Upper Devonian Biostratigraphy, Event Stratigraphy, and Late Frasnian Kellwasser Extinction Bioevents in the Iowa Basin: Western Euramerica

Day, Jed; Witzke, Brian J.

Abstract

Upper Devonian (Upper Frasnian) strata in the Iowa area (central United States) provide one of the best records in North America of Late Frasnian sea-level history and the associated Kellwasser Extinction Events within a detailed conodont biostratigraphic framework. Rich conodont faunas span Frasnian Zones 11 through 13c. Diverse benthic faunas of the Lime Creek Formation provide an unparalleled paleontologic record to examine the effects of the Kellwasser extinctions of benthic faunas in the tropical seaway. These strata preserve an onshore-to-offshore transect of depositional facies ranging from shallow-water carbonate shelf to basinal deeper water shale facies in an epeiric ramp system. Late Frasnian sedimentation was initiated above a deeply incised and karstified surface on underlying Givetian–Mid Frasnian carbonates. Regional stratigraphic relations require a minimal sea-level rise of at least 65–90 m to onlap this older surface. The Lime Creek Formation includes two stratigraphic sequences correlated with the global eustatic transgressive–regressive (T-R) cycles IId-1 and IId-2. The Lime Creek records a major extinction of benthic faunas through the Lower Kellwasser Extinction Event (LKE) associated with T-R cycle IId-2 deepening (upper part Zone 12) and onset of a major positive δ13Ccarb isotope excursion that spans the LKE and post-LKE recovery interval. The change from brachiopod-dominated to mollusk-dominated benthic associations is evidence of significant reorganization of benthic paleocommunity structure in the post-LKE survival-and-recovery interval. The near total extinction of the Late Frasnian conodont fauna during the Upper Kellwasser Event was coincident with regional expansion of Grassy Creek Shale organic-rich dysoxic–anoxic shale facies in southeast Iowa.

Citation

Day, J., & Witzke, B. J. (2017). Upper Devonian Biostratigraphy, Event Stratigraphy, and Late Frasnian Kellwasser Extinction Bioevents in the Iowa Basin: Western Euramerica. In M. Montenari (Ed.), Stratigraphy & Timescales (243-332). Elsevier. https://doi.org/10.1016/bs.sats.2017.08.002

• Online Publication Date: Oct 10, 2017
• Publication Date: 2017
• Deposit Date: Jun 7, 2023
• Publisher: Elsevier
• Pages: 243-332
• Series Title: Advances in Sequence Stratigraphy
• Series ISSN: 2468-5178
• Book Title: Stratigraphy & Timescales
• Chapter Number: 6
• ISBN: 978-0-12-813077-3
• DOI: https://doi.org/10.1016/bs.sats.2017.08.002