engleski

Upper Cretaceous - Paleogene Resedimented Carbonates - their significance for the dinamics of the Adriatic-Dinaric Carbonate Platform

Carbonate platform deposits are important constituents in the structure of the External Dinarids. The most impressive, both by its geometry and stratigraphc range, is a carbonate megasequence termed Adriatic-Dinaric Carbonate platform (ADCP). Upon a segmented hercynian basement, part of the Adriatic microplate, shallow marine carbonate deposition was established in the Late Triassic which lasted, with shorter or longer interruptions until the Lutetian transgression. These events - the initiation in the Late Triassic and the demise in the Lutetian - make the geodynamic framework of the ADCP. The sedimentary homogenity of the ADCP was interrupted toward the end of the Cenomanian. The intensive tectonics disintegrated the platform into several large segments. Each segment behaved independently and differently from another, producing the stratigraphic succession of the different range and different development in different areas. Due to Cenomanian tectonics, the northern part of the present Adriatic was emerged and subjected to west-south-west tilting, the consequence of which was the initiation of an intraplatform trough (basin). The signatures of that process are preserved in the deposits of the present-day north-Adriatic islands. This intraplatform trough accommodated large quantities of reworked shallow-water material, which were shed from the neighbouring platform margins. The amount of reworkwd material increases going stratigraphicaly upwards, that is, in the Senonian. This is in agreement with the sedimentation trend on the platform: the platform aggradation exceeds the place of subsidence. The consequence of this is the further enlargement of the previously emerged region. In central and southern Dalmatia and Slovenian Karst, however, the sedimentary sequence shows no emersion. Near the end of the Senonian, a new sea-level rise and the following subsidence further promoted the differentiation of the platform: new intraplatform trougs were formed, while those already existing became definitively filled up (Campanian) and the emerged areas become even more widespread. At the two opposing ends of the ADCP - in central and southern Dalmatia and the Slovenian Karst - very shallow marine deposition with regressive characteristics persisted, culminating in the formation of the widespread tidal flats during the Maastrichtian/Paleocene. In contrast to that, the continuous Maastrichtian-Paleocene pelagic sequences, recorded mostly in north Adriatic off-shore wells, contain redeposited limestones. An on-shore example is the Kotišina resedimented limestones, which is the subject of the present contribution. Based on lithofacies characteristics, two types of the carbonates are distinguished within the Kotišina limestone: the clast-supported packstones and the matrix-supported wackstone-packstones. These two different types repeatedly replace each other in succession, and occasionally can be interbedded with pelagic mudstones. At the present level of research, the depositional model has not been fully worked out. We have a clearly delimited northwestern margin, probably of a ramp type, which has been paleogeographically preserved. The northern and southern margins, primarily tectonically induced, have been subsequently disguised by younger tectonics and cannot be fully defined.

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