ABSTRACT

The upper Cenomanian shallow-marine, platform dolostone in northern Israel is topped by a calcrete crust. It is unconformably overlain by a chaotic unit, 8 m thick, consisting of various peritidal lithofacies, including tidalite, desiccated and brecciated tepee dolostone, and algal stromatolites, enveloped within a calcite matrix. The latter, originally mainly a carbonate mud, was exposed and dolomitized, but later underwent large-scale dedolomitization, leaving a massive, nonbedded, limestone host. Open-marine sedimentation resumed when sea level again rose, depositing Turonian biomicritic limestone. This chaotic unit is a manifestation of lowstand deposition at the Cenomanian/Turonian boundary in Israel, and may equate to a sea-level drop of similar age from the same period reported in Britain and France.

Field, petrographic, trace-element, and stable-isotope data suggest that the platform dolostone formed by seawater-dominated fluid dolomitization of foraminiferal carbonate mud. The tepee dolomite in the chaotic unit formed under the influence of mixed sea-water/fresh-water fluids associated with an intertidal setting. Certain geochemical variations suggest a subtle difference in the composition of the mud precursors rather than involvement of meteoric waters. Dedolomitization involved meteoric solutions depleted in ¹⁸O and ¹³C that reacted with decayed organic matter in soils. Sr, Fe, and Na were removed in solution together with the Mg in a relatively open system. An increase in P and K in the dedolomite suggests a better exchange mechanism between K and P with Ca as compared to Mg.