A MOLECULAR BIOMARKER APPROACH TO UNDERSTANDING PALEOCLIMATIC CONDITIONS ACROSS THE EOCENE-OLIGOCENE TRANSITION IN SOUTHERN PATAGONIA, ARGENTINA

Earth's climate transitioned from the greenhouse conditions of the Eocene to the icehouse of the Oligocene ∼34 million years ago. Global cooling was triggered by a decrease in atmospheric pCO₂ and is associated with the first appearance of large, permanent ice sheets in Antarctica. The tectonic separation of the Antarctic at that time and the creation of the circumpolar current, locking the Antarctic into an isolated frozen state is also responsible for global cooling. The Eocene–Oligocene transition (EOT) is marked by a large two-step increase in the 𝛿¹⁸O of benthic foraminifera, reflecting a combination of cooler global temperatures and continental ice growth. Paleoclimatic responses to the EOT in the southern Patagonia of the Argentina areas are poorly understood. Understanding the paleoclimate scenarios we studied the Cerro Colorado (CC) Formation from the Austral basin located in Tierra del Fuego, which contains a diverse nannoflora and foraminifera preserved in the CC Formation. To determine the specific climatic patterns in the southern Patagonia across EOT, 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 reconstruct the paleoclimate of that region. This study uses molecular fossils and indices derived from lipid wax n-alkane distributions to reveal the paleoclimate conditions. Using a set of 102 samples several types of data were gathered: the carbon preference index (CPI) to signify higher odd over even n-alkane abundances, and the P_aq index (the proxy for measuring types of terrestrial species). The CPI data from n-alkanes range from 1.31 to 2.63 which indicates that sediments are less likely to be influenced by post-depositional alteration. The P_aq index range from 0.16 to 0.33, implies the dominating submerged/floating aquatic macrophytes relative to emergent and terrestrial species. This research is relevant for understanding an extreme climatic event aka EOT, and these sites are particularly important because paleoclimate reconstructions in southern Patagonia using molecular biomarkers are scarce.