174 D15. Paleontology, Biogeography/Biostratigraphy (Posters)

Monday, 23 October 2017
9:00 AM - 6:30 PM
Halls 4EF

REVISION OF THE TYPE SIPHONODELLA PRAESULCATA CONODONT LOCALITY AT LICK CREEK, MONTANA

Paper number: 174-8
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The type section for the Siphonodella praesulcata conodont fauna in North America at the Lick Creek locality is important as a reference section for ongoing Devonian-Mississippian boundary (DCB) studies within the Sappington Formation and correlative Exshaw and Bakken formations. As originally described, the S. praesulcata conodonts occur in a 2 ft oolitic grainstone presumed to be at or near the top of the Sappington Formation (in Unit 5), but the exact stratigraphic position within the Sappington is poorly known. Because Unit 4 contains the latest Devonian Retispora lepidophyta spore assemblage, and the original authors did not find it, there was concern about the relative age of the newly defined S. praesulcata species to R. lepidophyta, and if the oolitic grainstones were part of Unit 5 elsewhere, or could possibly be part of the overlying Cottonwood Canyon Member.

Detailed stratigraphic studies of the Lick Creek section and other nearby sections resolve much of the uncertainty with the stratigraphic position of the S. praesulcata conodonts. The Sappington at Lick Creek consists of a normal Sappington succession from Unit 1 through Unit 5, with the addition of over 8 ft of oolitic grainstones near the top. Unit 4, which has been found beneath a veneer of cover, provides the key evidence to show that the oolitic grainstones occur near the top of Unit 5 (based on regional thickness). The overlying Cottonwood Canyon Member is only 4 cm thick at Lick Creek, but at other localities nearby it reaches more typical thicknesses of 3-4 ft, where it also rests on oolitic grainstones. These relationships suggest that very little of Unit 5 has been eroded at Lick Creek, thus placing the S. praesulcata locality somewhere near the top of Unit 5.

This new analysis confirms that the R. lepidophyta spore assemblage underlies the S. praesulcata fauna at Lick Creek, although they may overlap. Preliminary results from our continuing conodont and other microfossil biostratigraphic work at Lick Creek and regionally confirm earlier work that Sappington Unit 4 is Devonian in age, and that as expected the overlying upper Cottonwood Canyon Member is lower Mississippian. Thus the DCB lies within Unit 5. In this contribution, conodonts from Lick Creek are compared with conodonts from multiple locations in Unit 5.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-308600

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.