Carbonate Diagenesis Controlled by Glacioeustatic Sea-Level Changes: A Case Study from the Carboniferous-Permian Boundary Section at Xikou, China

Abstract

ABSTRACT The platform-facies carbonate rocks of the Carboniferous-Permian boundary strata are well developed and outcropped in Xikou ( ), Zhenan ( ) County, Shaanxi ( ) Province, China. The carbonate diagenesis in the Carboniferous-Permian boundary section at Xikou contains many processes with conspicuous effects, including micritization, cementation, mechanical and chemical compaction, neomorphism, and dissolution. Based on mineralogical composition and microfabrics, the diagenetic environments are distinguished into marine, near surface meteoric and burial environments. Detailed petrographical observation of abundant thin sections integrated with previous studies on sequence stratigraphy reveals that the carbonate diagenesis in the Carboniferous-Permian boundary section is related to the relative stratigraphic position of the rocks in the high-frequency cycles and controlled by the glacioeustatic sea-level changes. There are distinctive differences in diagenetic patterns between the lower transgressive sequence and the upper regressive sequence in a cyclothem. The diagenesis in the lower transgressive sequence is mainly characterized by pressure dissolution and recrystallization of mudstone and wackstone in a burial environment, and the diagenesis in the upper regressive sequence by cementation and leaching of freshwater in a meteoric environment.