Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel)

The Zohar Formation (Callovian, Middle Jurassic) is exposed as a sequence of limestones dolomites, siltstones, and shales near the center of Makhtesh Qatan in the Negev Desert of southern Israel. Two dolomite units near the top of these faultbounded exposures are deeply incised by two perpendicular sets of relatively straight channels. Bivalve borings (Gastrochaenolites) in these dolomites show that they were cemented limestones when they were exposed and eroded; dolomitization came later. The dimensions of the channels, along with their orientations and stratigraphic context (they contain later Jurassic sediment), show that they are a series of joints that were widened by bioerosion and erosive currents, most likely from tides and wave action within a rocky shore context. Other trace fossils in these units track the earlier lithification history of these sediments. The soles of the beds show a fabric of Planolites, tunnels excavated by deposit-feeding worms that require soft sediments, cut by a large network of Thalassinoides burrows, which were created by crustaceans in firm sediments. The Zohar Formation at Makhtesh Qatan thus shows the firming, dewatering, and early cementation of sediments that were then exposed and eroded as part of a rocky shore. This new hypothesis updates previous models, which interpreted these rocks as the products of sabkha deposition.