Spiniferous acritarchs from the lowest Cambrian, Emei, Sichuan, southwestern China

Abstract

Numerous spiniferous acritarchs, Baltisphaeridium, Micrhystridium, Coryphidium and Acanthodiacrodium, have been discovered in the lower Member of the Jiulaodong Fm of the lowest Cambrian Meishuucun Stage, in Maidiping, Emei, Sichuan, Southwestern China. Large (more than 20 μm) spiniferous acritarchs, Baltisphaeridium, etc., were discovered previously and described as taxa occurring contemporaneously with trilobites in Cambrian strata. The described Baltisphaeridium now has been found in sediments more than 120 m below the oldest trilobite bed. This is interesting for the following reasons: (1) the Baltisphaeridium evidently did not occur for the first time contemporaneously with trilobites, but already existed together with small shelly fauna in the early Meishucun or earlier; (2) the earliest trilobites possibly had occurred during the Meishucun Stage, but that is earlier than so far known; (3) the occurrence of Baltisphaeridium together with small shelly fossils in the Meishucun Fm not only increases the abundance and diversity of the Cambrian Meishucun fossil population and differentiates between the Cambrian and the Precambrian, but also raises the possibility of using Baltisphaeridium in determining the Precambrian-Cambrian boundary in the absence of small shelly fossils. The following taxa are described: Octaedryxium simplex n.sp., O. minutum n.sp., Baltispaeridium dictium n.sp., B. reticulum n.sp., B. jiulaodongense n.sp., Eomicrhystridium sp., Micrhystridium pseudozonale n.sp., M. maidipingense n.sp., Coryphidium sichuanense n.sp., Coryphidium sp., Acanthodiacrodium sp. and Cymatiosphaera sp.