Pioneer organisms after F-F mass extinction in Dushan region, Guizhou Province, and their significance in establishing new ecosystem

Abstract

After mass extinctions, most areas became "ecologically barren areas" lacking or even without ecosystem over an extensive region. Studying the pioneer organisms and the reconstruction process of a new ecosystem in the "ecologically barren area" is very important for revealing the evolution after bio-mass extinctions. In the Dushan region, Guizhou Province, China, the trace fossils appeared and flourished evidently earlier than body fossils after Frasnian-Famennian (F-F) mass extinction. The pioneer organisms and pathfinders in the "ecologically barren areas" are the trace-makers that are deposit-feeders with relatively simple structure and conformation on or near the deposit surface. The trace-makers have undergone an evolutionary process that their trace structures changed from simple to complex, and their living and moving areas and spaces enlarged from linear to planar and then to three-dimension spaces. Those characters show that the ability of the trace-makers to deposits and their efficiency of looking for food have been enhanced gradually and that those trace-makers constructed gradually a base for the new ecosystem. This process is similar to that of the trace fossils near the Precambrian-Cambrian boundary.In the Dushan area, only the recovery intervals have been identified for the Famennian body fossils, with no eminent radiation interval recognizable due to the Devonian-Carboniferous (C-D) mass extinction. However, both the recovery and radiation intervals may be clearly recognized in the Famennian trace fossils based on their conformation and diversity. The evolution and diversification of the trace fossils in the "ecologically barren area" is considered to have played a role of necessary foundation for the recovery of body fossils in the ecological chain.With the gradual disappearance of the unfavourable environment factors resulting in the F-F mass extinction, a new ecosystem was reconstructed in the "ecologically barren area" through a three-step process from the "original ecosystem" to "elementary ecosystem" and finally to the "developed ecosystem". The establishment of the new ecosystem has laid a foundation for the recovery of the body fossils thereafter.

Mid-late Devonian calcified marine algae and cyanobacteria, South China

“…Similar FrasnianFamennian facies have been examined at many other locations in the region (Gong et al, 2002;Ma et al, 2008). These include the localities described here at Yangdi (Xu et al, 2006) and Shenwan (Li and Wang, 1991), both near Guilin, at Liujing farther to the south near Nanning (Liao, 2002;Chen and Tucker, 2003), and at Dushan to the northwest in Guizhou (Wang et al, 2006(Wang et al, ). al., 2007.…”

“…The Frasnian-Famennian boundary at Dushan has traditionally been regarded as the contact of the Wangchengpo and Yaosuo formations (Guizhou Bureau of Geology and Mineral Resources, 1987). It has also tentatively been placed in the lower part of the dolomitic Sifangpo Member (Wang and Chen, 1999;Wang et al, 2006, fig. 3), but this remains uncertain.…”

Two episodes of evolution of trace fossils during the Early Triassic in the Guiyang area, Guizhou Province, South China

“…The development process of trace fossils faunas is similar to that documented around the Precambrian-Cambrian boundary and following the F-F mass extinction (Wang, et al, 2006). This seems to provide a biological recovery model after a mass extinction event: the marine biota suffered extinction and are battered by environmental conditions.…”

Two episodic changes of trace fossils through the Permian-Triassic transition in the Meishan cores, Zhejiang Province

“…(1) the change of marine bottom environments, such as increased anoxia, and thus the trace-building organisms did not have enough oxygen to survive; (2) the decrease in primary production, and thus they could not access enough food to meet energy metabolic demand within little radius from their fixed positions, and (3) the decline in ecological competition, and thus they did not have to hide deeply in sediments to escape predators [40][41][42].…”