Identification and characteristics of a new section of the Lower Carboniferous Lianxian Formation in the Lianzhou area, northwest Guangdong

This paper is the result of geological survey engineering.

Objective A large suite of carbonates developed in the Early Carboniferous in the Lianzhou area of northwest Guangdong, and the representative stratigraphic section of the Lianxian Formation is an ideal stratigraphic section for studying carbonate deposition in this period. The bottom boundary of the selected stratigraphic section of the Banling Village of the former Lianxian Formation is unclear and the outcrop is severely damaged, which has lost the functional value of the stratigraphic section. There is an urgent need to find a new stratigraphic section in the Lianxian Formation to provide a reference for the stratigraphic stratigraphy of the Lower Carboniferous and regional geological survey studies in the area.

Methods Tematically studied by means of large scale sectioning, rock identification and paleostratigraphy of the stratigraphic section in Longtan Shijietou village of Jiubei, Lianzhou city, Guangdong. The stratigraphic characteristics of the sequence were obtained and the age of the bottom boundary was determined.

Results Based on the evolutionary sequence of foraminifera, the disappearance of foraminiferal Quasiendothyra kobeitusana, Q. konensis and the first occurrence of Bisphaera irregularis birina reveal that the boundary between Devonian and Carboniferous in the Lianzhou area of northwestern Guangdong passed through the middle of the granular tuff at the top of the Changlai Formation. Combined with the stratigraphic, the developmental age of the Lianxian Formation can be the restricted to the Early Carboniferous Dunei stage.

Conclusions This section is the largest section with continuous deposition of Early Carboniferous early carbonate rocks known in the region, with complete stratigraphic sequence development and clear top and bottom interfaces, and is the most ideal secondary stratigraphic section found in the Lianxian Formation. This lays the foundation for the establishment of the substratigraphic type (reference section) of the Lianxian Formation. The above results are of great significance for the construction of the regional stratigraphic framework in northwestern Guangdong, the conduct of regional stratigraphic delineation and comparative studies, and the improvement of the regional geological background.