| 西藏色龙西山色龙群的时代及二叠系与三叠系的界线 |
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| 摘 要： | <正> 色龙群于1964年由希夏邦马峰登山队科学考察队(1982)命名,层型剖面在聂拉木县色龙村西北约1km的小山上,时代为二叠纪。穆恩之等(1973)认为色龙群的时代属早二叠世晚期。章炳高(1974)、吴望始(1975)、张守信、金玉玕(1976),王玉净、穆西南(1984)对色龙群的时代有类似的看法,均未提及它包含有长兴期地层的存在。饶荣标等(1985)将色龙群分为两组,上部为扒嘎组,下部为门多组。在色龙西山剖面,扒嘎组为生物碎屑灰岩,厚4.15m,含Gertholites curvatus,Thamnopora densa,Pseudofavosites irregularis,Trachypora sp.,Sinkiangopora sp.,时代属晚二叠世,与上覆下三叠统土隆组为整合接触。
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Age of the Selong Group in Xishan,Selong of Xizang and the Permian-Triassic boundary |
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| Abstract: | It has long been a controversial subject whether the Permian-Triassic strata in the Selo-ng-Xishan section are continuous or not. Established in this section are four conodont zones, the "Pre-changsingian" Neogondolella bisselli Assemblage-Zone, the "Changsingian" N. betteri Zone and N. rosenk.rantzi Zone and the Greisbachian N. carinata Assemblage-Zone. A conclusion has been drawn that 1) The "Pre-changsingian" in the upper part of the Selong Group is Middle Permian in age; 2) The "Changsingian" in the uppermost part of the Selong Group is Late Permian Wuchiapingian; 3) There is a major hiatus between the "Pre-changsingian" and the Changsingian" and all or a part of the Maokouan may be lacking; 4. At the bottom of the Greisbachian, the ammonoid Otoceras latilobatum Zone is not the bottommost biozone of Lower Triassic age because below the ammonoid zone there should be a lowest Triassic conodont Hindeodus parvus Zone (non "parvus-Zone" sensus Wang et al., 1989), which is absent in the study section; 5) The whole Maokouan and the middle and. upper parts of the Wuchiapingian in the Late Permian have been recognized as a major hiatus, and the uppermost Permian is lacking. Consequently, the Selong-Xishan section can not be us ed as an adquate potential global stratotype of the Permian-Triassic boundary as proposed by Wang Yigang and others at the 28th International Geological Congress in 1989. |
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