Journal of Paleontology; January 2008; v. 82; no. 1;
p. 176-182; DOI: 10.1666/05-049.1
© 2008 Paleontological Society
DISCOVERY OF UPPER LADINIAN AMMONOIDS AT THE TYPE LOCALITY OF THE LOWER CARNIAN DESATOYENSE ZONE (SOUTH CANYON, NEW PASS RANGE, NEVADA)
MARCO BALINI1
1 Dipartimento di Scienze della Terra "A. Desio," Università degli Studi di Milano, Via Mangiagalli 34, 20133 Milano, Italy, <marco.balini@unimi.it>
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INTRODUCTION
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SOUTH CANYON, located in the New Pass Range in central Nevada (Fig. 1), is one of the most important localities for Upper Triassic marine invertebrates in North America. This site yields very rich ammonoid faunas, as well as cnidarians (Muller, 1936; Stanley, 1979; Roniewicz and Stanley, 1998), foraminifers (Gazdzicki and Stanley, 1983), bivalves (Waller and Stanley, 1998, 2005; Hopkin and McRoberts, 2003), and brachiopods.
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FIGURE 1—Location map of South Canyon
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The significance of South Canyon, however, derives largely from its ammonoid faunas, since it is the type locality of the Desatoyense Zone of the North American Standard Triassic Scale (Fig. 2), currently the best-defined time scale for the Triassic System. Knowledge of the South Canyon ammonoid fauna is largely based on the work of Johnston (1941) who described a rich collection containing thirteen genera, seventeen new species, two varieties, and five taxa in open nomenclature. Johnston interpreted these as a single new fauna, recognized for the first time in North America. Although he noted its strong affinities to Tethyan faunas of the Lower Carnian "zone of Trachyceras aon," Johnston nevertheless designated his South Canyon fauna as a new biozone, the Joannites Zone, which he dated as Early Carnian by correlation with the Aon Zone. The Joannites Zone was subsequently renamed the Trachyceras Zone by Silberling (1956), and later the Desatoyense Zone (index Trachyceras desatoyense Johnston, 1941) by Silberling and Tozer (1968). They further demonstrated the position of the Desatoyense Zone with respect to the Upper Ladinian ammonoid succession of British Columbia by the discovery of a fauna with elements of the Sutherlandi Zone at South Canyon, "some hundreds of feet" below the Desatoyense Zone. More recently, Tozer . . . [Full Text of this Article]
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