New data on the Paleogene lithostratigraphic units’ distribution in the Avren Step south of Varna and Beloslav Lakes based on borehole data and seismic profiles’ interpretation

Abstract

The present article aims to provide new data on the spatial distribution and lithological features of the Paleogene lithostratigraphic units in the Avren Step, which is a part of the Moesian Platform in Eastern Bulgaria. On the basis of primary lithological data derived from 81 boreholes’ sections and lithostratigraphic interpretation of five seismic profiles, six formal Paleogene lithostratigraphic units were recognized. They are as follows: the Komarevo Fm. (Thanetian), the Beloslav Fm. (Ypresian), the Dikilitash Fm. (Ypresian), the Aladan Fm. (Ypresian), the Avren Fm. (uppermost Ypresian–Priabonian), and the Ruslar Fm. (Oligocene). Their spatial distribution and relationships in the northern part of the studied area are visualized by drawing up of five geological cross-sections, while the deep geological structure of the southern part is shown by lithostratigraphic interpretation of the five seismic profiles. Four of the units (the Beloslav, Dikilitash, Aladan and Ruslar Formations) demonstrate almost constant lithology throughout the whole studied area with some variations in their thickness. The Komarevo Formation, and especially the Avren Formation, show considerable lithologic and thickness variability.