PREDICTING THE OCCURRENCE OF EVAPORITES USING CLIMATE MODELING (FOAM)

Evaporites form under specific climatic conditions. Though the factors that control evaporite formation may complex (Peryt, 1987), the two principal variables are the mean annual temperature (MAT) and the annual amount of precipitation. Because modern evaporites have a limited extent, we have chosen to use the Yermosol-Solonchak soil type (Zobler, 1886) as a proxy for the conditions under which evaporites form and have constructed a model that predicts the likelihood that evaporites would form under varying temperature and precipitation conditions. Our results suggest that areas with mean annual temperatures between 21°C and 24°C, and average annual rainfall of less than 1 mm/month would be the mostly likely sites of evaporite formation.

From this bivariate description of evaporite formation, we have constructed a“climate envelop” that predicts the likelihood of evaporite formation. The climate envelop model can then be tested by comparing the predictions made by our model with the distribution of ancient evaporites (Boucot et al., in press). Predictions of the global occurrence of evaporites have been made for 18 time intervals during the Phanerozoic and Late Precambrian: late Miocene (10 ma), Oligocene (30 Ma), late Eocene (45 Ma), K/T boundary (65 Ma), Cenomanian/Turonian(90 Ma), early Aptian (120 Ma), earliest Cretaceous (140 Ma), late Jurassic (160 Ma), early Jurassic (180 Ma), Late Triassic (220 Ma), Permo-Triassic (250 Ma), early Permian (280 Ma), Mississippian (340 Ma), Late Devonian (360 Ma), Siluro-Devonian (400 Ma), latest Ordovician (430 Ma), Cambro-Ordovician (480 MA), and late Neoproterozoic (600 Ma). These predictions of evaporite occurence are based on the estimates temperature and precipitation made by the FOAM (Fast Ocean and Atmosphere Model) climate model in combination with the paleogeographic maps produced by the PALEOMAP Project. We will present paleoreconstructions com paring the predicted occurence of evaporites since the late Proterozoic with the known distribution of ancient evaporites.