engleski

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

Cres Island represents a part of the extensive and long-lasting Adriatic Carbonate platform. By interaction of synsedimentary tectonics, eustatic changes and anoxic event (OAE IC according to JENKYNS, 1991) during the late Albian and early Cenomamian different sedimentary environments were established (KORBAR, 1999). Two main lithostratigraphic units were recognized: "Calcisphaera limestone", deposited in deeper environment (probably slope and/or shallow intraplatform basin), and "Rudist limestone", deposited in transitional and shallow water environments (intraplatform basin margin and/or shallow platform). During Lower to Middle Cenomanian the "Rudist limestone" was deposited along high-energy marginal zone between deeper and shallow-water environments, where ichthyosarcolitid/caprinid (recumbent) communities flourished (steep margin complex according to ROSS & SKELTON 1993). Significant amount of grainy bioclastic material tended to fill the intraplatform basin. It seems that the basin was fast enough to keep pace with rapid sedimentation. During the same time the "Calcisphaera limestone" was deposited laterally. An important facies inside the "Calcisphaera limestone" is "Baldarin breccias" recorded in the Baldarin stratigraphic section. Lithified blocks of ichthyosarcolitid/caprinid bioclastic limestones were shed into deeper-water environment (probaly base-of-slope apron with possible marginal escarpment according to WRIGHT & BURCHETTE 1996) probably during lowstand. The "Baldarin breccias" could be considered as an equivalent of a lowstand wedge and the underlying surface could represent a 2nd order sequence boundary (Middle Cenomanian sea level fall according to HAQ et al. 1987. A probably steep shallow-to-deeper-water transition, which existed during the Lower to Middle Cenomanian, was changed to a more ramp-like geometry during Middle to Upper Cenomanian, when the "Rudist limestone" was deposited in more protected environments. Primary relationships between different Cenomanian deposits have been disquised by younger tectonic activity performed along probably inherited structures.

Adriatic carbonate platform; Island of Cres; Rudists; Sedimentary environments

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