Distribution by Latitude of Phanerozoic Evaporite Deposits

Abstract

Most modern evaporites are accumulating within 50° of latitude of the equator. Within this evaporite belt the distribution pattern is bimodal; evaporite deposition is concentrated in the subtropical high-pressure zones of each hemisphere. Few evaporites accumulate in the low-pressure equatorial zone. This bimodality results from the arrangement of atmospheric circulation and is matched by similar bimodality in the distributions of hot deserts, average marine surface salinity, and the difference between evaporation and precipitation. When ancient evaporites are analyzed in terms of their assumed latitudes of original deposition they are found to follow the present-day distribution model quite closely-at least as far back as the Permian, and possibly as far back as the beginning of the Phanerozoic. This essential constancy of the evaporite regime is taken as an indication that atmospheric circulation and hence the distribution of deserts and of marine salinity have also adhered in general to the modern model. The global evaporite belts in each hemisphere do not seem to have migrated in any consistent direction during the Phanerozoic. Permian to Jurassic time, perhaps approximately the time of existence of Pangaea, seems also to have been the time of peak accumulation of evaporites.