Exquisite Microfossils From Neoproterozoic China Contest Geochronoligical Placement of the Liulaobei Formation

Organic-walled microfossils from the early Neoproterozoic Liulaobei Formation in the Huainan region of North China and their biostratigraphic significance

Authors:

1. Qing Tang (a, b)
2. Ke Pang (a, b)
3. Shuhai Xiao (b)
4. Xunlai Yuan (a)
5. Zhiji Ou (a)
6. Bin Wan (a)

Affiliations:

a. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, 210008, China

b. Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA

Abstract:

Biostratigraphic subdivision and correlation of early Neoproterozoic strata is hampered by the limited number of widely distributed and age diagnostic fossils. The acanthomorphic acritarch Trachyhystrichosphaera aimika, among a few other microfossil taxa, has emerged as a potential early Neoproterozoic index fossil, but its temporal and spatial ranges have not been thoroughly documented. To improve our knowledge about early Neoproterozoic biodiversity, we carried out a micropaleontological investigation of the early Neoproterozoic Liulaobei Formation in northern Anhui of North China. Our investigation using a low-manipulation maceration technique revealed a diverse assemblage of organic-walled microfossils dominated by sphaeromorphs and filaments, with relatively few acanthomorph taxa. A total of 23 taxa were recovered, including three new species (Eotylotopalla? grandis n. sp., Siphonophycus gigas n. sp., and Trachyhystrichosphaera botula n. sp.). Also present in the Liulaobei Formation are Trachyhystrichosphaera aimika (a species widely present in pre-Cryogenian Neoproterozoic and latest Mesoproterozoic rocks) and Pololeptus rugosus (a species characterized by an ellipsoidal vesicle with transverse annulations). The new data add to the growing diversity of early Neoproterozoic fossils and strengthen the basis for improved biostratigraphic correlation of early Neoproterozoic strata. Correlation with other geochronologically dated successions that contain Trachyhystrichosphaera confirms Trachyhystrichosphaera and T. aimika as promising index fossils to define and subdivide the pre-Cryogenian Neoproterozoic Era in terms of Global Boundary Stratotype Section and Point (GSSP), as opposed to current system using Global Standard Stratigraphic Age (GSSA). Available biostratigraphic data, including the occurrence of Trachyhystrichosphaera, Chuaria, Tawuia, and Sinosabellidites, suggest that the Liulaobei Formation is of pre-Cryogenian Neoproterozoic age, not Cryogenian–Ediacaran age as some have suggested in the past.