SEDIMENTOLOGY AND GEOCHEMISTRY OF LOWSTAND PERITIDAL LITHOFACIES AT THE CENOMANIAN-TURONIAN BOUNDARY IN THE CRETACEOUS CARBONATE PLATFORM OF ISRAEL

The upper Cenomanian shallow-marine, platform dolostone in northern Is rael 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 alg al stromatolites, enveloped within a calcite matrix. The latter, origi nally mainly a carbonate mud, was exposed and dolomitized, but later u nderwent large-scale dedolomitization, leaving a massive, nonbedded, L imestone 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 boun dary 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 dolos tone formed by seawater-dominated fluid dolomitization of foraminifera l carbonate mud. The tepee dolomite in the chaotic unit formed ender t he influence of mixed sea-water/fresh-water fluids associated with an intertidal setting. Certain geochemical variations suggest a subtle di fference in the composition of the mud precursors rather than involvem ent of meteoric waters. Dedolomitization invoked meteoric solutions de pleted in O-18 and C-13 that reacted with decayed organic matter in so ils. Sr, Fe, and Na were removed in solution together with the Mg in a relatively open system. An increase in P and Ii in the dedolomite sug gests a better exchange mechanism between Ii and P with Ca as compared to Mg.