Selected Early Permian Ammonoids from Portuguese Springs, White Pine County, Nevada

Publication Date

12-1993

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Education, Earth Science

Department

Geosciences

Supervisory Committee Chair

Claude Spinosa

Abstract

Ammonoids occur abundantly within Lower Permian strata at Portuguese Springs, Northern Diamond Mountains, Nevada. They are recovered from a micritic concretionary interval that was deposited within a partially isolated sub-basin of the tectonically generated Early Permian Dry Mountain Trough. The diverse ammonoid fauna of Portuguese Springs contain taxa characteristic of a transitional biogeographic region. The fauna consists of North American forms, forms endemic to Portuguese Springs and cosmopolitan forms with either boreal or equatorial affinities. Endemism may have been associated with paleogeographic isolation of basins on the western margin of North America.

Representatives of the Adrianitidae, Perrinitidae and Medlicottiidae are described in this study. The adrianitins comprise over seventy-five percent of the ammonoid fauna and demonstrate a high level of morphologic diversity. Four genera are recognized; New Genus A, New Genus B, Crimites Toumansky, 1927 and Neocrimites Ruzhencev, 1940. Properrinites, Akmilleria and Bamyaniceras are less abundant.

The ammonoid concretionary zone at Portuguese Springs, Buck Mountain and Secret Canyon occurs within the Properrinites ammonoid biozone (Sakmarian) and the Sweetognathus whitei-Mesogondolella bisselli conodont zone of Upper Wolfcampian to Lower Leonardian (Sakmarian to Artinskian) age. Generally equivalent strata have been recognized in West Texas, Yukon and southern Ural Mountains but strata of the Bolorian horizon from the southeast Pamir Range, Tajikistan appear to be slightly younger.

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