西藏申扎地区晚石炭世牙形石Neognathodus动物群的特征及其意义

藏北申扎地区永珠组中上部发现了Neognathodus牙形石动物群,自下而上划分为Neognathodus cf.symmetricus-N.cf.asymmetricus组合、Neognathodus medadultimus-N.medexultimus-N.roundyi组合、Rhachistognathus sp.A-Neognathodus ultimussp.nov.组合。上述牙形石动物群指示永珠组中上部的时代为晚石炭世巴什基尔阶中期—莫斯科阶晚期。该牙形石动物群与俄罗斯地台区、北美地区和华南地区比较,显示出低分异度和低丰度的特点,表明该地区当时的生态环境并不十分利于牙形石生长,可能是当时该地区处于南半球中高纬度附近、水体温度偏冷所致。

The Late Carboniferous conodont Neognathodus fauna in Xainza, Tibet, China, and its significance

The conodont Neognathodus fauna is found in the middle and upper parts of the Yunzhug Formation in Xainza County, northern Tibet. Three assemblage zones are distinguished; they are in ascending order the Neognathodus cf. symmetricus-N. cf. asymmetricus Assemblage Zone, N. medadultimus-N. medexultimus-N. roundyi Assemblage Zone and Rhachistognathus sp. A-Neognathodus ultimus sp. nov. Assemblage Zone. The above-mentioned Neognathodus fauna suggests that the strata in question are Late Carboniferous middle Bashkirian to late Moscovian in age. The correlation of the fauna with those in the Russian platform, North America and South China shows that the fauna is characterized by low diversity and low abundance, suggesting that the eco-environment at that time was not quite favorable for the growth of conodonts, possibly because this area was located near the medium-high latitudes of the southern hemisphere then, where the temperature of the seawater was slightly cold.