Characteristics and Sources of Organic Matter from the Early Cambrian Niutitang Formtion and Its Preservation Environment in Guizhou

The Early Cambrian Niutitang Formation on the Yangtze Block is a set of high-quality marine source rock. However, hydrocarbon-forming organisms of these organic-rich shales was poorly understood. In this paper, the results of palynofacies analysis and hydrocarbon-forming organism characteristics of the Niutitang Formation from the Yangtze Block are reported for the first time, and the sedimentary environment is discussed in combination with geochemical data. Palynofacies analysis show that the organic matter (OM) of the Niutitang Formation is mainly composed of amorphous organic matter (AOM), with a small amount of structural organic matter (STOM) and palynomorphs (PL). The results of CONISS (stratigraphically constrained incremental sum of squares) cluster analysis show that the PL can be divided into three zones in the ascending order: Leiosphaeridia-Micrhystridium-fungal zone, algal bloom zone and fungal development zone, corresponding to three stages: transgression, high-stand and regression, respectively. The principal component analysis (PCA) shows that the main hydrocarbon-forming organisms include planktonic green microalgae or dinoflagellates that are related to Leiosphaeridia and Microcystidium. Palynofacies analysis and geochemical data show that the Niutitang Formation was deposited under anoxic or dysoxic condition which was favorable to the enrichment of organic matter.

Automated summary

This paper reports for the first time the characteristics of palynofacies and hydrocarbon-forming organisms of the Niutitang Formation on the Yangtze Block, and discusses the sedimentary environment using geochemical data. The results show that the Niutitang Formation is mainly composed of amorphous organic matter and the main hydrocarbon-forming organisms are planktonic green microalgae or dinoflagellates. The Niutitang Formation was deposited under anoxic or dysoxic conditions.