T260 Cambrian–Ordovician Faunas and Events: A Session in Honor of John F. Taylor and John E. Repetski

Wednesday, 12 October 2022
1:30 PM - 5:30 PM
Mile High Ballroom 4A

SEA-LEVEL FLUCTUATIONS, CARBON-ISOTOPE EXCURSIONS, AND CONODONT FAUNA AROUND THE ORDOVICIAN-SILURIAN TRANSITION, WILLISTON BASIN

Paper number: T260-12
Program: Technical Sessions
Time: 4:10 PM – 4:25 PM

Authors

Abstract

During the Late Ordovician-early Silurian, the Williston Basin occupied the southern tropics and was characterized by deposition in dominantly shallow-marine environments that were perennially isolated from the Cordilleran shelf and the surrounding epicratonic basins of North America. To test if the basin succession contains a high-resolution record of sea-level and δ13C fluctuations, this study uses five continuous cores from the basin center spanning the upper Red River (Aphelognathus grandis Zone, Late Ordovician, Katian) through the Lower Interlake interval (Psuedolonchodina expansa – D. staurognathoides zones, early Silurian, Aeronian – early Telychian). The cores were logged in detail and sampled for microfacies analysis, δ13Ccarb, and conodont biostratigraphy. Correlation between the studied cores was based on wireline logs (gamma ray, combined neutron-porosity and bulk density) with several regional marker beds identifiable. Sixteen identified depositional facies form twelve complete long-term sequences, ten of which are bounded by evaporites recording changes from humid (semi-arid) TSTs to arid late HSTs-LSTs. Six global positive δ13C excursions are recognized and tied to conodont biostratigraphy: (1) Whitewater (=Moe) in the upper Red River Fm. , (2) Elkhorn (=Paroveja) in the Gunton Mbr. of the Stony Mountain Fm., both within the Aphelognathus divergens Zone; (3) LHICE (KaH?) in the lower Stonewall Fm., Aphelognathus shatzeri Zone; (4) HICE in the upper Stonewall Fm., Ozarkodina hassi Zone; (5) early Aeronian within the Distomodus kentuckyensis – Pranognathaus tenuis zones and (6) late Aeronian – early Telychian within the Psuedolonchodina expansa – D. staurognathoides zones.

The Williston Basin retained a high-resolution record of sea-level fluctuations and carbon-isotope excursions that, when integrated with conodont biostratigraphy, enable correlations between Laurentian margins and its interior during the major biotic and environmental changes around the Ordovician-Silurian boundary.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-380617

© 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.