GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 39-11
Presentation Time: 9:00 AM-5:30 PM


MOORE, John L., Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA 93106, PORTER, Susannah M., Earth Science, University of California, Santa Barbara, 1006 Webb Hall, Santa Barbara, CA 93106 and WEBSTER, Mark, Dept. of Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637

The so-called small shelly fossils are a polyphyletic assemblage of shells, tubes, sclerites, and spicules obtained by acid maceration of Cambrian carbonates, and offer a major record of early animal biomineralization. There has been little detailed study of such fossils from the Great Basin, despite the rich and well-studied Cambrian successions preserved in this region. Herein we report preliminary results on small shelly fossils obtained from a section of the Poleta Formation (Montezuman–Dyeran, Cambrian Stages 3–4) from Gold Point, Slate Ridge, Esmeralda County, Nevada. The informal lower member of the Poleta Formation (Montezuman) consists of limestones hosting archaeocyath–microbial bioherms and associated debris, and maceration residues yield numerous small shelly fossils including abundant phosphatic tubes representing both hyolithelminths and paiutiids (which have longitudinal septa and have been interpreted to be cnidarians); a species of tall conical helcionelloid mollusc; rare chancelloriid sclerites, hyoliths, and enigmatic corrugated phosphatic plates; and linguliform brachiopods, trilobites, and echinoderms. The overlying middle member (Montezuman–Dyeran) consists of fine-grained siliciclastics with interbedded carbonate layers. Several samples yielded numerous chancelloriid sclerites, including morphotypes typical of the genera Chancelloria and Allonia, as well as a suite of strange sclerites with up to at least eighteen rays. Samples from the middle member also yielded the stem-group brachiopod Mickwitzia as well as hyoliths, echinoderms, and trilobites. Samples from the upper member (Dyeran) did not produce any small shelly fossils. While our samples from the Poleta Formation yielded a relatively small number of taxa—perhaps due in part to the limited occurrence of secondary phosphatization—they nonetheless demonstrate the presence of quite different assemblages in the two members (due to some combination of faunal turnover and facies change) and contribute to the understanding of several intriguing fossil groups.