Геохимические особенности микробиолитов миоцена (Юго-Западный Крым) по результатам ICP-MS исследований

Abstract

Background. In this paper, we provide new data on the morphology and geochemistry of heraclites, which are represented by specific products formed by degradation of the carbonate paleostructures of prokaryotes around the degassing zones of the Miocene age. The heraclites exhibiting siltstone and sandstone structures are referred to as micrometanolites. An analysis of literature data showed that heraclites had formed in the upper sedimentary strata under the conditions of increased methane levels in the affinity of the stream exits. Methods. The geochemical examination of heraclites of a different colour and morphology was carried out using ICP-MS at the facilities of the Geoanalytik centre, UB RAS Institute of Geology and Geochemistry, Ekaterinburg. Results. According to lithological characteristics and morphology, the following heraclite types were distinguished: slag-like, banded, angular and сementation slabs. Morphologically, the heraclites under study were characterized by high concentrations of Sr, Ba, Co, Ni, Bi, Ce, Nd and Yb, which significantly exceed those in carbonate rocks. The concentrations of Rb, Cs, Nb, Th, Cu, Tl, As, Sc, Sb, Eu, Gd, Tb, Dy and Er in some morphological differences were above the Clarke values, while others demonstrated their deficit. The samples under study showed low concentrations of some heavy REE. A high content of lithophilic, chalcophile, siderophilic and REE elements indicate paleo-fluids of a deep mantle-derived character. The data on the oxide environment during construction material formation was obtained, which is confirmed by low concentrations of U (0.579 to 2.096 ppm) and Bi (0.014-0.084 ppm), as well as the ratios of U/Th (0.4-2.1), V/Cr (0.3-0.9) and Mo/Mn (less than 0.0014). Such conditions existed near or within the cellular organism of prokaryotes. Low concentrations of U, Ti, Mn and Zr confirm a significant growth rate of heraclite carbonate substances. Minor differences in the concentrations of chemical elements in heraclites of a different morphology are believed to have resulted from the physic-geographical and chemical conditions of their formation across the areas of regional faults with an active tectonic regime. Conclusions. Our results have confirmed the assumption that the carbonate material of heraclites formed by processing of deep fluids. In the South-Western Crimea, heraclites constitute a geological phenomenon of the Miocene hydrocarbon paleo-degassing, which was associated with the neotectonic stage of the uplift of the Crimean Mountains. The presence of methane, ethane, propane and petroleum products in the composition of heraclites allows an assumption to be made about the presence of oil and gas deposits in the Sevastopol region.