Abstract

In two contiguous quarries located south of Mt. Magaggiaro, in the Sciacca region (south-western Sicily), a discontinuous pelagic succession is exposed, overlying the lower to (?) middle p.p. Early Jurassic peritidal limestone of the Inici Fm. The area belongs to the palaeogeographic "Saccense Domain". Posidoniids-rich pelagites, late Bajocian in age, generally overlie directly the peritidal limestone; the base of the pelagic succession corresponds to, and is concordant with, a planar surface that truncates tilted beds of the Inici Fm. A thin condensed horizon, exceptionally rich in ammonites and belemnites, is however locally interposed between the peritidal limestone and the Bajocian pelagic deposits. It bears a mixed ammonite assemblage indicating a late Toarcian (D. meneghini biozone) to middle Aalenian age. The biochronological meaning of this horizon serves to constrain better the drowning event that affected the platform. The angular nature of the unconformity, corresponding to a drowning unconformity, is interpreted as the product of synsedimentary extension that predated the drowning of the Inici platform.

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