Abstract:

The Early Cambrian sedimentary and tectonic paleogeographic evolution of the southern North China margin has been a research focus in geoscience. This paper focuses on the Cambrian Xinji Formation (Shimengou Lushan, western Henan) to analyze the sedimentary environment and its controlling factors via conventional sedimentological techniques (such as field profile observation), microscopic observations and grain-size analysis. We found that the Xinji Formation in the study area comprises a marine terrigenous clastic sequence, and the lithologies are featured by the transitional deposition from conglomerate to sandstone and mudstone. Sedimentary environment of the Xinji Formation is characterized by shallow marine gravity flow to tidal flat and lagoon and washover fans affected by storms. The grain-size probability cumulative curve of the Xinji Formation sandstones is characterized by steeply-dipping segment (1 or 2 segments) pattern and steeply-dipping abrupt change pattern, and the C-M plot shows that the hydrodynamic mechanism comprises both traction and gravity flow. Sedimentary environment of the Xinji Formation is closely related to the paleogeography, paleostructure, paleolatitude, and paleoclimate of the southern North China margin, which included an active continental margin, low latitude, rising global sea level, and medium to relatively high temperatures. The study of sedimentary environment and its controlling factors of the Xinji Formation has important significance for understanding the evolution of Early Cambrian sedimentary basins and lithofacies paleogeography of the southern North China margin.

Key words: southern North China margin, Xinji Formation, sedimentary environment, shallow marine gravity flow, grain-size analysis