Стратиграфия

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.

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.