Open AccessIsotope-geochemical characteristics of Wenlock carbonate and terrigenous-carbonate deposits of the Subpolar Urals and the southern part of the Chernyshev ridge
Author(s) -
Д. Н. Шеболкин
Publication year - 2021
Publication title -
litosfera
Language(s) - English
Resource type - Journals
eISSN - 2500-302X
pISSN - 1681-9004
DOI - 10.24930/1681-9004-2021-21-6-829-848
Subject(s) - outcrop , geology , terrigenous sediment , carbonate , isotopes of oxygen , isotopes of carbon , geochemistry , mineralogy , total organic carbon , chemistry , sedimentary rock , environmental chemistry , organic chemistry
Research subject. Wenlock deposits in the Subpolar Urals and southern part of the Chernyshev Ridge. Materials and methods. Carbonate and terrigenous-carbonate rock samples from sections of the Subpolar Urals (outcrops 212, 217) and the southern part of the Chernyshev Ridge (outcrop 479) were studied by isotope analysis of carbonate carbon and oxygen. Results. The isotopic composition of the studied sections varies across a wide range of δ 13 С (–6.4…–0.05‰) and δ 18 O (20.0–26.9‰). Therefore, three time intervals characterized by distinctive isotopic characteristics can be distinguished, roughly corresponding to early Sheinwoodian (I), late Sheinwoodian (II) and Homerian (III). Interval I is characterized exclusively by the rocks of outcrop 479 with δ13С (–3.6…–3.0‰) and δ 18 O (22.4–23.6‰). In Interval II, the average values of isotopic characteristics of outcrop 479 indicate a tendency to weighting carbon (–5.5…–3.5‰) and somewhat heavier oxygen (23.2–25.2‰) isotopes. In outcrop 212, the average isotopic values for carbon and oxygen vary from –2.9 to –1.3‰ and from 21.9 to 24.3‰, respectively. In outcrop 217, the average values are δ 13 C (–1.8…–0.8‰) and δ 18 O (22.4–25.4‰). In Interval III, the average values of carbon isotopic composition in outcrop 479 are becoming heavier from –2.5 to –0.7‰. In outcrop 212, the isotopic values of oxygen (21.9–23.1‰) and carbon (–4.9…–2.5‰) tend to become weighting; however, in outcrop 217, the average isotopic values of δ 13 C (–1.9…–0.5‰) and δ 18 O (22.3–24.5‰) remain constant. The conducted litho-facial studies showed that the weighting carbon isotopic composition ranging from –6.4…to –3.0‰ is associated with an increase in microbial activity in sediments, the manifestation of vadose-phreatic conditions, and the intake of light carbon dioxide with a flow of terrigenous material from the earth. In the latter case, oxygen isotopic values are also the most lightweight (20.0–23.0‰). Conclusions. The obtained isotopic characteristics of the Wenlock rocks under study indicate the expedience of identifying three time intervals and their correlation with paleogeographic reconstructions of Wenlockian sedimentation in the Timan-northern Ural region.