Vol 27, No 1 (2019)
- Year: 2019
- Articles: 6
- URL: https://journals.eco-vector.com/0869-592X/issue/view/701
- DOI: https://doi.org/10.31857/S0869-592X271
ARTICLES
Small shelly fossils in the cambrian basement of the West Siberian geosyneclise
Abstract
This paper describes for the first time the entire Cambrian skeletal problematics from the parametric well Vostok-1 (Tomsk region, eastern part of the West Siberian Plate) found in the Lower Cambrian Churbiga Formation, Middle Cambrian Pudzhelga Formation, and Upper Cambrian Kondes and Shedelga formations. The investigation has made it possible to detail the biostratigraphic division of the Lower Cambrian in the studied well using the small shelly fossils and to reveal confinement of the main findings of problematic skeletal remains to the shallow carbonate shelf settings.
3-11
Middle ordovician conodonts from the Chingiz Ridge (Kazakhstan): taxonomy of the Naiman Formation assemblage and its biogeographic affinity
Abstract
Conodonts from carbonate rocks of the Naiman Formation (Chingiz Ridge, East Kazakhstan) have been studied in detail for the first time. The mixed conodont complex is characterized by a high taxonomic diversity and includes species of the stratigraphic interval from the upper part of the Dapingian to the middle of the Darriwilian of the Middle Ordovician. The conodont assemblage includes oceanic/deep-sea species of wide geographic distribution, in particular, abundant Periodon macrodentatus and P. zgierzensis, which are typical for siliceous deposits of Kazakhstan. For the first time, the occurrence of species Scolopodus? mufushanensis, Drepanoistodus latus and Anodontus longus is noted in Kazakhstan. This indicates the existence of the biogeographic climatic zones typical for pelagic biota. The species Protopanderodus? nogamii indicates that the Kazakhstan conodont fauna belongs to the Australasian biogeographic province of the Eastern Gondwana. The conodont assemblage includes a number of regionally endemic taxa that characterize the Kazakhstan fauna as an independent biogeographic unit and confirm the relative remoteness of water basins of Kazakhstan from the eastern margin of Gondwana as well as from other paleocontinents in the Ordovician.
12-30
Middle–upper devonian terrigenous rocks of the Tsil’ma River basin and their palynological characteristics
Abstract
The results of biostratigraphic study of Givetian–Frasnian rocks of the Tsil’ma River basin (Middle Timan) are presented. The biostratigraphic division of the sections is based on palynological data: five palynocomplexes are distinguished in the Valsa, Tsil’ma, Ust’-Chirka, Ust’-Yarega, and Kraipol’e formations and are correlated with coeval palynocomplexes of adjacent of territories. The features of miospore associations from continental and coastal marine facies are identified. The clear cycle of origination of geological bodies corresponding to the formations is established at this territory.
31-56
Lower Moscovian limestones of the Bogdashan Range (NW China) as an indicator of cessation of arc magmatism in the Junggar region
Abstract
The field revision of the Carboniferous and Lower Permian stratigraphy of the northern Bogdashan (South Junggar, Northwest China) shows that the Lower to Middle Carboniferous island arc volcanic rocks, widely developed in this region, are overlapped everywhere by carbonate and terrigenous-carbonate sediments, containing occasional lava flows and overlain up the section by thick terrigenous series practically devoid of volcanic rocks. The deposition of limestone occurred at the stage of dying off of a volcanic arc, and the question of their age is of fundamental importance for dating this event. Carbonates are represented by facies of lagoons, shoals, and bioherms that formed on the leveled surface of the arc and on the slopes of the last active volcanoes. Bioherms are Waulsortian mounds and are mainly composed of algal limestones and carbonate mud. There are no framestones composed of corals and sponges (chaetetids) typical of the tropical zone. The facies of shallow crinoid-fusulinid limestones typical of the adjacent territories of the Southern Tien Shan and Tarim are poorly represented. Paleogeographically, the position of bioherms corresponds to the northern boundary of the realm of Pennsylvanian reefs. On the basis of foraminifers, brachiopods, and corals, the age of carbonates is early Moscovian (ca. 315–310 Ma). Cessation of island-arc volcanism, followed by the accumulation of limestone in Bogdashan, occurred sub-synchronously with formation of the West Junggar (Bayingou) suture and may reflect docking of the Bogdashan arc to the Yili active margin of the Kazakhstan continent. Further subsidence of Bogdashan and adjacent regions of the Junggar and Turfan basins, which was somewhat slower at the end of the Carboniferous and more intense in the Early and Middle Permian, may reflect the development of the foreland basin that formed along the northern flank of the Tien Shan orogen. Marine facies were locally preserved in this basin until the Artinskian (ca. 285 Ma), and later the Junggar and Turfan basins lost connection to the ocean and developed in continental environments.
