New tectonic map of Northern-Central-Eastern Asia: Position and evolution of Mesozoic sedimentary basins

I.Pospelov, O.Petrov, S.Shokalsky , Li T.D. and Dong S.W.

1. A. P. Karpinsky Russian Geological Research Institute (VSEGEI), St. Petersburg 199106, Russia; 2. Geological Institute, Russian Academy of Sciences, Moscow 119017, Russia; 3. Chinese Academy of Geological Sciences, Beijing 100037, China

New tectonic map of Northern-Central-Eastern Asia: Position and evolution of Mesozoic sedimentary basins

I.Pospelov1,2, O.Petrov1, S.Shokalsky1, Li T.D.3and Dong S.W.3

1.A.P.KarpinskyRussianGeologicalResearchInstitute(VSEGEI),St.Petersburg199106,Russia; 2.GeologicalInstitute,RussianAcademyofSciences,Moscow119017,Russia; 3.ChineseAcademyofGeologicalSciences,Beijing100037,China

The beginning of the XXI century was marked a new rising of the international tectonic cartography as a result of analysis and synthesis of a huge volume of geological information obtained for the territory of Asia especially during the last 30 years. The previous tectonic maps for Asia were created in the 1960s--1970s of the last century. Since that time, the national geological surveys have compiled tectonic maps exclusively in the limits of their own state boundaries. The international cooperation of five countries since 2002 (Russia, China, Mongolia, Kazakhstan and Republic of Korea) gave a unique possibility to join the data into a united cartographic form as Atlas of Geological Maps (since 2002-AtlasofGeologicalMapsofCentralAsiaand since 2007-AtlasofGeologicalMapsofNorthern-Central-EasternAsia). Both atlases include four maps: geological, tectonic, metallogenic, and energy resources.TectonicMapofNorthern-Central-EasternAsiaandAdjacentAreasatscale1∶2 500 000 was the key map for further compilation of the metallogenic and energy resources (coal, oil and gas) maps. By this reason, special attention was given to showing the structure and composition of the Mesozoic sedimentary basins in Northern-Central- Eastern Asia as the most perspective structures for oil-and-gas and coal prospect.

tectonic map; Mesozoic basins; platforms and fold belts; Northern, Central, Eastern Asia

New digitalTectonicMapofNorthern-Central-EasternAsiaandAdjacentAreasatscale1∶2 500 000 (Fig.1) was compiled by the Russian Geological Research Institute (CGMW Subcommission for Northern Eurasia) and Geological Institute, Russian Academy of Sciences, (CGMW Subcommission for Tectonic Maps) in the framework of the International project "3D Geological Structures and Metallogeny of Northern, Central and Eastern Asia" and published in September, 2014 (Petrovetal., 2014a). In February 2015, the Explanatory Note to this map was published by VSEGEI Printing House in St. Petersburg (Petrovetal., 2014b).

TectonicMapofNorthern-Central-EasternAsiaandAdjacentAreasatscale1∶2 500 000 is the result of 10-years international collaboration of geoscientists from five countries: Russia, China, Mongolia, Kazakhstan, and the Republic of Korea. In addition to the above-mentioned states, the map also demonstrates tectonic structure of a number of Central Asian countries: Uzbekistan, Turkmenistan, Kyrgyzstan, Tajikistan, as well as the Korean People’s Democratic Republic.

TectonicmapofNorthern-Central-EasternAsiaandAdjacentAreasatscale1∶2 500 000 is an extended version of theTectonicmapofCentralAsiaandAdjacentAreaatscale1∶2 500 000; which was published in 2008 (Petrovetal., 2008) and has become an intermediary for the map described in the Explanatory Note. In contrast to the previous map, the area of this map was expanded and now it incorporates continental areas of the whole Asian part of Russia (including the Urals and adjacent areas of the East European Platform) and the People’s Republic of China.

Fig.1 Tectonic map of Northern-Central-Eastern Asia and Adjacent Areas at scale 1∶2 500 000

Fig.2 Map of tectonic zoning of Northern, Central and Eastern Asia (inset map to the Tectonic map of Northern-Central-Eastern Asia and Adjacent Areas, 1∶2 500 000)

Structurally, theTectonicmapofNorthern-Central-EasternAsiaandAdjacentAreascovers three major Eurasian tectonic domains. The Central Asian (Ural-Mongolian) mobile belt is the central structure in the map. On the map, it covers such regions and structures as the Urals, Kazakhstan, Tien Shan, Altai and Sayan Mountains, Trans-Baikal region, Mongolia, and overlying younger platforms and sedimentary basins (West Siberian, Turan, Junggar, Amur-Zeya, and partially Songliao). The Central Asian mobile belt is located between the largest and most ancient cratons on the Earth: East European, Siberian, North China (Sino-Korean), and Tarim. On the south, the Central Asian mobile belt is constrained by the Tethyan domain including structures of the Pamir, Kunlun-Tibet-Himalayas, and Indochina. The eastern Pacific domain covers the following folded regions: Verkhoyansk-Kolyma, Chukotka-Koryak, Kamchatka, Sakhalin, and Sikhote Alin Mountains as well as the South-East Coast fold zone of Southern China.

