Mid-Eocene sea surface cooling in the easternmost proto-Paratethys sea: constraints from quantitative temperatures in halite fluid inclusions

Abstract

The temperature fluctuations in the Eocene climate are one of the most mysterious phenomena in Cenozoic climate dynamics, and they severely affected the marine and terrestrial biospheres. However, quantitative and comprehensive temperature reconstructions for middle Eocene climatic variations remain limited due to fragmentary paleotemperature records, especially in the easternmost proto-Paratethys sea (Kuqa Depression), where traditional paleoclimatic proxies are restricted by the occurrence of extensive and thick evaporite deposits. In this study, we reconstruct middle Eocene sea surface temperatures (SST) and even air temperatures in the Kuqa Depression based on 584 homogenization temperatures (Th) for fluid inclusions in cumulate and chevron halite crystals from cores DW1 and KL4. The Th values from core DW1 have ranges of 10.5–45.7 °C, the Th values from core KL4 have ranges of 12.6–35.2 °C. The measured Th values are mainly concentrated within 20–30 °C, and an average Th value of 25.6 °Crepresents the SST and is consistent with previous coeval research results. The highest recorded Th is 45.7 °C, clearly representing local hot climate conditions. The average and maximum SST in the middle Eocene Kuqa Depression are cooled by 5.2–11.3 °C and 6.5–14.1 °C, respectively. The cooling trend in the Kuqa Depression occurred in response to global and Tethyan realm cooling in the middle Eocene, but the cooling amplitude in the study area was greater than that of the global climate. The Th data for primary halite fluid inclusions can effectively and quantitatively track past environmental and climatic variations, especially in evaporitic basins where traditional paleoclimatic proxies are often not available.