A Physical Model for Accurate Paleotemperature Reconstruction From Fluid Inclusions in Halite

Fluid inclusions (FI) trapped in microscopic cavities in halite (NaCl) crystals from evaporitic sedimentary basins are remnants of hypersaline waterbodies. Halite FI provide valuable information on past climate conditions because the density of the enclosed brine can be used for quantitative reconstructions of waterbody temperature at the time of halite precipitation. The classical approach to determine the fluid density in FI is via the liquid-vapor homogenization temperature ( T h,obs ) using FI microthermometry. Recent breakthroughs have the potential to usher in a new era for halite FI in paleoclimate research: new analytical techniques, an equation that predicts the size above which FI deform plastically, an equation of state for multi-electrolyte solutions covering the relevant ranges of temperature, pressure and concentrations, and models that predict the effect of surface tension on T h,obs in constant-volume systems. Against this backdrop we present HaliBubble, a numerical model designed for paleothermometry of Na-K-Mg-Ca-Cl-SO 4 -HCO 3 -H 2 O halite FI that includes the effect of fluid-host interactions on the physico-chemical properties of the FI. HaliBubble allows calculation of (i) the liquid pressure P L and differential stress Δ P in monophasic FI as a function of temperature ( T ), external pressure ( P ext ) and composition ( x ); (ii) the Laplace pressure term Δ T L that corrects for the premature collapse of the vapor bubble due to surface tension; and (iii) the hydrostatic pressure correction term Δ T P that takes into account the water depth at which the halite crystals formed. Compared with an ideal isochoric FI, we find that fluid-host interactions in a halite FI significantly affect P L , Δ T L and Δ T P . We illustrate the model on a halite sample that grew on the floor of the Dead Sea. FI in this halite larger than 27 μm were likely altered by an excessive FI liquid pressure. We calculate a FI entrapment temperature 5.4 °C greater than the average T h,obs , which highlights the relevance of HaliBubble to the paleoenvironmental and paleoclimatic interpretations of halite FI data. Appendix tables and figures provide P L vs. Δ P lim , Δ T L and Δ T P for various chemical compositions. A user interface of HaliBubble is found at https://www.wolframcloud.com/obj/emmanuel.guillerm/HaliBubbleDataProcessing (https://www.wolframcloud.com/obj/emmanuel.guillerm/HaliBubbleDataProcessing).