Early-Middle Triassic boundary interval: Integrated chemo-bio-magneto-stratigraphy of potential GSSPs for the base of the Anisian Stage in South China
Early-Middle Triassic boundary interval: Integrated chemo-bio-magneto-stratigraphy of potential GSSPs for the base of the Anisian Stage in South China
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DOI：
10.1016/j.epsl.2019.115863
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发表时间：
2020-01
影响因子：
5.3
通讯作者：
Yan Chen;Haishui Jiang;J. Ogg;Yang Zhang;Yifan Gong;Chunbo Yan
中科院分区：
文献类型：
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作者：
Yan Chen;Haishui Jiang;J. Ogg;Yang Zhang;Yifan Gong;Chunbo Yan
摘要广西湾头和右坪剖面的岩石地层、火山事件、牙形石首次出现、菊石生物地层、地磁极性、无机碳同位素、牙形石-磷灰石氧同位素反演的海面温度和ID-TIMS U-Pb放射性定年等资料，提供了一个详细的早-中三叠世界线序列的高分辨率综合标定。上Spathian（早三叠世晚期）磁性地层学的特点是正常极性（magnetozone LT 9 n），包括典型的Spathian牙形刺Triassospathodus homeri和Gladigondolella carinata的FO，晚期Spathian Neopopanoceras haugi菊石带和无机碳同位素的逐步正移的开始。上覆的反极性间隔（LT 9 r）包含两个简短的正常极性子带（MT 1 n和MT 2n），可以在其他几个海洋和陆地部分中识别。Chiosella timorensis sensu stricto牙形刺的FO位于MT 1 n附近，接近δ 13 C碳正漂移的末端，是一个被认为是基-阿尼西亚族的全球标志。据报告，在δ 13 C碳水化合物上升期间，海面温度下降了4° C，表明二氧化碳被封存。湾头和油坪的最低层Anisian以正极性为主（MT3 n），并存在一个主要的反极性亚带MT3 n。1 r），含有典型的Anisian牙形刺（Gladigondolella tethydis/Magnigondolella alexanderi）的FO，无机碳同位素值开始出现平台（稳定在+ 4‰左右）。牙形石Chiosella timorensis ss.的FO，短的正常极性带（MT 1 n）和碳同位素上升趋势的最后部分适合作为早-中三叠世界线（Anisian基底）与其他海相和非海相背景全球对比的主要代用指标。湾头剖面和官道剖面的放射性测年，结合早三叠世至阿尼西期的复合旋回地层，表明牙形石Chiosella timorensis ss.大约是246.7 Ma。
Abstract The Wantou and Youping sections of Guangxi, South China provide a detailed high-resolution integrated calibration of the Early-Middle Triassic boundary succession for lithostratigraphy, volcanic episodes, conodont first occurrences (FOs), ammonoid biostratigraphy, geomagnetic polarity, inorganic carbon isotopes, sea-surface temperatures derived from conodont-apatite oxygen-isotopes, and ID-TIMS U–Pb radiometric dating. The upper Spathian (late Early Triassic) magnetostratigraphy is characterized by normal polarity (magnetozone LT9n) that encompasses the FOs of the typical Spathian conodonts Triassospathodus homeri and Gladigondolella carinata, the late Spathian Neopopanoceras haugi ammonoid zone and the beginning of a progressive positive shift in inorganic carbon isotopes. The overlying reversed polarity interval (LT9r) contains two brief normal-polarity subzones (MT1n and MT2n) that can be recognized in several other marine and terrestrial sections. The FO of conodont Chiosella timorensis sensu stricto, a proposed base-Anisian global marker, is near MT1n and near the end of the positive δ 13 C carb excursion. Sea-surface temperatures were reported to have cooled by 4° C during this rise in δ 13 C carb, suggesting a sequestration of carbon dioxide. The lowermost Anisian at Wantou and Youping is dominated by normal polarity (MT3n, with the presence of one major reversed-polarity subzone MT3n. 1r), contains the FO of typical Anisian conodonts (Gladigondolella tethydis/Magnigondolella alexanderi), and has the onset of a plateau in inorganic carbon isotopes values (stabilizing around+ 4‰). The combination of the FO of conodont Chiosella timorensis ss., the brief normal polarity zone (MT1n) and the last portion of the rising carbon-isotope trend are suitable for primary proxies for global correlation of the Early-Middle Triassic boundary (base of Anisian) to other marine and non-marine settings. Radiometric dates at the Wantou and at the Guandao sections, coupled with a composite cyclostratigraphy for Early Triassic through Anisian, indicate that the FO of the conodont Chiosella timorensis ss. is at approximately 246.7 Ma.