Mesozoic tectonics in Asia has caused not only the formation of fold-thrust (orogenic) belts, but also a number of sedimentary basins which formed at the end of Paleozoic-beginning of Mesozoic. These epi-Variscan basins are represented in Russia as West Siberian (oil-and-gas), Yenisei-Khatanga and Amur-Zeya (in the Russian Far East) basins, and in the Central Asia-Turan Basin. In China the most well-known Mesozoic and Meso-Cenozoic basins are either epi-Paleozoic (among them-Junggar, Qaidam, Songliao basins), or epi-cratonic (Sichuan, Jianghan, Huabei etc.). All these basins with their specific Mesozoic sedimentary successions have preserved the natural environments including different forms of fauna and flora developed practically throughout Mesozoic time.

Below we will give the geological and sedimentary characteristics of the largest Mesozoic basins: West Siberian Basin (West Siberian Plate), superimposed Meso-Cenozoic basins of the Siberian Craton and Turan Basin (Turan Plate). Another numerous but smaller Mesozoic basins are distributed in China or in its areas adjoining with Russia and Mongolia. All these Mesozoic basins with preserved terrestrial ecosystems are shown in Fig.2 (grey color) except the superimposed basins of the Siberian Platform.

West Siberian Basin (or epi-Variscan Platform; or “Plate” -by the Russian geological terminology) is the largest negative structure in Northern Eurasia (Fig.1), whose Mesozoic-Cenozoic platform cover formed in the place of Neoproterozoic-Paleozoic folded structures of the northwestern segment of the Central Asian Fold Belt. In the west, it is limited by folded structures of the Urals, in the east, by the Siberian Craton and the Yenisei mountain ridge, in the south, by Kazakhstan, Ob-Zaisan and Altay-Sayan fold areas. Their submerged parts form its basement. The basement is build up by a complex of structures of different age composed of the Precambrian-Permian sediments metamorphosed to a various degree that underlie the Meso-Cenozoic platform cover. In areas with the Variscan basement, the plate complex begins with the Middle Triassic sediments, and in areas with older basement it starts with the Lower Jurassic. The platform boundary is transgressive and controlled by thick continuous Mesozoic-Cenozoic sediments (Surkov & Smirnov, 2003).

Foldbasementcontains tectonic blocks of different time of consolidation: Variscan structures (Ob-Zaisan folded area); Caledonian structures of Northern Kazakhstan, Kuznetsk Alatau, and the Altay-Sayan area; Baikalian (Neoproterozoic) basement on the left bank of the Yenisei River(Geological structure..., 2005; Yolkinetal., 2007). Paleoproterozoic and Mesoproterozoic tectonic blocks with the Precambrian crust are supposed at the base of the platform in northwestern (Polar Urals) and eastern (Siberian Craton) parts.

In central areas of the West Siberian Plate, the basement is submerged to a depth of 3.0 to 3.5 km (Fig.1), and the difference of depths between the lowered and raised blocks does not exceed 0.5--1.0 km. In the north, the basement topography is very contrast. Maximum depth of the basement relief reaches 6--9 km, and the differences of depths between depressions and elevations are 3--5 km. All major negative structures of the plate basement are located in the northern part (Fig.1). The graben-rift system is clearly seen in the topography of the basement surface (Geology and Mineral Deposits..., 2000).

Sedimentarycoverconsists of an external belt up to 250--300 km wide and internal area. The external belt is characterized by a shallow dipping folded frame of the platform and wedge-like structure of the Cretaceous deposits in the cover. The internal area (megasyneclise) is a vast depression sloping northward with depths of the basement from 3.5 to 12 km.

Over 2 500 consedimentary structures (local elevations and depressions) that are important in the prediction and exploration of oil-and-gas fields have been identified against the regional background. Early Triassic rift system at the base of the cover that controls the Mesozoic and Cenozoic block tectonics affects spatial orientation of these structures (Surkovetal., 1998; Surkov, Smirnov, 2003; Geological Structure..., 2005).

Tectonically, West Siberia is part of the young Ural-Siberian Platform. The Altay-Sayan fold area is considered as a shield, and the West Siberian lowland, filled in thick Mesozoic-Cenozoic sediments is an epi-Variscan plate of young platform (Geology and Mineral Deposits..., 2000).

Permiansediments as lower part of sedimentary cover are known only in the central part of the platform: interbedded carbonaceous mudstone, sandstone, gravelite, conglomerate, tuffs (150 m). To the east, apparently, in the graben, boreholes penetrated a thick sedimentary sequence (1 700 m) composed of gravelite, conglomerate, sandstone, red siltstone, and mudstone.

Triassicsediments form a riftogenic complex intermediate between the basement and the sedimentary cover. Its thickness is maximum in the northern part of the platform. Continental Triassic complex has been exposed by the Tyumen superdeep well SG-6. This well penetrated the Lower Triassic section of flood-basalt and its tuffs with interbedded sandstone and mudstone. Their age is determined based on palynocomplexes. This interval is also characterized by carbonaceous mudstone, gabbro-diabase and dark grey clay sediments. They are overlain by the Middle-Upper Triassic sediments (Tampey Fm.). Its lower sequence consists of interbedded mudstone and siltstone with sandstone; the upper sequence is composed of dark grey mudstone and siltstone with occasional sandstone beds.

