The Weng'an Biota, found in the Doushantuo Formation in Guizhou Province, South China, is a remarkable fossil assemblage known for its well-preserved ancient life forms. These include small organisms called acritarchs, algae, and even embryo-like fossils. Among these, acritarchs, shaped like spiny spheres, have been essential for understanding the age and relationships of rocks from the Ediacaran Period. Previous studies mainly focused on larger spiny acritarchs, overlooking the smaller ones. In our study, we carefully examined over 500 thin sections and discovered a wealth of well-preserved small and medium-sized acritarchs. These tiny fossils, with diameters ranging 20–150 µm, help us understand the ancient ecosystems and how life evolved during this critical time in Earth's history. We identified several different species of small spiny acritarchs, e.g., Tanarium conoideum, Tanarium elegans, Mengeosphaera membranifera, Mengeosphaera minima, and Variomargosphaeridium gracile. Additionally, we found medium-sized acritarchs, e.g., Tanarium tuberosum and Weissiella cf. W. grandistella. These new findings provide important clues for correlating the rocks of the Doushantuo Formation in the Weng'an area with those in the Yangtze Gorges region. They also help us understand the evolution of acritarchs in different parts of the world, including Australia, Siberia, and the East European Platform.
The Weng'an Biota from the Ediacaran Doushantuo Formation in Guizhou Province, southwestern China, is known for its three-dimensionally phosphatized acritarchs, multicellular algae, and embryo-like animal fossils. Among these diverse microfossils, acanthomorphic acritarchs have played a significant role in the biostratigraphic subdivision and correlation of the lower-middle Ediacaran System. However, most previous studies on the biostratigraphy of the Doushantuo Formation in the Weng'an area have focused on large acanthomorphic acritarchs (LAAs, vesicle diameter >200 µm), whereas the smaller acanthomorphic acritarchs (SAAs, vesicle diameter <100 µm) from the Weng'an Biota have been largely overlooked. In this study, we examined >500 thin sections and discovered a large number of well-preserved, small (<100 µm) and medium-sized acanthomorphic acritarchs (MAAs, vesicle diameter ranging 100–200 µm). In total, we have identified SAAs in four genera and six species (Tanarium conoideum Kolosova, 1991, emend. Moczydłowska et al., 1993; Tanarium elegans Liu et al., 2014; Mengeosphaera membranifera Shang, Liu, and Moczydłowska, 2019; Mengeosphaera minima Liu et al., 2014; Estrella recta Liu and Moczydłowska, 2019; Variomargosphaeridium gracile Xiao et al., 2014), as well as two types of MAAs (Tanarium tuberosum Moczydłowska, Vidal, and Rudavskaya, 1993, emend. Moczydłowska, 2015; Weissiella cf. W. grandistella Vorob'eva, Sergeev, and Knoll, 2009, emend. Liu and Moczydłowska, 2019). This updated acritarch assemblage of the Weng'an Biota is valuable for correlating the Ediacaran Doushantuo Formation between the Weng'an and Yangtze Gorges areas. It also serves as a tool to test the proposed acritarch biozones in Ediacaran formations of South China and other localities, including Australia, Siberia, and the East European Platform.
