A model for the potential locations of Triassic evaporite basins driven by paleoclimatic GCM simulations

A simple model of evaporite basins is driven by seasonal meteorological forcing from general circulation model (GCM) simulation of the Triassic climate. The basin model bridges the gap between the GCM meteorology and (some of) the physical processes involved in evaporite deposition that are not included in the GCM. It serves as an explicit objective link between the large-scale GCM results and the small-scale occurrences of a particular climate proxy. The model consists of a single column of saline lake water at each GCM grid point. Negative annual precipitation minus evaporation at the lake surface is interpreted as a necessary condition for the formation of Triassic evaporite deposits. Good agreement is found between observed and predicted evaporite sites in the Carnian (225 Ma), with less agreement in the Scythian (245 Ma). We suggest that some of the disagreements may be due to the lack of small-scale topography and the lack of ocean dynamics in the GCM. The basic approach of using secondary land-surface models in conjunction with GCM meteorology could also be profitable for other paleoclimatic proxies such as coal, bauxites and karsts. We briefly discuss the importance of more objective methods for validating model maps against observed proxy distributions, the desirability of predicting both necessary and sufficient conditions for proxy formation, and uncertainties due to spatially incomplete geologic sampling.