Jurassicis characterized by an alternation of (up to 60 m) sandstone members and interbeds of conglomerates and gravelite (up to 35 m) with siltstone and mudstone members. It is distributed all over the platform, but outcropped only along the periphery. In the middle of the platform, at the level of the latitudinal course of the Ob River, continental facies common in the south are replaced by marine facies typical of the northern half of the platform. The thickness of both Jurassic and Triassic sediments increases northwards. In the Kolgotor-Urengoy graben in the north of the platform, thickness of the Lower-Middle Jurassic is up to 3 km. In the southern part of the platform, the thickness of the Jurassic sediments (sandstone, gravelite, mudstone) is less than 1 km. Coal-bearing sediments have been recorded in the Middle Jurassic in the south of the platform (Surkovetal., 1990). Upper Jurassic sediments contain bituminous sandstone, siltstone, and mudstone mainly of marine origin. The thickness of the Upper Jurassic is maximal in the northern part of the platform (> 1 000 m). The Jurassic section ends with black bituminous shale (native-oil Bazhenov Fm. -120 m) with very high content of organic matter.

Cretaceoussediments conformably overlay the Jurassic ones, and along the periphery of the platform, they sometimes lie unconformably on basement rocks. They are represented by marine, coastal-marine and continental (lacustrine-fluvial) facies (1 700 m in the Middle Cis-Ob region): sandstone, siltstone, mudstone, clay, sometimes marl. Lower Cretaceous sediments (till the Aptian) have a wedge-like structure. Clinoforms are recorded along the eastern and western edges of the platform, where they can be traced as bands of 25--30 km wide for hundreds of kilometers. They are rejuvenated from the southeast to the northwest. Upward the section, Aptian clay occurs with a regional unconformity. The upper part of the Lower Cretaceous section and Upper Cretaceous deposits are represented by continental facies in the lower part and by marine sediments in the upper part. Silt, sand, and sandstone with plant detritus and coal seams are common; marine sediments are dominated by clay.

WidespreadPaleogenerocks host marine, littoral (Paleocene, Eocene, Lower Oligocene), and continental (Upper Oligocene) facies. Paleocene in most of the platform is composed of clay with interlayers and lenses of siltstone or quartz-glauconite sandstone up to 250 m thick. The Eocene is characterized by opoka, diatomite, opoka-like and diatom clay, sometimes interbedded with glauconite sand, siderite (up to 100 m). The Upper Eocene - Lower Oligocene (up to 250 m) in most of the area is characterized by widespread clay with interbedded silt, sand with remains of marine fauna, and in the eastern part of the platform, continental anisomerous unequigranular gravel sand with clay, silt, gravel interlayers. Continental Upper Oligocene sediments (up to 100 m) are mainly represented by kaolinized sand with gravel, silt, clay, beds of lignite, coal.

For theNeogenecontinental facies are typical. The Miocene (up to 60 m) is composed of clay, silt with interbeds of sand, brown coal, and lignite. The Pliocene and sometimes, perhaps, the lowermost Quaternary (up to 50 m), are composed of marl, clay, sand, sometimes with loam, gravelite, carbonate concretions.

Quaternarysediments with maximum thickness of 150 to 200 m in the northern part of the area are ubiquitous. The lower part of the section (up to 70 m) is composed of alluvial sand with peat interlayers. It is overlain by marine clayey rocks (40--90 m), which give way to sandstone (up to 60 m). Marine sediments are covered with glacial and fluvio-glacial deposits (boulders, sandy loam, loam of total thickness up to 100 m). In river valleys and lakes, recent lacustrine-alluvial sediments (gravelite, clay, sand) of 50 to 60 m thick are common.

Geologicalevolution. Formation of the young platform cover began in the Late Permian. This phase includes intermediate riftogenic stage (P2-T1) and the stage of formation of the extensive sedimentary cover (T2-Q).

At the first stage, West Siberia underwent continental riftogenesis accompanied by mighty terrestrial basaltic and bimodal volcanism. Rifting of the Variscan dome uplift, fissure effusions of huge masses of basalt along graben-rifts and postrift submergence of the area took place. At this stage, volcano-sedimentary sequences composed of continental tholeiitic and alkaline basalts and alluvial-lacustrine-marsh sediments formed (Yapaskurt & Shikhanov, 2007).

Sustained postrift submergence begins from the Middle Triassic (Ladinian); West Siberia experiences the second stage of evolution. Thick sedimentary cover forms. Activation of tectonic block movements occurred during the Early-Middle Jurassic with peaks in the range of 210--200 and 180--160 Ma, Early Cretaceous with a peak at 130--120 Ma, and the Late Cretaceous - Paleocene with a peak at 80--70 Ma (Fedorovetal., 2004). Until the Eocene, the northern half of the platform submerged more intensively.

Pulses of postrift tectonic subsidence of the area resulted in the division of the sedimentary cover into two complexes. Lower complex covers mostly Middle-Upper Triassic continental sediments and facially different from continental to marine Lower-Middle Jurassic sediments.

The upper complex is represented by Upper Jurassic marine sediments, Cretaceous and Cenozoic coastal-marine and continental deposits.

Changing the direction of tectonic movements from submergence to rise and vice versa was often confined to the area of the latitudinal Ob River flow, to the Middle Ob regional stage. During the Mesozoic-Cenozoic, it served as a geomorphological and facial barrier (Surkov & Smirnov, 1994).

Beginning with the Late Eocene, the movement direction was changed: the northern part of the West Siberian basin experiences uplifting and the southern part, lowering, which explains the extensive sea regression, retreating northwards. From the Oligocene, West Siberia is a lacustrine-alluvial plain with peat and coal accumulation. Sedimentary complex with a distinct cyclicity of glacial and interglacial sediments formed during the Pliocene-Quaternary.

Superimposed Mesozoic basins of the Siberian Platform. Mesozoic sedimentary rocks that fill all negative structures of modern structural plan are rather widespread in the platform covered rock assemblages from Archean to Permian. Stratigraphic subdivision of the Triassic tuffaceous continental sediments is based on minor floristic material and freshwater fauna.

