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Marine Jurassic gastropods, central and southern Utah

1965; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp503d

2330-7102

Norman F. Sohl,

Space Exploration and Technology

This ,paper describes a gastropod fauna of 19 species assigned to 17 genera from the lower limy units of the Carmel Formation and from the Twelvemile Canyon Member of the Arapien Shale (Bajocian to Callovian) in central and southwestern Utah.These descriptions constitute the first report for most of the genera from the Jurassic of North America.The Carmel gastropod fauna is a shallow-water one dominated by Archaeogastropoda and Mesogastropoda, primarily the cerithiaceans, naticaceans, and neritaceans such as Lyosmna.Neogastropoda are absent, and Euthyneura are represented only by the nerineids and the cephalas,pid genus OylindrobulUna.Of special note is the neritid Lyoswna, which heretofore has been thought to lack an inner lip septum.Silicified specimens retain such a lip and show that its loss is probably due to differential replacement of shell layers.Gastropods are most common in the central area of outcrop of the Carmel Formation and lessen in diversity and abundance in the thinner sandier, nearer shore sediments to the east.The fauna is most similar to that found in member B of the Twin Creek Limestone of Utah, Idaho, and Wyoming; but it also has a close relationship to that in the Gypsum Spring Formation and "Lower Sundance Formation" of Wyoming.A survey of the Jurassic gastropods of North America indicates that they are not so diverse as are those of Europe.Taxonomically, they are dominated by the Archaeogastropoda (especially Neritacea and Amberleyacea) and Mesogastropoda (primarily Pseudomelaniacea and Ceritheacea).No Neogastropoda are present.The Jurassic gastropods are very provincial.The gulf coast and west Texas gastropod faunas are similar in some respects, but have no species in common with those of the western interior.Similarly, the Alaskan gastropod fauna is distinct from those faunas to the south.Such differences are seen even at the family level where the Neritidae and Nerineacea, so common in the southern faunas, are absent or poorly represented in Alaska.In Alaska the Purpurinidae and Amberleyiidae are common but decrease in abundance southward to Mexico.In terms of age the Late Jurassic is the time of greatest gastropod diversity in the gulf coast and west Texas, but in the western interior and Alaska, the Middle Jurassic (Bathonianlower Callovian) interval shows the greatest flowering of gastropod faunas.R 0 N C 0 37°---------------tions, many representing different stratigraphic levels at the 42 localities, are reported on herein.Special thanks are due my colleague R. W. Imlay of the U.S. Geological Survey, who first interested me in the present study.He has not only aided as a critical reviewer but has also guided me to many of the collecting localities