EVAPORITE STRATIGRAPHIC SIGNALS OF BASE LEVEL CHANGE IN THE GEOLOGIC RECORD

Sequence stratigraphic interpretations depend in part on the subdivision of the sedimentary section by time significant and widespread surfaces recording sharp changes in sedimentary character, erosion and/or non-deposition. Bounding surfaces of evaporites form distinct and widespread stratigraphic markers where they are constrained by time and depositional setting. In updip supratidal sabkha evaporite cycles the upper bounding surface is preserved in regressive coastlines and matches the sea level position of the late high stand system tract. The upper surface of the downdip restricted playas and basin evaporites coincides with the sea level position of the lowstand system tract. Sabkha lithofacies tend to be matrix rich, circumscribe the basin of deposition, are interbedded updip with wadii sediments and aeolian sand, and downdip with cycles of shallow water carbonate. Evaporite lithofacies deposited in standing water bodies tend to be matrix poor, lie in the deeper parts of the isolated evaporite basin, and are massive. In detail they may have a thin interbedded character related to the seasonal evaporative cycles reflecting the circum basin climate variations. Unique and strong ties exist between linear belts of evaporites, arid climates and plate tectonic setting constraining the timing of accumulation in both marine and lacustrian settings. Arid climatic depositional settings result at specific times when the depositional setting is: 1. Enveloped by widespread adjacent continental plates; 2. Adjacent to uplifted crust marginal to linear belt of depressed crust; 3. A linear belt of depressed crust, whose surface was often below sea level; 4. A location with internal drainage and/or limited access to open ocean waters and; 5. Located within an arid climatic belt. These settings are often adjacent to margins of recently rifted continental plates, in compressional terrains of colliding margins, or in areas of local tectonic uplift or sediment accumulation that have isolated standing bodies of water from the sea.