engleski

Shallow Marine Benthic Biota as Proxy for Sea-Level and Sedimentary History, Carbonates of Bahama-Type Mesozoic Platform, Southern Croatia

The Mesozoic, Barremian-Aptian deposits of southern Croatia comprise a succession of shallow tropical-water, inner platform deposits that formed on a Bahama-type isolated platform in the Dinarides. This succession is dominated by benthic foraminifera and calcareous algae, and is exposed in a nearly continuous outcrop section on the island of Mljet, southern Croatia. It has been studied in terms of biostratigraphy, paleoecology and sedimentary facies. The analysis of the microfossil association has provided a detailed biostratigraphic zonation based on the stratigraphic distribution of either benthic foraminifera or calcareous algae. The present study, calibrated against the standard regional biostratigraphic zonation for the Eastern Adriatic Lower Cretaceous, documents that several species of benthic foraminifera and calcareous algae have exceptional age-diagnostic value for the Early Cretaceous biostratigraphy. These Barremian calcareous algae species Salpingoporella melitae and S. muehlbergii, and Early Aptian benthic foraminifera Palorbitolina lenticularis and Voloshinoides murgensis are abundant, have a widespread distribution and a restricted stratigraphic range. They evolved rapidly and became extinct suddenly. The carbonate platform, because of its isolated position within the Late Mesozoic Tethyan Ocean, was free of terrigenous influences. The region was also tectonically quiet during most of the Early Cretaceous. Consequently, benthic distribution within oligotrophic habitats of the study area was primarily controlled by sea-level oscillations, variations in oceanic circulation rate and nutrient availability in surface waters. This study shows that Early Cretaceous diversification of benthic foraminifera in the area investigated, follows the regional relative sea-level curve for that period and the major foraminiferal turnovers coincide with sea-level rise and fall. During relative sea-level rises associated with reduced oceanic circulation and the expansion of nutrient-poor, shallow tropical waters, organisms were able to diversify into various euphotic habitats within the shallow subtidal platform interior. Regressive episodes resulted in reduction of oligotrophic habitats and decreased species richness.

benthic foraminifera; calcareous algae; sea-level; carbonate platform; Dinarides; Croatia

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