Geology of the Eagle Mills Formation

Abstract

ABSTRACT In the subsurface of south Arkansas, the Eagle Mills formation and the overlying Werner formation and Louann salt occur below definite Upper Jurassic and above definite Paleozoic beds. For more than two decades, a controversy has existed over a Permian versus Jurassic age assignment for this sequence. Identification of fossil plant impressions from a recent well indicates a late Triassic age for the Eagle Mills formation. The Eagle Mills deposits consist of non-marine red beds, gray and white siltstones and sandstones with associated diabase intrusives. The formation is interpreted to occupy a deep, narrow trough (perhaps a graben or half graben). The framework of sedimentation, igneous activity, and depositional environments show a marked similarity to those of the Newark group of the eastern United States. The depositional environments and interpretation of climate are also similar to those of the late Triassic deposits of the southwest United States and Mexico. Triassic beds of the Eagle Mills type probably underlie portions of the coastal plains from Florida to Mexico.