Triassicdeposits of the central and northwestern parts of the platform are represented by continental volcanogenic strata exclusively of the Lower Triassic typical of the whole complex of pyroclastic rocks and basalts.

LowerTriassicmainly consists of tuffite-sandstone formation (tuff sandstone, tuff siltstone, tuff mudstone, agglomerate, basalt and ash tuffs interbedded with siltstone, anhydrite, rarely limestone) alternating with tholeiite-basaltic formation (basalt, andesite-basalt, leucobasalt). Thickness of the Lower Triassic in the southern part of the Tungus syneclise is 150--300 m, and in the northwestern part, up to 3,500 m. They are covered with often variegated clay-siltstone-sandstone regressive sequence (up to 900 m) with conglomerate-breccias.

MiddleandUpperTriassicis widespread exclusively in the Vilyui paleorift structure and neighboring areas of the Pre-Verkhoyansk depression. The Middle Triassic is composed of floristic-characterized sandstone with siltstone and mudstone interlayers and conglomerate and gritstone intercalations of total thickness of 500 m. The Upper Triassic is represented in the lower part of the section by similar rocks up to 550 m thick, which are overlain by quartz-like sandstone of weathering crusts (up to 100 m), and after the unconformity, by sandstone, siltstone, and mudstone (up to 70 m) with faunal fossils.

Jurassicsedimentary deposits lie transgressively on the platform on deposits of various ages (from Cambrian to Triassic); they are represented by continental and marine terrigenous facies, whose subdivision into stages is very conditional.

LowerJurassicalmost everywhere consists of continental and lagoon-continental deposits of variable facies. It is represented by a 200-m thick conglomerate-sandstone-siltstone sequence, sometimes interbedded with coal layers. In the mouth of the Vilyui River, it is replaced by coastal-marine glauconite-sandstone sequence. The Vilyui syneclise is dominated by oligomictic sandstone of coastal plains (40 m), which up the section gives way to the marine clay sequence (clay, siltstone, mudstone) 60 m thick (Fig.3). To the west and southwest (superimposed Mesozoic depression of the Pre-Sayan - Yenisei syneclise), they are replaced by sand-clay-siltstone coal-bearing sediments containing gritstone, conglomerate, breccias near the orogenic frame of the platform. In the South Yakutia coal-bearing basin, the Lower Jurassic section that starts with Pliensbachian sediments is represented by oligomictic sandstone, siltstone, conglomerate, and gritstone up to 400 m thick, which formed under coastal plain environment (see Fig.3).

MiddleJurassicis represented by marine and continental facies (see Fig.3). Marine sediments widespread in the eastern part of the platform (Vilyui and Amga river basins), are composed of sandstone, siltstone, shale, mudstone of total thickness up to 240 meters. South and south-west, they are replaced by continental sediments (sand, sandstone, siltstone, mudstone, coal lenses). In the southwestern part of the platform, this age is represented by coal-bearing sand-clay-siltstone deposits that form, combined with similar Lower Jurassic sediments, the Early-Middle Jurassic coal-bearing sequence (700--800 m) of the Pre-Sayan and Kansk coal basins. In the South Yakutia basin, Middle Jurassic deposits are continental coal-bearing strata 580 m thick (M-4, Fig.3).

UpperJurassiclies conformably on the Middle Jurassic and consists exclusively of continental, often rhythmically constructed, silty sandstone, coal-bearing sediments (sandstone, siltstone, mudstone, clay, coal) with freshwater pelecypods and plant remains. In the depressions of the South Yakutia coal-bearing basin (M-4, Fig.3), the Upper Jurassic succession con-

1--12- Sedimentary complexes: 1.sandstone-conglomerate; 2.sandstone; 3.siltstone-sandstone; 4.clayey; 5.tuff-conglomerate-gravelite-sandstone; 6.kaolin-clayey-sandstone of residual soil; 7.coal-bearing sandstone-conglomerate; 8.coal-bearing sandstone; 9.coal-bearing sandstone-siltstone; 10.coal-bearing sandstone-siltstone-argillite; 11.coal-bearing kaolinite-clayey-sandstone; 12.coal-bearing tuff-sandstone-conglomerate; 13.stratigraphic unconformity; 14.angular unconformity.Fig.3 Correlation of Jurassic and Cretaceous stratigraphic columns of Siberian Platform

tains andesite, rhyolite. Thickness of the Upper Jurassic reaches here 1 600--2 100 m, but in other areas it is not more than 100--200 meters.

In adjoining graben-type depressions along the southern boundary of Aldan-Stanovoy Shield, Middle-Upper Jurassic sediments, which occur with erosion on the Triassic deposits, are a conglomerate-sandstone sequence (about 4 000 m) with andesite-dacite and coal.

Cretaceousoverlies conformably the Jurassic and is represented by continental facies with flora and freshwater faunal fossils.

