PL-Q WRENCHING in the SE PART of the PANNONIAN F3asin and ITS ROLE in PETROLEUM DISTRIBUTIO N

P512 PL-Q WRENCHING IN THE SE PART OF THE PANNONIAN f3ASIN AND ITS ROLE IN PETROLEUM DISTRIBUTIO N

JOVAN PESLAC and VERA KNE2EVR -GOJKOV NIS-Naftagas, Sutjeska 1, 21000 Novi Sad, Yugoslavia

A few years ago detailed structural and stratigraphical analysis of the south-east part of the Pannonian Basin, which belongs to Yugoslavia, was carried out specially in the North Backa and North Banat. It was based on the existing 2D migrated seismic time sections and numerous geological data . Evolution of the Pannonian Basin is very well known ; it is classified as Mediterranean backarc or interarc type basin formed during westward and southward subduction of the European plate beneath the inner Carpathians (STEGENA etol ., 1975) . The Pannonian Basin was a part of the Central Parathetys sea which extended from Oligocene to Pliocene and which formed a chain of epicontinental sea basins from the East Alpean foredeep to Transylvania (NAGYMAROSY ., 1981 .). It is important to emphasize that, at the end of the Middle Miocene, the Pannonian Basin was isolated from the ocean, forming a lake . Generally speaking, the Pannonian Basin passed through two phases of the tectonic evolution : * Syn-rift tectonic phas e * Post-rift tectonic phas e The basement of Neogene sediments in the SE part of the Pannonian Basin is made up of Mesozoic (Triassic, Jurassic, Cretaceous), Palaeozoic and Volcanic rocks . In the Syn-rift period of evolution, the basin deposited the Badenian and Sarmatian sediments . The Badenian is represented by biogenic limestone of shallow water origin, clay, conglomerate and sendstone. The Sarmatian sediments were deposited predominantly in lithoral facies rocks, limestone and siltstone in the deepest parts of the depressions . The post-rift sedimentary fi11 in the SE part of the Pannonian Basin is represented by thick sedimentary serie, deposited under the conditions where the sediments input rate was generally higher than basin subsidance rates . The Pannonian (S.Str.) sediments are deposited during the post-rift tectonic phase, and consist of calcareous marl rarely interbedded with sandstone which is mainly deposited in transgression zones of the subsided area. The lower Pontian is very thick sedimentary complex which is in the lowermost part, primarly, made up of clay, marl and silt, local sandstone and sandy gravel or are present as intercalation resulting from periodically turbiditic events . The upper Pontian sediments are the result of the prograding deltaic system with delta plain, delta front and prodelta facies . Pliocene-Quaternary sediments are deposited mainly in the fluvial and lacustrine environment . In the SE part of the Pannonian Basin, the scenery of the syn-rift period was typical for this phase of tectonic evolution . The post-rift phase is much more complicated than usually, more precisely, in the North Backa and part of the North Banat, in the Pliocene and during the Quarternary, strike-slip faults system was activated . This system consists of three strike-slip faults with very clean wrench-related negative flower structures concentrated along through going narrow zone at strike-slip movement . Strike-slip faults are the following :

1 . Turija strike-slip fault zon e

EAGE 59th Conference and Technical Exhibition - Geneva, Switzerland, 26 - 30 May 1997 - Petroleum Division 2 . Ada strike-slip fault zone 3 . Velebit strike-slip fault zone . The direction of Turija strike-slip fault zone is E-W, with left lateral character and is probably joined westwards with Drava depression . There is an indication that the old strike-slip zone is reactivated . Ada strike-slip fault zone is ENE-WSW oriented fault line probably with a left lateral character and is joined west-south-westwards to the village S .Miletic . Velebit strike-slip fault zone, NE-SW direction also with left lateral character is joined southwestwards near the village Lipar . The magnitude of the lateral movement is provisory determined and probably ranges from a few hundred meters to a less than one kilometre . lf we have in mind the fact that strike-slip zones are big geofractures which affect the continental crust all over its thickness, we can conclude that these fracture-beits are good migration paths . This open migration paths usually connect deeper source rocks with overlying reservoirs, contributing in such a manner to natural oil shallow accumulations formation . These migration paths can also set up the conditions for long-range migration . The detailerf analysis of strike-slip fault system in the North Backa, North Banat and discovered oil and gas fields, show that these fields are concentrated along one narrow zone or are very near to the zone of strike-slip movement . If we consider the possibility of existing the connection between the defined strike-slip faults and discovered oil and gas fields in the North Backa, it can be concluded that such an idea brings a new perspective, opens the way for further speculations in petroleum exploration .

NW SE NW SE

tiw.

0 1 2 (km) 0 1 2 (km)

Migrated seismic section across Ada fault zone uninterpreted (left), interpreted (right) . T=displacement forward viewer, A=displacement away from viewer.

REFERENCES : Royden L., F.Horvath, The Panonnian Basin , A Study in Basin Evolution, AAPG Memoir 45, 1988 . Zolnai G ., Continental Wrench-Tectonics and Hydrocarbon Habitat-ELF Aquitaine., 1989.