A Silicified Microfossil Assemblage with Problematic Membranous Structures from the Late Ediacaran Shibantan Member, Dengying Formation

The late Ediacaran Shibantan Member of the Dengying Formation in South China has yielded an array of diverse macrofossils, while the composition of microfossils from the same unit remains largely unexplored. Over the past decade, we have conducted extensive micropaleontological investigations on chert bands and nodules from the Shibantan Member deposited in various environments. Major fossil findings include the sphaeromorphic acritarch Leiosphaeridia, various forms of the filamentous sheath of Siphonophycus, the septate trichomes of Oscilatoriopsis, the bundled filaments Polytrichoides, the coiled filaments Obruchevella, the fungus-like Vanavarataenia, a likely uniseriate filamentous form with individual filament possibly multicellular and comparable to those of Aataenia and Talakania, and a rod-shaped form with an elongated end and a pointed end that resembles Primoflagella. Although many of these fossils have long stratigraphic ranges and appear insignificant on their own, the collective presence of these forms, along with the absence of acanthomorphic acritarchs characteristic of early Ediacaran strata, allows for correlation with other late Ediacaran microfossil assemblages from the East European Platform. Notably, Primoflagella is one of only a few Ediacaran microfossil taxa stratigraphically limited to late Ediacaran strata, while its previous reports have been restricted to localities in the East European Platform. The tentative identification of Primoflagella in our study may therefore provide a new locality for this taxon and enhance its biostratigraphic utility.Among the fossil findings, one type of carbonaceous structures has the highest relative abundance and even predominates in most fossiliferous samples from lower subtidal environments. These structures are characterized by brownish color, thin membranous nature, and irregular outline. They often exhibit folded or wrapped morphologies with a considerably large size range, suggesting that they represent fragments of larger structures. In some of the very well-preserved specimens, filamentous and spheroidal structures are also observed within these membranous structures. These structures have not been reported in older microfossil assemblages either in South China or in other blocks. On the contrary, they share similar morphological features with microfossils described from late Ediacaran to early Cambrian strata in the East European Platform, including Vendotaenia fragments, “donut-shaped” filamentous clusters, and a variety of unnamed structures. The similarity in overall morphology and stratigraphic range indicate that these structures may represent related life forms. A comprehensive comparison among such structures in different localities may provide key insights into their biological affinity and possible stratigraphic significance.