Paleogeography

paleogeography

[¦pāl·ē·ō·jē′äg·rə·fē] (geology) The geography of the geologic past; concerns all physical aspects of an area that can be determined from the study of the rocks. Paleogeography is used to describe the changing positions of the continents and the ancient extent of land, mountains, shallow sea, and deep ocean basins.

Paleogeography

the branch of science dealing with the physical geographic conditions of the geologic past; the part of historical geology that provides information about the development of the earth’s crust and of the earth as a whole. Paleogeog-raphy is also a branch of general physical geography: it studies the physical geographic conditions of the past in order to explain current natural processes on earth. Paleogeographic research is based primarily on a detailed study of rocks (composition, structure, texture, nature of occurrence) and of the macroscopic and microscopic organic remains contained in them. The science is closely related to the study of facies, lithology, stratigraphy, tectonics, paleontology, paleoecology, climatology, geochemistry, and geophysics.

Paleogeography emerged in the mid-19th century. Its appearance followed the development of a relative geochronological scale based on biostratigraphic data; the formulation by the Swiss geologist A. Gressly of the theory of facies, according to which deposits of the same age represented by different types of sedimentary rock reflect different physical geographic conditions of accumulation; and the substantiation by the British geologist C. Lyell of the method of actualism, which made it possible to re-create the physical geographic conditions of past geologic periods by comparing them with modern conditions.

The compilation of various types of maps is fundamental in paleogeography. The first paleogeographic maps appeared in the 1860’s and depicted the distribution of ancient marine basins on the modern continents. Among such maps were J. Marcou’s maps of the world and European Russia during the Jurassic period (1860) and J. Dana’s map of North America during the Cretaceous (1863). A series of paleogeographic maps of European Russia for a number of successive geologic periods was compiled by G. A. Trautshol’d (1877), A. P. Karpinskii (1880), and A. A. Inostrantsev (1884). It was, however, Karpinskii’s maps of 1887 and 1894 that became best known. On the basis of these maps he formulated very important conclusions about the movement of the earth’s crust within the boundaries of the Russian plain and coordinated the movement with the development of adjacent mountain systems.

World paleogeographic maps for individual periods and epochs were published in the late 19th and early 20th centuries by the French geologists A.-A. Lapparent and E. Haug, the Austrian geologist M. Neumayr, and the Russian scientist I. D. Lukashevich. In these maps an attempt was made to re-create the distribution of land and sea not only on the continents but also in the area of the modern oceans—by extrapolating from data from the surrounding land. Haug imparted paleotectonic meaning to paleogeographic by representing the geosynclinal and platform regions of the land and sea. In 1912 the German geophysicist A. Wegener, having introduced the theory of mobilism to geology, depicted in a series of maps the conjectured disintegration of the hypothetical supercontinent Pangaea and the formation of the Atlantic and Indian oceans.

In the early 20th century scientists moved from generalized paleogeographic maps for individual periods and epochs to more detailed maps of small regions for geologic ages and even smaller time intervals. N. I. Andrusov mapped the Neogenic basins of the Black Sea-Caspian region, A. P. Pavlov the Early Cretaceous basins of European Russia, and A. D. Arkhangel’skii the Late Cretaceous of the Volga Region and Turkestan. Andrusov’s studies laid the foundations of paleoecology, while Arkhangel’-skii’s research marked the origin of the comparative lithological school of paleogeography. In 1910, C. Schuchert published the first major series of paleogeographic maps of North America; these maps were revised several times as new materials became available. The offering of courses in paleogeography at institutions of higher learning (University of Munich, E. Dacqué, 1912) and publication of the first paleogeographic handbooks (Dacqué, 1915; T. Arldt, 1919 and 1922) helped establish paleogeography as an independent science.

Beginning in the 1930’s paleogeographic reconstructions became vital in the search for such minerals as petroleum, gas, coal, salts, bauxites, phosphorites, and diamonds. One of the principal bases of paleogeography, the theory of facies, was further developed by W. Twenhofel and D. V. Nalivkin. The work of L. B. Rukhin (1959), B. P. Zhizhchenko (1959), and K. K. Markov (1960) has been particularly important for paleogeographic research.

There are several schools of paleogeography, each dealing with different aspects of the physical geographic conditions of the geologic past and each using its own particular methods.

Paleoecology involves analysis of the composition and other characteristics of sedimentary rocks and the organic remains enclosed in them. Such analysis determines the way of life and the habitat of plants and animals of the geologic past and identifies parts of basins and their connections with adjacent seas. Index organisms are used to determine the climatic conditions, the degree of salinity, and other characteristics of the basin. Research of this type has been conducted by the Soviet paleontologist R. F. Gekker.

Paleobiogeography identifies the zoogeographical and floristic provinces and regions for individual periods and epochs of the geologic past. World maps identifying such regions were prepared by the French scientists P. Termier and H. Termier.

Paleobiogeographic, lithological-geochemical, and paleotem-perature data are used for paleoclimatic reconstructions. The world maps of L. B. Rukhin (1959), N. M. Strakhov (1960), and M. Shvartsbakh (1961) identified substantial differences between the ancient climatic zonality and the modern one. Paleoclimatology deals with the climates of the geologic past.

