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1 2006

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New data on the Jurassic evolution of the Panormide Carbonate Platform (Sicily)

Zarcone G., Mindszenty A., Di Stefano P.

Volumina Jurassica

2006

Vol. 4, no. 1

107-107

The Jurassic of the Panormide Carbonate Platform records several discontinuity surfaces reflecting a complex sedimentary dynamics at a time of general extension in the western Tethyan realm. Previous studies documented subaerial exposure with karst bauxites between Upper Triassic and Upper Jurassic in the internal sector of the platform. On the contrary, at same time the marginal sectors of the platform record Rosso Ammonitico type sedimentation and the subsequent progradation of a new, Upper Jurassic platform. Latest sedimentological and stratigraphical studies added new data on these discontinuity surfaces in the Palermo Mountains. The succession of Mt. Castellaccio is characterized by Upper Triassic peritidal dolostones crosscut by various generations of neptunian dykes filled by pelagic limestones with crinoids, brachiopods, ammonites and filaments (Pliensbachian to Middle Jurassic). They are covered by red sediments rich in ferric ooids and lithoclasts enclosed in a red, argillaceous matrix. Petrographics and X-ray analyses have confirmed the presence of boehmite, kaolinite and hematite in these rocks, on the basis of which they may be qualified as low-grade bauxites. Above, with an angular unconformity, there follow Kimmeridgian loferitic limestones interbedded to bioclastic grainstone/packstone with Clypeina sulcata (Alth). At Punta Raisi, a stratigraphically equivalent, but sedimentologically different succession has been studied. The Upper Triassic peritidal dolostones are overlain by Lower Jurassic cyclic peritidal limestone with very poor microfauna. It is repeatedly interrupted by yellow to browinsh paleosoil levels. The top of this succession is red-coloured and is marked by a complex dissolution surface, with pinnacles and grooves. It is capped by a thick Fe-Mn crust with Foraminifera, small ammonites and filaments [Bajocian-Callovian(?)]. Based on preliminary petrographical and geochemical analyses a brief subaerial event may be hypothesized. However, the very same petrographic analyses revealed the effects of undoubtedly submarine bioerosion (action of sponge, fungi and bacteria), too. So even if we accept the idea of a transient subaerial phase, a strong submarine overprint during subsequent drowning, possibly contributing to the development of the pinnacle-and-groove topography can not be excluded, either. The Fe-Mn-crust is overlain by pelagic sediments displaying a coarsening upward trend and gradually passing into bioclastic grainstones/packstones with abundant carbonate platform elements (Kimmeridgian). This work is intended to add new arguments to the stratigraphic evolution and, consequently, to the subsidence history of the Panormide Carbonate Platform. Results are as follows: * evidence for an Early Jurassic shallow water depositional environment; * restriction of the size of the hiatus between Lower and Middle Jurassic; * verification of the presence of a submarine dissolution surface analogous to that of the Trapanese Platform; * increase of the areal extension of bauxites on the Panormide Platform; * confimation of the synchroneity of the re-establishment of the shallow-water carbonate sedimentation during the Late Jurassic. This data moreover allow a better paleogeographic reconstruction and a key to understand the combined effects of sea-level changes, tectonics and thermal (?)updoming at the time of an overall extensional regime.