Genesis and geological significance of pyrite in the First Member of the Cretaceous Qingshankou formation of the Songliao Basin, NE China

Abstract

Pyrite is an important component for reconstructing the biogeochemical conditions and sedimentary environments of the earth’s surface in the past. The study on pyrite of Cretaceous Qingshankou Formation in the Songliao Basin not only helps elucidate the depositional processes of high-quality source rocks in the area, but is also important for reconstructing the Cretaceous paleoenvironment. Pyrite in the Qingshankou Formation includes euhedral pyrite, anhedral pyrite, fine-grained pyrite aggregates, pyrite framboids and polyframboids. The euhedral pyrite can be further divided into authigenic and secondary pyrite. Authigenic euhedral pyrite is directly precipitated from solution, while secondary euhedral pyrite is formed by recrystallization of pyrite framboids. The secondary pyrite can be further divided into compaction type and cementation type, indicating that the transformation of pyrite framboids into secondary euhedral pyrite is controlled by compaction and cementation, respectively. Anhedral pyrite is usually precipitated on the surface of iron-rich clay minerals (e.g., chlorite), or by metasomatism of other minerals, biological skeletons, and microorganisms. Framboidal pyrite is formed from greigite, and the amount, number of microcrystalline layers and particle size are related to the flow intensity of the water. This study provides a new understanding of the genetic mechanism of different types of pyrite.