Stromatolitic biotic systems in the mid-Triassic of Israel — A product of stress on an epicontinental margin

Abstract Phanerozoic microbialites are carbonate-precipitating biotic forms that are often described in modern systems from inter- or supratidal, hypersaline or fresh-water environments, and from beds associated with a variety of ecologically stressed environments, over geologic time. Middle to Late Triassic microbialitic successions from southern Israel were commonly subtidal, and thrived under cryptic ecological stress conditions related to the regional configuration of the Levant margin at that time. The Ladinian and Carnian sequence at the Ramon outcrop contains 18 successions with 28 microbialitic horizons. These microbialites form isolated patches, small bioherms and biostromes interleaved with other calcareous sediments including poorly diverse molluscan accumulations. Three distinct microbialitic facies and two associated molluscan facies were identified. Most were distinctly subtidal. The two associated molluscan biofacies include a subtidal bivalve boundstone forming mounds, and a bedded packstone of minute gastropods. The Ladinian–Carnian microbialites were not climatically forced. Environmental stress was caused by partial restriction of marine circulation due to tectonic movements and biotic accumulation on the outer edge of the Levant margin. Comparison of coeval successions from central and northern Israel and the North Calcareous Alps and Southern Alps in Europe, indicates a Tethyan or global carbonate system of microbial producers separated from the open marine environment by shelf-edge barriers. Therefore, we conclude that the Ramon microbialites represent a response to ecological stress of the carbonate system within the subtidal environment, rather than solely to normal stresses of the intertidal environment.