LowerCretaceousof the Vilyui syneclise is composed of siltstone, mudstone, sandstone, clay, coal, and sand, which, together with the Upper Jurassic form the Lena coal-bearing limnic formation up to 1 300 m thick. At the top of the Lower Cretaceous section, they are overlapped, sometimes with a gap, by coal-bearing quartz-feldspathic sandstone and sand up to 1 600 m thick (see Fig.3). In the South Yakutia basin, the Berriasian-Hauterivian sediments (Chul’man zone) are siltstone, arkose sandstone and coal (300 m) in the west and conglomerate, sandstone, tuff-sandstone, siltstone, and coal (420 m) in the east. Bordering graben-type depressions located along the southern limit of the Aldan-Stanovoy Shield are characterized by a conglomerate-sandstone sequence (from 800 to 1 650 m) with coal. Upper horizons of the Lower Cretaceous (Aptian-Albian), which occur with a stratigraphical break and unconformity on the underlying rocks, are represented by plagioporphyry, quartz porphyry, rhyolite and tuff, and in the Upper Zeya depression, by sand-clay-lignite sequence up to 400 m. In the southwestern part of the platform, variegated sandstone, sand, clay, siltstone, gritstone, and carbonaceous rocks have been conditionally assigned to the Lower Cretaceous.

UpperCretaceousof the Vilyui syneclise with total thickness up to 1 000 m in the lower part is composed of sand, sandstone, shale, and siltstone, and in the upper part, which lies with a gap, kaolinized sand, clay, gravel (see Fig.3). In the Upper Zeya depression, the section is composed of sand-clay-brown-coal sediments 200 m thick. In the rest of the platform, the Upper Cretaceous sediments are thin grey and variegated sandy clay, sand, kaolinized siltstone, gritstone, bauxite, and phosphate rock.

Paleogenedeposits are lithologically closely associated with the Upper Cretaceous deposits. They form small isolated outcrops represented by kaolinite and montmorillonite clays, clay siltstones, interbedded sand, lignite, coal, and bauxite with total thickness of 30 to 100 m. In the superimposed piedmont Lower Aldan depression (Vilyui syneclise) the Paleogene (Oligocene) up to 770 m thick, at the base is composed of alluvial sand with pebbles overlain up the section by a rhythmically constructed sequence of lacustrine-boggy-alluvial finer sediments: sand, sandstone, argillaceous rocks, lignite, and coal. In the Upper Zeya depression of apparently riftogenous origin, sediments of this age are clay with lenses and interlayers of sandy loam, loam, and coal with total thickness of 300 m.

Neogeneis common in the west of the platform, in the Pre-Sayan depression and Vilyui syneclise and mainly composed of alluvial-lacustrine clay, siltstone, lignite, clay-carbonate, often variegated rocks (～60 m) with the Miocene and Pliocene gastropod fauna. In the Lower Aldan depression, the Neogene is represented by the Miocene and Lower Pliocene sediments up to 170 m thick (alluvial sand with gravel and clay lenses and interlayers). In the Pre-Stanovoy shear zone, the Neogene is volcanogenic: Middle Miocene alkali-basaltic formation (up to 300 m), Lower-Middle Pliocene trachyte-alkali-basaltic formation (700 m), and Upper Pliocene trachybasalt-trachytic formation. In the Upper Zeya depression, the Neogene is mostly psephytic (boulders, lumps, pebbles, gravel, sand with clay and coal) with total thickness of 1 220 m.

Quaternaryup to 800 m maximum is common in the northern part of the platform. Accumulation of stratified deposits during the Quaternary was subject to alternation of glaciations and interglacial periods. Glaciation resulted in the formation of complexes of intra-glacial deposits consisting of sediments of fluvioglacial and glacial-lacustrine origin. Incision of river valleys, accompanied by the formation of alluvium, slope sediments and eluvium took place during interglacial times (in thermochrons). Lithologically, climate and sedimentation rhythms are represented by large boulders, lumps, gravel, conglomerate, sand, silt, loam, sandy loam, silt, and permafrost rocks with fauna of mammals, freshwater mollusks, and wood residues. Section of the Quaternary sediments in the Upper Zeya depression contains at the base a basalt lava sheet overlapped at the top by a succession of boulders, pebbles, gravel, and sand.

Tectono-sedimentaryevolutionoftheMesozoicbasinswithin the Siberian Platform started from theTriassicstagelike that of the West Siberian Basin (see above). This stage marks the development epoch associated with the planetary rifting processes that caused fragmentation of the western part of the platform, which was involved in intraplate scattered rifting accompanied by the Early Triassic trap magmatism associated with a mantle plume (Dobretsov, 1997). Volcanic strata to 3 km thick were formed; their depocenter in the Tungus syneclise roughly corresponds to that of the Paleozoic basin (Nikishinetal., 2010).

In the Middle-Late Triassic (between the time of trap magmatism and the Early Jurassic) mainly the western part of the platform was subject to significant intraplate compression, as evidenced by structural and stratigraphic unconformities at the base of the Jurassic.

During theJurassic-Paleogenecycle, active structure formation localizes in the peripheral platform parts, where it is due to the processes occurring in the neighboring areas, and low-activity Central Siberian lowland uplifting preserves in the middle. The history of the cycle formation includes the Early-Late Jurassic (Kimmeridgian), Late Jurassic-Early Cretaceous, Late Cretaceous, and Paleogene stages of the structural plan formation.

