贵州三叠系拉丁阶-卡尼阶界线层牙形石生物地层

对贵州关岭拉丁阶-卡尼阶界线层附近的竹杆坡组和瓦窑组等间距采集牙形石样品,在详细区分牙形石Paragondolella属内各种特征的基础上,结合地层分布情况,认为Paragondolella属在晚拉丁末期沿两个分支方向演化:P.foliatainclinata→P.polygnathiformis→P.maantangensis和P.foliatainclinata→P.foliatafoliata→P.tadpole。从谱系观点出发认为P.polygnathiformis的首次出现点作为卡尼阶底界的标志是合理的,并在竹杆坡剖面首次将拉丁阶-卡尼阶界线置于第2层距底3.38m处,即杨柳井组和竹杆坡组岩石界线以上3.38m处。以上谱系关系的识别也为P.polygnathiformis带细化打下了基础。

CONODONT BIOSTRATIGRAPHY NEAR THE LADINIAN-CARNIAN BOUNDARY INTERVAL IN GUANLING OF GUIZHOU

Conodont samples from the Ladinian-Carnian boundary interval at the Zhuganpo and Maowa sections located in Guanling County,Guizhou Province, were analysed. Based on the transitional characters of the species among the genus Paragondolella and their biogeographic distribution, their evolutionary relationships is discussed. Near the uppermost Late Ladinian P. foliata inclinata branched into two branches: one is P. foliata inclinata→P. polygnathiformis→P. maantangensis; the other is P. foliata inclinata→P. foliata foliata→P. tadpole. In addition, the first occurrence of P. polygnathiformis was regarded as the indicator of the base of the Carnian and the Ladinian-Carnian boundary was first placed 3.38m above the boundary between the Zhuganpo and Yangliujing Formations. The recognition of evolutionary relationship among Paragondolella described above helps to make a subdivision of P. polygnathiformis Zone.