Jurassic system stratigraphy at the Kamianka village. Part 3. The Pidluzhna formation

Abstract

Introduction. The paper is devoted to the study of the Pidluzhna Formation of the Jurassic system of the North-Western outskirts of the Donetsk folded structure and is a continuation of a series of publications highlighting the stratigraphy of Jurassic deposits in key areas near the town of Izyum and the village of Kamianka.

Analysis of previous publications. The Pidluzhna Formation was first identified by L.F. Lungershausen in 1941, he noted the homogeneity of the lithological composition and the somewhat different nature of the sediments in the zones of relative uplift and subsidence. Later, these deposits were not considered in the rank of Formation, but were attributed to the Upper Bajoсian - Lower Bathonian.

Material and methods. The Pidluzhna Formation is widespread in the Kamianskaya area. Since the deposits are composed mainly of clays, there are no more or less significant outcrops of it.

The scientific search was based on the analysis of literature, results of previous drilling and mapping works, as well as own field, laboratory and analytical studies. Micropaleontological analysis and generalized data on the distribution of fossil remains were carried out. The palynological analysis of these deposits was also carried out, namely, stratified deposits with the help of microphytofossils.

Results and discussion. Since the stratotype of the Pidluzhna Formation has not been precisely specified and currently the stratotype area is under urban development and only its small fragments are exposed, it is possible to propose as a neostratotype the outcrop of this Formation near the village of Sukha Kamyanka, in a ravine that extends north parallel to the Sukha Kamyanka - Yaremivka road.

Lithology. The lithological composition of the Pidluzhna Formation was studied in detail by G.V. Karpova and V.G. Kosmachev. The main, clayey, part of the formation is composed of hydromicas with a slight admixture of montmorillonite group minerals and kaolin.

Paleontological remains and Stratigraphy. This work summarizes previous paleontological data of scientists and supplements them with their own research. In general, these are brachiopods, cephalopods, gastropods, bivalves, malacostraca, ostracods, foraminifera, wood cuticles and tracheids, remains of prasinophyte and dinophyte algae, acritarchs, and spores and pollen of higher plants.

Paleontological remains, including leading ammonite species, are found in the Pidluzhna Formation quite often. In the lower part of the Formation (Bajoсian) - the Garantiana garanti and Parkinsonia parkinsoni zones stand out, in the upper part (Bathonian) - lones of the Pseudocosmoceras michalskii.

According to the data of palynological analysis, the conclusions regarding the age of the sediments of the Pidluzhna Formation are confirmed. A characteristic feature, namely the Bajoсian, is the dominance of fern-like Dictyophyllidites and the appearance of spores of Neoraistrickia rotundiformis, Duplexisporites anagrammensis, Converrucosisporites disparituberculatus, Laevigatosporites ovatus, Leptolepidites major, Densoisporites velatus and pollen of gymnosperms Callialasporites dampieri, Araucariacites australis, Vitreisporites pallidus. Foveosporites, Klukisporites, Lycopodiacidites and Uvaesporites, as well as fern-like Clathropteris obovata var. magna and the dominance of Concavisporites distinguishes the Bathonian deposits, which we observe in the Kamianka sections.