Early-LateJurassic(Kimmeridgian)stageis characterized by the extensive development of terrigenous gray-colored formations of transgressive and inundation types distributed mainly along the outer platform limits. Western and northwestern platform margins dip intensely and are overlapped by sediments of the young West Siberian Plate. Intensely flexing Pre-Verkhoyansk pericratonic depression filled with clayey-sandy marine strata develops on the northeastern and eastern margins. Vilyui syneclise (M-3, see Fig.3), merging in the northeast with the Pre-Verkhoyansk pericratonic depression, originates above the Paleozoic Patom-Vilyui riftogenous system zone. Angara-Vilyui intra-platform depression (M-2, see Fig.3), which is the southwestern extension of the Vilyui syneclise and connects the West Siberian and Early-Middle Jurassic Pre-Verkhoyansk sedimentary basins, originates in the central part of the platform in the Early Jurassic and dies away in the Middle Jurassic. In the southwest, activation structures are represented mainly by near-orogenic molasse coal-bearing depressions. Peculiar terrigenous coal-bearing arched-plutonic activation area localized mainly within the Aldan-Stanovoy Shield develops in the southeast of the platform. A number of unilateral basement grabens, obviously, of the unified South Yakutsk molasse coal-bearing basin arise in the apical part of the emerging arch along the northern boundary of the Pre-Stanovoy suture zone.

LateJurassic-EarlyCretaceousstageis the stage of considerable platform compression, phase of the main Mesozoic structure formation in the eastern part of the platform adjacent to the Cimmerian Kolyma-Chukotka fold area. Sublatitudinal shear zones appear in the platform body; consedimentary transpression structures and compression structures are widespread in the sedimentary cover complex, their amplitude increase was at that time 80%--90%. Synchronously with the sea regression to the north there is a significant reduction in the sedimentation regions characterized by widespread coal accumulation.

LateCretaceousstageis characterized by final formation of the Mesozoic structural plan of sedimentation areas, filled within the study area mainly with sediments of redeposited weathering crusts, and completion of magmatism activity in the southeast of the platform.

Paleogenestageis the time of relative stability on the Siberian Platform. The Central Siberian uplift expands with formation of bauxite weathering crusts and redeposition of their destruction products in local structures of its framing. During the Late Eocene-Early Oligocene, base denudation surface forms in a hot and humid climate; at the end of the Oligocene it is subject to multidirectional and multiamplitude deformation. At the same time, active deflection of certain territories revitalizes in the Vilyui syneclise area.

Neogene-Quaternarycycleconsists of the Neogene and Pleistocene-Holocene stages. During theNeogenestage, against the background of calm tectonic conditions, uplifts and river valleys inherited from the previous time continue to form within the platform limits, and only in the southeast along its boundary with the Mongol-Okhotsk fold system the origination of rift zones takes place, followed by an effusion of trachybasalt lavas. Abrupt global cooling takes place with the appearance of the first signs of permafrost.

During thePleistocene-Holocenestagelasting for 1.8 Ma, reactivation of tectonic movements takes place with effusion of trachybasalt in previously emerged rift structures. "Decrepitating" valleys of the previous stage filled with silty-clayey alluvium rejuvenate; cutting, erosion, redeposition, and accumulation of alluvial, slope and lake sediments increase. Against the background of intensification of tectonic movements fourfold glaciation takes place with the occurrence in the periglacial zone of cryogenic landforms and loess accumulation.

Turan Plate (or Turan epi-Variscan Platform, Turan Basin) envelops the territories of Turan lowland, depression and Amu-Darya plain to the Fergana depression in the east (Fig.4).

In the west, geological boundary of the Turan Plate passes in limits of the Caspian Sea aquatorium and has compound outlines (Atlas of the Lithology...,

1. Akkulkov strike-slip; 2. Zeravshan faul; 3. Mangyshlack uplift and main fault system; 4. Bolshoy Balkhan; 5. Maly Balkhan.Fig.4 Structural elements of the Turan Plate (fragment of the Tectonic map of Northern-Central-Eastern Asia and Adjacent Areas, 1∶2 500 000)

2002). Here, Turan Plate joints with the Scythian Plate forming united Scythian-Turan young epi-Variscan platform. In the tectonic map, western boundary of the Turan Plate is drawn by coast line of the Caspian Sea.

Like all plates, Turan Plate is formed by three structural stages:

- lower-crystalline folded basement;

- intermediate, or pre-plate (quasi-platform); its sediments are not included into the basement (although some researchers relate them to the basement);

- platform sedimentary cover.

Turan Plate represents a recent intracontinental sedimentation basin inherited from the Early Mesozoic spacious depression in limits of which shelf basins of the northern continental margin of the Tethys Ocean (Para-Tethys) and superimposed on them Cenozoic basins of the fore-deep depressions of the Alpine collision fold belt were situated.

Modern conceptions on tectonic structure are reflected in published in the 70--80-ies and present time tectonic maps of the USSR, Northern Eurasia, Europe and Asia compiled by international scientific collectives (Yanshin, 1966; Petrovetal., Petrovetal., 1980; Tectonic map of Europe..., 1979; Atlas of Lithology..., 2002; Petrovetal., 2008; Petrovetal., 2014a). In all these maps, the northern part of the considered territory is related to the Scythian-Turan Plate in composition of young (epi-Variscan) Central Eurasian Platform.

There are three main disputable problems of the deep geological structure: 1) age of basement of the Scythian-Turan Plate; 2) stratigraphic volume and rock complex composition of the Pre-Jurassic part of sedimentary cover succession; 3) genesis of contrastly expressed linear structures of the Scythian-Turan Plate.

But in recent tectonic maps of 2008 and 2014 (Petrovetal., 2008; 2014a), Turan Plate is shown as the epi-Early Cimmerian plate, although its fragmentary sedimentary cover begins from the Permian deposits only of intermediate structural stage whereas the platform continuous layered sedimentary cover started to form only from the Jurassic.

