Evolution and Petroleum Potential of the Pre-Dobrodian Foredeep, Northwest Black Sea Region

Abstract

The pre-Dobrodian foredeep formed during the Paleozoic and early Triassic by some phases of crustal stretching. Throughout most of the Paleozoic, the area was dominated by relatively stable, shallow water shelf and/or lagoonal conditions, as indicated by the dominance of limestones, dolomites, shales, and evaporites. During the Permian and early Triassic, terrigenous, volcanic, and evaporitic series accumulated in individual, fault-controlled depocenters. Two phases of active contraction, regional uplift and folding, can be deduced from analysis of structural features. The southwestern part of the Dobrudian foredeep is characterized by the northeast-verging imbricate structures of the lower Prut and Tulcha zones which involve thick Paleozoic sequences. Variations in hydrocarbon generation, accumulation and retention in the Paleozoic rocks of the pre-Dobrudian foredeep result from repeated changes in its geodynamic setting. During the Late Paleozoic, conditions were favorable for petroleum generation in the Middle Devonian and Lower Carboniferous series in two areas located to the southwest and southeast of the foredeep. A second phase of hydrocarbon generation from these series occurred during the Permian and Triassic. Early Cretaceous contraction of the basin resulted in destruction of earlier hydrocarbon accumulations contained in Paleozoic reservoirs and development of new traps in Paleozoic strata. In the evaluationmore » of the hydrocarbon potential of the Dobrudian foredeep, trap preservation plays an important role. On the basis of hydrocarbon gas-geochemical surveys, it is assumed that seal integrity is better in the imbricated lower Prut zone than in other areas of the pre-Dobrudian foredeep. This suggests that the generally negative views on the poor prospectivity of this basin should be revised, particularly regarding the potential of Devonian and Carboniferous reservoirs which extend in an autochthonous position beneath the lower Prut and Tulcha thrust zones.« less