Stratigraphy and Geological Correlation最新文献

Abstract—

Lithology of the Lower Frasnian (Upper Devonian) sections, including the Zhelon Regional Stage and the Saria Beds of the Sargaevo Regional Stage, exposed in the basin of the Saryanka River, the Latvian Saddle, is described. The complete lithological description of the Sargaevo and Semiluki deposits (Frasnian) in the Gralevo quarry of the Vitebsk Region, Orsha Depression is presented. Photographic images of macro- and micro-dimensional remains of heterostracans, placoderms, acanthodians, sarcopterygians, actinopterygians, as well as scolecodonts and conodonts found in the Lower Frasnian deposits are presented. For the first time, the Sr isotope composition was measured in remains of ichthyofauna from the Zhelon and Sargaevo deposits of Belarus. Paleoichthyological and taphonomic data, lithology and Sr isotope composition of ichthyofauna fragments, depositional environments in the Zhelon and Saria times were clarified, and the distant sections were correlated. The ⁸⁷Sr/⁸⁶Sr values in ichthyofauna samples from the Saria Beds in sections of the Latvian Saddle (sections of Kalyuty 5a and 6, Virenka 1) and the Orsha Depression (Gralevo quarry) lie within similar ranges: 0.70825–0.70842 and 0.70837–0.70856, respectively. The ⁸⁷Sr/⁸⁶Sr values in ichthyofauna from the Zhelon deposits in the Kalyuty 2 and Obukhovo 1 sections (Latvian Saddle) vary within 0.70898–0.70932 and 0.71065–0.71102, respectively. High ⁸⁷Sr/⁸⁶Sr values in the fossil ichthyofauna of both regional stages suggest that the Early Frasnian paleobasin was significantly desalinated, while the salinity in the Saria paleobasin was comparable to the salinity of the modern Baltic Sea.

An Erratum to this paper has been published: https://doi.org/10.1134/S0869593823970014

Abstract—

Northwestern segment of the Precambrian Yenisei Ridge contains ophiolite and is known in literature as the Isakovka Terrane or Isakovka domain. We suggest to divide it into two belts: Kiselikha (western) and Torzhikha (eastern), which differed in geodynamic regime during the Late Neoproterozoic (750–600 Ma). It is believed that the Kiselikha belt is mostly composed of volcanic rocks erupted at island arc setting in the second half of the Neoproterozoic, and that collision of this arc with the Siberian Continent formed the Yenisei Ridge orogen. This idea has not been sufficiently supported by geological and geochronological data. Dating of four detrital zircons samples extracted from sedimentary and volcanic-sedimentary rocks in the southern part of the belt revealed that the sampled strata belong to three different Precambrian levels: the Mesoproterozoic, the mid-Neoproterozoic (800–750 Ma), and the end of the Neoproterozoic (620–600 Ma). Thus the authorized stratigraphic layout of the belt, as well as its proposed island-arc origin requires revision. By this paper we announce the identification of the Kiselikha Terrane , which was a part of active margin of the Siberian Paleocontinent at the beginning of the Neoproterozoic. Approximately in the middle of the Neoproterozoic, this block was rifted off Siberia and further evolved as a microcontinent bounded by an active margin from the outer side.

Abstract—

The results of the palynological study of the Kurshskaya Formation stratotype (Primorsky quarry, Kaliningrad Oblast) are presented. The lower part of the Kurshskaya Formation (Member of “chocolate” clays) contains an assemblage of latest Eocene dinoflagellate cysts Areosphaeridium diktyoplokum, Glaphyrocysta semitecta, and Cordosphaeridium funiculatum. The formation is characterized by four spore-pollen assemblages: (1) latest Eocene Pinuspollenites–Inaperturopollenites–Sciadopityspollenites assemblage in the “chocolate” clays and in the lower part of brown sands; (2) early Oligocene Sequoiapollenites–Betulaepollenites betuloides assemblage in the lower part of the brown sands member; (3) early Oligocene Boehlensipollis hohli–Carpinipites carpinoides in the middle part of brown sands member; (4) late Oligocene–early Miocene Alnipollenites–Corylopollis assemblage in the upper part of the brown sands of the Kurshskaya Formation. In total, the Kurshskaya Formation is terminal Eocene–early Miocene in age. The lower part of the Zamland Formation, which overlies the Kurshskaya Formation, contains the presumably middle Miocene Pinuspollenites–Tricolporopollenites pseudocingulum–T. euphorii assemblage. Based on the obtained palynological data, the depositional settings at the end of the Eocene–Oligocene–early Miocene in the South Baltic region are reconstructed. The regression of the marine basin began as early as the end of the Priabonian, the climate was still quite warm and humid, close to subtropical. Mesophytic mixed coniferous-broad-leaved forests grew along the shores of the strait, lowlands were occupied by marsh vegetation. Cooling at the Eocene/Oligocene boundary resulted in the appearance of hemlock in plant communities and increase in the proportion of catkins (alder, birch, hornbeam). Presumably, in the late Oligocene–early Miocene, the proportion of small-leaved trees, especially alder and hazel, sharply increased in mesophytic forests, while the number of pine trees decreased. Wetter and warmer climatic conditions are assumed for the early Miocene: this time is characterized by an increase in the number of walnut, cypress, and Cyrillaceae. In the middle Miocene, the climate was still quite warm, but drier, and such moisture-loving species as Podocarpus, spruce, Glyptostrobus, and swamp cypress disappeared from plant communities.

Abstract

Larger benthic foraminifera (LBF) in Southeast Asia developed prosperously in the Neogene. So, they play a meaningful role in defining the stratigraphy and depositional environment of carbonate formations. Many studies from a lot of localities in this region have been published to present their prevalence, diversity and their significance. However, they remain poorly published in Vietnam even though they are recorded abundantly in the Miocene carbonate deposits in the Tertiary basins on the Vietnam continental shelf, especially in the Nam Con Son Basin, in the southeast. This paper presents the first review on LBF in Miocene carbonate sediments and their stratigraphic range in the Nam Con Son Basin. As a result, a stratigraphic framework for the Miocene LBF of the basin, ranging from Te5 to Tg letter stages, is established. This may be used to identify the geological age and to support the correlation of carbonate deposits in this area. In general, their evolution demonstrates the development of carbonate formations in the basin, which are connected to the opening of the South China Sea; foraminifers follow the main evolutionary lineages of the Indo-Pacific province but have distinctive characteristics. In the Early Miocene, LBF appeared sparsely in Te5, then became frequent in lower Tf1. In the Middle Miocene, they presented their diversity and abundance in the fauna of Miogypsina, Lepidocyclina (Nephrolepidina), Cycloclypeus and Katacycloclypeus. In the Late Miocene, some of them were recorded in the carbonate formations in the high structures in the southeast of the basin.