Pre-Jurassicintermediatecomplexofsedimentarycoveris a distributed fragmentary filling separated by graben-like depressions. Usually the succession begins from the Carboniferous mainly carbonate and terrigenous rocks and finishes by the Upper Permian-Triassic terrigenous and volcanogenic-terrigenous series. The latter overlies on underlying deposits with a sharp angular unconformity which divides the section into two structural stages: lower-folded and upper-weakly deformed. Thickness of deposits of each stage reaches 2 000--5 000 m.

In West Turan area in the Pre-Jurassic part of sedimentary cover, the most ancient deposits registered by drillings are the Upper Devonian terrigenous-carbonate rocks. Here, boreholes penetrate mainly the Carboniferous carbonate and clayey-carbonate deposits, the Upper Carboniferous-Lower Permian effusive and volcano-sedimentary series and also the Upper Permian-Triassic red- and multi-color terrigenous, sometimes volcanogenic-terrigenous deposits (Bakirovetal., 1970; Garetskyetal., 1971; Knyazevetal., 1970; Kunin, 1974; Shlesinger, 1974; Volozhetal., 1981). Maximum thicknesses are determined both for the lower (to 4 000 m) and upper (to 5 000 m) stages. Thickness changing of both stages correlates with the basement topography. Zones of maximum thickness are connected with downwarping of basement, and of minimum thickness-with its uplifts.

Thus, sedimentary cover of the Turan Plate and inter-mountain depressions of Central Asia consists of the Devonian-Triassic pre-plate (intermediate) complex and Jurassic (Middle Jurassic)-Quaternary plate complex, and also Upper Oligocene-Quaternary orogenic complex.

Platecomplex(sedimentarycover) composes the main volume of sedimentary cover of the Turan Plate. Its deposits also take part in filling of inter-mountain depressions and downwarpings of epi-platform orogenic areas in the east of Central Asia. Formation of plate complex began in the Jurassic. Solid sedimentary cover had been formed in western and southern parts of the Turan Plate to the end of Middle Jurassic. In its northeast part (Syr-Darya, Chu-Sarysu depressions), formation of the solid sedimentary cover started in the second half of the Early-Late Cretaceous. Upper Cretaceous and Paleogene deposits are mostly distributed in time when spacious areas of recent uplifts of Kyzyl-Kum and Tien Shan were involved in processes of downwarping and sedimentation. Starting from the Late Oligocene, the area of plate complex sedimentation progressively decreased due to the growth of Tien Shan, Northern Pamirs and Kopet Dagh mountain ranges, formation of molasses at their peripheries and in depressions. Middle Pliocene-Quaternary deposits are minimally distributed in the plate complex section. That time, the largest territory of the Turan Plate was involved in processes of uplift and erosions.

Marine and lagoon sediments of epi-continental basin predominate in the plate complex composition. Carbonates, carbonate-terrigenous, and terrigenous series, changing each other either in successions or in areas, are distributed approximately in equal degrees. Maximum of carbonate sedimentation fell within the Late Jurassic, Neokomian, and Late Cretaceous. Epochs of carbonate sedimentation also correspond to that of saliferous accumulation. Salt deposits are widely distributed among the Upper Jurassic and Neokomian rocks.

Continental sedimentation predominated in the Early Jurassic and in the first half of Middle Jurassic when coal-bearing terrigenous series were formed. Hauterivian-Lower Barremian multi-color series of alluvial genesis is widely distributed. In the eastern part of Turan Plate, the Upper Jurassic and Early Cretaceous continental basin (subaeral) and alluvium red-color rocks are distributed (They can be determined as sedimentary wedges of an orogenic complex of the Late Mesozoides of Central Asia). Jurassic, Cretaceous, and Paleogene (without Upper Oligocene) series of plate complex are usually similar by their composition to more thick complexes of Kopet Dagh, Bolshoy and Maly Balkhan. Upper Oligocene-Quaternary series are represented by orogenic molasses situated around the epi-platform orogen of Tien Shan and Northern Pamirs and also deformed sedimentary cover complex in Kopet Dagh. Everywhere they represent the molasses and only in limits of recent Turan Plate they are included into the plate complex.

Thickness of plate complex reaches 6 000-7 000 m (Amu-Darya syncline), 5 000 m (Ustiurt syncline and South Mangyshlack-Ustiurt system of depressions), 2 000--3 000 m (Syr-Darya and Chu-Sarysu synclines), and 3 000--4 000 m (Turkmenistan anticline). About one third of plate complex thickness in the deepest Amu-Darya, Ustiurt synclines and South Mangyshlack-Ustiurt system of depressions belongs to the Jurassic deposits.

In depressions of the east of Central Asia, the orogenic complex is represented by continental aerial molasses. The latter are characterized by a sharp change in thickness and composition depending on the remoteness from sources of detrital drift, by uncontinuity of sedimentation, presence of numerous disconformities and erosion cuttings. At the edges of depressions, coarse-detrital deposits prevail, but in the central part of depressions they associate with lacustrine thin-detrital and saliferous deposits. Usually, thickness of orogenic complex reaches here 5 000--6 000 m and more.

In Western Turkmenistan depression, sandy-clayey deposits of intra-continental basin predominate and are characterized by changing of salinity. Along the Pre-Kopet Dag fore-deep depression from west to east and from below upward the succession, basin deposits are gradually replaced by alluvium, and at Kopet Dagh foothills-by coarse-detrital alluvium and proluvium ones. Simultaneously, deposit thicknesses decrease to 3 500--4 000 m and numerous discontinuities and unconformities appear the in succession.

