MULTIPLE PROXIES TO DESCRIBE AND CONSTRAIN REGIONAL CONDITIONS OF THE NORTH AMERICAN CONTINENTAL INTERIOR AS RESPONSE TO THE EARLY EOCENE CLIMATIC OPTIMUM

The early Eocene climatic optimum (EECO), a warm period ~50 million years ago, is considered a model for warm-world conditions in a high emissions anthropogenic climate change scenario. Our understanding of this time period can shed light on what the continental interior may look like with elevated CO₂ levels and elevated temperature predicted as early as 2100. The Greater Green River Basin, made up of accumulated sediment in a hypersaline lake (paleo-lake Gosiute) at the foot of the forming Rocky Mountains, is known for its high resolution, well-preserved records of the EECO from floodplain and lacustrine sediments. The response of this region to elevated CO₂ and temperatures may make this already harsh, arid location intolerable, so we look to past records of the region to elucidate our expectations. The Bridger Formation (Southwest Wyoming, USA) records alluvial and fluvial sedimentation from ~50-45.5 million years ago, and includes an extremely well preserved and well characterized flora at the Blue Rim fossil quarries (>49.29 to 48.29 Ma). Because of the formation of the Fold and Thrust Belt to the west, Uinta uplift to the south, and Wind River uplift to the northeast, scientists are concerned about the interference and misinterpretation of differential sediment source pattern signals as climate signals. Using multiple paleosol- and flora- based geochemical proxies, we demonstrated that the rim of paleo-lake Gosiute was a moist forest with warm temperatures, had moderate but consistent weathering, and contained sediments coming from consistent provenance. Though mountain ranges were weathering from multiple sides, the fluvial patterns were consistent over this million year period and geochemically derived climate signals (e.g. CIA-K, floral humidity province, Holdridge Life Zones) demonstrate that this present-day desert was once a productive wet forest as supported by fossils present: dicotyledonous taxa including tall trees and some lianas, some monocots, and ferns.