57-78
Duration and geodynamic nature of giant Central Asian batholiths: geological and geochronological studies of the Khangai batholith
Abstract
In the Late Paleozoic and Early Mesozoic, during about 100 m.y., the world’s three largest batholiths (Angara-Vitim, Khangai, and Khentei, each up to 1 000 000 km3 in volume) had formed within the limits of the Central Asian orogenic belt. Considering the case of the Khangai batholith, the problem of how, when, and why such an extensive granite formation took place is analyzed. The geochronological data for granitoids of the batholith by U–Pb (ID-TIMS) and 40Ar/39Ar dating methods are systematized to distinguish three age groups of rocks. These rock groups are correlated to the geological events occurred in the region. The earliest group includes granitoids formed in the interval of 302–283 Ma. They tend to the western and southern framings of the batholith and correspond to the fragments of two igneous belts that crossed the region, where the batholith formed later, and reached the areas far beyond. The youngest group of igneous rocks (230–200 Ma) is developed in the eastern periphery of the batholith and corresponds to the marginal part of the large Early Mesozoic Mongol-Transbaikalian igneous zone, with the main part being located far away to the east of there. Igneous complexes that formed in the interval of 273–238 Ma correspond to the batholith proper. They are concentrated within the zone of 350 × 400 km in size and are represented by rocks of two associations: granite-granodiorite (Khangai complex) and granite-leucogranite (Sharaus Gol complex). The coeval analogs of these rocks are reported only in the framing of the batholith.
The comparison between the Khangai batholith and two other giant ones (Angara-Vitim and Khentei) revealed their similarity in terms of structure and evolution. They are all composed of similar rock associations and are of comparable sizes and age intervals of formation. For example, the Angara-Vitim and Khentei batholiths formed mainly in the intervals of 305–275 and 229–195 Ma, respectively. The obtained estimates of formation time of ~30 m.y. should seemingly be considered as the time necessary for chambers of anatectic magmas, which to certain degree formed giant (~1 000 000 km3 in volume) batholiths, to cool down in the Earth’s interior. The formation of giant batholiths is attributed to the effect of mantle plumes on the lithosphere of a young fold zone that appeared as a result of accretionary-collisional events in the marginal part of the Siberian paleocontinent.
79-102
Ammonites and infrazonal stratigraphy of the lower bathonian besnosovi zone of the Russian plate
Abstract
Ammonites and deposits of the Lower Bathonian Besnosovi Zone of the central and southern regions of the Russian Plate are studied. The paper discusses the infrazonal stratigraphy and correlation of two reference sections: the Pletnyovka Quarry in the north of the Penza oblast and the Sokur Quarry near the city of Saratov. The successive biohorizons Oraniceras issae, O. calvum, and O. besnosovi are recognized on the basis of ammonites of the genus Oraniceras (family Parkinsoniidae) in the Besnosovi Zone. Provisional O. mojarowskii and O. scythicum biohorizons are proposed below the above-mentioned biohorizons, whereas the O. cf./aff. besnosovi Biohorizon is proposed above them. The Besnosovi Zone corresponds to the middle part of the Western European Zigzag Zone. The Michalskii Zone underlining the Besnosovi Zone apparently corresponds to the Bajocian–Bathonian boundary interval. It is suggested that only one A. excentricum migrational biohorizon, corresponding to the upper part of the O. besnosovi Biohorizon and correlating with the lowermost part of the Ishmae Zone of the Boreal scale, can be established on the basis of Boreal ammonites of the genus Arcticoceras in the Sokur Section. Central Russian representatives of the genera Oraniceras [M] and Sokurella [m] are assigned here to the subfamily Pseudocosmoceratinae that is eudemic to the Central Russian late Bajocian–early Bathonian sea. It is suggested that the above-mentioned genera evolved from Pseudocosmoceras [M and m] that is cryptogenic neoendemic of the East European Peritethyan marine basin. New species are described: Oraniceras issae sp. nov. [M], O. calvum sp. nov. [M], Sokurella pletniovkae sp. nov. [m], and S. elshankae sp. nov. [m].
103-125