贵州埃迪卡拉纪瓮安生物群化石含量的统计分析

QUANTITATIVE ANALYSIS ON THE FOSSIL ABUNDANCE OF THE EDIACARAN WENG'AN BIOTA,GUIZHOU

贵州瓮安埃迪卡拉纪陡山沱组(635—551Ma)上磷矿段保存了大量精美的磷酸盐化微体球粒化石,它们主要由多细胞藻类、疑源类和处于不同发育阶段的多种动物胚胎化石组成,此外还包括少量后生动物的幼、成体化石。本文以贵州瓮福磷矿陡山沱组上磷矿段灰白色球粒状白云质磷块岩为研究对象,在总结瓮安生物群中不同生物化石的鉴别特征基础上,定量统计采自该层位的两组岩石样品(WA-Ι和WA-Π)的酸处理砂样中的所有化石。统计结果表明,瓮安陡山沱组该磷块岩中化石质量和岩石中磷酸盐组分质量成正线性相关,两个样品中化石占全部磷酸盐组分的质量百分比均在10%左右,其中多细胞藻类和疑源类化石占全部化石含量均少于10%。这一结果客观地反映了瓮安生物群的化石丰度,证实了保存在瓮安陡山沱组上磷矿段灰色富氧含磷埋藏相中的瓮安生物群主要由动物胚胎化石组成的特征。

The Ediacaran Weng＇ an biota from the phosphorite of the upper Doushantuo Formation （635- 551Ma） at Weng＇ an, Guizhou Province, South China, consists of animal eggs, embryos, larvae and adults, as well as abundant aeritarchs and multicellular algae. The three-dimensional preservation of putative phosphatized animal microfossils with cellular structures provides valuable insight into the origin and early evolution of metazoans. Here we report experimental and statistical investigations on the fossil abundance of the Weng＇an Bi- ota. The result indicates that ca. 10% of the acid residue in rock samples collected from the upper Doushantuo Formation at Beidoushan quarry of the Weng＇ an phosphate mine are composed of the phosphatized fossils, among them only less than 10% are acritarchs and multicellular algae. The high abundance of the embryo fossils in the Weng＇ an biota provides evidence for the rapid radiation of cryptic metazoans before Cambrian.