engleski

Sequence development influenced by intermittent cooling events in Cretaceous Aptian greenhouse, Adriatic Platform, Croatia

Depositional sequences capped by peritidal carbonates and breccias on the Aptian Adriatic carbonate platform, Croatia, were studied to evaluate evidence for glacio-eustasy within an age framework constrained by carbon-isotope chemostratigraphy. Sequence Ad1 (17 to 60 m thick ; uppermost Barremian-Lower Aptian) is dominated by shallow subtidal parasequences. Sequence Ad2 (7 to 13 m thick ; Lower Aptian to lowermost Upper Aptian) contains oceanic anoxic event (OAE) 1a, associated with lagoonal laminated carbonates. Sequence Ad3 (3 to 8 m thick) probably is lower Upper Aptian, and likely is separated by a major hiatus from sequence Ad4 (8 to 20 m thick ; uppermost Aptian) which spans OAE1b. Both Ad2 and Ad3 are dominated by peritidal parasequences updip in the early TST and late HST, and subtidal parasequences elsewhere, whereas sequence Ad4 is dominated by shallow subtidal parasequences. Low accommodation rates (4 to 6 cm in the earliest Aptian, decreasing to ~1 cm/k.y. later) promoted widespread breccia development during relative sea level falls, aided by tectonic warping. The sequence capping breccias , the eccentricity- dominated cyclicity, restriction of peritidal facies to late highstands, and coeval off-shelf oxygen isotope records all suggest sea level falls occurred during times of cooling and had a significant glacio-eustatic component. These intermittent cooler periods and continental ice buildup punctuated the Aptian greenhouse climate.

Aptian; greenhouse; oceanic anoxic event; Adriatic platform; Croatia

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