Palynological data on the Givetian and Frasnian stage boundary within the East European platform

Abstract

Introduction: The level of the boundary of the Middle and Upper Devonian according to palynological data in the sections within the East European Platform (EEP) still does not have a clear solution. In the regional stratigraphic schemes of the EEP for different groups of fossils and structural features of the rocks, four points of view on the level of the boundary are reflected: the first is at the base of the Pashiya Horizon; the second is at the base of the Timan Horizon; the third is at the base of the Upper Timan Subhorizon; the fourth is at the base of the Sargaevo Horizon. The level of the lower boundary of the Frasnian stage according to miospores has not been established yet. The history of the study, the results of research and their interpretation: The levels of the boundary between the Givetian and Frasnian stages according to palynological data in some regions of the EEP are considered: Belarus, Timan-Pechora Province, Perm Kama Region, Volgograd Volga Region, Voronezh Anteclise. The Chaplygin Formation was studied on the basis of new palynological material (Voronezh and Kursk regions) and on the basis of restudying of the previous material (Voronezh, Lipetsk and Belgorod regions). The following successive palynological assemblages were identified: PK1 in the Yastrebov Formation; PK2, PK3 and PK4 in the Chaplygin Formation. The PK2 assemblage (in the lower part of the clay layer at the base of the Chaplygin Formation) contains species, which are typical to the Raistrickia bucera-RBu Lone first found in the Zhelon Horizon (Lower Frasnian), Belarus, correlated with the Lower Timan subhorizon of the CDF. The authors believe that R. bucera is a common zone, based on its wide geographical distribution. The palynological marker of this zone is R. bucera. The general systematic composition and percentages of miospores species allow to compare the PK2 assemblage with the assemblage from the base of the Raistrickia bucera zone. Most probably, PK2 represents the 1st phase of incomplete development of the miospores of the R. bucera zone, which we called R. bucera-1. The PK3 assemblage, established in the middle part of the substantially clay bundle, is characterized by the richest taxonomic composition of the miospores of the Chaplygin Formation and compared with the palynological assemblage of the Raistrickia bucera zone from the middle part of the Zhelon layers of Belarus. This level represents a more complete phase of development, for which the name R. bucera-2 is proposed. PK4 from the uppermost part of the sections of the Chaplygin Formation correlated with miospores of the Sinuosisporis vermiculatus-SV zone which was isolated in the upper parts of the Zhelon Horizon. The R. bucera zone (with two phases of development) and the Sinuosisporis vermiculatus zone were established in the Chaplygin formation make it possible to clarify the belonging of its lower parts to the Lower Timan Subhorizon of the Lower Frasnian Stage. Conclusion: For the first time, in the sections of the Voronezh Anteclise, the lowest level of the boundary of the Givetian and Frasnian Stages was recorded at the base of the Lower Timan Subhorizon (the base of the Zhelon Horizon - Belarus and the Chaplygin Formation - VA). Comparison with the levels of boundaries of regional stratigraphic schemes of the EEP shows that this boundary on miospores for Belarus and the Voronezh Anteclise coincides with the boundary proposed at the base of the Timan horizon of the VolgaUral region.