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The Smackover and Buckner Formations and the Cotton Valley Group, which is composed in ascending order of the Bossier and Schuler Formations, are of definite' Late Jurassic age. The Norphlet Formation, although considered to be of Late Jurassic age, is unfossiliferous and its age is unproven. The Haynesville Formation, which is composed of part of the Cotton Valley Group and the Buckner Formation, is' not used here. . The Upper Jurassic rocks are found only in the suibsurface at depths generally ranging from 1,000 feet along the north edge of the gulf coast embayment to 12,000 feet in Louisiana. Their thicknesses and lithologic characteristics were affected by contemporaneous regional movement along the Sabine uplift and the north Louisiana basin and by local movement of anticlines and faults along the margin of the gulf coast embayment. The Smackover and Buckner Forma:tions and the Cotton Valley Group are characterized by varied lithology and by lack of lateral cm11tinuity. No regional unconformities are apparent in the Upper Jurassic rocks. The Smackover Formation is divided into three informal members-lower, middle, and upper. The lower member consists predominantly of d-ark-brown silty to argill-aceous limestone that is commonly laminated. It is recognized over a much wider region, particularly in downdip areas, than the middle and upper members. The middle member, which is predominantly dense limestone, and the upper member, which is predominantly oolitic limestone, are confined to the north margins of the gulf coast embayment in the report area. Southward from downdip areas the middle and upper members grade laterally into the Bossier Formation. The Buckner Formation, which in the report area is confined to the north margin of the gulf coast embayment, is divided informally into lower and upper members. The lower member, which consists mostly of anhydrite and anhydritic mudstone, was deposited in a narrow basin that paralleled the margin of the embayment. It is apparently limited along its south side by a series of salt-cored anticlines that were forming at the time of deposition and were partly responsible for restricting the outflow of hypersaline water from the marginal basin. The upper member, which consists mostly of mudstone and shale, is found throughout the area of the lower member and even farther south where it is thickest. It is apparently limited on the south by a second series of anticlines. An earlier concept fua:t reef growth within the Smackover Formation was the principal cause of evaporite deposition in the Buckner Formntion now seems to be incorrect. The Bossier Formation is here redefined to include all darkgray shale above the lower member of the Smackover Formation and below the basal sandstone of the Schuler Formation. It thus includes' equivalelllts of the middle and upper members of the Smackover Formation, all the Buckner Formation, and part of the Schuler Formation. A thin upper part of the Bossier extends northward into the lower part of the Schuler Forma.tion and is here informally termed the Q tongue of the Bossier Formation . The Schuler Formation is here redefined to inC'lude all rocks between the top of the Buckner Formation and the base of the Cretaceous rocks, except for the Q tongue of the Bossier F'ormation. A sandstone and shale tongue that underlies the Q tongue of the Bossier is here informally termed the P tongue of the Schuler. In updip areas the Schuler Formation is largely near shore or nonmarine in origin, and in downdip areas to the! south it is marine. The near-shor'e or nonmarine facies: consists of lenticular light-gray, pink, or reddish-brown fine-grained sandstone and pastel varicolored and reddish-brown shale. The normal marine facies consists of light-gray fine-grained sandstone, clark-gray fissile fossiliferous shale, and some limestone. T·,vo conspicuous unconnected conglomera tic facies are found in the lower part of the Schuler Formation; one is updip in the nonmarine facies and the other is downdip in the marine facies.

Upper Jurassic stratigraphy of some adjacent parts of Texas, Louisiana, and Arkansas