The Paleogeographic Conditions for the Late Eocene sediments of Zhytomyr Polissya in connection with their amber content (on the example of the «Pravoberezhnа» site)

Abstract

Problems Statement and Purpose. The work is relevant because of the need to create a reliable history of the formation of the physical and geographical environment of the Paleogene in the territory of Zhytomyr Polissya to decipher the processes of amber accumulation. In accordance with the mineragenic zoning, the territory of the amber-bearing site "Pravoberezhna" is located within the Perha amber-bearing region. The latter is located within the Volyn-Podilskyi plutonic belt and is separated from the adjacent regions by the Hlynnensky and Sushchan-Perha tectonic zones. The main difference between the Klesiv-Rokytnyansky, Sloveschansky-Ovrutsky and Barashiv-Perha amber-bearing zones is the different age of the amber-bearing rocks.

Data and Methods. A comprehensive lithological-micropaleontological and palynofacial analysis of amber-bearing deposits of the «Pravoberezhna» site of the Perha amber-bearing district of Zhytomyr Polissya was conducted. 38 sections exposing Paleogene deposits have been described.

Results and Discussion. The age of the host rocks was reinterpreted based on dinocysts. For the first time in this territory, the dating of amber deposits to the Late Eocene interval was proven. The Obukhiv sediments, isolated from the Paleogene sequence, are characterized by a complex of dinocysts from Rhombodinium perforatum, Thalassiphora reticulata, Charlesdowniea clathrata angulosa, Glaphyrocysta semitecta, etc. zone DP11 of the biozonal scheme of A.S. Andreeva-Grigorovich (1991). The granulometric and material composition of the Obukhivian sediments was studied. A model scheme shows the change in the occurrence of sediments of the Obukhiv regiostage according to the evolution of ancient tectonic valleys. New data about the Obukhiv marine palynological association within the «Pravoberezhna» site which contributes to the little-studied area of marine environments of the Late Eocene of Northern Ukraine was presented. Palynobiota includes representatives of Dinoflagellata, Prasynophyta, Acritarcha, pollen and spores of terrestrial plants, as well as transparent and opaque phytoclasts, fungal palynomorphs, «palynoforaminifera», scolecodonts. Palynofacies analysis shows that the sediments containing amber deposits within the «Pravoberezhna» site were formed by a shallow warm sea with high hydrodynamics under the high influence of river systems. It was found that the largest accumulations of amber are probably associated with paleodelta facies.