Faunas from the Permian Limestone Blocks at the Yarlung Zangbo Suture Zone in Southern Xizang(Tibet) and Its Paleogeographical Implications
Faunas from the Permian Limestone Blocks at the Yarlung Zangbo Suture Zone in Southern Xizang(Tibet) and Its Paleogeographical Implications
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发表时间：
2005
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通讯作者：
Shen Shuzhong
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作者：
Shen Shuzhong
中国西藏南部雅鲁藏布江缝合带最壮观的特征之一是它含有鹅卵石大小到更大规模的石灰岩块。由于这些区块孤立于周围的基质岩中，没有明显的地层序列，因此对这些区块的起源的解释长期以来一直是一个相当有争议的话题。对这些灰岩块体动物群的研究表明，它们都具有华夏暖水动物群和冈瓦纳冷水动物群的混合特征。雅鲁藏布江缝合带石灰岩块体中的动物群总体上是相似的，因此可能代表了大致相似的沉积环境和古地理背景。这些动物群的范围从早二叠世晚期到长兴期的石灰岩块，可大致分为两个类型的基础上珊瑚，fusulinids和腕足动物。其中一个的特点是优势的孤生珊瑚，没有fusulinids和更多的冷水腕足动物，并可能代表一个古地理环境更接近冈瓦纳边缘。另一个是以复合珊瑚，fusulinids和更多的温水腕足动物的存在为特征，因此表明古地理环境更接近拉萨地块。灰岩块体多为红色或灰色块状生物碎屑灰岩，常与火山岩发生断层或具火山岩基底。因此，这些地块很可能代表了冈瓦纳周边地区外陆架上的一些碳酸盐沉积或新特提斯早期裂谷阶段的海山沉积，但随后在印度和欧亚板块碰撞期间被夹在中/新生代沉积中。
One of the most spectacular features in the Yarlung Zangbo (Indus-Tsangpo) Suture Zone in southern Xizang (Tibet), China, is that it contains pebble-sized to kilometer-scale limestone blocks. Because these blocks are isolated in the surrounding matrix rocks and have no obvious stratigraphical sequences, the interpretations of their origins of the blocks have been the subject of considerable debate for a long time. Studies of the faunas in the limestone blocks suggest that they are all characterized by the mixed characters between the Cathaysian warm-water faunas and the Gondwanan cold-water faunas. The faunas in the limestone blocks in the Yarlung Zangbo Suture Zone, as a whole, are similar one another, and therefore may represent a generally similar sedimentary environment and paleogeographical setting. These faunas range from the late Early Permian to Changhsingian in the limestone blocks and can be largely divided into two types based on corals, fusulinids and brachiopods. One is characterized by the dominance of solitary corals, absence of fusulinids and more cold-water brachiopods, and probably represents a paleogeographical setting closer to the peri-Gondwanan margin. The other is characterized by the presence of compound corals, fusulinids and more warm-water brachiopods and therefore indicates a paleogeographical setting closer to the Lhasa Block. The limestone blocks are mostly composed of reddish or gray massive bioclastic limestone and commonly faulted with volcanic rocks or have a volcanic basement. Therefore, it is most likely that these blocks represent some carbonate deposits on the outer shelves of the peri-Gondwanan region or seamount deposits in the initial rifting stage of the Neo-Tethys, but subsequently sandwiched into the Mesozoic/Cenozoic deposits during the collision between the Indian and Eurasian Plates.