A series of micromarker beds in the Permian Castile Formation has been identified in cores from four drill holes located along the west edge of the Delaware Basin in west Texas and southeastern New Mexico. These marker beds are from 0.5 mm to 20 mm thick, dark gray, and consist of anhydrite, calcite or dolomite, authigenic albite and pyrite, and minor amounts of marcasite, fluorite, and mica. The Castile Formation consists principally of laminated anhydrite with some beds of massive anhydrite and halite. The micromarker beds are found within intervals of laminated anhydrite and are concordant with the laminae. The micromarker beds can be correlated between drill holes for many miles, as can the calcite anhydrite couplets of the laminated anhydrite (Anderson and Kirkland 1966). These micromarker beds may represent volcanic ash falls, a slowing in the rate of sedimentation, or an organic bloom across the basin.

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