High-resolution stratigraphy and palaeoenvironments of the intertidal flats to lagoons of the Cenomanian (Upper Cretaceous) of Hvar Island, Croatia, on the Adriatic Carbonate Platform

Abstract

The Middle to Upper Cenomanian (Upper Cretaceous) carbonate series of the Starigrad Limestone Formation outcropping on Hvar (studied sections equal 217 m) is characterized as six recurring facies associations that dominantly represent shallowing upwards parasequences comprising shallow marine/lagoonal through to supratidal flat strata. Facies Association 1 represents a shallow carbonate ramp–coastal environment patch reefs composed of rudists, other various bivalves and characteristic giant clams of unclear systematic position. Those giant clam/rudist patch reefs built benthic islands with other small oysters and spondylids in which a large number of small reef-dwelling Echinids lived. Facies Association 2 comprises platy limestones that are interpreted to represent low-energy lagoonal sedimentation. This lagoon paleoenvironment was at times exposed to hypersaline and anoxic bottom conditions, which resulted in the preservation of many marine vertebrate skeletons (fish and lizards) reported over the past two centuries. Only two different macroalgae, the calcareous Thaumatoporella, and a large currently unnamed probably non-calcareous form, are commonly observed within the platy limestones. Facies Associations 3 through 6 represent a complex range of hypersaline-associated strata that is dominated locally by anhydrite (Facies Association 3) and biolaminites of distal intertidal (Facies Association 4), middle intertidal (Facies Association 5), and upper intertidal/supratidal (Facies Association 6) affinity. Previously unrecognized are the intertidal Upper Cenomanian stromatolites and biolaminates at the top of the shallowing upward sequences. On those extended biolaminate-dominated sandflats dinosaurs migrated at minimum in the Mediterranean leaving extensive trackway systems at several places in Croatia.