engleski

Integrated stratigraphy of the Upper Cretaceous carbonate deposits on the Island of Čiovo (central Dalmatia, Croatia)

The Upper Cretaceous carbonate succession on the Island of Čiovo in central Dalmatia, Croatia, differs from the typical platform development in the region (e.g. the Island of Brač), implying different depositional setting. Several methods, including integrated stratigraphy (litho-, bio-, and chemo-stratigraphy of C and Sr stable isotopes) and petrological analysis, are being used in order to constrain the regional stratigraphic correlation. Approx. 300 m thick succession of Cretaceous carbonates is measured and analyzed on the westernmost coast of the island. The succession is unconformably overlain by the Paleogene Foraminiferal limestones. Lower 66m of the succession is referred to as the Dol formation (Santonian-Campanian) characterized by bioclastic W/P containing calcispheres, planktonic foraminifera (globotruncanoids), agglutinated foraminifera and calcite fragments (SMF 3), and with chert nodules in a few horizons. Horizon Č-9 represents an intercalation of resedimented allochthonous bio-lithoclastic P/R (platform derived fragments of rudists and other mollusks) (SMF 4-5) with admixtures of pelagic bioclastic W/P (SMF 3), which shows normal gradation. Integrated stratigraphic analysis indicates Campanian age of the Dol formation. Depositional setting of the Dol formation is presumed to be toe-of-slope/slope. Two intra-Campanian discontinuity surfaces occur in the uppermost part (at 56 and 66 m) of the Dol formation. Bioclastic P/G intercalated within the surfaces shows a generally fining upward trend. These surfaces can be described as hard-/firm-grounds with traces of bioturbation, bioerosion, nodularization and mineralization. Several methods (field and laboratory) will be used in order to describe their petrological and mineralogical characterictics, as well as to explain their genesis. There is a possible correlation to some regional or global process of hard-/firm-ground formation, potentially to the regional intra-Campanian relative sea-level fall (Adriatic platform ; Apulian platform) or some global eustatic/isotopic event. The succession between 66 and 296 m is in general represented by massive to thick-bedded resedimented allochthonous grainy limestones, which are in places highly neomorphosed, and sporadically dolomitized. These are mostly bio-lithoclastic P (rarely G/R) (SMF 4-5-12-Crin, encrinite) with predominantly echinoderm fragments (mostly crinoids but also echinoids) with syntaxial overgrowths (commonly the only components), mollusk fragments (bivalves: rudist fragments and other bivalves), benthic foraminifera, bryozoans, coralinacean algae, other calcite fragments (heterozoan grain association), cortoids and wholly micritized grains, lithoclasts, as well as pelagic admixtures (SMF 3). The benthic foraminifera association of the whole succession indicates (late middle) late Campanian (?Maastrichtian) age. The strata between 66 and 296 m were deposited in slope/toe-of-slope settings, indicated as well by the benthic foraminfera assemblage. During subaerial exposure, “paleokarstic pockets” in the form of paleosols with Microcodium structures developed in the uppermost ~10 m of this Upper Cretaceous succession, which is unconformably overlain by the transgressive Paleogene (?Eocene) Foraminiferal limestones over the regional type 1 sequence boundary. Although the depositional setting and lithology of the bio-lithoclastic packestones in the upper part (66-296 m) of the Upper Cretaceous succession on the Island of Čiovo can be correlated with that of the Bra~ “marble” member of the Pučišća formation or “atypical” facies (Dračevica) of the Dol formation on the Island of Brač, the stratigraphic range and the relationships with overlying rocks demand to define a new formation, which is called here the Čiovo formation. While the Sumartin formation on the Island of Brač represents a typical inner-platform development, penecontemporaneous deposits of the Čiovo formation likely represent deeper water slope/toe-of-slope depositional settings, presumably facing the NE Adriatic trough. According to the current interpretations, the trough represents the extension of the Budva-Cukali basin in the form of either an intra platform embayment (tongue of the ocean) that ends in the area near Split, or an inter-platform trough that completely separated the Adriatic and Dinaridic platforms during the latest Cretaceous and earliest Paleogene, and is today completely covered by the Dinaridic thrust further to the NW (as hypothesized).

lithostratigraphy; biostratigraphy; chemostratigraphy; slope carbonates; carbonate platform

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