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Sedimentary Geology, 72 (1991), 97-115 ORDOVICIAN ALLUVIAL FAN TO MARINE SHELF TRANSITION IN SW SARDINIA, WESTERN MEDITERRANEAN SEA: TECTONICALLY ("SARDIC PHASE") INFLUENCED CLASTIC SEDIMENTATION I.P.MARTINI1, M.TONGIORGI2, G. OGGIANO3 and T. COCOZZA4
1Department of Land Resource Science, University of Guelph, Guelph, Ont.
N1G 2Wl, Canada ¡¡  A localized Lower Ordovician, early Caledonian structural event ("Sardic
phase") is recorded in SW Sardinia by an angular and erosional
unconforrnity, fauJting, and mild folding. This event was accompanied by
sedimentation of a transgressive, clastic unit ("Puddinga Beds") that
is particularly well developed along a major fault system (Gonnesa fault zone).
There, the "Puddinga Beds" range from basal interfingering fans (some
formed by coarse carbonate and schist-clasts others by schist-clasts only), to
fluvio-lacustrine mud and gravelly sandstone, to coastal muddy and sandy
deposits, and to fossiliferous restricted marine shelf sediments.The existence of the slightly compressive "Sardic phase" in SW Sardinia and a quasi-coeval calc-alkaline volcanism and an extensional structural phase ("Sarrabese phase") in central-east Sardinia, suggest transcurrent faulting. The calc-alkaline acid volcanism is also interpreted by some authors to indicate that the rifted basins developed in backarc position. The non-volcanic sequence of SW Sardinia analyzed in this paper was probably formed in basins developed on the northern margin of the Gondwanaland craton. This Sardinian system may be the eastward extension ot transcurrent rifts which have also been recently reported from NW Spain. Structural activity has been the predominant control on sedimentation; however, worldwide, recurring, low sea-level stands may have influenced the sedimentation of the lower part of the "Puddinga Beds", and the deglaciation of the Saharan Ice Sheet has contributed to the uppermost Ordovician-early Silurian deepening of the euxinic shelf. |
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