Anachronistic facies in the Lower Triassic of South China and their implications to the ecosystems during the recovery time

• Published in: Science China. Earth sciences Vol. 51; no. 11; pp. 1646 - 1657
• Main Authors: Zhao, XiaoMing, Tong, JinNan, Yao, HuaZhou, Zhang, KeXin, Zq, Chen
• Format: Journal Article
• Language: English
• Published: Heidelberg SP Science in China Press 01.11.2008; Springer Nature B.V
• Subjects: Earth and Environmental Science; Earth Sciences; Ecosystems; Extinction; Geochemistry; Marine; Metazoa; Sedimentary geology; Stratigraphy; China, People's Rep., Sichuan Prov., Changjiang R., Three Gorges Dam; China, People's Rep., Hubei Prov; China, People's Rep; biotic recovery; ecosystem; anachronistic facies; South China; Early Triassic; Three Gorges area
• ISSN: 1006-9313; 1674-7313; 1862-2801; 1869-1897
• DOI: 10.1007/s11430-008-0128-y

The end-Permian mass extinction not only severely distressed the Paleozoic ecosystems but also dramatically changed the sedimentary systems, resulting in a peculiar Early Triassic ecosystem and submarine environment during the recovery time following the mass extinction. The Lower Triassic is characteristic of the wide occurrence of various distinctive sediments and related sedimentary structures, such as flat-pebble conglomerates, vermicular limestone, subtidal wrinkle structures, microbialite, carbonate seafloor fans, thin-bedded limestone and zebra limestone-mudstone. These sediments were common in the Precambrian to Early Ordovician marine settings, and then they occurred only in some extreme and unusual environments with the expansion of metazoan faunas. However, the Early Triassic witnessed an “anachronistic” reappearance of some distinctive sedimentary records in normal shallow marine settings. The study of these anachronistic facies should be of great importance for the understanding of the unique ecosystem and marine environment through the great Paleozoic-Mesozoic transition. The anachronistic facies characterized by vermicular limestone have been documented in many localities in South China and occur at various horizons of the Lower Triassic. Most types of reported distinctive sediments over the world have been observed in the Lower Triassic of South China. This provides an excellent opportunity for understanding the Early Triassic environment and its coevolution with the biotic recovery. Among the anachronistic facies the vermicular limestone is the most characteristic and common distinctive sediments in the Lower Triassic of South China but has received relatively few investigations. Taking it as a case study, we will detail the variation of vermicular limestone and its stratigraphic distribution in the Three Gorges area, Hubei Province. The investigation on the vermicular limestone and other distinctive sediments from the Lower Triassic of South China further indicates that the appearance of anachronistic facies immediately following the mass extinction and the elimination from normal shallow marine facies with the radiation of Mesozoic marine faunas imply the natural response of the sedimentary systems and ecosystems to the great Paleozoic-Mesozoic transitional events and their induced harsh environments. Therefore, the ups and downs of the anachronistic facies may act as a proxy for the evolution of ecosystems independent of fossil analyses.