220-9 New lithostratigraphic sections of Maastrichtian formations in central Wyoming: Implications for biostratigraphy, geochronology, and stratigraphic correlation.

Session: Life and Environments Through Time and Space: Multi-Record Approaches to Stratigraphic Paleobiology (Posters)

Poster Booth No.: 135

Presenting Author:

Zachary Tenney

Authors:

Tenney, Zachary David¹, Mautz, Blake Weston², McElroy, Brandon³, Currano, Ellen⁴, Slattery, Joshua S.⁵

(1) University of Wyoming, Geology & Geophysics, Laramie, WY, USA, (2) University of Wyoming, Geology & Geophysics, Laramie, WY, USA, (3) University of Wyoming, Geology & Geophysics, Laramie, WY, USA, (4) University of Wyoming, Laramie, WY, USA, (5) University of Wyoming, Cheyenne, WY, USA,

Abstract:

The Maastrichtian nonmarine formations of Wyoming have been extensively collected for fossils since the end of the Bone Wars to the present day. Despite this, minimal research has emphasized the biostratigraphy and chronostratigraphy of these units. Developing an improved geochronological framework for these units will enhance regional correlation, clarify the timing and nature of the regression of the Western Interior Seaway (WIS), elucidate the influence of active Laramide tectonics on coastal plain evolution, and shed light on the evolution of faunal and floral communities prior to the K/Pg Boundary. Our study involved measuring six new lithostratigraphic sections through the Lewis Shale, Meeteetse Formation, Fox Hills Sandstone, and Lance Formation in the eastern Wind River Basin and southwestern Powder River Basin. Stratigraphic positions of fossil occurrences, both within or adjacent to our stratigraphic sections were documented, and preliminary geochronologic correlations were made using the established U.S. Western Interior Ammonite Biozonation with additional data from the USGS Denver Mesozoic Catalog. We also integrated our new lithostratigraphic sections with previously published section data and newly collected data on fluvial bedform and barform sedimentary structures to investigate spatial and temporal changes in the depositional system, both stratigraphically and between the two basins. 

Our analyses show that the regression of the WIS in Wyoming was interrupted by at least two transgressive events during the latest Campanian and Maastrichtian. The marine Lewis Shale lower tongue (~73.2 – 72.3 Ma) and upper tongue (~71.5 –69.9 Ma) occur stratigraphically above and below the nonmarine Meeteetse Formation in the eastern Wind River Basin. Lithostratigraphic and paleohydraulic reconstructions suggest that fluvial channels were larger in the Wind River Basin and contained an active alluvial system, whereas the Powder River basin was dominated by lower-energy wetland environments. Marine invertebrate fossil collections from our study improve the correlation within our study area with many species co-occurring in both basins. Based on the ammonite biostratigraphy and lack of disconformities, the maximum age of the Lance Formation is greater than 69 Ma, suggesting it may preserve the most complete nonmarine depositional record of the upper Maastrichtian in North America. Further stratigraphic work within the Lance Formation is required to understand the stratigraphic distribution of dinosaur specimens for a more accurate comparison with other upper Maastrichtian strata.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9580

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