Bacterial hydrocarbon seepage structures with a cone-in-cone texture in the rocks of the Taurian series of the Mountain Crimea (South Coast of Crimea)

Research subject . Paleogeographic conditions for the formation of structures with cone-to-cone textures by living organisms. Methods. The morphology of polished sections was studied using an Olympus BX 5 microscope equipped with an Olympus DP 12 camera. Geochemical analysis was performed using an ICP ELAN 9000 (Perkin Elmer). Carbon isotope composition was determined by mass spectrometry on a Deltaplus Advantage device. Results. The structures were formed on solid ground. They had several growth phases. The tree-like skeleton of the cone-to-cone structures has a modular structure. Micron-thick laminae extended from its walls. They formed rolls of cones, fused petals with a corrugated surface. The upper surface of the structures is covered with lamina petals and calcite spherulites. Their mineral composition is represented by columnar anthraconite with the presence of rhodochrosite, quartz, and pyrite framboids. The isotopic composition of carbon in carbonate structures varied from –19.14 to –13.59‰, and that of its biogenic material δ13С = –36.64‰. The relationship between carbonate formation and chemosynthesis of archaea and prokaryotes is indicated by the results of carbon isotope composition, δ13C isotope difference between carbonate and biogenic matter, presence of carbonate spherulites, pyrite framboids, biomarkers, light and heavy oil. High contents of lithophile, chalcophile, rare earth elements in the material of the structures, as well as the isotope composition of sulfur (+11.28; +1.72‰), carbon (from –19.14 to –13.59‰) and oxygen (from –14.52 to –13.45‰) confirm the use of deep volcanic fluids by living organisms. Conclusions. Structures with cone-to-cone textures were created by protozoa in symbiosis with prokaryotes and archaea, which processed hydrocarbon volcanic fluids into organic matter and carbonate. The presence of large fauna near the biocenosis structures and other features allow us to attribute the cone-to-cone formations to ancient hydrocarbon seepage carbonates or Triassic methane-liths. Postmagmatic hydrocarbon fluids, which have fed the microorganisms, have a deep genesis.