Insoluble organic matter in source rocks: derived from organic macromolecules in the skeleton, cell wall and shell of organisms

Abstract

Ultramicroscopic organic petrology analysis and other techniques were used to examine the relationships between organic detritus (from different types of biological skeleton, cell wall and shell) and insoluble organic matter in excellent source rocks from the point of view of molecular structure and stability of biological cells. Previous studies have shown that the organic skeleton, cell wall, shell and detritus in source rocks could be assigned to three main categories: (a) benthic algae, fungi, bacteria, pelagic algae and acritarchs; (b) shell, skin, hair and tendon as the connective tissue of zooplankton; (c) aquatic and vascular plants. The organic detritus playing the role of supporting or protecting the organisms were composed of inactive carbohydrate (e.g., cellulose, chitin, pectin, peptidoglycan) and inactive protein (e.g., scleroprotein). These biopolymers were chemically stable and insoluble in organic solvents and water. They were preserved in the form of insoluble organic matter (nonlipid) during the formation of excellent source rocks but without the ability to generate oil. They had hydrocarbon gas-generating capacity in the highly to early over-mature stage with a general conversion rate of hydrocarbon lower than 15%, which was equivalent to type Ⅲ kerogen or vitrinite.

Keywords

• biological skeleton, cell wall and shell
• organic detritus
• insoluble organic matter
• chemical stability
• hydrocarbon gas-generating potential