engleski

Geodynamics of the Middle Adriatic offshore area, Croatia, based on stratigraphic and seismic analysis of Paleogene beds

Stratigraphic interpretation of the Paleogene deposits clearly displays two different sedimentary realms, which are recognized as belonging to different tectonostratigraphic units. The western unit belongs to the Adriatic indenter and the eastern one to the Dinaridic thrust belt. In the western realm the stratigraphic succession of the deep marine sediments ranges from the Upper Cretaceous to the Middle/Upper Eocene. Carbonate turbidites deposited on the deeper part of a platform slope are characterized by a mixture of wackestone/mudstone rich in planktonic formainifers and packstone/rudstone with shallow-water, platform-derived detritus. Based on the data from the wells Koraljka-1 (Kok-1), Ksenija-1 (Kse-1), Jadran-1 (J-1), Jadran-2 (J-2), Jadran-21/1 (J-21/1) and Jadran-10 (J-10), at the end of the Upper Eocene (Priabonian) period the area was drowned and covered by siliciclastic turbidites. This complete succession of Cretaceous to Paleocene sediments has no onshore equivalent. In the eastern realm Paleogene shallow-water carbonates are identical to the same deposits of the External Dinarides. A long hiatus between the Upper Cretaceous and the Cuisian is evident in wells Jadran-9 (J-9), Jadran-3 (J-3), Kornati More-4 (KM-4) and Susak More-1 (SM-1). Only in the area of the Kate-1 well is a certain continuity of the sedimentation present in the environment of shallow restricted lagoons, repeatedly interrupted by short phases of exposure at the time of overall regional emersion in the Early Paleogene. In the remainder of the platform the stratigraphic succession begins with a transgression of the uppermost Paleocene and/or Cuisian limestone that overlies karstified Cretaceous deposits. Transgressive succession started with fenestral and Charophita limestone (facies X) which was followed by foraminiferal wackestone/packestone, marl with ostracodes and fine-grained breccia conglomerate (facies A), foraminiferal packstone/grainstone limestone and miliolid mudstone/wackestone limestone (facies B and C), porous limestone?, grainstone? (facies Y), fossiliferous mudstone/packstone limestone (facies D), algal boundstone/bindstone and wackestone (facies E), foraminiferal mudstone/packstone (facies F) and Nummulite-Discocyclinae floatstone/packstone and grainstone/rudstone (facies G). These sediments were deposited close to the carbonate platform margin. Beds of the X-facies are younger than Cretaceous and older than Cuisian. A transgressive sequence from A- to Y-facies was formed during the Cuisian whereas the others belong to the Lutetian and partly to the Biarritzian. At the end of the Middle Eocene they were tectonically compressed and covered by flysch deposits. At Paleogene time the deep marine sediments were deposited at a considerable distance from the Dinaridic carbonate platform (DCP). A comprehensive study of the flysch deposits suggests that the drainage area was located to the west and not realated to the DCP. Underthrusting of A to the northeast created the imbrications of the Dinaridic frontal thrust which is clearly expressed in the tectonic repetition of Paleogene sequences in the J-9 and SM-1 wells. The continuing compression caused the inversion of the Adriatic indenter during the Miocene.

Paleogene; offshore wells; tectonostratigraphy; Adriatic; Dinarides

nije evidentirano