--> Abstract: Sequence Stratigraphy in Evaporitic Systems, by A. C. Kendall and G. M. Harwood; #91012 (1992).

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ABSTRACT: Sequence Stratigraphy in Evaporitic Systems

KENDALL, ALAN C., and GILL M. HARWOOD, University of East Anglia, Norwich, U.K.

Some evaporite basins are entirely nonmarine. Variations in their evaporite sequences can only be ascribed to climatic and tectonic factors. Other evaporite basins are linked to the marine system and, in them, sea level changes are a further factor influencing evaporite development. The degree of decoupling of these evaporitic areas from the ocean is variable, but nowhere is there direct connection to open marine conditions. Two major facies groupings of evaporites occur in marine-influenced basins. The same basin may also exhibit alternations between these two facies groupings through time.

Marginal marine (salina, sabkha) facies develop on the flanks of open marine basins. Their development commonly occurs at, or near, sea level highstands when preceding carbonate depositional rates were sufficient to establish permeable barriers to the evaporite systems. Sea level changes control evaporite mineralogy and depositional rates.

In contrast, basin-central evaporites formed when sea level dropped below a barrier to a major depositional, but starved, basin. These evaporites are not necessarily low-stand deposits, and they may form during falling or rising sea levels. As soon as sea level falls below the barrier, evaporative drawdown causes brine levels to fall well below sea level. If sea level falls close to or below the basin floor, however, no marine-derived evaporites can be formed. Onlapping evaporites on basin flanks cannot be used to establish rises in sea level--they merely record sediment aggradation toward sea level. Evaporite mineralogy and depositional rates are controlled by rates of water inflow, evaporation, and brine outflow. Climatic and tectonic factors may outweigh the influence of sea level hanges.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)