STAGES OF GEOLOGICAL DEVELOPMENT AND GENETIC TYPES OF THE ROOT PRIMARY SOURCE OF AMBER-SUCCINITE PLACERS OF UKRAINE

Abstract

The most crucial problem of placer geology is the determination of its root source. Despite the large number of works dedicated to the study of amber placers formed in the territory from the Baltic coast to the Black and Azov Seas, so far, no native source has been established. Therefore, this article aims to establish the genetic type of the source of ambersuccinite placers formed under optimal climatic conditions of the first half of the Middle Eocene (Buchak time, Lutetian) on the territory of the low plains of the Ukrainian Shield surrounded by shallow sea basins. The article discusses a set of factors that contributed to forming the source of amber-succinites and forming its placers within the Ukrainian Shield and its slopes, covering the bordering areas of the Pripyat Trough, the Dnieper-Donetsk and the Black Sea depressions, and the Volyn-Podilsk Plate.For the first time, the authors have established that the primary source of amber-succinite placers is not the generally recognized “amber-bearing” pines of Scandinavia. Instead, it is the primary biogenic-sedimentary deposits of tar secretions (according to the authors — proto-amber, resin bodies at the early stage of fossilization) mainly of coniferous trees. These secretions were fossilized in the humidified forest bedding of the Buchak time in the lower half of the Middle Eocene. Only as a result of erosion of these biogenic-sedimentary deposits by river waters and other agents of denudation, proto-amber was transported in the post-Buchak time to various areas of sedimentation, where the formation of various mineral species of fossil resins took place. Amber-succinite was not found in the marine sediments of Buchak time, that indicates immaturity of the proto-amber for conversion into succinite at that time.On the territory of Ukraine only in the sea paleo-basin, which surrounded the Ukrainian Shield from the north, east, and south-west, the proto-amber acquired all the features and properties of amber-succinites at the end of the MiddleUpper Eocene — Early Oligocene. Thus, it is the paleo peat bogs of the Lower Middle Eocene that contain the protoamber (resin bodies at the early stage of fossilization) that are the root source of amber-succinite placers.Based on the comprehensive geological and palaeogeographical analysis of the region’s natural conditions in the Eocene—Oligocene, when the tar bodies accumulated in this area and transformed into fossil resins, the authors identified the main stages of tar resin fossilization during the long transition from the biosphere to the lithosphere. These are three transformation stages: terrestrial, marine, and post-diagenetic. Secondary placers of amber-succinites have accumulated in the coastal, estuarine, and remote parts of the sea shelf. They are covered by sediments from the Kyiv, Obukhiv, and Mezhyhirya regional stages formed at the end of the Oligocene when primary biogenic-sedimentary deposits were eroded.