* United Institute of Geology, Geophysics and Mineralogy of SB RAS, Novosibirsk, Russia.

** Siberian Research Institute of Geology, Geophysics and Mineral Resources, Novosibirsk, Russia.

The population of different marine basins of geological past is not uniform. There are communities that are typical only of one basin or its part. At the same time, there are known animal and plant species and groups of species widely distributed within two neighbouring or spaced apart paleobasins. Just these very organisms allow wide correlation of coeval strata and thereby revealing similar conditions of their habitat using detailed analysis of material composition of sediments being formed in basins synchronously with organism communities inhabiting there. There is a particular relationship found between the organism distribution in biostratons and geological past geography. The authors take this relationship as a basis for reconstruction of geological past landscapes.

In this context the authors prefer the following definition of the notion “paleolandscape”: it is a part of the earth surface (territory or water area) that is defined by a combination of natural components determing geographical features of geological region distinguished from adjacent regions by conditions of sediment formation, volcanism and inhabitancy of animal and vegetable kingdoms. All these constitute a single system of clearly interacting natural phenomena such as water and air temperature, solar radiation, hydrodynamics, water salinity, destruction of rock associations, their lateral displacements, composition of organism communities. Definition of marine paleolandscape (refined) fits well in the above definition as a part of water area with relatively homogeneous association of natural components constituting sea floor with inherent relief and overlying water body. In total, marine paleolandscape is association of geomorphological and climatic natural components with different composition of sea floor substrata reflecting a state of tectonic and volcanic settings, hydrodynamic regime, water volcanic salinity, specific composition of animal and plant organisms. All these components of marine paleolandscape are in close interaction and development (Dubatolov, Krasnov, 1997). Based on the above definition of landscapes and detailed analysis of biostratigraphic data, the authors made an attempt to reconstruct paleolandscapes of seas from the Lochkovian, Pragian, Emsian, Eifelian, Givetian, Frasnian, and Famennian for the main geological regions of Siberia where marine formations are most widely represented. Theses volume does not allow us to give detailed characteristic and all paleolandscape maps. The authors offer three maps for the Eifelian, Givetian and Frasnian as examples.

The Lochkovian was marked by a wide development of marine basins, particularly within western and partially northwestern East Siberia. A set of paleolandscapes and paleolandscape regions with certain composition and rich specific communities - tabulate, tetracorals, brachiopods, crinoids, and other groups has been distinguished. The most characteristic property of the Lochkovian landscapes was intensive volcanic activity in the western West Siberian sea (Dubatolov, Krasnov, 1997).

In Pragian the Siberian sea landscapes were more differentiated as compared to the Lochkovian ones. Dominant features are as follows. The West Siberian sea was a vast shallow basin which western regions were distinguished by the greater tectonic and volcanic activities resulted in thick effusive complexes. The central portion of the sea was marked by passive tectonic development. Mainly carbonate and argillaceous-carbonate muds were deposited there. Of particular place in paleolandscape structure were destruction zones represented by the continents of Kazakhstania and Angarida. Farther north-eastwards of the West Siberian basin within the Taimyr sea shallow marine environments prevailed. Cherty-lime, lime muds, clay and siltstone were generated there. On the north-west of the present Siberian Platform there was a shallow sea where silty-argillaceous sediment accumulated.

The Emsian in Siberian seas was characterized by great differentiation of environmental conditions. Some landscapes such as Pri-Urals and East Urals are retained as a whole as they were in the Lochkovian and Pragian. Marine conditions governed over vast expanses except for the southern Siberian Platform. Active tectonic and accompanying volcanic activities were inherited from previous epochs; argillaceous-lime and dolomite muds were deposited in the central part. The continents of Kazakhstania and Angarida decreased in their sizes; on the east the West Siberian sea was bounded by the vast Pri-Yenisei alluvial plain. Marine conditions were dominant within the Taimyr peninsula and northwestern Siberian platform. In Emsian there was intense penetration of marine waters not only into the West Siberian plain but also the Altai-Sayan region (Tashtyp transgression). Emsian was inherent in a wide diversity of benthos population. It is proved by dispersal of rich marine communities known far beyond Siberian seas (Dubatolov, Krasnov, 1997).

In Eifelian paleolandscape differentiation remained complicated. Marine conditions were retained in vast expanses. Active effusive activity marked by submerged intermediate and basic lava flows continued within the western margins of the West Siberian sea. Only seas adjacent to the continent of Kazakhstania were not affected by effusive activity and the continent itself penetrated deep into the West Siberian sea extending northwards beyond the limits of the Middle Pri-Ob area. There are identified 14 landscapes and 12 landscape regions (Fig. 1).