Junggar Basin is situated in the southeast part of the Junggar-Balkhash fold series. Sedimentation of the terrestrial coarse clastic rocks since the Triassic to Paleogene means the area entered the period of unitary stage of depression development and fluvio-lacustrine facies conglomerate, sandstone and pelite formed. Sediments thickened southwards and the thickness abruptly increased at the southern margin of the basin, which was coalesced with the coal-bearing molasses of Jurassic and the foreland molasse of Pliocene epoch-Early Pleistocene epoch in the foreland depressions in Northern Tien Shan Mountains.

Qaidam Basin occupies the area between the Eastern Kunlun tectonic belt in the south and the Qilian tectonic belt in the north. Fillings in the basin are predominantly terrestrial strata of the Mesozoic to Cenozoic (Triassic is absent), among them, the Jurassic consists of coal-bearing clastic formation and the Cretaceous to Cenozoic are represented by red gypsum-bearing clastic formation with many intercalations of conglomerate and their thickness is up to 9 000 m.

Sichuan Basin is situated in the western Yangtze Platform (Upper Yangtze block) and developed initially in the Late Triassic and its attribute similar to the Ordos basin. The tectonic movement at the end of Middle Triassic made the overall uplift of the Yangtze Platform and formed gentle NE strike anticline structures inside the Sichuan Basin. Along the Kangdian uplift area in the western basin, Late Triassic rifting and volcanic activity occurred resulting in the deposition of Upper Triassic clastic rocks and pyroclastic deposits, which in turn were overlain with unconformity by the Jurassic sediments, meanwhile the Jurassic basins migrated eastwards and overlapped the whole Sichuan Basin. The tectonic movement during the Late Jurassic was responsible for the arc fold uplifting in eastern Sichuan Province and westwards migration of the inland lake basins to the Chengdu plain during the Cretaceous-Early Paleogene.

Jianghan Basin is located east of the Sichuan Basin and includes the region of northern Hunan and Jiangxi Provinces and large area of Hubei Province. The basin deposits of the Late Triassic-Jurassic of the area can be correlated with that of the Sichuan Basin. The difference is that the Jianghan Basin was relatively uplifted in the Paleozoic and the Precambrian crystalline basement was shallowly buried and the faults developed indicate the block uplifting feature. Some basin sequence of Cretaceous-Paleogene directly overlies the Precambrian metamorphic basement and the structural development of the basin during the Cretaceous to Early Paleogene has evolved from small fault depressions to a large depression.

Songliao Basin of NEE strike and semilunar in shape is situated in northeastern China. Its main part is to the north and overlaying the Xilinhot and Zhangguangcai fold belts. On the basis of the outcrops and drilling records, fillings of the basin consist of the Mesozoic-Cenozoic sequence which with unconformity overlies the sequence folded in the Late Paleozoic and granites of the same time. Sedimentation began in the Middle Jurassic, the Triassic-Lower Jurassic series are absent, suggesting the basin was in a state of uplifting during the Triassic to Early Jurassic. Meanwhile, the extension produced a series of NNE and NW running faults which controlled the comparted fault groups of small basins. In these small basins, quick sedimentation of the Middle Jurassic series includes sandstone conglomerate, sandstone interbedded with mudstone, tuffaceous siltstone and thin coal measures (of alluvial and lacustrine facies). From the Late Jurassic to Early Cretaceous, the basins were further subsided, widened, and connected, finally forming a faulted basin of large area. The Upper Jurassic series are dominated by tuffs, tuffaceous conglomerate, and basalt with intercalations of thin layers of mudstone and coal measures of lacustrine facies. The Lower Cretaceous series were grayish-black, grayish-green, interleaving fossil-rich sandstone-siltstone, siltstone and marlite interbedded with sandstone-conglomerate, middle-coarse grained sandstone of various thickness, which were sediments of the subaqueous fan, lake floor fan, deep to semi-deep lake facies and pelagic facies setting. In the early period of Late Cretaceous, the basin was at its flourishing stage and represented a faulted basin of huge area. The lower part of the Upper Cretaceous contains strata of sandstone-conglomerate, sandstone and mudstone, which constitute several sedimentary cycles of mainly lacustrine facies and alluvial facies and have a sharp unconformable contact with the underlying Upper Jurassic-Lower Cretaceous. The overlying Upper Cretaceous strata have an obvious overlapping towards the basin margin. Sediments of the latest Late Cretaceous to Neogene are red clastic formation composed of red sandstone-conglomerate interleaved with varicolored mudstone, implying the deposits of shrinking stage of crust uplifting and basin folding. Tectonic phases between the Early and Late Cretaceous and between the Late Cretaceous and Paleogene demonstrate the structure periods of alternating intrabasin anticlines and synclines formation. The basin folding was evident in the east and weak in the west and the depression center continuously migrated from east to west. The overlying Upper Cretaceous and younger sequence manifests gentle and open folds. Thus, among other similar Mesozoic basins, Songliao Basin lived with very active tectonic and volcanic events with constantly changing environments and consequently basin terrestrial ecosystem.

Acknowledgments

The work was performed under the project of the Federal Agency for Scientific Organizations of the Ministry of Education and Science of the Russian Federation (Registration Number 0135-2014-0065) with the support of the Russian Science Foundation (Grant 16-17-10251).

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10.3969/j.issn.1673-9736.2016.04.07

1673-9736(2016)04-0261-16

Received 30 September 2016, accepted 25 October 2016