RESPONSE OF TRACEMAKERS TO TEMPORARY PLATFORM DROWNING: LOWER CENOMANIAN OF SOUTHERN ISTRIA (WESTERN CROATIA)

Abstract

The Early–Late Cretaceous transition marked the beginning of the final disintegration of the Adriatic Carbonate Platform, which eventually resulted in the formation of the Dinarides mountain belt in the Paleogene, Neogene, and Quaternary. In southern Istria (Croatia) a continuous succession crops out that shows deepening from shallow subtidal to carbonate ramp in the latest Albian followed by gradual shallowing in the early Cenomanian, including well-preserved Ophiomorpha and Thalassinoides burrow systems in sections from Cintinera Cove and Vinkuran quarry. Burrow systems that overlie hummocky cross-stratified deposits are good indicators of specific environmental conditions during deposition. During transgression, favorable conditions for suspension- and deposit-feeding crustaceans were established which resulted in complex networks of Ophiomorpha and Thalassinoides. The increase in bioturbation up-section is recorded by a gradual increase in the bioturbation index as well as the size of burrow systems during transgressive events; a completely bioturbated interval in Vinkuran quarry indicates the maximum flooding surface. Formation of burrow systems was interrupted by subsequent clinoform progradation interpreted as a highstand shedding of shallow-marine bioclasts caused by high carbonate production and intense bioerosion of rudist and chondrodont shells, causing the relatively rapid infilling of the basin and re-establishment of the shallow-marine peritidal deposition in the entire northwestern part of the Adriatic Carbonate Platform.