Cimmerian and Alpine Stratigraphy and Structural Evolution of the Moesian Platform (Romania/Bulgaria)
Gabor Tari, Oprea Dicea, Joe Faulkerson, Georgi Georgiev, Svetlozar Popov, Mihai Stefanescu, Gary Weir, 1997. "Cimmerian and Alpine Stratigraphy and Structural Evolution of the Moesian Platform (Romania/Bulgaria)", Regional and Petroleum Geology of the Black Sea and Surrounding Region, A. G. Robinson
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The vast thickness (>10 km) of relatively undeformed Cambrian to Recent sedimentary cover of the Moesian Platform in Romania and Bulgaria offers an exceptional record of Cimmerian and Alpine tectonics in the surrounding Carpathian and Balkan thrust-fold belts.
Above the Hercynian unconformity, Permian to Middle Triassic continental to shallow marine sediments deposited in a facies succession are quite typical for the European passive margin. Widespread Anisian-Carnian vol- canism indicates an aborted rifting period also marked by locally very thick (>2000 m) evaporites. Based on systematic analysis of reflection seismic data and isopach maps, we interpret two large-scale subsurface features (Optasi- Peris uplift and North Bulgarian arch) as Middle Triassic rift flanks associat-ed with two aborted, E-trending branches of the Paleotethys Basin. The striking appearance of the crystalline basement and the deeper levels of the Paleozoic succession (Cambrian-Silurian systems) in the subcrop of the over-lying Jurassic can be understood in terms of rapid uplift and severe denuda-tion of the rift shoulders.
The extensional period was replaced during the Norian-Rhaetian times by a compressional regime in the whole Moesian Platform. Although these Late Triassic Cimmerian folds were undoubtedly formed due to compression, detailed structural analysis permitted a more specific interpretation of the deformation in terms of fault-bend folding in a north-vergent, thin-skinned thrust-fold belt. Structural modeling of the anticlines suggests relatively minor shortening (9-18%). Whereas these structures are very characteristic for North Bulgaria, their structural significance is gradually diminishing to the north, in the Romanian part of the platform. In a wider paleotectonic sce-nario, the north-vergent anticlines beneath the Moesian Platform are inter-preted as the frontal, foreland thrust-fold belt of the Mediterranean Cimmerides propagating into the foreland.
Above the Cimmerian unconformity, the sedimentary facies and thickness relations of Lower to Middle Jurassic carbonates clearly show the develop-ment of a south-facing passive margin. East-west-trending Jurassic troughs bounded by normal faults can be documented in the southern, Bulgarian side of the Moesian Platform. From the Early Cretaceous on, sedimentation was clearly influenced by successive compressional periods in the Balkans approaching the southern edge of the Moesian Platform. These consecutive Cretaceous through Eocene Alpine compressive periods, such as the Austrian, Mediterranean, Laramian, Illyrian, and Pyrenean, created the north-vergent thrust-fold belt of the Balkans separated from the platform sequence by a series of relatively narrow foredeeps. Whereas the final docking of the Balkans on the Moesian Platform margin occurred at the end of the Eocene, this did not happen on the northern edge until the late Miocene, when the Carpathians stopped moving onto the platform.
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Regional and Petroleum Geology of the Black Sea and Surrounding Region
In 1967 and 1969, two oceanographic cruises were made in the Black Sea under the guidance of the Woods Hole Oceanographic Institute: The cruises included scientists from many countries and disciplines. Their aims were to determine the recent geological and geochemical evolution of the Black Sea, to map the shallow structure of the basin, and to study the interaction between the oxidized surface waters and the anoxic waters beneath them. The results were published 23 years ago, as AAPG Memoir 20 (Ross and Degens, 1974). During the 1969 cruise, the vessel Atlantis II collected 40 piston cores, which formed the basis of most of the subsequent geological studies that were restricted to very recent sedimentation. Speculations concerning the origin of the basin and the relationship of the geology offshore to that exposed around the margins of the Black Sea were rooted in pre-plate tectonic concepts of basin formation and were in any case hampered by a lack of relevant data (Brinkmann, 1974).
In 1976, the Glomar Challenger visited the Black Sea on Leg 42B of the Deep Sea Drilling Project and drilled and cored three deep-water sites (379, 380, and 381). Well 381 north of the Bosporus encountered sediments as old as Miocene, including some apparently deposited in shallow water (Ross, 1978).
The next major volume in Western literature to deal with the Black Sea was published a decade later, collecting papers presented two years earlier at a conference in Yalta. In this volume, a number of seismic reflection lines