Introduction

Modern evaporite depositional environments have received extensive scrutiny in the literature including several books (Busson and Schreiber 1997; Logan 1987; Schreiber 1988; Technicians 1982; Warren 1989; Warren 1999) devoted exclusively to the subject. The attention given these depositional settings has facilitated greatly the interpretation of ancient evaporite bearing sequences. While comprehensive on the subject, books on evaporites fall short of the accessibility afforded by the internet. We at CRC Enterprises believe a pictorial synopsis on the web would facilitate the educational process on these important sediments and have put together this and related web pages with that in mind. The available content on these pages is not complete. Furthermore, the focus is on gypsum and anhydrite rather than the full range of evaporite deposits. Hence, contributions to and suggestions for improvement of our coverage on evaporites are graciously accepted.

Following Kendall (1982) and Schreiber et al. (1982) we divide evaporitic environments into four basic settings: 1) continental sabkhas (subaerial and subaqueous), 2) marine sabkhas, 3) salinas and salterns (shallow subaqueous evaporite pans), and 4) deep hypersaline seas. Subtle changes in environments have an enormous impact on evaporite deposition and result in distinctive subenvironments. Many of these subtle depositional settings produce evaporite deposits with distinct morphologic and textural evaporite deposits within the general depositional setting. These subtle variations are of particular interest as they commonly offer significant clues for environmental interpretation. It is always of enormous benefit to have a grasp of all the basic information for interpreting ancient sedimentary sequences and this statement is perhaps a greater truism for evaporite sequences that are highly prone to diagenetic alteration.

Continetal Sabkhas

Continental sabkhas or playas develop in the central parts of enclosed drainage basins where evaporation exceeds river recharge. Surrounded by continental clastic deposits these evaporitic base-level plains are nearly horizontal, largely devoid of vegetation and commonly have a ephemeral brine lake toward their center. This depositional setting features nearly a dozen subenvironments whose description is detailed in (Hardie et al. 1978).

Much evaporite deposition occurs within exposed wet sediments and subaqueously in ephemeral or perennial saline lakes. The evaporite mineralization and mineral morphology is exceedingly varied because the continental water chemistry exhibits a significantly wider range of solutes then seawater. Kendall (1982) notes continental runoff is enriched in calcium bicarbonate and calcium sulphate relative to seawater, a condition that favors sodium carbonate (e.g. trona) and sodium sulphate (e.g. mirabilite) precipitation in addition to sodium chloride and calcium sulphate. Brine fractionation also tends to happen quickly because evaporation is rapid and complete given a limited water supply. Chemically ‘simple’ brines evolve in response to fractional dissolution during wet periods such that “only one or two major solute species (e.g., NaCl, Na2SO4 or Na2CO3), reach the basin center (Kendall 1982).

References

• HARDIE, L.A., SMOOT, J.P., and EUGSTER, H.P., 1978, Saline lakes and their deposits: A sedimentologic approach, in Matter, A., and Tucker, M.E., eds., Modern and Ancient Lake Sediments: IAS Special Publication, International Association Sedimentologists, p. 7-41
• KENDALL, A.C., 1982, Evaporites, in Walker, R.G., ed., Facies Models: Geoscience Reprint Series 1: Newfoundland, Canada, Geological Association of Canada, p. 259-296.
• SCHLEDER, Z., BURLIGA, S., and URAI, J.L., 2004, Comparison of halite microstructures from different tectonic settings: implications for deformation mechanism, fluid flow and reology, Rheinsh-Westfausche Technische Hochschule.
• SCHREIBER, B.C., ROTH, M.S., and HELMAN, M.L., 1982, Recognition of primary facies characteristics of evaporites and the differentiation of these forms from diagenetic overprints, in Handford, C.R., Loucks, R.G., and Davies, G.R., eds., Depositional and Diagenetic Spectra of Evaporites - A Core Workshop: SEPM Core Workshop No. 3: Calgary, Society of Economic Paleontologists and Mineralogists, p. 1-32.