TY - JOUR

T1 - Trilobites, biostratigraphy, and geochemistry of the middle cambrian kuonamka formation (Northeastern siberian platform, Kyulenke River)

AU - Korovnikov, I. V.

AU - Parfenova, T. M.

N1 - Funding Information: The work was carried out in the framework of projects 0331-2019-0003 (“Paleontological and ecostratigraphic substantiation of zonal stratigraphic schemes of the Paleozoic of Siberia; paleogeographic and biofacies zoning of sedimentary basins”) and 0331-2019-0022 (“Organic geochemistry and geologic evolution of major Neoproterozoic and Phanerozoic oil and gas systems of Siberia”) from the Russian Foundation for Basic Research. Publisher Copyright: © 2021, Novosibirsk State University.

PY - 2021/11

Y1 - 2021/11

N2 - We studied the middle Cambrian unit of the Kuonamka Formation section on the Kyulenke River (Siberian Platform) and performed its biostratigraphic subdivision based on trilobites. The middle Cambrian section has intervals corresponding to the regional zones of the Amginian Stage. Six levels with mass accumulation of fauna remains have been identified: Two levels are located within the Ovatoryctocara Zone; the third level is at the boundary between the Ovatoryctocara and Kounamkites zones; the fourth layer is confined to the roof of the Triplagnostus gibbus Zone; and the fifth and sixth levels are located within the Tomagnostus fissus–Paradoxides sacheri Zone. The composition of rocks and bitumens of their organic matter (OM) has been studied, including the geochemical specifics of the mineral components of rocks (iron, sulfur, and СО2) and of saturated hydrocarbons of bitumens as well as noncarbonate carbon isotopes in the OM. It has been established that the OM sedimentation took place under normal aeration of the sea basin waters, without hydrogen sulfide contamination of the bottom waters. The intensity of chemical and biochemical transformations of mineral and organic components during diagenesis was controlled by the contents of organic carbon and sulfate ion, the activity of the anaerobic prokaryote community, and the rate of sediment mineralization. We have also established relationships between the content of organic carbon in potentially oil source rocks and the contents of iron oxide, total sulfur, and sulfide and sulfate sulfur as well as the ratios of saturated hydrocarbons. The alternation of highly carbonaceous black shales and carbonaceous rocks is apparently due to a change in the composition of biologic communities of microorganisms (sources of hydrocarbon biomarkers) and in the intensity of OM transformation during diagenesis. We assume that the OM transformation included sulfate reduction and dealkylation of high-molecular steroids in the unconsolidated OM-enriched marine sediments with the participation of bacteria. The intensity of these processes depended on the mass of the primary OM, the amount of sulfate ion, and, hence, the pH and Eh of the medium.

AB - We studied the middle Cambrian unit of the Kuonamka Formation section on the Kyulenke River (Siberian Platform) and performed its biostratigraphic subdivision based on trilobites. The middle Cambrian section has intervals corresponding to the regional zones of the Amginian Stage. Six levels with mass accumulation of fauna remains have been identified: Two levels are located within the Ovatoryctocara Zone; the third level is at the boundary between the Ovatoryctocara and Kounamkites zones; the fourth layer is confined to the roof of the Triplagnostus gibbus Zone; and the fifth and sixth levels are located within the Tomagnostus fissus–Paradoxides sacheri Zone. The composition of rocks and bitumens of their organic matter (OM) has been studied, including the geochemical specifics of the mineral components of rocks (iron, sulfur, and СО2) and of saturated hydrocarbons of bitumens as well as noncarbonate carbon isotopes in the OM. It has been established that the OM sedimentation took place under normal aeration of the sea basin waters, without hydrogen sulfide contamination of the bottom waters. The intensity of chemical and biochemical transformations of mineral and organic components during diagenesis was controlled by the contents of organic carbon and sulfate ion, the activity of the anaerobic prokaryote community, and the rate of sediment mineralization. We have also established relationships between the content of organic carbon in potentially oil source rocks and the contents of iron oxide, total sulfur, and sulfide and sulfate sulfur as well as the ratios of saturated hydrocarbons. The alternation of highly carbonaceous black shales and carbonaceous rocks is apparently due to a change in the composition of biologic communities of microorganisms (sources of hydrocarbon biomarkers) and in the intensity of OM transformation during diagenesis. We assume that the OM transformation included sulfate reduction and dealkylation of high-molecular steroids in the unconsolidated OM-enriched marine sediments with the participation of bacteria. The intensity of these processes depended on the mass of the primary OM, the amount of sulfate ion, and, hence, the pH and Eh of the medium.

KW - Biostratigraphy

KW - Bitumen

KW - Carbon

KW - Diagenesis

KW - Hydrocarbon biomarkers

KW - Kuonamka Formation

KW - Middle Cambrian

KW - Oil source rocks

KW - Sedimentation

KW - Siberian Platform

KW - Trilobites

UR - http://www.scopus.com/inward/record.url?scp=85119895472&partnerID=8YFLogxK

U2 - 10.2113/RGG20204217

DO - 10.2113/RGG20204217

M3 - Article

AN - SCOPUS:85119895472

VL - 62

SP - 1256

EP - 1268

JO - Russian Geology and Geophysics

JF - Russian Geology and Geophysics

SN - 1068-7971

IS - 11

ER -