engleski

Rudist communities and sedimentary environments along shallow-platform to intraplatform basin transition in the Cenomanian of the Island of Cres - Adriatic Sea, Croatia

The island of Cres represents a part of the extensive and long-lasting Adriatic Carbonate Platform. Owing to interaction of synsedimentary tectonics, eustatic changes and anoxic during the Late Albian-Early Cenomanian, different sedimentary environments were established on the southern part of the island. Two main lithostratigraphic units were recognized: � Calcisphaera limestone� , deposited in deeper environment (probably slope and/or intraplatform basin), and � Rudist limestone� , deposited in transitional and protected shallow-water environments (intraplatform basin margin and/or shallow platform). During the Early-Middle Cenomanian the � Rudist limestone� was deposited along high-energy marginal zone between deeper and protected shallow-water environments, where ichthyosarcolitid/caprinid communities flourished. Significant amount of coarse bioclastic material tended to fill the intraplatform basin. It seems that the basin was deep enough and/or relative sea level rise was fast enough to keep pace with rapid sedimentation. During the same time the � Calcisphaera limestone� was deposited laterally, in the intraplatform basin. An important facies inside the � Calcisphaera limestone� is the � Baldarin breccia� recorded in Baldarin stratigraphic section. Lithoclasts of the ichthyosarcolitid/caprinid bioclastic � Rudist limestone� were shed into deeper-water environment along with rudist bioclasts, probably during lowstand. The � Baldarin breccia� could be considered as an equivalent of a lowstand wedge and the underlying surface could represent a 3rd order. A probably steep shallow-to-deeper-water transition that existed during the Early-Middle Cenomanian was changed to a more ramp-like geometry during the Middle-Late Cenomanian, when the � Rudist limestone� was deposited in more protected environments. The primary relationships between different Cenomanian deposits have been disguised by younger tectonic activity.

Adriatic carbonate platform; the island of Cres; Cenomanian; rudists; sedimentary environments.

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