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The Black Shale basin of West Texas covers an area in excess of 21,000 square miles and includes the region from Terrell and Pecos counties eastward to Menard and Kimble counties. It extends from Real, Edwards, and Val Verde northward beyond Glasscock and Upton counties. This basin includes such local basins as the Midland basin, the Val Verde basin of Frank E. Lewis, the Sheffield channel, and the Kerr basin.
Reasons are given for the belief that the black shale sediments in this basin were derived from rocks south of this area.
The shale ranges in age from Bend (Lower Pennsylvanian) through Clear Fork (Middle Permian). The shale of the Midland basin has been divided into three distinct zones.
Pre-Cretaceous erosion has removed the overlapping Permian shale in the extreme southern portion of the area, leaving Pennsylvanian directly beneath the Trinity (basal Cretaceous).
The problem of stratigraphy is complicated by gradation and lack of diagnostic fossils with a short vertical range. There is a great divergence of opinion, derived from the study of well cuttings, as to correlative formational units.
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