The Black Sea deep-water depression is a sedimentary basin filled by thick Cenozoic deposits. Present there in addition to structural swells and downwarps are such interesting features as clay diapirs, mud volcanoes, and large deltaic deposits. The geology indicates high favorability for oil and gas and also special forms of hydrocarbons as gas hydrates.
The structure of the sedimentary fill of this deep-water basin has become known only since 1978 when "Yuzhmorgeologiya" began a systematic common depth point seismic survey. Before that time there was no clear understanding as to the stratigraphy or structure.
The stratigraphic subdivision of the sediments of the basin is based on recognition and correlation of seismic marker reflecting horizons. This 12-kilometer pile of sediment cannot with accuracy be subdivided and correlated with onshore sections. Among the numerous reflecting interfaces are recognized five marker horizons. In addition to the top of the pre-Mesozoic rocks there is the top of the Eocene, top of the Maykop Series, an horizon close to the base of the Meotis, and an horizon at the base of the Quaternary. Even though the age boundaries are only approximate, they are traced without interruption on the seismic profiles.
Syn-sedimentary subsidence of the basin is accepted as well as deep-water conditions beginning with the Paleogene, Two depressions isolated from one another existed in the Paleogene: West Black Sea and East Black Sea. They subsequently merged to form the single Black Sea depression. Individual sectors along the margin continued to be involved in the overall subsidence as the depression broadened. This process continues at the present time.
An enormous flexure is present along the entire border of the Black Sea depression. Thickness of the Cenozoic sediments is several times greater on the subsided limb of this flexure than on the uplifted limb. On the connecting segment, that is, on the border of the depression, each bed thins to pinchout.
The border of the depression is best expressed on the top of the Mesozoic, where the amount of flexure ranges from 6 to 12 km, At the upper bend of the flexure thin Cenozoic sediments are practically horizontal and are represented by all the recognized seismic units. At the lower bend of the flexure the thick Cenozoic sediments are almost horizontal but thin and bend upward on approach to the border. On the connecting segment thinning of the beds creates the impression that the seismic units have merged into a single unit.
According to morphology the border slope of the Black Sea
depression is an analog of the continental slopes of the oceans.
Continued next week
Taken from Maysner and Tugolesov, 2001; digested in Petroleum
Geology, vol. 36, no. 3, 2002, in preparation, one seismic section,
one structure map, and one cross section.
Copyright 2002 James Clarke. You are encouraged to print out this
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