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Biostratigraphy, Sequence Stratigraphy and Lithofacies Distribution of the Upper Cretaceous to Eocene Carbonate Deposits in the Off-shore Wells (Mid-Adriatic, Croatia)

Studied wells are situated in the central part of the Adriatic offshore. Two different depositional environments during Upper Cretaceous to Eocene were recognised. Deep water depositionaI environment: Lithofacies X- Maastrichtian-Paleocene-Eocene (NC 21-NC23, P1-P6, NP1-NP4 zones) mud supported limestone (MDST/WKST), rich with planktonic foraminifera, intercalated with bioclastic limestone (PKST/GRNST/FLTST), allochthonous lowstand debris. Lithofacies Y- L. Eocene, chaotic breccia, autochthonous wedge. Shallow-water depositional environment on carbonate platform: Lithofacies A - Maastrichtian (Fleuryana adriatica) dolomitised coquina and microcoquina limestone. Back reef lagoon, late HST. Lithofacies B - Uppermost Maastrichtian-Paleocene (small rotalids) fenestral (WKST/MDST) limestones. Very shallow restricted lagoon and tidal flats, LST. Lithofacies C - L. Eocene (Rotalia trochidifonrmis) limestone with variable portion of pellets and peloids, micritised benthic shells, gastropods and ostracods. Restricted shoals, TST. Interpretation: At the end of the Cretaceous, in the wider region of the Adriatic Carbonate Platform sea level was changed, emersion took place. Carbonates were karstified, diagenetically changed (lithofacies A) and the bauxite deposits were widespread. Only in places the sedimentation continuity at the K/T boundary is documented in brackish lagoons (Lithofacies B). In the L. Eocene (Cuisian) the entire platform was flooded again (Lithofacies C). At the same time in the deeper water environment the depositional continuity at the K/T boundary is obvious. Upper Maastrichtian and Paleocene deposits which were eroded on the platform during the LST are via slope transported to the basin (Lithofacies X). Chaotic breccia in the L. Eocene (Lithofacies Y), however, should be interpreted as the drowned debris flows and carbonate sands during the early stage of the sea level rise. During the late TST deeper water deposits are significantly thinner

Stratigraphy; Cretaceous; tertiary; Carbonates

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