Trace fossils from the precambrian - cambrian boundary candidate at meishucun, jinning, Yunnan, China
- 641-649pp. Photos
The Precambrian–Cambrian boundary candidate section at Meishucun, China, has yielded trace fossils which are abundant at some horizons. The earliest occur in Unit 3 of the Zhongyicun Member approximately 8 m above the lower selected stratotype reference point for the boundary and include Arenicolites sp., Asteriacites sp., Neonereites biserialis, N. uniserialis and Sellaulichnus meishacunensis. The next trace-fossil-bearing horizon is in Unit 6 of the Zhongyicun Member where Cochlichnus sp., Monomorphichnus sp., Neonereites biserialis and N. uniserialis occur. Immediately above, in Unit 7, are Cruziana sp., Didymaulichnus miettensis, Monomorphichnus sp. and Rusophycus sp. In the Badaowan Member at the top of the section there are Didymaulichnus sp. and Taphrhelminthopsis circularis in Unit 9, Arenicolites sp., Diplocraterion sp., Gordia molassica, Skolithos sp. and T. circularis in Unit 11, and Gordia meandria, ? Plagiogmus sp., Skolithos sp. and T. circularis in Unit 12.
Comparison of this trace-fossil distribution with that in key Precambrian–Cambrian boundary sections in other countries indicates that the ranges of a few trace fossils cross the boundary (e.g. Didymaulichnus, Neonereites, Planolites) but most appear only in the Cambrian. Different ichnogenera seem to appear at various levels above the boundary. Arenicolites and Asteriacites are among the first, while Taphrhelminthopsis circularis is only encountered higher in all sequences. Some have only been recorded at much higher levels and relatively close to the first appearance of trilobites (e.g. Cruziana, Diplocraterion, Rusophycus). This suggests that the first appearance of specific trace fossils or groups of trace fossils may be valuable for locating the boundary in some sections and for correlating late Precambrian and early Cambrian strata.