MIO-PLIOCENE CLIMATE RECORD OF THE ATACAMA DESERT FROM GEOCHEMISTRY AND AGES OF FRESHWATER CARBONATES

Freshwater carbonates from the Opache Formation (5.7 -2.4 Ma) within the Calama Basin, Atacama Desert, Chile, record Miocene-Pliocene paleoclimate changes. Opache Formation sections from the eastern basin between the rising Andes and the Precordillera, and also from an elongate basin west of the Precordillera (de Wet et al., 2015, 2019) were studied. Separating these basins is a major strike-slip fault with evidence for vertical movement that may account for some of the topographic differences between sample locations. New carbonate Metal/Ca and Sr isotopes in carbonate and detrital phases are presented. Carbonates from each section are considerably different in ⁸⁷Sr/⁸⁶Sr until the top of each section, indicating initial hydrologic separation of the two sites, joining towards the end of deposition. The eastern section has a 45-meter range of data points, and the western section has a 30-meter range with more rapid changes in the detrital phase. ⁸⁷Sr/⁸⁶Sr data for the east and west are similar, but peaks in the west are not correlative with the east, and there are no distinct patterns between detrital and carbonate data. The Atacama Desert experienced short duration climate events during this period (de Wet et al., 2019), as well as fault motion and tectonic uplift of the volcanically active Andes. Distinguishing between these sources of variability requires the sections to be correlated. Elemental maps from thin sections were used to find suitable areas for U/Pb dating and preliminary U/Pb dates of carbonates constrain correlations between the eastern and western sections. High resolution dates from stromatolites in the western basin (Cannato et al., 2022) provides additional information about climatic conditions during Opache depositional time. Ultimately, U/Pb dates will deepen our understanding of the climate record to better understand Miocene/Pliocene paleoenvironmental parameters in this region.

de Wet, C., et al. 2019 GSA Bulletin, 132, 1795-1816

de Wet, C., et al. 2015 Palaeogeog. Paleoclim. Paleocol., 426, 46-6

Cannato, J., et al. 2022 GSA Abstracts with Programs. 5-6, Vol. 54, No. 3