The Upper Jurassic Cotton Valley Group is a sedimentary wedge, pinching northward, under the Gulf Coastal Plain from Texas to Alabama. In northern Louisiana, formations in this group are, in descending order, the Knowles Limestone, the Hico Shale which grades southward into the regressive, massive Terryville Sandstone, and the southward-thickening wedge of shale and limestone comprising the Bossier Formation. These formations grade northward into terrestrial red beds of the Schuler Formation, in Arkansas. Across northern Louisiana, a west-trending, longshore barrier island of (Terryville) sandstone supplied by a delta to the ancestral Mississippi river separated a coastal lagoon (Hico shale) from the open gulf (marine Bossier Formation).

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