Givetian is not an exclusion. Marine conditions have been preserved over the most part of Siberia. The western regions of the West Siberian sea continued to reveal most active tectonic movements with accompanied volcanic activity as subwater outflows mainly of intermediate and basic lava. On the background of significant sea transgression being most strongly manifested within the Siberian Platform and Altai-Sayan region the extensive Kazakhstan plain appeared on the north of the Kazakhstania continent. Processes favouring the accumulation of terrigenous sediments accompanied by outflows of basic, intermediate and acid volcanites were in progress in the western part of the plain. The greater eastern part of the Kazakhstania continent represented a constructional plain with accumulation of sandy-pebble sediments against the background of acid lava outflow in the central continent. Thus, the huge portion of the former land in Eifelian appeared to be so downthrown that gave way to formation of an alluvial plain. The Givetian transgression mostly affected the aquatoria of the Taimyr and Middle Siberian landscapes where calcareous muds were essentially formed. In the Altai-Sayan region marine transgression penetrated so eastern regions where earlier in Middle Paleozoic sea never occurred (Fig. 2). 21 landscapes and 4 landscape regions have been established for Givetian. Some of them were inherited from the Eifelian landscapes, but there appeared new ones that essentially complicated the Givetian paleolandscape environment. As compared to Eifelian the specific diversity of organism communities was somewhat increased. At the same time systematic composition of marine inhabitants were significantly changed, i. e. there occurred rejuvenation of most organism groups. Many species enlarged areals. Obviously, of great importance was the subsidence of the Kazakhstania continent and the decrease of the Angarida size, that caused disappearance of some geographical barriers resulted in the increase of fauna migration due to the new close relationships with aquatoria of the north-eastern and northwestern Russia, Urals, Altai-Sayan region and China.

Frasnian was marked by gradual shoaling of the West Siberian sea in its western portion and deepening in its eastern part, emergence of more deep-water part of shallow sea. Narrow denudation islands (island arcs) appeared on the west, and the land portion of Kazakhstania was somewhat expanded on the south. The Irtysh-Vakh and Pri-Ob uplands appeared. Volcanic activity was almost terminated in the western part of the west Siberian plain, in the central part acid lava was occasionally concentrated in the deep-water portion of shallow sea. It is significant that in Givetian and Frasnian reefs, bioherms and brachiopod banks were distributed within the northern portions of the Kolyvan-Tom and Nyurol-Varyogan landscapes (Fig. 3). Eight landscapes and four landscape regions have been defined. Specific diversity of marine organisms was decreased, though quantitatively all species were relatively numerous. Nevertheless, on the general background of continuing extensive sea transgression in some regions there occurred tectonic upwarping resulted in sea regression. It was characteristic mainly of the Altai-Sayan region, where carbonate accumulations and marine organism communities were known only in the northern and southern areas of Kuzbass, and in Minusinsk depressions indications of marine transgression are marked by thin clay-mudstone mottled sediments with phyllopods, ostracods and fishes (Kokhaiskay Formation).

In Famennian marine regime still persisted but essential shoaling of the West Siberian sea took place. Terrigenous sediments, from clay in the center to silt, sand, occasionally gravelstone over the rest sea, were mainly developed. The area of Kazakhstania continent was severely reduced, but there appeared the so-called Pri-Ob upland located in the very middle part of the West Siberian sea (Middle Pri-Ob). The Angarida area was sharply increased on the right bank of the Yenisei River, and the Pri-Yenisei alluvial plain with accumulation of silt-sandy sediments appeared again on the left bank. The landscape differentiation remained similar to that in Frasnian. Some of them continued to be inherited from Frasnian. 17 landscapes and 7 landscape regions have been established. Specific diversity of organisms, except for foraminifera, was sharply and essentially rejuvenated. It is primarily peculiar to the Tabulata and Rugosa corals. The whole families and most genera disappeared. Primitive Anthozoa mainly survived. As for tabulates, syringoporids and auloporids remained. First Michelinia flourishing in Carboniferous, survived among favositides. Only individual tetracorals with simple morphology could accommodate to the modified conditions.

The presented analysis of the Siberian sea paleolandscape evolution in Devonian at the level of regional units (Fig. 4) revealed a close relationship between biostratigraphic units and paleolandscapes, thus close relationship between the marine aquatoria of Siberia and those of other seas within geological regions of the Urals, North-East Russia, Kazakhstan and others.

The work was supported by RFFI, grant No. 96-05-65892.

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