黔东早-中寒武世凯里组疑源类组合及其界线意义

ACRITARCH ASSEMBLAGES FROM THE EARLY - MIDDLE CAMBRIAN KAILI FORMATION OF EAST GUIZHOU PROVINCE AND BIOSTRATIGRAPHIC IMPLICATION

通过对台江八郎和丹寨平寨两条剖面凯里组中疑源类化石的分析、研究 ,台江剖面产疑源类化石有 17属 35种 (12未定种 ) ,其中以 L eiosphaeridia,Synsphaeridium,Cymatiosphaera,Pterospermella最为丰富 ;可划分为 3个组合 ,即 Cymatiosphaera cf.cristata- Fimbriaglomerella membrancea组合 ,Cristallinium- Micrhystridium - Pterosper-mella组合和 Dictyotidium- Granomarginata组合。丹寨平寨剖面凯里组所产疑源类化石有 :13属 2 1种 (5未定种 ) ,同样划分为 3个组合 ,即 L eiosphaeridia- Tasmanites组合 ,Retisphaeridium- Micrhystridium tentatium组合和Baltisphaeridium - Bubomorpha hunjiangensis组合。本文对两条剖面中的疑源类化石的组成、相对含量做了详细的统计 ,发现在八郎剖面 9- 2层和平寨剖面 3层疑源类的丰度、分异度开始发生明显的变化 ,表现由早寒武世向中寒武世疑源类组合面貌的转变 ,这一疑源类转变层位正好是与三叶虫划分的中、下寒武统界线的层位位置相一致。这充分表明疑源类化石可作为划分中。

Acritarch fossils from the Early Middle Cambrian Kaili Formation at both the Balang and Pingzhai sections, Guizhou Province, have been studied. seventeen genera and 35 species of acritarchs from the Kaili Formation of the Balang section have been identified, in which Leiosphaeridia, Synsphaeridium, Cymatiosphaera, Pterospermella are abundant. Three acritarch assemblages near the Early and the Middle Cambrian boundary have been established as follows (in ascending order): Cymatiosphaera cf. cristata Fimbriaglomerella membrancea assemblage; Cristallinium Micrhystridium Pterospermella assemblage; Dictyotidium Granomarginata assemblage. thirteen genera and 21 species of acritarchs from the Pingzhai section have been identified, and three acritarch assemblages have been established near the Early and the Middle Cambrian boundary, which are (in ascending order): Leiosphaeridia Tasmanites assemblage; Retisphaeridium Micrhystridium tentatium assemblage; Baltisphaeridium Bubomorpha hunjiangensis assemblage. A detailed study, concerning the relative abundance of major genera and the variation of acritarch abundance in each acritarch assemblage, has been conducted. The acritarch assemblages of the Kaili Formation are very well correlated with those from Lower and Middle Cambrian elsewhere in the world. It suggests that the boundary between the Early and the Middle Cambrian should be placed at the bottom of layer 9 2 in the Balang section in Taijiang. This boundary defined by the acritarch assemblages is consistent with the boundary marked by the appearance of trilobite Oryctocephalus indicus or the extinction of large number of species of Bathynotus, Redlichia, and Protoryctocephalus. Present study suggests that acritarch assemblages are of particular importance for the biostratigraphy correlation of Cambrian stratigraphy in the area where other index fossils are absent.