Depositional Conditions in the Dead Sea and Reinterpretations of Ancient Deep-Water Evaporites

KENDALL, ALAN C., University of East Anglia, Norwich, U.K.

Published work on post-1979 changes affecting the Dead Sea brine body imply that alternative explanations for some ancient deep-water evaporites are possible. Seasonally variable thermohaline stratification in the Dead Sea brine body allows gypsum-supersaturated brines to be transported to the basin floor, permitting growth of gypsum crusts, as long as the basin floor lies above the thermocline (20-25 m). Below this, only laminated gypsum and carbonates are likely to form in appreciable amounts. Complete brine overturns are ephemeral events, unlikely to cause significant growth of bottom-grown gypsum.

The occurrence of numerous basin-wide layers of former gypsum crusts (now nodular anhydrite layers) in such deep-water evaporites as the Castile, Elk Point, and Zechstein suggests that these evaporite layers were deposited in brine depths less than that of the local thermocline, i.e. at depths of only a few tens of meters. Abrupt brine-deepening events caused laminated sediments to be deposited above former gypsum crusts. The continuation of calcium sulfate precipitation in these laminated sediments from the Castile and Zechstein evaporites indicates brine deepening was not accompanied by brine dilutions sufficient to cause gypsum undersaturation. This imposes limits upon the amount of brine deepening and implies that even the deepest of the laminated sulfate sediments were deposited rom brines only tens of meters deep. Where crusts are overlain by laminated carbonates (Elk Point and some Zechstein evaporites), greater amounts of brine deepening and dilution are suggested.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)