Trace fossils from Serpukhovian (Mississipian) sediments of Mospanivska geological structure (Dniper-Donetsk depression)

Abstract

Introduction. Exhaustion of large oil and gas deposits leads to exploring smaller geological structures, from which large amount of core cannot be extracted. Therefore, value of trace fossils analysis increases due to necessity of receiving more geological information from less core material. Therefore, new core processing practices must be implemented. The paper is devoted to the study, description and systematization of the trace fossils that have been found in the Serpukhovian stage of Carboniferous system inside of Mospanivska geological structure.

Analysis of previous publications. There are only a few Ukrainian publications, that have been written over past decades, that briefly touch the topic of trace fossils analysis. Such mentions can be found in works of V. Dernov, A. Menasova, A. Matveev and a few others. Last complex work on trace fossils in Ukraine was written over fifty years ago by O. Vyalov. On the contrary, in world sedimentology practice trace fossils analysis doesn’t lack attention. Some important publications were made by Seilacher, Ecdale, Bromley, Knaust, Hasiotis and others. The main goal of this publication is to highlight prospects of using trace-fossils analysis as an important aspect of core description.

Material and methods. Full-lenth core from four different wells was used. The scientific search was based on the analysis of literature, as well as own field, laboratory and analytical studies. Trace fossils were described from longitudinal core cutting plains. To create images of trace fossils, core panoramic photographs in white light were done. Systematization of trace fossils was done in accordance with ichnotaxobasis method, described by D. Knaust. For each trace fossil morphology description included orientation, bifurcation, overall form, lining presence or absence, visible sizes and typical cutting projections.

Results and discussion. Lithological composition of the studied beds includes sandstones, siltstones, siliclastic mudstones, thin beds of coal and carbonate mudstones. Taxonomical composition of studied Serpukhovian trace fossils in Mospanivska structure consists of 10 genes. They are Arenicolites, Gastrochaenolites, Lingulichnus, Macaronichnus, Palaeophycus, Planolites, Skolithos, Teichichnus, Thalasinoides and plant roots traces. Such ichnodiversity is considered to be high, which points out to miscellaneous rock deposition conditions, varying from continental to distal-marine. It is highly important to notice, that all described trace fossils, which are typical for sandy nearshore deposits (Arenicolites, Lingulichnus and Skolithos) have producer organisms that can tolerate fluctuations in water salinity. It can be considered as an indicator of salinity fluctuations during sedimentation in nearshore facies.

For every genus high-resolution photos and conceptual schemes are provided. These graphics are considered to be essential as trace fossils appearance in core and in the outcrop, where they were first described, may vary significantly. Every genus is described in terms of its morphology, ethology, palaeoecological value and probable producers. It helped to rule out significant facial diversity and justify subsequent detailed facial analysis of studied Serpukhovian beds.