Aromatic compounds in lacustrine sediments from the Lower Cretaceous Jiufotang Formation, Chaoyang Basin (NE China)

• Published in: Marine and petroleum geology Vol. 129; p. 105111
• Main Authors: Li, Li, Jiang, Lian, George, Simon C., Liu, Zhaojun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2021
• Subjects: Aromatic hydrocarbons; Chaoyang Basin; Jiufotang Formation; Lower Cretaceous; Oil shales; Aromatic hydrocarbons; Oil shales; Jiufotang Formation; Lower Cretaceous; Chaoyang Basin
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2021.105111

Twenty-three lacustrine sediment samples from the ZK1006 well in the third member of the Lower Cretaceous Jiufotang Formation in the Chaoyang Basin (NE China), were studied using gas chromatography-mass spectrometry to investigate their aromatic compounds. Aromatic fractions in these sediments are mainly composed of alkylbenzenes, biphenyl, naphthalene, phenanthrene, fluorene, dibenzofuran, dibenzothiophene and their alkyl derivatives, benzohopanes, aromatic triterpenoids, and mono- and tri-aromatic steroids. Environment-related aromatic parameters (e.g. ternary plot of fluorene, dibenzofuran and dibenzothiophene, and dibenzothiophene/phenanthrene) suggest the sediments were deposited in a brackish, lacustrine sedimentary environment with low sulphur content. Maturity-related aromatic parameters (e.g. methylphenanthrene index, methyldibenzothiophene ratio, triaromatic steroids ratio) show that all the samples have reached the early oil generation window. Source-related aromatic parameters (e.g. retene/(retene + cadalene), arborane/fernane-derived triterpenes) are controlled by vertical variation of primary productivity in the early Cretaceous lake, from a higher plant-dominated shallow lake to an aquatic organism-dominated semi-deep to deep lake. The large variation in the origins of the organic matter in the oil shales, siltstones and mudstones is interpreted to be due to the effects of volcanic ash and gravity-flow deposition, which directly contributed to the local biomass. •Lake sediments deposited under brackish and low sulphur depositional conditions.•Both higher plants and aquatic organisms are sources of the organic matter.•Monoaromatic polyprenoids present in immature lake sediments.•Unknown compounds (base peak m/z 169, MW 350) detected.•Volcanic ash affected organic matter accumulation.