Abstract
The present paper contains new results of complex studies on the geological structure, lithology, and fauna of the Middle Eocene siliceous rocks of the Ukrainian Shield Ingul megablock located in the vicinity of the villages of Tsybulevo, Verblyuzhka and Pervozvanovka of Kirovograd Oblast and Voronovka village of Mykolayiv Oblast. Based on new findings and analysis of malacofauna, the Middle Eocene age of the gaize-like sandstones of Verblyuzhka village was confirmed. For the first time, numerous remains of rock-forming organisms such as sponges (lithistid Demospongiae), coralline (Corallinaceae) and green algae (Dasycladales, Halimedaceae) have been found in the siliceous deposits of this region. In addition, biogenic buildups formed by organisms with carbonate (coralline and green algae, large foraminifera) and silicate (lithistid sponges) skeletons were found for the first time in the siliceous rocks of the Pervozvanovka deposit. The observed biogenic lepispheres in the studied rocks suggests that the latter have been formed with active participation of silica-producing bacterial communities. Based on the first finds of zeolites, as well as montmorillonite traces, it is forecast that "disguised" pyroclastic material is present in the gaize-like sandstones of Voronovka village. Analysis of the lithological features and the mineral and faunal composition of the studied rocks allow us to draw a conclusion about the multi-stage genesis of the Middle Eocene siliceous deposits in the central part of the Ukrainian Shield and the influence of Paleogene volcanism on their formation. It appears that volcanic activity and denudation of volcanic products caused a massive flow of SiO2 into the waters of the Middle Eocene paleobasin. This contributed to the widespread development of siliceous-skeleton organisms (in particular, silica-producing bacterial communities) that actively participated in the formation of siliceous rocks.
Highlights
Siliceous rocks of the Eocene age are widely distributed in the Ingul megablock territory of the Ukrainian Shield and along both banks of the Southern Bug River in the lower reaches
They outcrop to the surface and are opened by many boreholes and mine workings (Faas, 1904; Slodkevich, 1932; Kljushnikov, 1951a, 1951b, 1953, 1958; Makarenko et al, 1987; Stefanskyi, 1992; Berezovsky, 2004, 2009; Zosimovich and Shevchenko, 2015; Shekhunova et al, 2015a, 2015b, 2016)
The examined mollusk complex includes typically Middle Eocene species of bivalves; this complex has significant similarities and small differences with the Middle Eocene malacofauna of the gaize-like rocks of Tsybulevo, Voronovka, Kalinovka and Pervozvanovka villages, as well as the marls of the Kiev Regiostage of the Ingulets river basin; the malacofauna of Verblyuzhka is sharply distinguished from the Upper Eocene complex of the Mandrykovka Layers and proves the Middle Eocene age of the host siliceous rocks
Summary
Приведены новые результаты комплексных исследований геологического строения, литологии и фауны опоковидных пород среднего эоцена Ингульского мегаблока Украинского щита В силицитах Первозвановского месторождения впервые доказано присутствие биогенных построек, сформированных организмами с карбонатным (кораллиновые и зеленые водоросли, крупные фораминиферы, моллюски, кораллы) и силикатным (литистидные губки) скелетами. Наличие в силицитах биогенных леписфер предполагает активное участие в формировании изученных пород кремнеобразующих, бактериальных сообществ. Минерального и фаунистического состава пород позволяет сделать вывод о многостадийном характере генезиса силицитов среднего эоцена центральной части Украинского щита и влиянии на их формирование палеогенового вулканизма. Вулканическая деятельность и денудация продуктов вулканизма обусловили массовое поступление в воды среднеэоценового палеобассейна необходимого количества SiO2, что способствовало широкому развитию кремнистых организмов и, в частности, кремнеобразующих бактериальных сообществ, активно участвующих в процессах образования силицитов. Ключевые слова: силициты, цеолиты, вулканизм, моллюски, фораминиферы, зеленые водоросли, красные водоросли, кораллы, средний эоцен, биостратиграфия, литология, Украинский щит, Украина
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