贵州台江早、中寒武世凯里组的疑源类

EARLY—MIDDLE CAMBRIAN ACRITARCHS IN THE KAILI FORMATION FROM TAIJIANG COUNTY, GUIZHOU, CHINA

产凯里生物群的台江八郎剖面凯里组疑源类组合包含 18形态属 ,2 0形态种和 11未定种 ,疑源类化石以无明显附属突起的球形亚类和翼环亚类最多 ,网面和棘剌亚类次之 ,而梭形亚类和对弧亚类很少。具有明显装饰的疑源类类型Micrhystridium ,Retisphaeridium ,Goniophaeridium仅在第 9层、第 2 1— 2 4层出现。在与国内外同期疑源类对比的基础上 ,对下、中寒武统界线进行了划分 ,划分的界线与三叶虫划分的界线位置大体一致 ,并根据疑源类组合特征 ,对沉积环境进行探讨。

The Early—Middle Cambrian acritarchs have been extracted from the Kaili Formation at the Balang section in Taijiang County, Guizhou Province, 31 species belonging to 18 genera are described in this paper. Acritarchs of Sphaeromorphitae and Pteromorphitae in the Kaili Formation. occur rather frequently, Hercomorphitae and Acanthomorphitae occur in proper order, Netromorphitae and Diacromorphitae are rare. Sphaeromorphic vesicles with distinct processes and polygonal net, such as Micrhystridium, Dictyotidium, Retisphaeridium, Goniosphaeridium only occur in No.9 layer and No.20—24 layers of the Kaili Formation. In addition, the above horizons contain abundant thin walled specimens of Leiosphaeridia , and it might imply that the shallow marine condition were dominated some times. In comparison with known acritarch assemblages from Early—Middle Cambrian deposits elsewhere in the world, since more typical Middle Cambrian acritarchs, such as Cristallinium cambriense, C.dubium, Micrhystridium brevicornum, M.pallidum, first occur in No.9 layer of the Kaili Formation., the Lower—Middle Cambrian boundary could be suggested at the base of No.9 layer of the Kaili Formation. This tentative boundary between Lower and Middle Cambrian, based on the remarkable change of acritarch assemblage, roughly coincides with the boundary drawn from trilobites, i.e. at the base of Xingrenaspis Oryctocephalus Zone (Zhao et al., 1994; Yuan et al., 1997).