Transition from coral to stromatoporoid patch reefs in Middle Jurassic equatorial warm waters

Middle Jurassic reefs are known and studied from a wide range of palaeolatitudes, yet southern Tethyan reefs have been relatively understudied. The high abundance of stromatoporoids in southern Tethyan reefs was suggested to indicate a tolerance to oligotrophic and overheated waters. Recent studies affirmed the longtime hypothesis of a warm equable climate in low palaeolatitudes during the Jurassic, which could account for the documented low diversities of low-latitudinal coral reefs during this time interval. We present a case study showing possible evidence for the suggested connection between heat stress, low coral diversity and the success of stromatoporoids in the southern Tethys. The study focuses on the unique erosional depression of Makhtesh Gadol, southern Israel, which preserves a continuous section of the Callovian (Middle Jurassic). It is rich in fossils of benthic macrofauna, especially patch reefs of corals and stromatoporoids. Our quantitative analysis shows, for the first time: (1) a variation between a low-and high-diversity of coral patch reefs; and (2) a major shift from coral-dominated patch reefs in the lower part of the section to dominating stromatoporoids in the upper part. The faunal assemblage is used to reconstruct the depositional environment, indicating a shallowing upwards and increasing warmer waters. Patch reef beds showing low coral diversity are correlated with isotopic reconstructions from the same section, providing evidence for elevated water temperatures. The faunal transition from corals to stromatoporoids is correlated with a similar shift in Saudi Arabia, improving the regional correlation to the Arabian Carbonate Platform.