Tectonic evolution of the southwestern Black Sea margin, offshore Turkey

Abstract

The southwestern margin of the Black Sea was under the influence of a regional extensional tectonic regime behind an island arc during Late Cretaceous time. During this period, andesitic submarine volcanics covered the margin which was connected to the Srednogorie intra-arc zone in Bulgaria. Following back-arc extension, the whole margin was affected by a compressional tectonic regime during Paleocene-early Eocene time. Under this regime, a series of thrust faults formed, which were connected to the Stara Planina and the Fore-Balkan overthrust system, offshore Bulgaria. In the middle Eocene, the regional compressional regime gave way to an extensional phase which caused block faulting in the basement and triggered rapid subsidence on the outer shelf along these block faults. As a result, a transgressive period began across the region. In the south of the study area, a small basin formed and became isolated from the outer shelf behind a marginal rise which is bordered by several margin faults from the south and the north. The middle Eocene transgression reached its maximum during early Oligocene by covering the most of the land areas in the south. A regression in Late Oligocene deposited shallow marine sediments on the margin. During early to middle Mocene time, a delta system was formed by sediments that by-passed through a narrow corridor in the marginal rise and that were derived from the Srednogorie Zone. During early stages in the development of the North Anatolian Fault system and its probable northern strand in the Thrace Basin at the end of the middle Miocene, the southern and southeastern parts of the margin were left subaerially exposed. Late Miocene deposition was characterized by a long erosional period along the margin. Fluvial and shallow marine deposits of Pliocene age were deposited over the eroded Miocene unit during a sea-level rise. A sea-level fall in late Pliocene time formed a deep incised valley system on the shelf. A transgressive period during Quaternary time filled this valley system, and formed the present day Turkish Black Sea coast.