107-21 The End of Paleogene White River Group Deposition in Wyoming and Nebraska, USA: A Disal Effect of the Emplacement of the ~23 Ma Markagunt Gravity Slide

Session: Sedimentary Geology Division/SEPM Student Research Poster Competition: Dynamics of Stratigraphy and Sedimentation

Poster Booth No.: 164

Presenting Author:

Megan Grobe

Authors:

Grobe, Megan E¹, Malone, David H², Moll, Joseph³, Rivera, Tiffany⁴, Biek, Robert F.⁵, Hacker, David B.⁶, Griffith, William Ashley⁷, Braunagel, Michael J.⁸

(1) Geography, Geology and the Environment, Illinois State University, Normal, IL, USA, (2) Geography, Geology and the Environment, Illinois State University, Normal, IL, USA, (3) Earth Sciences, Montana State University, Bozeman, MT, USA, (4) Geological Sciences, University of Missouri, Columbia, MO, USA, (5) Geological Sciences, University of Texas, Austin, TX, USA, (6) Geology, Kent State University, Kent, OH, USA, (7) Earth Sciences, The Ohio State University, Columbus, OH, USA, (8) Earth & Environmental Sciences, University of Minnesota Duluth, Duluth, MN, USA,

Abstract:

The late Paleogene White River Group is a post-Laramide stratigraphic succession that occurs in the Rocky Mountains and western Great Plains. It occurs within Laramide intermontane basins and atop some basement-cored uplifts. It consists of a light-colored tuffaceous sandstone, siltstone, mudstone, and conglomerate. Four samples of tuffaceous sandstone from the uppermost White River Group strata were sampled in eastern Wyoming and western Nebraska. Zircons extracted from these units (n=722) were analyzed for U/PB dates by LA-ICPMS at the University of Arizona Laserchron Center. The maximum depositional ages of the samples range from 22.61 Ma to 23.40 Ma, which correlates to the emplacement of the Markagunt gravity slide in Utah’s Marysvale volcanic field at 23.05 + 0.22/−0.20 Ma. The Marysvale volcanic field was part of the Nevadaplano, a longstanding highland that supplied sediment to the White River depositional system. The prominent age peaks are ~1660 Ma, ~1430 Ma, and ~1000 Ma, which were likely sourced from Proterozoic basement rocks of the Laramide uplifts of the southern Rocky Mountains. An additional age peak of ~169 Ma could have been derived from the Blue Mountains of Oregon or recycled from Sevier-Laramide synorogenic strata. There is a notable absence of Archean zircons, suggesting local central Rocky Mountain Laramide uplifts were not important sediment source areas. The temporal relationship between the cessation of White River Group sedimentation and the collapse and emplacement of the Markagunt gravity slide suggests that after collapse, the Marysvale volcanic field highlands were no longer prominent. This led to a change in the provenance and sediment characteristics in the distal depositional basin at the Oligocene-Miocene boundary. 

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

doi: 10.1130/abs/2025AM-8581

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