On the basis of lithology and sedimentary structure, a stratigraphic correlation of the three sites drilled during DSDP Leg 42B is attempted. Data reveal an almost continuous section from the upper Miocene to the present. The sediments can be grouped into an upper terrigenous and a lower chemical facies. The chemical facies covers the time interval: upper Miocene-Cromerian. The three major European glacial periods: Elsterian, Saalien, and Weichselian produce a massive terrigenous section up to 450 meters thick. During the Holsteinian, Eemian, and Holocene interglacials, brief marine invasions are indicated by a few meters of nannofossil ooze, sapropel, and micrite intercalations.The chemical facies formed under shallow water conditions first in a restricted marine, upper Miocene-Pliocene basin, and subsequently in an intermediately deep and fresh water-saline environment. During the Cromerian and extending towards the present, the Black Sea changed into the deep basin of today. Major unconformities recognized at the two western sites (380 and 381) at the contact of the terrigenous-chemical facies are a result of this tectonic development. BACKGROUND INFORMATION
This paper summarizes results from important previous Black Sea sedimentary studies in order to provide background information useful for the interpretation of data from Leg 42B drilling. The information presented is basically derived from Atlantis II Cruise 49 (Degens and Ross, 1974) by the Woods Hole Oceanographic Institution and from cruises of the research vessels Akademik S. Vavilov, Vityaz, and Academik Shirshov of the Institute of Oceanology of Academy of Sciences of the Soviet Union (summarized by Shimkus and Trimonis, 1974). A listing of important literature concerning the biology, geology, chemistry, and geophysics of the Black Sea has been compiled by Laking, 1974. BLACK SEA DRAINAGE AREA The drainage area of the Black Sea is about 1,864,000 km 2 (Figure 1) of which approximately 85% belongs to the Russian Platform, and about 15% to high mountain areas. Generally low relief is found on the Russian Platform and Walachian Lowlands to the north and west. The rivers (Danube, Dnester, Bug, Dneper, Don) draining these areas have low velocity and limans at their mouths (see Shimkus and Trimonis, 1974, for a more detailed discussion). In the southwest, south, and east, the Black Sea is surrounded by mountainous regions (Balkan, Pontic, and Caucasus mountains). In contrast with the wide, large rivers of the north and northwest, this area has numerous small, but extremely erosive, rivers. As shown by Table 1, all rivers deposit a total of about 150 million tons of solid material per year into the Black Sea. This number should be considered as a minimum value, because the quantity of sediments transported by the Turkish rivers is probably larger than 17 million tons per year. The importance of organic productivity and river detritus to the sediment budget of the Black Sea can be seen from Figure 2. Based on the data of Table 1 and Figure 2, the Danube is presently by far the most important river draining into the Black Sea. REGIONAL GEOLOGY The Black Sea is located between the Paleozoic Russian Platform and the Mediterranean geosyncline which was folded during the Alpine orogeny. The Russian Platform represents a peneplain surface of Paleozoic, Mesozoic, and Tertiary sedimentary rocks (Figure 3). White chalks, marls, and argillaceous and sandy sedimentary units of Mesozoic and Tertiary age dominate the middle and southern part of the
The distributions of calcium carbonate, of amorphous silica, and of 21 chemical compounds and elements in sediments of Holes 515A, 515B, 516, 516F, 517, and 518 are highly nonuniform; they change depending on the sediment types, grain size, and mineral composition.The main source of the lithogenous elements (K, Li, Rb, Fe, Ti, Zr, Ni, Cr, Sn) is terrigenous matter of South America. These elements correlate well or at least satisfactorily with each other and with the sum of clay minerals. CaCO 3 , amorphous SiO 2 and organic C form a second group, the main source of which is biota of the ocean. Zn, Cu, Ba, Mo, (V, Na) are a third group, which is supplied by both terrigenous and biogenic matter.Judging by the distribution of chemical elements and components in sediments of Site 515, this area of the Brazil Basin is characterized by the rather constant conditions of pelagic terrigenous sedimentation from upper Eocene till Holocene. Small changes in chemical composition of sediments throughout the section are linked mainly to the evolution of subaerial source provinces, changes in hydrodynamic regime, and fluctuations of the ocean level.The chemical composition of sediments from the Rio Grande Rise sites suggests the existence of three main stages of sedimentation in this area. The first stage is the initial period of sediment accumulation on basalts at the beginning of the Late Cretaceous. Then followed sedimentary conditions notable for their sharp changes in chemical composition and type. Beginning in the middle Eocene and persisting into the Holocene, stable conditions of sedimentation characterize a third stage, represented by the formation of approximately 700 m of nannofossil oozes of rather monotonous chemical composition. METHODS
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.