Rijumon Nandy / Earth & Environmental Sciences / Faculty Mentor: Majie Fan
Loess deposits are key archives of past wind activity, exemplified by the extensive Chinese Loess Plateau. Isolated latest Eocene–Oligocene (~37–31 million years ago) loess outcrops. suggest a past more extensive loess plateau in the western U.S. In southwestern Montana, deposits from the Renova Formation were largely fluvial but may partially be deposited by wind. This study tests the hypothesis that wind played a role in their transport and deposition. Grain size analysis was conducted on 64 sandstone and siltstone samples from low-energy floodplain environments, which revealed multimodal distributions with a common peak at ~10 μm. End-member analysis identified three modes: 10 μm (EM1), 100 μm (EM2), and 500 μm (EM3). Comparisons with Wyoming loess suggest EM1 and EM2 represent long- and short-term aerial suspension, while EM3 indicated fluvial deposition. Eolian sediments are best preserved in sheetflood and floodplain fines deposits, supporting wind deposition in the Sage Creek Basin during the mid-Eocene to early Oligocene. This likely resulted from aridification due to global cooling and uplift in the southern Cordillera. Future work will use SEM imaging of quartz grains to confirm micro-scale eolian features. These findings will enhance understanding of paleowind dynamics and climate shifts during the Eocene-Oligocene transition.nfants.
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