The terrigenous mineralogical school (V. P. Baturin) of paleogeography uses the composition of heavy and light fractions of accessory minerals (quartz, feldspar) in correlating sedimentary strata. It thereby determines the areas of removal, transfer routes, and areas of accumulation of detrital sediments of a definite composition and origin.

Paleogeographers who have based their research on geochemi-cal features include the Soviet scientists A. P. Vinogradov, L. V. Pustovalov, A. B. Ronov, G. I. Teodorovich, I. S. Gramberg, and L. A. Guliaeva and the American scientists W. Krumbein and R. Garrels. Such an approach determines the salinity, physicochemical conditions, and evolution of ancient basins, as well as changes in the composition of the atmosphere over time. It is based on the study of autogenous minerals, the concentrations and ratios of typical elements (Cl, F, B, Br, Ca, Mg, and Sr), and the degree of oxidation of FeO(Fe₂O₃) in clay and carbonate rocks. In the 1960’s and 1970’s, the determination of the various characteristics of ancient bodies of water by means of precise physicochemical methods has become increasingly important. Paleotemperatures are determined by studying the ratio of Ca/Mg isotopes of oxygen [¹⁸O/¹⁶O] in the shells of ancient organisms (H. Lowenstam and S. Epstein in the United States; R. V. Teis and others in the USSR).

Dynamic paleogeography deals with the dynamics of ancient bodies of water. Currents are identified, and the nature of the medium of accumulation of sediments (river channel, sea) is determined. Scientists, such as A. V. Khabakov, study the tex-tural characteristics of sedimentary rocks: for example, the orientation of cross bedding and the signs of ripples.

Paleotectonics, which is based on analysis of the distribution of facies and the thickness and formation of ancient beds, developed extensively in the 1930’s. The first Soviet paleotectonic maps were prepared by V. V. Belousov, A. B. Ronov, and V. E. Khain.

Paleovolcanology has developed as a special branch of paleogeography. Scholars in this field provide a paleogeographic reconstruction of volcanic regions, where the normal course of sediment accumulation has been periodically interrupted by lava flows and deposits of large amounts of volcanic ash and other volcanic products. Paleovolcanologists use structural and forma-tional analysis and modern methods of physical and chemical investigation (F. Iu. Levinson-Lessing, A. N. Zavaritskii, and I. V. Luchitskii).

Ancient relief is the subject of paleogeomorphology (K. K. Markov, I. P. Gerasimov, and Iu. A. Meshcheriakov). Relicts of relief in open or buried form—and also those that have been buried and reexposed—are partially decomposed and transformed to different degrees by endogenous and exogenous processes. Paleogeomorphology reconstructs the relief that existed in different geologic epochs and re-creates the history and development by general geomorphological analysis of relict forms and materials from paleogeographic and paleotectonic analysis. In the 1950’s the paleomagnetic method for determining ancient latitudes was introduced, and the study of variable-sign linear magnetic anomalies in the oceans was initiated. The principles of mobilism were reborn, and paleogeographic reconstructions based on the hypotheses of the existence of a single continental mass called Pangaea at the end of the Precambrian and the existence of the supercontinent of Gondwana in the Paleozoic again became widespread.

The deep drilling of the ocean floor that was begun in 1968 made possible the direct reconstruction of the paleogeography of the oceans. In recent decades the amount of information received from deep boring of the continental sedimentary strata has increased. This has led to the replacement of small-scale maps with large-scale maps of the USSR and other countries; these large-scale maps are now compiled into lithological-paleogeographic atlases.

The international journal Palaeogeography, Palaeoclima-tology, Palaeoecology, which has been published in Amsterdam since 1965, deals with questions of paleogeography.

REFERENCES

Zhizhchenko, B. P. Metody paleogeograficheskikh issledovanii. Leningrad, 1959.
Markov, K. K. Paleogeografiia, 2nd ed. Moscow, 1960.
Rukhin, L. B. Osnovy obshchei paleogeografii, 2nd ed. Leningrad, 1962.
Ronov, A. B. “Obshchie tendentsii v evoliutsii sostava zemnoi kory, okeana i atmosfery.” Geokhimiia, 1964, no. 8.
Sinitsyn, V. M. Vvedenie v paleoklimatologiiu. Leningrad, 1967.
Luchitskii, I. V. Osnovy paleovulkanologii, vols. 1–2. Moscow, 1971.
Solov’ev, Iu. Ia. “Paleografiia.” In Istoriia geologii. Moscow, 1973.
Gramberg, I. S. Paleogidrokhimiia terrigennykh tolsch. Leningrad, 1973.

A. B. RONOV and V. E. KHAIN

paleogeography

pa•le•o•ge•og•ra•phy

paleogeography, palaeogeography

paleogeography

Paleogeography

paleogeography

Paleogeography

REFERENCES

paleogeography

Synonyms for paleogeography

noun the study of the geography of ancient times or ancient epochs

Synonyms

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