7-12 Reinvestigation of Cisuralian (Lower Permian) Biostratigraphy at Ferguson Mountain, Elko County, Nevada

Session: Earth Life Sciences across the Cordillera (Posters)

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Abstract:

The Upper Pennsylvanian–Cisuralian Ferguson Mountain Formation at Ferguson Mountain, Nevada, preserves a mixed carbonate-siliciclastic succession of post-Antler foreland basin deposits within the so-called Ferguson Trough. These strata are correlative with the tightly constrained Strathearn and Buckskin Mountain formations of Carlin Canyon, Nevada, and the Riepe Spring Limestone of Spruce Mountain, Nevada. The latter localities were the subjects of several detailed biostratigraphic studies in the past decade concerned with fusulinid and conodont occurrences. To date, only the work of Slade (1961) has described the abundant fusulinid faunas of the Ferguson Mountain Formation in its type area. A much thinner section of the Ferguson Mountain Formation near the Kungurian GSSP candidate (the “Rockland Section”) in the central Pequop Mountains was discussed by Robinson (1961) in the same volume, but study of the fusulinid biostratigraphy was restricted to the overlying Pequop Formation. Unfortunately, several of the critical identifications made by Slade (1961) are dubious or incorrect, and the conodont faunas of the area have not been studied, thereby prompting further investigation and biostratigraphic refinement. Recently, cursory sampling of a new interval of the Ferguson Mountain Formation south of the type section yielded both Asselian and Sakmarian (early Cisuralian) fusulinids and conodont elements, including fusulinid taxa associated with the North American regional Pennsylvanian–Permian boundary (i.e., Virgilian–Wolfcampian). The transitional assemblage comprises the highly advanced triticitid taxon Triticites cellamagnus co-occurring with early morphotypes of Pseudofusulina and Schwagerina. The co-occurrence of these genera is biostratigraphically significant, as the ranges of Triticites and Schwagerina do not overlap at nearby Spruce Mountain, indicating the Ferguson Mountain Formation preserves a more continuous systemic boundary than the unconformable transition in the Riepe Spring Limestone. A second, slightly younger sample yielded Schwagerina aculeata and the conodont species Sweetognathus expansus, the latter of which is characteristic of Asselian marine successions globally. A third sample produced Schwagerina cf. wellsensis and Sweetognathus binodosus, both of which occur in the Sakmarian part of the upper member of the Riepe Spring Limestone at Spruce Mountain. The present preliminary study precedes a forthcoming, more complete reinvestigation of the fusulinid biostratigraphy of the Ferguson Mountain area that will continue integrating conodont and fusulinid assemblages to further constrain the regional and international biozonation of the Ferguson Mountain Formation.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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