中国科学院南京地质古生物研究所机构知识库

The late Mesoproterozoic to Tonian (similar to 1100 Ma to similar to 720 Ma) witnessed a critical evolutionary transition in Earth history. Several fossil taxa, including acritarchs and vase-shaped microfossils, have been suggested as potential diagnostic fossils for this time interval. The acanthomorphic acritarch Trachyhystrichosphaera aimika has become a focus of recent biostratigraphic investigations, showing great potential to assist the definition of the Tonian Global Boundary Stratotype Section and Point (GSSP). Although T. aimika has been extensively reported in the Proterozoic sequences, little is known about its phylogenetic interpretation. Its palaeogeographic and stratigraphic distributions need to be critically scrutinized with recently emended diagnosis of the taxon and new published age constraints. In this study, we report new palaeobiological data of T. aimika specimens from the Tonian Liulaobei Formation in the Huainan region, North China, using transmitted light microscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Our analyses reveal a multilayered ultrastructure from the vesicle wall of T. aimika that has experienced advanced diagenesis to low-grade metamorphism with the peak palaeotemperature of similar to 212 degrees C. In addition, a compilation of palaeogeographic occurrences of T. aitnika shows the taxon is preserved in a wide range of palaeoenvironments and has a broad palaeogeographic distribution with a relatively limited stratigraphic range from similar to 1150 Ma to similar to 720 Ma, suggesting that T. aimika has great potential to become an index fossil for the late Mesoproterozoic to Tonian interval. (C) 2020 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.