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marine geology[mə′rēn jē′äl·ə·jē]
the branch of geology that studies the geological structure and development of that part of the earth’s crust that makes up the floor of the seas and oceans. In studying the sea floor marine geology encompasses all the major branches of geological science: lithology, petrology, tectonics, Quaternary and historical geology, stratigraphy, paleogeography, and the science of mineral resources. Marine geology uses the methods and findings of these branches and of related sciences such as geomorphology, geophysics, and geochemistry. Geological research in the ocean is carried on by means of boring, dragging, and the use of submarines and submersible apparatus with special equipment.
Scientific geological study of the sea floor began with the investigations of floor deposits by the English oceanographic expedition on the Challenger in 1872–76. The results were summarized in a classic monograph by J. Murray and A. Renard (1891). After the Challenger, major oceanographic expeditions in the late 19th and early 20th centuries aboard the Albatross, Planet, Valdivia, Meteor, and other ships continued deep-water investigations of the ocean. During the expeditions the basic characteristics of the ocean floor relief and types of floor deposits were determined, knowledge of the distribution of floor deposits was gained, methods of collecting samples were developed, echo sounding was introduced, and the first scientific reports appeared. The study of submarine geology subsequently became an established part of oceanographic research. The geology of the seas surrounding the territory of what is now the USSR was first described by N. I. Andrusov (1890’s), A. D. Arkhangel’skii, la. V. Samoilov, and M. V. Klenova (1920’s). The first major monograph on the geology of the Black Sea was published in 1938 by A. D. Arkhangel’skii and N. M. Strakhov. Marine geology developed swiftly in the mid-1950’s with the development of new types of ships and technical means and methods of deep-water geological, geophysical, and geomorphological research. The scientific and practical tasks of marine geology were expanded; specifically, the question of developing the mineral resources of the sea floor, above all the shelves, was raised. International cooperation played an important role in the study of the oceans as evidenced by such projects as the International Geophysical Year, the International Geophysical Cooperation, and the International Indian Ocean Expedition. Major contributions to marine geology were made by Soviet investigators including P. L. Bezrukov, V. P. Zenkovich, M. V. Klenova, O. K. Leont’ev, A. P. Lisitsyn, Iu. P. Neprochnov, and G. B. Udintsev, as well as by American investigators such as F. Shepard K. Emery, M. Ewing, B. Heezen, and H. Menard. In the USSR, geological investigations of all the oceans were conducted by the research ships Vitiaz\ Ob\ MikhailLomonosov, Akademik Kurchatov, Knipovich, Dmitrii Mendeleev, and others; in the Arctic Ocean floating stations were also used. American geologists conducted their studies on vessels such as the Vima, Crowford, and Pioneer. The Glomar Challenger, a ship especially designed for deep-water drilling, drilled 320 boreholes between 1968 and early 1974. Complete sections of marine sediments from the Cenozoic and Cretaceous were obtained, and some boreholes also produced sediments of the Upper Jurassic, making it possible to determine the structure of the sedimentary layer of the oceanic crust and the geological history of the oceans much more precisely. In addition to the USSR and the United States, marine geological research is carried on by Great Britain, France, Japan, the Federal Republic of Germany, Canada, Sweden, the Nether-lands, and other countries.
The principal theoretical task of modern marine geology, as for geology as a whole, is to determine the basic principles governing the geological structure of the earth’s crust and the history of development of the crust. In this marine geology relies above all on the comparative study of sections of the continents and floor of the oceans. The stratigraphy of the sediments of the present-day seas and oceans is based primarily on the study of microfauna and microflora (foraminifera, radiolarians, nanno-plankton, diatoms, and silicoflagellates). Paleomagnetic methods and the methods of nuclear geochronology are also used. Also important are lithological investigations for the purpose of studying modern and ancient sediment and ore formation in different physicogeographical and tectonic conditions (the theory of marine lithogenesis). These investigations are closely linked to the study of the mineralogy and geochemistry of floor sediments. Special petrological investigations of the igneous and metamorphic rocks of the sea floor are being conducted; the connections between these rocks and underwater volcanic activity and processes occurring in the earth’s crust and upper mantle are being studied. The theory of sedimentary and magmatic formations in the seas and oceans is being developed. Study of the tectonics of the sea and ocean floor is based primarily on material from marine geomorphology, which is obtained by echo sounding and analyzing the factors of relief formation in the oceans. It is also based on the findings of marine geophysics, including seismology, seismoacoustics, magnetometry, gravimetry, and geothermal research, and data on the distribution, relationships, thickness, and deformations of the rock complexes that make up the sea and ocean floor, the islands, and adjacent parts of the continents. Deep-water drilling is very important for studying the stratigraphy and tectonics of the floor of the ocean. Results of deep-sea drilling and interpretations of geophysical investigations of the earth’s crust and, in particular, the data of continuous seismoacoustic profiling make it possible to determine the paleogeography and historical geology of the oceans.
The main practical tasks of marine geology are studying the mineral resources of the surface and depths of the sea floor and the conditions of formation of minerals of marine origin that are distributed on land and providing for the needs of navigation, fishing, hydraulic engineering, and other economic sectors that are linked to the sea.
The most important center for marine geology in the USSR is the Institute of Oceanography of the Academy of Sciences of the USSR. In addition, problems of marine geology are studied at the Geological Institute of the Academy of Sciences of the USSR and other academy institutes, at a number of establishments of the Ministry of Geology of the USSR, at the All-Union Scientific Institute of Marine Fisheries and Oceanography (VNIRO) and its branches, and at Moscow State University (the departments of geography and geology). Centers of marine geology abroad include the Scripps Institution of Oceanography, the Woods Hole Oceanographic Institution, and the Lamont-Doherty Geological Observatory in the United States. An international periodical, Marine Geology, has been published in Amsterdam since 1964.
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P. L. BEZRUKOV and O. K. LEONT’EV