The Development of the Eocene Platform Carbonates from Wells in the Middle Adriatic Off-Shore Area, Croatia

In the Middle Adriatic deep off-shore wells the following sedimentary facies exist: fenestral and Charophyte limestone facies (X); facies of foraminiferal wackestone-packstone, ostracod marls and fine grained breccia conglomerate (A); facies of foraminiferal packstone-grainstone (B) and miliolidal mudstone-wackestone (C); facies of porous limestone?, grainstone? (Y); facies of fossiliferous mudstone-packstone (D); algal boundstone/bindstone and wackestone facies (E); facies of the foraminiferal mudstone-packstone (F); Nummulites-Discocyclina floatstone-packstone and grainstone-rudstone facies (G). The sediments were deposited close to the carbonate platform margin. Beds of facies X have an uncertain stratigraphic position; younger than the Cretaceous but older than the Cuisian. A transgressive sequence that is composed of facies A, B, C and Y was formed during the Cuisian, whereas the others belong to Lutetian (and Biarritzian). At the end of the Middle Eocene they were tectonically compressed and covered by flysch deposits. Good stratigraphic correlation between the wells along the Dinaric strike strongly suggests that the facies are laterally extensive in this direction. Perpendicular to the trend they are considerably reduced. Oil shows in the Kate-1 well originated from the Lower Cretaceous source rocks (evaporite complex)

Calcareous nannofossil age constraints on Miocene flysch sedimentation in the Outer Dinarides (Slovenia, Croatia, Bosnia-Herzegovina and Montenegro)

Flysch deposits are associated with the Outer Dinaride nappe front. They overlie Eocene platform carbonate to bathyal marl successions that subsequently cover Cretaceous platform carbonates of Apulia and the Dinaride nappes. Planktonic foraminifer biostratigraphy indicates Eocene age of flysch sedimentation. New calcareous nannofossil data reveal that several assemblages are present; besides the dominant Mid-Eocene species, Cretaceous, Paleocene, Oligocene and Miocene taxa were also identified throughout the entire flysch belt. Widespread occurrence of nannofossil species of zone NN4-6 indicates that flysch deposition lasted up to at least the Mid-Miocene. Ubiquitous occurrence of various pre-Miocene taxa demonstrates that extensive, possibly submarine, sediment recycling has occurred in the Cenozoic. As flysch remnants are typically sandwiched between thrust sheets, these new stratigraphic ages give a lower bracket on deformation age of the coastal range. The data provide a link between Cretaceous compression in the Bosnian Flysch and recent deformation in the Adriatic offshore area

The Development of the Eocene Platform Carbonates from Wells in the Middle Adriatic Off-Shore Area, Croatia

In the Middle Adriatic deep off-shore wells the following sedimentary facies exist: fenestral and Charophyte limestone facies (X); facies of foraminiferal wackestone-packstone, ostracod marls and fine grained breccia conglomerate (A); facies of foraminiferal packstone-grainstone (B) and miliolidal mudstone-wackestone (C); facies of porous limestone?, grainstone? (Y); facies of fossiliferous mudstone-packstone (D); algal boundstone/bindstone and wackestone facies (E); facies of the foraminiferal mudstone-packstone (F); Nummulites-Discocyclina floatstone-packstone and grainstone-rudstone facies (G). The sediments were deposited close to the carbonate platform margin. Beds of facies X have an uncertain stratigraphic position; younger than the Cretaceous but older than the Cuisian. A transgressive sequence that is composed of facies A, B, C and Y was formed during the Cuisian, whereas the others belong to Lutetian (and Biarritzian). At the end of the Middle Eocene they were tectonically compressed and covered by flysch deposits. Good stratigraphic correlation between the wells along the Dinaric strike strongly suggests that the facies are laterally extensive in this direction. Perpendicular to the trend they are considerably reduced. Oil shows in the Kate-1 well originated from the Lower Cretaceous source rocks (evaporite complex)

Stratigraphy and petroleum geology of the Croatian part of the Adriatic Basin

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

The tectonic evolution of a critical segment of the Dinarides‐Alps connection: Kinematic and geochronological inferences from the Medvednica Mountains, NE Croatia

The transition zone between the Alps and Dinarides is a key area to investigate kinematic interactions of neighboring orogens with different subduction polarities. A study combining field kinematic and sedimentary data, microstructural observations, thermochronological data (Rb‐Sr and fission track), and regional structures in the area of Medvednica Mountains has revealed a complex polyphase tectonic evolution. We document two novel stages of extensional exhumation. The first stage of extension took place along a Late Cretaceous detachment following the late Early Cretaceous nappe stacking, burial, and greenschist facies metamorphism. Two other shortening events that occurred during the latest Cretaceous‐Oligocene were followed by a second event of extensional exhumation, characterized by asymmetric top‐NE extension during the Miocene. Top‐NW thrusting took place subsequently during the Pliocene inversion of the Pannonian Basin. The Cretaceous nappe burial, Late Cretaceous extension, and the Oligocene(‐Earliest Miocene) contraction are events driven by the Alps evolution. In contrast, the latest Cretaceous‐Eocene deformation reflects phases of Dinaridic contraction. Furthermore, the Miocene extension and subsequent inversion display kinematics similar with observations elsewhere in the Dinarides and Eastern Alps. All these processes demonstrate that the Medvednica Mountains were affected by Alpine phases of deformations to a much higher degree than previously thought. Similarly with what has been observed in other areas of contractional polarity changes, such as the Mediterranean, Black Sea, or New Guinea systems, the respective tectonic events are triggered by rheological weak zones which are critical for localizing the deformation created by both orogens