSE FORMATION TRACK SITES OF THE PALUXY RIVER, GLEN ROSE, TEXAS

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. While many track sites 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). These reveal 6 meters of strata separating two track-bearing horizons exposed in the river. Seven distinctive beds can be correlated: 1) the lowest, the Main Tracklayer, a dolomitic mud with Arenicolites burrows and finely preserved footprints, 2) a hardground 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 clams steinkerns, 5) a fine-grained packstone riddled with Thallassinoides burrows and occupied by sparsely-scattered meter-sized serpulid mounds, 6) the Taylor Tracklayer, containing poorly-preserved footprints and mudcracks, and 7) the highest, a wackestone ledge characterized by Diplocraterion.

The Main Tracklayer is underlain by a sparsely- exposed meter of silt, suggesting high-stand or forced regression, and the tracklayer itself suggests initial transgression above the sequence boundary at the base of the bed. The encrusted, bored cobbles followed by a fining-upward succession of concretionary fossil-rich beds suggest episodic deposition and low sedimentation rates of the transgressive systems tract, culminating in the condensed, diagenetically altered Corbula accumulation. Subsequent deposits, with the exception of the serpulid mounds are increasingly silty, suggesting highstand deposits culminating in another sequence boundary at the base of the Taylor Tracklayer.

Local structural relief exposes the Main Tracklayer in the northern/central park area, and exposes the higher Tayler Tracklayer at the eastern and western/southern part of the park. This possible monocline trends WNW-ESE.