Middle and Upper Jurassic stratigraphy and sedimentary evolution of Lebanon (Levantine margin): palaeoenvironmental and geodynamic implications

Abstract

AbstractThe Arabian, African and Eurasian plates interact in the Levantine region. Despite numerous studies of the region, many geological issues relating to Mesozoic times remain unresolved. The Lebanon passive margin is a key area for understanding Neo-Tethyan sedimentary history during this period. The Jurassic succession in Lebanon is well exposed and thick (more than 1000 m). It is more or less complete and relatively undeformed. With a few recent exceptions most studies of the area were made in the 1950s and so the sedimentary evolution of the Jurassic is only partly understood.This study provides (1) a new sedimentary and sequence stratigraphic framework, and (2) a new biostratigraphic framework based on benthic foraminifera and calcareous algae. Palaeoenvironmental and geodynamic conclusions are inferred.Jurassic outcrops occur in both the Mount Lebanon and the Anti-Lebanon areas. Here, they were studied essentially in Mount Lebanon. The Jurassic succession can be divided into three parts: (1) the lower part (Kesrouane Formation) is a thick succession of marine limestones or dolomites; (2) the middle part (Bhannes Formation) consists mainly of basaltic eruptive rocks associated with pyroclastic strata; (3) the upper part (Bikfaya Formation) is a succession of marine limestones.During the Bathonian, Callovian, Oxfordian and parts of the Kimmeridgian, a large epicontinental shelf, with very shallow marine environments, extended across Lebanon (Kesrouane Formation). The period was characterized by a stable platform morphology. It was a tectonically quiet period, although intense subsidence allowed the accumulation of a thick sediment package. During the Kimmeridgian, the carbonate platform regime that had dominated Lebanon during the Middle Jurassic came to an abrupt end, as evidenced by a regional unconformity, a regression and block faulting. This rifting phase is associated with a volcanic event (Bhannes Formation) that is recognized from northern to southern Lebanon. During the Lower Jurassic (Kimmeridgianp.p.to Tithonianp.p.) shallow marine carbonate shelf deposits are observed again (Bikfaya Formation), indicating a marine transgression. This last formation exhibits rapid lateral thickness variations, because of active block faulting and erosion, and is overlain by continental sandstones of the basal Cretaceous.