西藏羌塘南部发现奥陶纪—泥盆纪地层

Discovery of Ordovician-Devonian strata in the south of the Qiangtang area, Tibet

西藏羌塘地区出露大面积的浅变质岩,由于没有获得可靠化石等年代证据,地层的时代归属争议很大。笔者等在冈塘错以北的塔石山发现了头足类、海百合茎、笔石和竹节石等化石。经初步鉴定,头足化石有Sinoceras,Miche-linoceras,Wennanoceras,Archigeisonoceras等;笔石主要是单笔石类。Sinoceras-Michelinoceras组合是中奥陶世宝塔期的标准化石,头足类化石主要反映中奥陶世的面貌。在含中奥陶世头足类化石的层位之下,有数十米不含化石的碎屑岩,可能是早奥陶世的沉积。羌南地区奥陶纪—泥盆纪生物和地层的发现,为与邻区地层划分对比和探讨羌塘构造演化提供了重要依据。

Low-grade metamorphic rocks are exposed extensively in the Qiangtang area, Tibet. There is a great dispute about the age of the strata because of no reliable fossil evidence and other chronological evidence. Cephalopods, crinoids, graptolites and tentaculites fossils are discovered at Tashi Hill north of Gangtang Co. Primary identification indicates that the cephalopod is Sinoceras,Michelinoceras, Wennanoceras, Archigeisonoceras etc. and the crinoid is Monograptus. The Sinoceras-Michelinoceras assemblage is the key fossil assemblage of Mid Ordovician Baotaan age, which reflects the Mid Ordovician aspects. There are several tens of meters of fossil-free clastic rocks below the Mid Ordovician cephalopod-bearing horizon, which are probably Ordovician sediments. The discovery of Ordovician-Devonian biotas and strata provide new important evidence for the stratigraphic division and correlation and the study of the tectonic evolution of the Qiangtang area.