TEXAS MOJSISOVICZIINAE (AMMONOIDEA) AND THE ZONATION OF THE FREDERICKSBURG

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Abstract
The Fredericksburg Division of Texas ranges in age from the Middle Albian zones of subdelaruei or nitidus upward into the Upper Albian cristatum zone. The overlying Kiamichi Formation of the Washita Division is largely the equivalent of the varicosum zone. The base of the Upper Albian falls within the Goodland Formation of Texas. Previously the stratigraphic range of Venezoliceras has been misunderstood. In Texas this genus is restricted to the uppermost Middle Albian and the lowermost Upper Albian. Common occurrence in Texas with other South American ammonites, such as Oxytropidoceras buarquianum (White), O. douglasi Knechtel, Manuaniceras carbonarium (Gabb), and M. peruvianum multifidum (Steinmann), indicates that the range of Venezoliceras cannot be greatly different in South America. Venezoliceras is most abundant in the Comanche Peak and Goodland Formations but appears in the top of the Walnut Formation, and one species continues into the basal Kiamichi. In Texas Adkinsites is restricted to the Kiamichi Formation and most basal Duck Creek Formation, Washita Division. Oxytropidoceras first appears just above the middle of the Walnut Formation, in the Keys Valley Marl, and ranges upward through most of the Comanche Peak and Good-land Formations. Manuaniceras first appears in the Keys Valley Marl and ranges upward through the Comanche Peak and Goodland and Kiamichi Formations into the basal Duck Creek Formation. All of the specimens of Dipoloceras are from the Goodland Limestone of Tarrant County, Texas. Four Mojsisovicziinae ammonite zones are delineated below the lower Duck Creek zone of Craginites serratescens (Cragin); these, in descending order, are the zones of Adkinsites bravoensis (Böse), Manuaniceras powelli n. sp., Manuaniceras carbonarium (Gabb), and Oxytropidoceras salasi n. sp. Twenty-nine species of Albian Mojsisovicziinae of Texas represent the genera Adkinsites with 4 species, 2 new; Venezoliceras with 6 species, 3 new; Oxytropidoceras with 5 species, 3 new; Manuaniceras with 10 species, 6 new; and Dipoloceras with 4 species, one of which remains unnamed, and one of which is not described in the present work.

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