The syn-sedimentary nature of the downwarping of the Black Sea basin during the Cenozoic is a basis for calculating rates of sedimen- tation and downwarping. Maps of thickness on scale of 1:500,000 were used to detertmine average rates of deposition.
A sharp increase in rates of deposition has been found for the Quaternery in comparison with those for the Paleogene and Neogene. This is due in part to the Danube, which during the Cenozoic filled the Cis-Carpathian downwarp and then in Quaternary time flowed into the Black Sea. The rate of Quaternary sedimentation in the submarine Danube delta reached almost 1.5 mm/year, and for the rest of the basin - 0.44 mm/year. Average rates for the Paleogene and Neogene were from 0.06 to 0.13 mm/year, reaching 0.17 to 0.24 mm/year in the most subsided part of the West Black Sea depression. Rate of deposition and rate of downwarping were approximately equal in both the West and East Black Sea depressions because in spite of thick sediment accumulation the basins remained deep-water features.
A significant role in formation of the thick sedimentary fill of the Black Sea basin has been played by debris cones of rivers. These are particularly numerous in the Quaternary section, showing up clearly on the sea floor. These debris cones constitute more than half of the modern slope of the depression. They are grouped in several sectors.
The largest of these sectors is the Danube debris cone, which formed during the course of the entire Quaternary. Sediments of its fore-delta add 2.5-3 km to the total thickness of the Quaternary section. They comprise a considerable part of the northwest shelf. Below the lip of the shelf the broad, gentle slope consists of numerous submarine debris cones, which are expressed in varying degree in the relief of the sea floor.
Alternation of thick lenses of lateral accumulation (debris cones) with much thinner members of predominantly vertical accumulation show up clearly on the seismic time sections. It is quite clear that both forms of sedimentation took place simultaneously.
The Don-Kuban debris cone formed in a similar way; however, its area is several times less than that of the Danube although its thickness is about the same. The debris cones of the Georgian sector of the shelf are similar, although average thickness of the Quaternary there is less. Numerous submarine canyons cut deeply into these debris cones. They appaer to have formed at the same time as the cones themselves.
No large amounts of submarine deltaic sediments collected
before the Quaternary because in addition the the Danube
emptying into the Cis-Carpathian downwarp, the Don and Kuban
emptied into the Indolo-Kuban downwarp.
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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