Paleotemperature proxies from deep time lacustrine carbonates

BOWEN, GABRIEL; BREEDEN, BENJAMIN; IRMIS, RANDALL; BENAVENTE, CECILIA ANDREA; MANCUSO, ADRIANA CECILIA

Virtual

Congreso; XII Congreso Argentino de Paleontología; 2021

Paleotemperature proxy data from lacustrine sediments and their adjacent deposits such as paleosols are fundamental to understanding terrestrial paleoclimate. The oxygen isotope composition of continental carbonates (δ18Oc) can be applied for deep time paleotemperature calculations, but this is challenging because δ18Ow is affected by geographic and climatic factors and lake water evaporation, all of which controls precipitation isotope ratios. We combined δ18O and CIA data from lacustrine carbonates and paleosols of the Cerro de las Cabras, Cerro Puntudo (Anisian), Santa Clara Arriba (Ladinian), Chañares, Los Rastros and Ischigualasto (Carnian) formations of the Cuyana and Ischigualasto-Villa Unión rift Basins from Argentina (SW Gondwana) to obtain paleotemperature calculations. We aim to constrain them with global terrestrial and marine paleotemperature records for the Triassic to assemble a global paleotemperature data base. We estimated δ18Ow using a geographic relationship to predict precipitation of δ18O, with two end members of paleolatitude calculated from paleopole data and two end members of paleoelevation from the range of East African Rift modern lake systems. Applying the traditional lacustrine paleotemperature equation, this yielded four different estimates for each δ18Oc value. This approach is limited in that it: a) is imprecise; b) assumes a modern geographic distribution of precipitation isotope ratios, and c) does not account for possible lake water evaporation. Therefore, we explore a multiproxy analysis using the joint proxy inversion method, combining δ18O and CIA data from our lake carbonates and paleosols with global contemporaneous marine and terrestrial isotopic data. Results suggest warmer conditions without a substantially different pole to equator gradient, a δ18O-temp relationship probably different than modern and spatial heterogeneity in δ18Oppt possibly due to paleotopography. The resulting analysis provides a promising path forward for developing more accurate and precise continental paleotemperature reconstructions from deep time lake systems.