Carbonate facies evolution from the late albian to Middle Cenomanian in Southern Istria (Croatia): influence of synsedimentary tectonics and extensive organic carbonate production |
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Authors: | Prof Dr Josip Tišljar MSc Igor Vlahović Dr Ivo Velić Dr Dubravko Matičec Dr Julie Robson |
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Institution: | (1) Faculty of Mining, Geology & Petroleum Engineering, University of Zagreb, Pierottijeva 6, P. O. Box 679, HR-10000 Zagreb, Croatia;(2) Institute of Geology, Sachsova 2, P.O. Box 268, HR-10000 Zagreb, Croatia;(3) Demandkey Ltd., 2 Newmoor Cottages, Northwycke, CMO 7DR Southminster, Essex, UK |
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Abstract: | Summary During the Late Albian, Early and Middle Cenomanian in the NW part of the Adriatic Carbonate Platform (presentday Istria)
specific depositional systems characterised by frequent lateral and vertical facies variations were established within a formerly
homogeneous area, ranging from peritidal and barrier bars to the offshore-transition zone. In southern Istria this period
is represented by the following succession: thin-bedded peritidal peloidal and stromatolitic limestones (Upper Albian); well-bedded
foreshore to shoreface packstones/grainstones with synsedimentary dliding and slumping (Vraconian-lowermost Cenomanian); shoreface
to off-shore storm-generated limestones (Lower Cenomanian); massive off-shore to shoreface carbonate sand bodies (Lower Cenomanian);
prograding rudist bioclastic subaqueous dunes (Lower to Middle Cenomanian); rudist biostromes (Lower to Middle Cenomanian),
and high-energy rudist and ostreid coquina beds within skeletal wackestones/packstones (Middle Cenomanian).
Rapid changes of depositional systems near the Albian/Cenomanian transition in Istria are mainly the result of synsedimentary
tectonics and the establishment of extensive rudist colonies producing enormous quantities of bioclastic material rather than
the influence of eustatic changes. Tectonism is evidenced by the occurrence of sliding scars, slumps, small-scale synsedimentary
faults and conspicuous bathymetric changes in formerly corresponding environments. Consequently, during the Early Cenomanian
in the region of southern Istria, a deepening of the sedimentary environments occurred towards the SE, resulting in the establishment
of a carbonate ramp system. Deeper parts of the ramp were below fair-weather wave base (FWWB), while the shallower parts were
characterised by high-energy environments with extensive rudist colonies, and high organic production leading to the progradation
of bioclastic subaqueous dunes. This resulted in numerous shallowing- and coarsening-upwards clinostratified sequences completely
infilling formerly deeper environments, and the final re-establishment of the shallow-water environments over the entire area
during the Middle Cenomanian. |
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Keywords: | Peritidal Carbonates Tempestites Subaqueous Dunes Rudist Biostromes Synsedimentary Tectonics Adriatic carbonateplatform southern istria (Croatia) Upper Albian to Middle Cenomanian |
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