TERTIARY DELTAIC AND LACUSTRINE ORGANIC FACIES - COMPARISON OF BIOMARKER AND KEROGEN DISTRIBUTIONS

Biological marker and kerogen compositional data in Tertiary deltaic and lacustrine settings were compared and contrasted. The two settings are represented by (a) coals and organic-carbon-rich shales in a thick deltaic sequence from the Far East, constituting three distinct organic facies, and (b) humic coals and sapropelic oil shales in a restricted intermontane (freshwater) lacustrine sequence from western Montana (U.S.A.), constituting two distinct organic facies. We distinguish the organic facies in each depositional setting by systematic differences in gross compound class distributions, kerogen and infrared spectral characteristics, molecular character of pyrolyzates, sterane carbon number distribution and sterane/hopane ratios. The kerogens of the three deltaic organic facies are characterized by varying quantities of vitrinite, resinite, sporinite, cutinite and fluorescent amorphinite. Triterpane distributions reveal numerous terrigenous compounds, including oleanane, oleanenes, and unidentified C30 (presumably) resin-derived components. The two organic facies of the freshwater lacustrine setting are distinguished based upon either a vitrinite or an alginite/fluorescent amorphinite predominance in the kerogen. Numerous characteristic facies-related markers are also present, including dehydroabietane (land plant resins) and 4-methylsteranes (perhaps from freshwater dinoflagellate input). The available molecular and petrographic data are evaluated, and characteristics are proposed for distinguishing five organic facies of these two depositional settings. The successful simultaneous use of molecular geochemistry and organic petrography in this study provides a format for refining the organic facies concept.