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Cretaceous Syn- to Postrift Sedimentation on the Southern Continental Margin of the Western Black Sea Basin

Naci Görür
Naci Görür
Istanbul Technical University (İ.T.Ü.) Ayazaga, Istanbul, Turkey
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January 01, 1997


The Western Black Sea Basin began opening as a back-arc basin by the rift-ing of a juvenile continental margin magmatic arc during the Aptian. Its southern continental margin succession is well exposed in the Western Pontides, Northwest Turkey. This succession consists predominantly of vol- canogenic coarse clastic rocks, shales, and carbonates with a deepening- upward character. The volcanogenic clastic rocks are mostly turbidites and mass-flow deposits in places with huge exotic blocks. The volume and nature of this clastic material were controlled by both relief of nearby sediment sources and arc volcanism, whereas the carbonates depended on ocean circulation and surface organic productivity. The Aptian to lower Cenomanian part of the succession formed during the synrift stage, whereas the rest accumulated during the postrift stage. The synbreakup stage is marked by the upper Cenomanian to Campanian sedimentary facies.

The synrift sediments commence locally with Aptian lagoonal black shales, rich in organic matter. They pass laterally and upward into an Albian unit, comprising marginal marine glauconitic sandstones succeeded by siliciclastic turbidites, marls, sandy limestones, and blue to black shales with abundant glauconite. This unit includes several levels of mass-flow deposits, comprising mostly conglomerates and olistoliths of various sizes, ranging from a few centimeters to hundreds of meters in diameter. The synrift sedi-ments end with a Cenomanian succession of blue to black shales and clayey limestones, in part with exotic blocks derived from the underlying rocks.

The postrift sediments at the base of upper Cenomanian to Campanian consist of pelagic red micrites and marls followed by mainly volcanogenic (both andesitic and basaltic) terrigeneous and carbonate turbidites and deep- water sediments, ranging from Turonian to lower Eocene. The basal pelagic carbonates rest with a slightly angular unconformity on the synrift deposits and represent the breakup facies.

Facies analyses of the rift succession indicate that the Western Black Sea Basin was isolated during its synrift stage from free interchange with the Intra-Pontide Ocean to the south, and therefore was euxinic. During the rift- drift transition in the late Cenomanian, the euxinic conditions largely disap-peared, and the water column above the arc margin of this basin became well mixed. The volcanic activity in the arc also increased in intensity soon after this transition, and largely controlled the postrift sedimentation.

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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
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Publication date:
January 01, 1997




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