--> Abstract: Structural Framework, Seismic Stratigraphic and 3 D Building Model of Creataceous-Oligocene in Romanian Black Sea Offshore, by M. Gageanu; #90923 (1999)

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GAGEANU, M., Romanian Oil Corporation; PETROM S.A., Geological Exploration Research and Design Center, Bucharest, Romania

Abstract: Structural Framework, Seismic Stratigraphic and 3 D Building Model of Creataceous-Oligocene in Romanian Black Sea Offshore

Input into the 3 D model includes a conceptual depositional model, sequence stratigraphic framework interpretation, mapped stratigraphic surfaces, well logs, core and 3 D seismic profiles (fig. 1). The Romanian Black Sea offshore formed in a back-arc setting above the northward subducting Tethys Ocean, close to the Pliocene, having a single depocentre at present. The western Black Sea was initiated in Aptian, when a part of Moesian Platform (now the western Pontide of Turkey) began to rift and moved away to the southeast.

The late Paleocene to Middle Eocene was a time of passive infill of both basins with limestones deposited on the shelves, and clastic turbidites fed into the deep basins in Romanian offshore. In the Late Eocene, the extensional basin geometry was modified and it probably changed the sediment distribution and water circulation.

The basins floor were filled with mud and basin floor clastics until the earliest Late Miocene when the basin suffered a major fall of water level due to changes in regional drainage pattern associated with the growth of the Charpatians.

In Istria Depression, the developed turbidite systems may constitute the play, based on the deposits formed during the Late Eocene to Oligocene, in Minerva, Poseidon,Albatros structures.

Development of the southern part of the basin as a passive margin is closely related to considerations of the pre-drift position of continental platform during the Cretaceous time.

Creataceous strata in the basin comprise a southern-thickening gross succession of sediments on which eustatic sea-level fluctuations and a sequence of unconformities related to pulses of transgressive and regressive depositional trends are superimposed. Recognition of these trends has provided the basis for classifications of the strata into parasequence representing distinct areas with regard to time stratigraphy, sedimentation, tectonics, depositional environments, and hydrocarbon potential.

This paper has been based on the results of seismic surveys and drilling and is among the first attempts to decipher the structure of the Romanian offshore area. Knowing the onshore Dobrogea structure, the question of its continuity offshore has arisen. Correlation at the pre-Albian level was used because the interval below the structure is identical both offshore and onshore, where it is known in Dobrogea.

Interpretation results have proven the continuity of the structural elements from onshore to offshore. Structural interpretation of seismic data from the Romanian Black Sea revealed, from south to north, three important structural units: the Moesian Platform (MP), the North Dobrogean Orogene (NDO) and the Scythian Platform (SP).These are affected by two fault systems.The first is an E-W system represented by reverse faults, overthrusting faults, and sometimes normal faults.The following faults are representative of this system: Delfin, Capidava-Ovidiu, Peceneaga-Camena, Heraclea, Pelican and Sf. Ghoerghe faults.The second is a N-S system represented by normal or strike-slipe faults. These faults delimit several downthrown or uplifted blocks. The most important faults are the Razelm, Lacu Rosu and West Midia faults.

These fault systems result in the different structural configuration of the three main units. From south to north the following elements can be recognized.

In the southern unit (Moesian Platform), the main element is represented by an uplifted block, the Midia Block, formed of Proterozoic formations (greenschists or other similar formations). Two other blocks, the Vadu and Constanta horsts, are connected with the main uplift. The three blocks, along with the onshore Dobrogean horst, delimit two lagoons, Corbu in the north and Constanta in the south, filled with Jurrasic-Cretaceous formations.The northeastern limit of the Moesian Platform is formed by the Peceneaga-Camena fault. It is a crustal reverse fault.

Identifying the sedimentary formations as basic lithostratigraphic units, by defining the sedimentary facies and identification of the depositional system characteristic to each formation, by determining their precise position within the major depositional systems, there are possible to be made closely substantiated appraisals on the hydrocarbon potential of the sedimentary rocks accumulated within a sedimentary basin, with bearings on the exploration programs direction (fig .2).

Seismic Stratigraphic and 3D Building

Seven sequences have been revealed through the Cretaceous, seven sequences for Eocene and ten parasequences for Oligocene. Some sequences of the stratigraphic succession are partially lacking due to subaerial erosion or non-deposition; condensed sections have been outlined. Fence diagram extracted from the shelf —margin 3D model shows stratigraphic sequences distribution (fig. 3).

The recognized parasequences have been grouped in sets of parasequences, defining the depositional sequences based on the seismic stratigraphic data and the ones of the depositional profiles.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England