Evolution of Fluvial Landscapes during the Eocene-Oligocene Transition in Central North America: Reconstructions from Toadstool Geologic Park, Nebraska, U. S. A.

• DOI: 10.31223/x5nx2c
• Publication Date: 2024-06-14T20:22:49Z
• Authors: Queenie Chang; Anjali Fernandes; Michael Hren; Virginia Smith; David Luffman; Mia Rhodes; Madelyn Kurtz
• Keywords: Aggradation

Rivers drive geomorphic change at Earth’s surface by transporting sediment from mountains to sedimentary basins. They are sensitive changes in water and flux driven tectonism, climatic perturbation or volcanism. We characterized fluvial landscapes during a major Cenozoic cooling event, the Eocene-Oligocene Transition (EOT) 33.9 Ma. The EOT is long term ~4-5°C decrease global mean annual temperature, punctuated short, intense fluctuations. In Great Plains region of central North America, temperature decreased ~7°C precipitation declined ~50% across EOT. Preceding EOT, renewed Cordilleran uplift near northeastern Nevada began ~39 Ma extensive volcanism Basin occurred ~36 reconstruct characteristics rivers floodplains through Late Eocene-Early Oligocene deposits White River Group (WRG), exposed Toadstool Geologic Park northwestern Nebraska, U.S.A., evaluate how river responded these events. identified five stages paleo-rivers -floodplain strata Group: (1) Following Laramide uplift, Eocene Chamberlain Pass Formation adjusted steep gradients (~10-3) gentler ones (~10-4), transitioned shallow, mobile channels deeper, stable floodplains. transition Chadron saw shift relatively coarse-grained system with an extremely fine-grained, aggradational, floodplain-dominated influenced high volcanogenic loads. (3) Early Orella Member Brule associated onset marked coarse ephemeral that display evidence significant, likely seasonality-driven, discharge variability. (4) (33.9 - 31.6 Ma) also show compelling recurrent episodes sustained channel incision fill we connect climate fluctuations early phase rapid cooling. (5) deposited 33.4 no significant erosional surfaces continue reflect variability, loads, after end initial