Stratigraphy and Age of the Permian-Triassic Boundary Siliceous Rocks of the Mino Terrane in the Mt. Funabuseyama Area, Central Japan
Stratigraphy and Age of the Permian-Triassic Boundary Siliceous Rocks of the Mino Terrane in the Mt. Funabuseyama Area, Central Japan
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DOI：
10.2517/1342-8144-16.2.124
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发表时间：
2012-07
期刊：
影响因子：
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通讯作者：
H. Sano;Kiyoko Kuwahara;A. Yao;Sachiko Agematsu
中科院分区：
文献类型：
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作者：
H. Sano;Kiyoko Kuwahara;A. Yao;Sachiko Agematsu
抽象的。本文介绍了潘塔拉萨大洋中部海山下侧二叠系-三叠系界线(PTB)硅质岩的岩石和生物地层。研究剖面与本区米诺地体下二叠统上部至下三叠统Hashikadani组对比。日本中部的船尾山地区。岩性序列包括下部单元(厚约6.2m)，下部单元以灰色硅质岩为主，夹杂少量黑色硅质岩和黑色粘土岩；中部单元(约0.7m)以黑色硅质岩为主，顶部辅以黑色粘土岩和灰色硅质岩，包括黄铁矿结核；上部单元(约0.9m)以黑色粘土岩和薄层黑色硅质岩为特征。岩性由中单元向上单元变化剧烈而陡峭。下部单元和中部单元对应于乌家坪上统至长兴统(鸟形新阿尔贝拉到北缘最佳带)。上单元包括下印度河，因为其中部的黑色硅质层产生Hindeodus parvus。这些床也出产Triassospongocyrtis？Sp.，一个原始的中生代类型的Nassellaria，有几种类型的球状海泡虫。二叠纪放射虫在中部和上部单元之间的岩性边界上表现出明显的多样性丧失。我们推测，这一岩性界线标志着二叠纪放射虫的主要灭绝层位。此外，放射虫在这一水平上发生了深刻的动物群更替。在全球界线层型剖面和点(GSSP)的基础上，将PTB定位在上部单元中产H.parvus的硅质层的底部是合理的。然而，将PTB放在这个水平仍然是试探性的，因为上层单位的下部没有年龄诊断化石。另外，为了与新近报道的Hashikadani组PTB段对比，研究段的PTB最好位于中上部单元之间的陡峭岩性边界上。考虑到这种选择，PTB对应于二叠纪放射虫的主要灭绝事件，而这反过来又被认为与重大的环境变化相对应。
Abstract. This paper presents the litho- and biostratigraphy of the Permian-Triassic boundary (PTB) siliceous rocks that accumulated on the lower flank of a seamount in a mid-oceanic realm of the Panthalassa Ocean. The study section correlates with the upper part of the Lower Permian to Lower Triassic Hashikadani Formation of the Mino terrane in the Mt. Funabuseyama area, central Japan. The lithologic succession comprises a lower unit (ca. 6.2 m thick) dominated by gray chert with small amounts of black chert and black claystone, middle unit (ca. 0.7 m) of black chert with subordinate black claystone and gray chert including pyrite nodules near the top, and upper unit (ca. 0.9 m) characterized by black claystone with thin black chert beds. The lithologic change from the middle unit to the upper unit is sharp and abrupt. The lower and middle units correlate to the upper Wuchiapingian to Changhsingian (Neoalbaillella ornithoformis to N. optima zones). The upper unit includes the lower Induan, as the black chert bed in its middle part yields Hindeodus parvus. These beds also yield Triassospongocyrtis? sp., a primitive Mesozoic-type Nassellaria, with several types of the sphaeroid spumellarians. The Permian radiolarians exhibit a marked loss in diversity across the lithologic boundary between the middle and upper units. We hypothesize that this lithologic boundary marks the main extinction horizon of the Permian radiolarians. Also a profound faunal turnover of radiolarians occurred at this level. On the basis of the Global Boundary Stratotype Section and Point (GSSP) designation, it is reasonable to position the PTB at the bottom of the H. parvus-yielding chert bed in the upper unit. Nevertheless placing the PTB at this level remains tentative, because age-diagnostic fossils are absent from the lower part of the upper unit. Alternatively, with the emphasis upon correlation with the recently reported PTB section of the Hashikadani Formation, the PTB of the study section is preferably positioned at the sharp lithologic boundary between the middle and upper units. Given this alternative, the PTB corresponds to the main extinction event of Permian radiolarians, which, in turn, is thought to correspond to significant environmental changes.