Early cretaceous anoxic basin of the Russian plate: Organic geochemistry

Compositions of organic matter in the bituminous shale accumulated under anoxic conditions and in the underlying clay deposited in aerated basin are noticeably different. Organic matter (OM) of the clay is depleted in hydrogen and kerogen of the clay during pyrolysis produces 2.5 times less aliphatic hydrocarbons than kerogen, which is separated from the bituminous shale, and dozens of times less sulfurous compounds, such as thiophenes and benzothiophenes. Accumulation of OM in the clay was primarily related to the direct inheritance of polymeric lipid biochemical components of the initial OM and lignin included in the higher plants. Changes of gas regime in the basin and sediments, expressed in the origin of anoxic conditions during the accumulation of bituminous shales, intensified the early diagenetic sulfuration and the consequent formation of sulfur- and hydrogen-rich kerogen in the shales. At the same time, less stable lipids and, possibly, carbohydrates were also conserved.