Geological Society of America

28 Paleozoic Stratigraphy and Tectonics of the Southwestern Cordillera and Rocky Mountain Region

Wednesday, 16 March 2022
1:30 PM - 5:30 PM
CBC-A 112

DICING AND SPICING UP THE CAMBRIAN: CHEMOSTRATIGRAPHY OF THE TONTO GROUP, GRAND CANYON AREA, ARIZONA AND NEVADA

Paper number: 28-2
Program: Theme Sessions
Time: 1:50 PM – 2:10 PM

Authors

Carol Dehler Presenting Author
Utah State University, Logan, UT
Karl Karlstrom
University of New Mexico, Albuquerque, NM
Laura Crossey
University of New Mexico, Albuquerque, NM
Hannah Cothren
Boise, ID
James W. Hagadorn
Denver Museum of Nature and Science, Denver, CO
Stephen Reynolds
Arizona State University, Tempe, AZ
Fred A. Sundberg
Flagstaff, AZ
Eben Rose
Denver Museum of Nature & Science, Denver, CO
John R. Foster
Vernal, UT
Thomas Farrell
Boise State University, Boise, ID
Mark Schmitz
Boise State University, Boise, ID
Kory Kirchner
University of New Mexico, Albuquerque, NM

Abstract

Here we present a biostratigraphically and geochronologically constrained δ¹³C chemostratigraphy for the iconic Tonto Group of Arizona and Nevada, based on integrated analysis of seven hingeline-crossing cratonal sections spanning the Grand Canyon (east) to Las Vegas (west) regions. The Tonto succession (<650 m), although condensed and truncated by pre-Late Devonian unconformities eastward, spans more than 13 Ma (Dyeran (Stage 4) to Steptoan (Paibian Stage)), comprising two Sauk sequences. Carbonates in this succession predominantly reflect shallow subtidal to peritidal deposition in mixed carbonate-siliciclastic settings. In the Bright Angel Formation (Lyndon Limestone Member) and Muav Formation (Spencer Canyon Member), regionally extensive negative δ¹³C excursions (the N5 and N6, < -6 ‰) are recognized. Near the top of the Gateway Member of the Muav Formation, a striking offset in δ¹³C trends suggests a cryptic unconformity that is also present in the Banded Mountain Member of the Bonanza King Formation to the west. The lower part of the overlying Frenchman Mountain Dolostone records two negative δ¹³C excursions to -2.7 ‰ that are interpreted as the Drumian Carbon Isotope Excursion (DICE). The upper Frenchman Mountain Dolostone contains a conspicuous positive δ¹³C excursion to 3.5 ‰, which is interpreted as the Steptoan Positive Carbon Isotope Excursion (SPICE).

Geological Society of America Abstracts with Programs. Vol. 54, No. 2

doi: 10.1130/abs/2022CD-374369

© Copyright 2022 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.