Upper Jurassic of Northeastern Texas

Abstract

The entirely subsurface Upper Jurassic of northeastern Texas includes, in ascending order, the Eagle Mills, Smackover, Buckner, Bossier, and Schuler formations; the last two constitute the Cotton Valley group. The stratigraphy of the units in northeastern Texas is described. Present evidence suggests that, in the East Texas basin, the Buckner formation passes downdip into the upper part of the Smackover formation. The Bossier formation is thinner than in Louisiana and contains oolitic limestone beds that suggest deposition in a sea that was shallower than in northwestern Louisiana. The Schuler formation in Texas, as in Arkansas and Louisiana, consists of two members, each of which occurs in a marine and a non-marine facies. The lower, or Shongaloo, member in Texas is similar lithologically to occurrences farther east, but its change of facies is farther updip than in Arkansas and Louisiana. The Dorcheat member is similar in general lithologic character to its occurrences in Arkansas and Louisiana but in Texas it almost entirely lacks zones of spherulitic siderite that are characteristically developed farther east. Zones of this material are reported to indicate intervals of prolonged weathering in the Coal Measures of England. Absence of the siderite in the Dorcheat of Texas suggests that deposition was more continuous. Several species of Ostracoda from the Schuler formation are illustrated.