LATE EOCENE PALEOCLIMATIC AND PALEOENVIRONMENTAL RECORDS OF WESTERN INTERIOR OF THE UNITED STATES: BIOMARKER EVIDENCE FROM THE FROM A PALEOLAKE IN CENTRAL COLORADO

Paleoclimatic and environmental responses to the late Eocene warmhouse in the western interior of the United States areas are poorly understood. Understanding the paleoclimate scenarios we studied the latest Eocene Lagerstätte Florissant Formation (FF, 34.1 Ma, radiometrically dated of detrital sanidine) at Florissant, central Colorado, which contains a diverse flora and fauna preserved in lacustrine facies. Lacustrine sedimentation in FF and its driving mechanisms in the Eocene warmhouse climate are important to evaluating paleoclimatic and paleoenvironmental changes. To determine the specific climatic patterns in the western United States during the late Eocene, scientists rely on proxy data such as sedimentary records, fossil evidence, and geological studies, which provide insights into past climate conditions and can indirectly help to reconstruct the paleoclimate of that region. This study uses molecular fossils and indices derived from lipid wax n-alkane distributions to reveal the paleoclimate and paleoenvironment. Using a set of 84 samples several types of data were gathered: the carbon preference index (CPI) to signify higher odd over even n-alkane abundances, the P_aq index (the proxy for measuring types of terrestrial species), and Pristane/Phytane (Pr/Ph) ratio to reveal the paleoredox (< 1 anoxic and >1 oxic). The CPI data from n-alkanes range from 2.2 to 4.5 which indicates that sediments are less likely to be influenced by post-depositional alteration. The P_aq index range from 0.21 to 0.39, implies the dominating submerged/floating aquatic macrophytes relative to emergent and terrestrial species. Pr/Ph ratios range from 0.55 to 1.2 constraining the paleoenvironment to primarily reducing and/anoxic. Periods of stable lake sedimentation were frequently interrupted by rapid influxes of suspended fine clays, perhaps as mud-dominated turbidites that prograded into the lake at intervals of high runoff triggered by climatic, volcanic, or tectonic events.