ABSTRACT

Skeletal constituents consisting of high-magnesian calcite, such as those of coralline algae, are prone to dolomitization. This observation has been known from Pacific (Schlanger, 1957) and Bermuda examples (Gross, 1965). A third example, from the Negev of Israel (Buchbinder, in preparation), has now become known.

Micritic envelopes lining skeletal particles in modern environments consist of high-magnesian calcite (Winland, 1968) or aragonite (Allen, Gavish, Friedman, and Sanders, 1969). In reef talus facies of Miocene rocks from the Negev of Israel micritic envelopes show preferential dolomitization together with coralline algal fragments which are found in the same rocks. All other constituents, like pelecypods or corals, resist dolomitization. Hence like coralline algae the micritic envelopes must have consisted of high-magnesian calcite before dolomitization. This paper is the first to provide evidence on the original composition of micritic envelopes in ancient rocks.