No 5 (2024)

This publication completes the consideration of the lithogeochemical features study of a pilot collection of the Riphean and the Vendian sandstones, siltstones and mudstones (last one identified based on the interpretation results) of the Belarus. Data on the age of detrital zircon published in recent years suggest that the source rocks for the Upper Precambrian deposits of this region were the Osnitsk-Mikashevichi and the Trans-Scandinavian igneous belts, the Volyn-Brest large igneous province, rapakivi granites, as well as various associations of rocks of Sarmatia, the Danopolonian orogen and Svecofennides. The distribution of clastic rocks data points of our collection on provenance, paleogeodynamic, paleogeographic and paleoclimatic discriminant diagrams, which based mainly on the lithogeochemical composition, allows us to draw a number of conclusions. We are considering that the Riphean and the Vendian strata of the Belarus are composed mainly of intraplate granitoids erosion products, as well as various felsic igneous rocks of island-arc and syncollisional genesis. The part of mafic rocks erosion products among them generally does not exceed 30%. It`s noticeable mainly in rocks of the Volyn series (products of the Volyn-Brest large igneous province erosion), as well as in some samples of the Nizov, Selyavy and Kotlin formations (fragments of mafic rocks from other sources?). Source to sink transporting was carried out mainly by large rivers. Paleogeodynamic settings varied from quite active to quite passive. The paleoclimate in the Riphean was most likely arid/semiarid, and in the Vendian it was humid, from subtropical in the early (except for the Glussk Formation) to tropical in the Late Vendian. The research results also make it possible to show some work features for known paleoclimate reconstruction methods and techniques.

The results of regional studies of the Early Miocene deposits of the Western Ciscaucasia, carried out on the basis of seismic stratigraphic analysis, are presented. The spatial pattern of sediment accumulation is analyzed and the paleogeographic conditions during the regressive stages of the Late Miocene in the Western Ciscaucasia are clarified. Erosion incisions of several levels were identified, which developed during the fall of the erosion base level during major regressions in the studied time interval. By spatial correlation of paleochannels based on a selected series of intersecting seismic profiles, the buried river valleys of the Paleo-Don and Paleo-Donts were reconstructed and constructed at the Sarmatian‒Meotis boundaries and within the Late Meotis‒Late Pontian interval.

Using a complex of analytical methods, clay minerals were studied in Pleistocene sediments from Hole ODP 1038B, 120.50 m deep, drilled on the northwestern edge of the Central Hill, located in the Escanaba Trough (Gorda Ridge) near a hydrothermal source with a temperature of 108°C, as well as in Pleistocene background terrigenous sediments from reference Hole ODP 1037B, drilled in the Escanaba Trough, 5 km south of Central Hill. The association of terrigenous clay minerals in sediments from Hole 1037B consists of mixed-layer smectite-illites, smectite, chlorite, illite, and kaolinite. In sediments from Hole 1038B in the interval from the bottom surface to a depth of 5–7 m, clay minerals are terrigenous. In the rest of the sedimentary section, clay minerals are represented by newly formed biotite, chlorite, and dioctahedral smectite. Their formation occurred under the conditions that arose during the intrusion of basaltic melt into the Escanaba trough with the formation of a laccolith and the subsequent rapid cooling of its flank; the intrusion was accompanied by the ascent of high-temperature hydrothermal fluid in the central discharge channel, interacting with the adjacent sediments. As a result, at the high-temperature stage of this interaction, finely dispersed biotite was formed in the sediments due to the original terrigenous clay minerals, K-feldspar and amphiboles. Then, at the rapid cooling of the hydrothermal fluid to a temperature presumably 270–330°C, partial replacement of biotite by chlorite. With further rapid cooling of the hydrothermal fluid to a temperature of 200°C and below and its mixing with sea water seeping into the sediments of the Central Hill, smectite was formed.