Tectonic And Structural Framework And Geological Evoluation Of The Istria Depression
Authors: Constantinescu Nicolae , Tambrea Dorina , Matresu Justin , Sampetrean Emanuil 
Published: October 2008

The Istria Depression is situated in the central part of the Romanian shelf of the Black Sea, between the Heracleea fault to the north and the offshore extension of the Peceneaga-Camena fault to the south. The analysis of the geological and structural evolution from Paleogene to Neogene was performed using wells, seismic lines, gravimetric and magnetometric data from this basin and the neighbouring geological provinces, as well as all other available information. The structural-tectonic framework of this depression is mainly represented by a series of faults and morpho-structural elements. The Depression's faults can be classified into two big categories: faults affecting the pre-Oligocene formations and faults affecting the younger formations. The pre-Oligocene faults from the southern and the northern parts of Istria Depression influenced its formation process. A few of them, such as: Sinoe, South Portita and Lebada, affect also the lower part of the Oligocene formations. The young faults influenced post-Oligocene deposits and two zones of concentration can be distinguished: an eastern one in which the faults have a NE-SW trending and a western one, with a near concentric disposition. As a conclusion thereof, the authors can affirm that the analysis of the geological and structural framework in the Istria Depression must be approached in the general context of the Black Sea, and particularly of the Romanian shelf. Throwing light upon the structural framework and related to it, upon the geological evolution of the Istria Depression, during the Paleogene-Neogene, formations that include the main source rock - the Oligocene - on the one hand, as well as some reservoir rocks - in the Eocene, Pontian and Dacian is of a very great importance both in the evaluation of the petroleum potential and related to it in the management of the exploration works.

Introduction

The study area lies in the western side of the Black Sea in the area of Romanian Continental Plateau, (Fig. 1). To locate it more accurately, it is worth mentioning the main structural element that is to be found in this area, namely "Euxinic Slope". "The Euxinic Slope" has been defined as a paleorelief probably generated by flexure processes of the Pre-Eocene sedimentary formations, processes that caused the fast sinking and increasing of the sedimentary cover thickness towards the deep area of the Black Sea. This paleorelief is overlaid by the Oligocene and post-Oligocene deposits, (Fig. 2), and morphologically speaking, they have the following characteristics: average dip of about 10 degrees, ranging from 5 degrees to 25 degrees; the difference in level between the shelf-break and the slope base is between 1000 and 3500 m. (Refs 1).

The Euxinic Slope route (path, course, shape) across the Romanian shelf displays two main branches: the northern branch having a E-W trend, which seems to be parallel to the Heracleea fault. The Southern branch has generally NNWSSE trend, which might be the extension of Peceneaga-Camena fault.