Types, chemical and porosity characteristics of hydrocarbon-generating organisms of the lower Paleozoic, south China——Taking Longmaxi Formation and Qiongzhusi Formation in Sichuan Basin as examples

Abstract

In this study, the biotypes, chemical structures and porosity characteristics of hydrocarbon-generating organisms in the Wufeng Formation-Longmaxi Formation of the Well Jiaoye-1 and in the Qiongzhusi Formation of the Well Jinye-1, Sichuan Basin, are studied through the systematic organic petrology and geochemical analysis. The hydrocarbon-generating organisms in the Wufeng Formation-Longmaxi Formation mainly consist acritarchs and graptolites, with other animal fossils observed. The hydrocarbon-generating organisms of the Qiongzhusi Formation are mainly acritarchs, benthic macroalgae and cyanobacteria, together with some animal fossils such as embryos, sponge spicules. Besides, cryptospore fossils are found in the bottom of Qiongzhusi Formation, Fortunian of the Lower Cambrian for the first time ever. According to raman parameters, the change of pyritized acritarch and bitumen in the same thermal evolution process is greater, followed by that of organic acritarch, and the structural change of graptolite is the smallest. FTIR spectra shows ether bonds, a few aromatic rings, some aliphatic chains in the structures of acritarchs and very low content of aliphatic hydrocarbon, a large amount of carboxyl groups, ether bonds, aromatic rings in both graptolite and chitinozoan. The acritarch has well-developed pores which is of excellent connectivity. The epidermis of graptolite is composed of multiple layers of fiber, between which develop a lot of narrow pores of good connectivity. Conodont has many isolated nano-pores, while the pores of chitinozoan are not developed.