Stratigraphy of the Glen Rose Formation, Western Gulf Coastal Plain

ABSTRACT Strata of the Glen Rose Formation and equivalent units crop out in Mexico and West Texas and in a continuous band across the Edwards Plateau, the area of outcrop skirting the Llano Uplift, the Lampasas Cutplain, north-central Texas, southeastern Oklahoma, and southwestern Arkansas. These rocks dip into the the subsurface of the Gulf Coastal Plain. Although the Glen Rose interval has been studied on outcrop and in the subsurface in these areas through numerous investigations of local scale and several regional review papers, a synthesis integrating subsurface with outcrop across the broad region and a more detailed stratigraphic framework are needed. Outcrop-to-subsurface correlation may be achieved on the Edwards Plateau, in the area of the Paluxy River Valley, and in southwestern Arkansas. These correlations establish the stratigraphic equivalence of certain distinctive beds on outcrop with beds and zones which may be observed on well logs. The Corbula Interval and Salenia texana Zone, which mark the boundary between the upper and lower Glen Rose, occur just below an evaporite zone (solution zone on outcrop) on the Edwards Plateau that lies at the stratigraphic position of the third anhydrite stringer above the Ferry Lake Anhydrite in the subsurface of east Texas. The lower four anhydrite stringers above the Ferry Lake lie at the stratigraphic position of the lower part of the Thorp Spring limestone and subjacent beds, including the Corbula Interval and Salenia texana Zone, in the Paluxy River Valley. The uppermost anhydrite stringer above the Ferry Lake in east Texas, the Stray Anhydrite Stringer, lies at the stratigraphic position of the upper evaporite zone of the Edwards Plateau. The Thorp Spring limestone is equivalent to a massive limestone interval lying at a correspondent stratigraphic position on the Edwards Plateau. The Ferry Lake Anhydrite is equivalent to the reef interval in the upper part of the lower Glen Rose on the Edwards Plateau. These correlations stimulate thought and discussion concerning several topics including (1) the relationship between evaporite deposition and the development of reefs on the Edwards Plateau; (2) the evidence of cyclic sedimentation in the Glen Rose; (3) the regional continuity of beds; (4) the need for biostratigraphic studies; (5) the amount of loss of section between deep areas of the subsurface and equivalent outcrop sections; and (6) the relationship between evaporite deposition and extensive dinosaur trackbeds.