Constraining the Ediacaran–Cambrian boundary in South China using acanthomorphic acritarchs and uniserial modular microfossils

The Ediacaran–Cambrian boundary, representing one of Earth’s most critical transitions, is currently defined by the Fortune Head (Newfoundland, Canada) GSSP (Global Standard Stratotype Section and Point) at a point once regarded as the first appearance of the branching trace fossil Treptichnus pedum. However, T. pedum has subsequently been found below the GSSP, and its global distribution is primarily restricted to siliciclastic facies where application of alternative biostratigraphic and chemostratigraphic correlation tools is challenging. Investigations of acanthomorphic acritarchs in basal Cambrian strata of South China suggest that these microfossils could provide a robust complementary biostratigraphic marker for the Ediacaran–Cambrian boundary. Acanthomorphic acritarchs are widely distributed across the Yangtze Platform in chert–phosphorite layers intercalated with carbonates and shales, thereby allowing their biostratigraphic occurrences to be calibrated with small shelly fossil biozones and carbon isotope data. Here, the earliest Cambrian Asteridium–Heliosphaeridium–Comasphaeridium (AHC) assemblage biozone is identified at 11 localities within the Yanjiahe, lower Niutitang, and upper Liuchapo formations, representing diverse depositional environments. Two latest Ediacaran microfossils, both characterized by uniserially chained modules and representing a characteristic Ediacaran assemblage (the Horodyskia minor – Nenoxites jiumenensis , or HmNj, assemblage biozone), are also identified in the Liuchapo Formation, but do not overlap with the Cambrian AHC acritarch biozone. The AHC assemblage biozone is demonstrated to be stratigraphically equivalent to basal Cambrian small shelly fossils and a negative δ 13 C isotope excursion known to occur at the Ediacaran–Cambrian boundary. Thus, in South China, the AHC and HmNj assemblage biozones can be used to effectively and reliably constrain the Ediacaran–Cambrian boundary. UUID: http://zoobank.org/2fd52705-f7ef-4276-897e-10e89efb04ad