GSA Connects 2022 meeting in Denver, Colorado

Paper No. 260-10
Presentation Time: 4:10 PM


HUSINEC, Antun, St. Lawrence University, 23 Romoda Drive, Canton, NY 13617 and LESLIE, Stephen, Department of Geology and Environmental Science, James Madison University, 801 Carrier Drive, MSC 6903, Harrisonburg, VA 22807

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.