Homogenization temperature of fluid inclusions in laboratory grown halite and its implication for paleotemperature reconstruction

Halite is a major evaporate mineral in the surface environment, and it contains abundant fluid inclusions formed during crystal formation, which can record the brine temperatures of crystal growth in ancient oceanic salt ponds and salt lakes in geological history. Using the "cooling nucleation method", homogenization temperature of fluid inclusions in halite can be measured. However, the interpretation and application of the homogenization temperature in palaeotemperature reconstruction is not straightforward. Fluid inclusions in halite can be captured in cumulate halite crystals formed at the air-water interface or in chevron halite crystals formed at the water-sediment interface. Lowenstein et al. (1998) carried out a microthermometric analysis on halite crystals grown in the laboratory through evaporation of halite-saturated brines in flasks submerged in water baths; however how to translate brine temperature into air temperature is the key question of paleoclimate. In this study, we measured a series of homogenization temperature of fluid inclusions in both cumulate and chevron halite crystals grown in the laboratory at a temperature of 40 degrees C (air temperature) in a thermostatic air drying oven in 20cm deep brine in order to reconstruct the paleotemperature using homogenization temperatures directly. The homogenization temperatures range from 10. 6 degrees C to 39. 9 degrees C. The results show that only the maximum homogenization temperature of fluid inclusions (T(h max)) matches brine temperatures. Both cumulate halite and chevron halite have a similar T(h max), both types of halite can be used in paleotemperature reconstruction in shallow water.