CLIMS

Evaporites are of great interest to reconstruct past temperatures in continental settings as they are the result of either water column evaporation or from pore waters. However, the existing proxies to achieve these reconstructions are quite limited. We have developed a new paleo-thermometer based on Brillouin spectroscopy (BS) on fluid inclusions (FIs) trapped in natural quartz as well as laboratory grown halite. In this project we want to further apply this novel method to natural halite sequences containing FIs to produce accurate paleotemperature reconstructions. The method measures the sound velocity in the liquid phase, which depends on its composition, temperature, and pressure. This new method will be applied to natural halite to reconstruct seasonal temperatures from two sites: The Dead Sea Basin in the Levant region and the Oligocene Bresse Basin in Western Europe. A pre-requisite to obtain seasonal variability in temperature is to have a proxy registering a continuous record throughout the year. In temperate climates, however, tree rings only record spring and summer, the growing season, therefore they are not suitable to document seasonal changes. In tropical regions speleothems allow for monthly scale continuous records provided that the water residence time does not exceed a month. Mollusc shells in high latitudes only record the warm season. Recent investigations have shown that the modern coarse and cumulate halites crystals precipitating in the Dead Sea are seasonal, and a good analogue to ancient halite deposits. This is a twofold project. Firstly, we aim to obtain seasonal temperatures from a Dead Sea core with a well-constrained age model and compare them with other datasets (speleothems, corals, etc.) from the region. This comparison will allow an overall assessment of the temperature evolution during the Last Interglacial (LIG). Secondly, we will analyze a series of sedimentary cores from the Bresse Basin to reconstruct seasonal variations in temperature for western Europe during the Eocene-Oligocene Transition(EOT). Additionally, the H and O isotopic composition of the water trapped in the FIs will be analyzed in both sites to identify the origin of the fluid responsible for the formation of the evaporites. Finally, when organic matter extractions are possible we will complement our results with those from the glycerol dialkyl glycerol tetraethers (GDGTs) paleo-thermometer. The latter result from the membrane lipids produced by bacteria in the mud layers that alternate with halite layers allowing a continuous temperature reconstruction.