寒武纪早期全球广布的小壳化石不仅是寒武纪大爆发的主要见证者, 亦是前三叶虫阶段地层划分与对比研究的重要依据。目前寒武系第二阶底界界线层型剖面和点位(GSSP)尚未确定, 软体动物Watsonella crosbyi或Aldanella attleborensis的首现(FAD)被建议作为寒武系第二阶底界GSSP的候选标准分子。Watsonella crosbyi和A. attleborensis在我国滇东、川西南、鄂西、陕南等地均见报道, 但由于其在川北宽川铺组尚未发现, 严重阻碍了该区纽芬兰统的精确划分与对比。本文以川北长滩河剖面宽川铺组顶部新发现的W. crosbyi和A. attleborensis为依据, 建立了川北宽川铺组W. crosbyi组合带, 表明川北宽川铺组顶部存在小壳化石第Ⅲ组合带, 属于寒武系第二阶, 可与滇东朱家箐组大海段、川西南麦地坪组顶部、鄂西天柱山段和岩家河组第五段, 以及陕南宽川铺组顶部等进行生物地层对比, 为华南地区寒武系纽芬兰统的划分提供了重要的化石证据。

The sudden appearance of Small Shelly Fossils (SSFs) in the early Cambrian represents a crucial episode of the Cambrian radiation. The abundant and diverse SSFs also mark the origin of biomineralization of metazoans. SSFs are distributed globally in the lower Cambrian strata and several SSF assemblages have been established for the subdivision and correlation of pre-trilobitic Cambrian sequences. Currently, the Global Stratotype Section and Point (GSSP) of Cambrian Stage 2 (Terreneuvian Series) has not yet been formally defined. The first appearance data (FAD) of the widely distributed Watsonella crosbyi and Aldanella attleborensis, important components of the Watsonella crosbyi Assemblage (SSF Ⅲ), has been proposed as a potential biostratigraphic marker for defining the base of Cambrian Stage 2. Watsonella crosbyi and A. attleborensis are common mollusks in Cambrian strata of South China, particularly in eastern Yunnan, western and southern Sichuan, western Hubei, and southern Shaanxi. However, these two fossils have not been discovered previously in northern Sichuan, making it difficult to subdivide the Cambrian Terreneuvian strata in this region. Recently, we collected abundant SSFs, including W. crosbyi and A. attleborensis, from the uppermost Kuanchuanpu Formation at the Changtanhe section in northern Sichuan. Based on these SSFs, we establish the Watsonella crosbyi Assemblage in the uppermost Kuanchuanpu Formation of northern Sichuan, enabling biostratigraphic correlations with the Dahai Member of the Zhujiaqing Formation in eastern Yunnan, the uppermost Maidiping Formation in western and southern Sichuan, the Tianzhushan Member of the Dengying Formation and Member 5 of the Yanjiahe Formation in western Hubei, and the uppermost Kuanchuanpu Formation in southern Shaanxi. Moreover, the occurrence of W. crosbyi and A. attleborensis in northern Sichuan can be correlated with similar faunas in Siberia, Avalonia, Mongolia and Australia, indicating the significant role of the Watsonella crosbyi assemblage zone for global subdivision and correlation of Cambrian Stage 2 strata.

国家自然科学基金(42172016)、甘肃省科学院人才引进与培养项目(2025QD-18)联合资助