Lopingian (Late Permian) stratigraphy, sedimentation and palaeobiogeography in southern Tibet
Lopingian (Late Permian) stratigraphy, sedimentation and palaeobiogeography in southern Tibet
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DOI：
10.1127/nos/39/2003/157
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发表时间：
2003-03
影响因子：
2.2
通讯作者：
S. Shen;Changqun Cao;G. Shi;Xiangdong Wang;Shilong Mei
中科院分区：
文献类型：
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作者：
S. Shen;Changqun Cao;G. Shi;Xiangdong Wang;Shilong Mei
对西藏南部雅鲁藏布江缝合带内二叠纪 - 三叠纪地层剖面以及零散分布的石灰岩块的研究表明，乐平统地层广泛分布。乐平统沉积层顶部大多含有丰富的腕足动物化石以及长兴期末期深沟牙形石（Mesogondolella shenz）带的特征牙形石。腕足动物组合与巴基斯坦盐岭的上瓦尔加尔组和奇德鲁组、克什米尔的泽万组、印度斯皮提的库林群上部以及西澳大利亚的哈德曼组中的已知组合大体相似。对西藏南部色龙群及其相当层位提出了修订后的乐平世（晚二叠世）年龄。西藏南部的乐平统沉积可分为三种不同的沉积类型，每种类型都反映了冈瓦纳北缘从滨海到大陆架环境的不同沉积环境。曲布型层序代表了海平面逐渐上升期间的滨海和近岸障壁 - 泻湖沉积。在乐平世晚期海平面下降期间发育了具有丰富孢粉和疑源类的退积成因的云母砂岩和页岩，随后在二叠纪末期发生了一次大规模的快速海侵。色龙地区的色龙型层序下部由生物碎屑灰岩和钙质页岩组成，上部由海百合颗粒岩组成。上部被认为是在高能的内陆架浅滩环境中形成的。赤土春型层序作为小石灰岩块零星分布在雅鲁藏布江缝合带沿线，由含菊石Cyclolobus动物群的纯生物碎屑亮晶灰岩组成。它被解释为海山和/或在外陆架环境中发育的小型孤立碳酸盐建隆的破碎产物。
Investigations of the Permian-Triassic sections and limestone blocks scattered in the Indus-Tsangbo Suture Zone in southern Tibet show widespread distribution of the Lopingian strata. The Lopingian deposits mostly contain rich brachiopod fossils and characteristic conodonts of the Mesogondolella shenz Zone of latest Changhsingian age in the topmost part. Brachiopod assemblages are largely comparable with those known from the upper Wargal and Chhidru Formations of the Salt Range, Pakistan, the Zewan Formation of Kashmir, the upper part of the Kuling Group in Spiti of India and the Hardman Formation of Western Australia. A revised Lopingian (Late Permian) age is proposed for the Selong Group and its equivalents in southern Tibet. The Lopingian deposits in southern Tibet can be grouped into three different sedimentary types, each of which reflects different sedimentary environments from coastal to continental shelfal settings on the northern peri-Gondwanan margin. The Qubu-type sequence represents marine coastal and proximal barrier-lagoon sediments during a gradual sea-level rise. Micaceous sandstone and shale of regressive origin, with abundant palynomorphs and acritarches, developed during the Late Lopingian sea-level lowstand, which is followed by a major rapid transgression at the very end of Permian. The Selong-type sequence in the Selong area consists of bioclastic limestone and calcareous shale in the lower part, and crinoid grainstone in the upper part. The latter part is believed to have been formed in a high-energy inner shelf shoal setting. The Chitichun-type sequence, sporadically distributed along the Indus-Tsangbo suture zone as small limestone blocks, consists of pure bioclastic sparite with the ammonoid Cyclolobus fauna. It is interpreted as the break-up products of sea-mounts and/or small isolated carbonate build-ups developed on the outer shelfal settings.