The Earth's ecosystem underwent a dramatic transformation around the Ediacaran-Cambrian boundary (ECB). Our previous understanding of this critical evolutionary event primarily relied on the fossil record from shallow-water facies. However, a disconformity is broadly developed at the ECB in shallow-water deposits worldwide, and this hindered our complete understanding of the evolutionary processes. Here, combining published data and new data from eight sections in South China, we propose that the fossil record in cherts provides a new window into the biological revolution at the ECB.
      Two distinct fossil assemblages were recognized in cherts across the ECB throughout the Yangtze craton. The Ediacaran assemblage is characterized by string- and strap-like fossils of undetermined affinities. In contrast, the basal Cambrian assemblage encompasses diverse algal and animal microfossils with well-preserved anatomical details. Notably, the Cambrian assemblage also contains numerous complex carbonaceous filmy fossils, whose morphology differs from algae and has never been reported in Precambrian cherts. This indicates innovations of the soft-tissue structures of multicellular eukaryotes in the earliest Cambrian.
      The contrasting fossil assemblages reveal a rapid shift in the biosphere across the ECB, although a few Ediacaran taxa persisted into the Cambrian, and some Cambrian-specific animal skeletal fossils appeared predating the nadir of the basal Cambrian carbon isotope negative excursion (BACE). This is consistent with and reinforces the paleontological observations from other taphonomic windows. Being distributed across various water depths around the ECB and able to preserve the fine structures of non-mineralized organic tissues, cherty deposits are expected to provide more valuable supplements to our understanding of the Ediacaran-Cambrian biological revolution, which was previously mainly established on shallow-water facies and animal skeletal fossils.

Ediacaran,cambrian,South China,chert,carbonaceous,non-biomineralized