High-resolution Stratigraphy of the Lowermost Cambrian Sequence at the Xiaolantian Section, Yunnan, South China: Lithofacies, Key Bed, and Local/Regional Correlation

Abstract

 Detailed lithostratigraphy of the Lower Cambrian in South China, composed mostly of phosphorite and carbonate, is analyzed at the Xiaolantian section in the Chengjiang area, Yunnan. Six distinct lithostratigraphic units (Units 1 to 6 in ascending order) are recognized in the small shelly fossil (SSF)–bearing Zhongyicun Member, together with one particular terrigenous clastic unit (Unit 3) in the middle. Sedimentary features of these beds indicate that they were deposited in shallow marine settings in off–shore to upper slope of the Kangdian rift-related basin in western South China. The lithostratigraphy of the Xiaolantian section correlates not only with those of the neighboring sections at Hongjiachong and Maotianshan in Chengjiang, but also with those of five other sections (Meishucun, Wangjiawan, Xiaohuangcaoling, Zhujiaqing, and Laolin) in Yunnan. This regional correlation highlights a particular unit composed of terrigenous clastics solely in the middle of the Zhongyicun Member, e.g., Unit 3 of the Xiaolantian section. This unit serves as a useful key bed for a lithostatigraphical correlation within the basin because a similar unit (interval) was recognized at the same horizon in seven other sections in Yunnan. This key bed and its stratigraphic horizon are noteworthy, as this marks a significant horizon of SSF zone boundary; i.e., between the Anabarites trisulcatus–Protohertzina anabarica Zone and the Paragloborilus subglobosus–Purella squamulosa Zone of the Terreneuvian, Lower Cambrian.