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Vol 33, No 5 (2025)
The Age of the Devonian Barzas Formation of the Kuznetsk Coal Basin Based on Palynological Data
Abstract
Barzas liptobiolitic coals are the first transformation of primitive plants into something like coal in the history of the Earth. Based on palynological data, the Early Devonian age of the Barzas Formation was determined in the stratotype section (Barzas settlement, Kemerovo region, Berezovsky district). A palynological complex was established in which the leading species are various taxa of spores with a thin membranous perispore (Calyptosporites, Diaphanospora, Grandispora, etc.) and the palynological zone of Diaphanospora inassueta was defined, which characterizes the Koyvensky horizon and the lower part of the Biysky horizon (upper part of the Emsian stage, Lower Devonian) in the eastern regions of the Russian platform and the Urals. For the first time, documentary evidence of the age of the Barzas Formation is published – photographs of spores from terrigenous rocks of barzasites.
Stratigrafiâ. Geologičeskaâ korrelâciâ. 2025;33(5):3-14
3-14
Basal horizons of the sedimentary cover of the Stoilensky iron ore deposit (Belgorod region, Russia): their age, palaeontological characteristics and conditions of their formation
Abstract
For the first time, a comprehensive geological study of the basal sections of sedimentary formations in the Stoilensky opencast mine (Stary Oskol, Belgorod Region) was carried out. It was established that Devonian (lower Frasnian) sediments are present only fragmentarily. They are distributed in palaeodepressions confined to the top of the weathering crust developed after Precambrian metasandstones and metashales. The palaeodepressions are predominantly filled with Lower Jurassic (Pliensbachian–Toarcian) and Middle Jurassic (Bajocian–Callovian) deposits. The age of sedimentary formations was established on the basis of a complex of palaeontological remains. The work provides a detailed description of three representative sections located in different parts of the quarry. Several levels of palaeosols were identified. Microphytofossils, macroplant remains, and fish fragments were described.
Stratigrafiâ. Geologičeskaâ korrelâciâ. 2025;33(5):15-36
15-36
New Data on the Lower Permian Kushtau Reef Massif, Southern Urals: Biostratigraphy and Lithofacies
Abstract
The obtained results of the core study of 12 wells drilled on Mount Kushtau (Southern Urals) and uncovering the most complete section of the Asselian and Sakmarian biohermal limestones made it possible to reveal details of the structure of the reef massif based on the biostratigraphic subdivision of sediments. The sediments were dated according to the foraminifera fauna, horizons and zones were identified, and the hypsometric position of the horizon boundaries was established, indicating the bedded structure of the Shikhan Kushtau with a gentle monoclinal dip of the layers to the north-west. The character of the distribution of bioherm facies across the section and laterally was clarified, and the evolution of reef paleobiocenoses from tubiphyites-bryozone bioherms of the quietwater zone to fusulinid sands of the hydrodynamically active zone was determined. Granular fusulinid and polybioclastic limestones (grainstones and packstones), which were formed under conditions of active hydrodynamics, are common on the boundary of the Asselian and Sakmarian layers, which may indicate regressive shelf shallowing. The boundary is drawn by the change of fusulinid fauna and is not lithologically represented. Numerous neptunian dykes are found in the carbonate massif of Mount Kushtau. The nature of secondary changes, the degree of their influence on carbonate rocks and the time of their appearance are shown. These data can be used in the study of Lower Permian reef deposits in other regions.
Stratigrafiâ. Geologičeskaâ korrelâciâ. 2025;33(5):37-71
37-71
U–Th–Pb (LA-ICP-MS) dating of detrital zircons from Jurassic deposits of the Franz Josef Land archipelago (Russian Arctic) and the evolution of their provenance
Abstract
Jurassic terrigenous strata are widely developed on the territory of the Franz Josef Land (FJL) archipelago, however, the poor knowledge of the territory due to the development of glaciers does not allow us to fully assess the evolution of paleobasins, including identification of the provenance areas. The paper presents the results of U–Pb dating of detrital zircons from Lower–Middle Jurassic sedimentary rocks sampled from natural outcrops during field work on the archipelago islands of Hooker, Hayes, Ziegler, Jackson and Graham Bell. The geographical position of the studied samples allowed us to characterize the age distribution of detrital zircons in sedimentary rocks at the Early Jurassic (Pliensbachian) and Middle Jurassic (Bajocian–Bathonian) age intervals, and thus to assess the evolution of demolition sources both in time and space. In the Pliensbachian and Bajocian, the provenace areas were uplifts composed of metamorphic (Meso-Neoproterozoic), igneous (Cambrian and Late Devonian–Carboniferous) and Cambrian–Triassic sedimentary rocks. The Triassic sedimentary strata of the FJL, exposed to the surface during the Late Triassic–Early Jurassic uplift of the northeastern part of the Barents Sea region, were also eroded and redeposited. At the Bajocian–Bathonian boundary, most of the uplifts that acted as sources of clastics in the Early Jurassic were mainly eroded, and the extensive transgression that began in the Toarcian led to the expansion of the marine basin and to a significant reduction in the continental land area at the end of the Bajocian. The main provenance areas were represented by small areas composed of Permian and/or Lower–Middle Triassic sediments.
Stratigrafiâ. Geologičeskaâ korrelâciâ. 2025;33(5):72-92
72-92
Sedimentary environments, biota and stratigraphy of the Bajocian–Oxfordian of the northern wing of the Chekurovskaya anticline (Lower Lena River, northern East Siberia)
Abstract
The article summarizes the new data on the paleontological, litho-, bio- and chemostratigraphic characteristics of the Middle Jurassic section (upper Bajocian–lower Callovian) of the northern wing of the Chekurovskaya anticline (lower reaches of the Lena River, northern East Siberia). New data on the overlying lower Oxfordian deposits are also presented. It has been established that the accumulation of sediments of the uppermost Kelimyar and uppermost Chekurovskii formations occurred mainly in the conditions from the outer zone of the upper sublittoral to the inner zone of the middle sublittoral, while the formation of the greater part of the Chekurovskii Formation is associated with the inner (closest to shore) zone of the upper sublittoral. The Stan-Yuryakh Formation was mainly deposited in the conditions of the outer zone of the upper sublittoral. Beginning from the middle Bathonian, until the onset of the Late Jurassic, three sedimentation pauses are recorded in the marine sedimentation regime in the studied area; ideas about their duration have been adjusted. It was established that the dynamics of biodiversity in the studied shallow-water marine area of the paleobasin was mainly controlled by transgressive-regressive events, which in turn were largely determined by regional tectonic processes. New maps-schemes of the paleogeographic situation for the territory covering the coast of the Laptev Sea for key time slices in the interval of the late Bajocian–Bathonian are proposed.
Stratigrafiâ. Geologičeskaâ korrelâciâ. 2025;33(5):93-134
93-134