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Book Chapter

Cimmerian and Alpine Stratigraphy and Structural Evolution of the Moesian Platform (Romania/Bulgaria)

By
Gabor Tari
Gabor Tari
Amoco Production Houston, Texas, U.S.A.
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;
Oprea Dicea
Oprea Dicea
Prospectiuni S.A. Bucharest, Romania
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;
Joe Faulkerson
Joe Faulkerson
Amoco Production Houston, Texas, U.S.A.
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;
Georgi Georgiev
Georgi Georgiev
St. Kliment Ohridski University Sofia, Bulgaria
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;
Svetlozar Popov
Svetlozar Popov
Geology and Geophysics Corporation Sofia, Bulgaria
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;
Mihai Stefanescu
Mihai Stefanescu
Amoco-Romania Bucharest, Romania
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;
Gary Weir
Gary Weir
Amoco Production Houston, Texas, U.S.A.
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Published:
January 01, 1997

Abstract

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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Contents

AAPG Studies in Geology

Regional and Petroleum Geology of the Black Sea and Surrounding Region

A. G. Robinson
A. G. Robinson
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American Association of Petroleum Geologists
ISBN electronic:
9781629810782
Publication date:
January 01, 1997

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