Facies development and sequence stratigraphy of the Ludfordian (Upper Silurian) deposits in the Zbruch River Valley, Podolia, western Ukraine: Local facies overprint on the δ13Ccarb record of a global stable carbon isotope excursion

Emilia Jarochowska*, Wojciech Kozłowski

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The Ludfordian (Upper Silurian) succession in Podolia, western Ukraine, represents a Silurian carbonate platform developed in an epicontinental sea on the shelf of the paleocontinent of Baltica. Coeval deposits throughout this basin record a positive stable carbon isotope excursion known as the Lau excursion. The record of this excursion in Podolia exhibits an unusual amplitude from highly positive (+6.9 ‰) to highly negative (-5.0 ‰) δ13Ccarb values. In order to link δ13Ccarb development with facies, five sections in the Zbruch River Valley were examined, providing microfacies characterization and revised definitions of the Isakivtsy, Prygorodok, and Varnytsya Formations. The Isakivtsy Fm. is developed as dolosparite replacing originally bioclastic limestone. The Prygorodok Fm., recording strongly depleted (down to -10.53 ‰) to near zero (0.12 ‰) δ13Ccarb values is developed as laminated, organic-rich dolomicrite with metabentonite and quartz siltstone beds. The Varnytsya Fm. is characterized by peritidal deposition with consistent, slightly negative δ13Ccarb values (-0.57 to -3.20 ‰). It is proposed that dolomitization of the Isakivtsy Fm. is associated with a sequence boundary and erosional surface. The overlying Prygorodok Fm. represents the proximal part of a TST deposited in restricted and laterally extremely variable environments dominated by microbial carbonate production. The transition to the overlying Varnytsya Fm. facies is marked by a maximum flooding surface. The SB and MFS are potentially correlative within the basin and support a global rapid sea-level fall previously proposed for this interval. The interpretation of the Prygorodok Fm. as coastal lake deposits may explain the unusual δ13Ccarb values and constitute one of the few records of this type of environment identified in the early Paleozoic.

Original languageEnglish
Pages (from-to)347-369
Number of pages23
JournalFacies
Volume60
Issue number1
DOIs
Publication statusPublished - Jan 2014

Bibliographical note

Funding Information:
Acknowledgments EJ acknowledges the financial support of the Consultation Board for the Student Scientific Movement, University of Warsaw (grants no. 5/III/2010 and 1/III/2011) and of the Deutsche Forschungsgemeinschaft (project no. Mu 2352/3). We are grateful to the Facies Editor M. Tucker and the anonymous reviewer for many constructive suggestions, which helped us to improve an earlier version of the manuscript, and for language corrections to M. Tucker and J. Spicer. We thank R. Nawrot, K. Biernacki and T. Segit for help in fieldwork, S. Skompski, and P. Łuczyński for helpful suggestions, G. Widlicki for preparing thin sections, Z. Remin for sharing part of the isotope measurements, and M. Łoziński for help in performing dumpy leveling. We are also grateful to V. Grytsenko and G. Anfimova (Natural History Museum, Kiev) for providing access to Ukrainian literature on the Silurian of Podolia and to museum collections. This paper is a contribution to the International Geoscience Programme (IGCP) Project 591—The Early to Middle Paleozoic Revolution.

Funding

Acknowledgments EJ acknowledges the financial support of the Consultation Board for the Student Scientific Movement, University of Warsaw (grants no. 5/III/2010 and 1/III/2011) and of the Deutsche Forschungsgemeinschaft (project no. Mu 2352/3). We are grateful to the Facies Editor M. Tucker and the anonymous reviewer for many constructive suggestions, which helped us to improve an earlier version of the manuscript, and for language corrections to M. Tucker and J. Spicer. We thank R. Nawrot, K. Biernacki and T. Segit for help in fieldwork, S. Skompski, and P. Łuczyński for helpful suggestions, G. Widlicki for preparing thin sections, Z. Remin for sharing part of the isotope measurements, and M. Łoziński for help in performing dumpy leveling. We are also grateful to V. Grytsenko and G. Anfimova (Natural History Museum, Kiev) for providing access to Ukrainian literature on the Silurian of Podolia and to museum collections. This paper is a contribution to the International Geoscience Programme (IGCP) Project 591—The Early to Middle Paleozoic Revolution.

Keywords

  • Baltica
  • Lacustrine environments
  • Lau Event
  • Microbial dolomite precipitation
  • Stable carbon isotopes

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