STRATIGRAPHY AND PETROLEUM GEOLOGY OF THE CROATIAN PART OF THE ADRIATIC BASIN

J. Velić¹, T.  Malvić², M. Cvetković¹* and I.  Velić³

¹ Faculty of Mining, Geology and Geological Engineering, Department of Geology and Geological Engineering, Pierottijeva 6, 10 000 Zagreb, Croatia.

² INA-Industry of Oil plc., E&P of Oil and Gas, Sector for Geology and Engineering, Šubićeva 29, 10000 Zagreb, Croatia; and University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Department for Geology and Geological Engineering, Pierottijeva 6, 10000 Zagreb, Croatia.

³ Croatian Geological Summer School, Pančićeva 5, 10 000 Zagreb, Croatia.

* corresponding author: marko.cvetkovic@rgn.hr

Coastal parts of Croatia are dominated by the SW-verging Dinaric foldbelt, to the west and SW of which is the Adriatic Basin (the stable foreland). In both areas, the stratigraphic column is dominated by a thick carbonate succession ranging from Carboniferous to Miocene. Four megasequences have been identified: (i) a pre-platform succession ranging in age from Late Carboniferous (Middle Pennsylvanian: Moscovian) to Early Jurassic (Early Toarcian; Brušane and Baške Ostarije Formations); (ii) an Early Jurassic to Late Cretaceous platform megasequence (Mali Alan Formation); (iii) a Paleogene to Neogene post-platform megasequence (Raša Formation); and (iv) a Neogene to Quaternary (Pliocene to Holocene) megasequence (Istra and Ivana Formations).

A number of organic-rich intervals with source rock potential have been identified on- and offshore Croatia: Middle and Upper Carboniferous, Upper Permian, Lower and Middle Triassic, Lower and Upper Jurassic, Lower and Upper Cretaceous, Eocene, and Pliocene – Pleistocene. Traps and potential plays have been identified from seismic data in the Dinaric belt and adjacent foreland. Evaporites of Permian, Triassic and Neogene (Messinian) ages form potential regional seals, and carbonates with secondary porosity form potential reservoirs. Oil and gas shows in wells in the Croatian part of the Adriatic Basin have been recorded but no oil accumulations of commercial value have yet been discovered.

In the northern Adriatic offshore Croatia, Pliocene hemi-pelagic marlstones and shales include source rocks which produce commercial volumes of biogenic gas. The gas is reservoired in unconsolidated sands of the Pleistocene Ivana Formation.

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