Isozaki Yukio, Yao Jianxin, Ji Zhangshen, Saitoh Masafumi, Kobayashi Noritada, Sakai Harutaka
Department of Earth Science and Astronomy, The University of Tokyo, Tokyo, Japan.
Proc Jpn Acad Ser B Phys Biol Sci. 2008;84(8):344-53. doi: 10.2183/pjab.84.344.
The Capitanian (Late Guadalupian) Maokou Formation at Chaotian in northern Sichuan, South China, is composed mainly of shallow marine shelf carbonates deposited on the Tethyan side of South China. By detailed field mapping and scientific drilling, we newly found out unique fossil assemblages and a sharp lithologic change in the upper part of the Maokou Formation. The main part of the Maokou Formation (over 130 m thick) is composed of algal packstone with Wordian-Capitanian large-tested fusulines, rugose corals and other sessile benthos, whereas the Uppermost Member (13 m thick) is composed of black limy mudstone/chert with Capitanian offshore biota (ammonoids, radiolarians, and conodonts). The topmost Capitanian conodont zones are missing; however, the Maokou Formation is disconformably overlain by 260+/-4 Ma volcanic ash (Wangpo bed) and the Early Lopingian Wujiaping Formation with plant-bearing coaly mudstone and shallow marine carbonates (packstone). The newly identified facies change indicates that northern Sichuan has experienced rapid sea-level changes in the late Guadalupian, i.e., first a transgression in the mid-Capitanian and then a regression across the Guadalupian-Lopingian boundary. As the end-Guadalupian is characterized by a global regression, such a volatile sea-level fluctuation, in particular the sea-level rise, is unique to the Tethyan side of South China. The newly recognized relatively deep-water late Guadalupian sequence adds new paleo-environmental information and further provides a paleotectonic interpretation of the low-latitude eastern Tethyan margin immediately before the end-Guadalupian mass extinction.
中国南方四川北部朝天地区的卡匹敦期（瓜德鲁普晚期）茅口组，主要由沉积于华南特提斯洋一侧的浅海陆架碳酸盐岩组成。通过详细的野外填图和科学钻探，我们在茅口组上部新发现了独特的化石组合和明显的岩性变化。茅口组主体部分（厚度超过130米）由含有沃德期 - 卡匹敦期大型房室纺锤蜓、皱纹珊瑚和其他固着底栖生物的藻粘结灰岩组成，而最上部层段（厚度13米）由含有卡匹敦期近海生物群（菊石、放射虫和牙形石）的黑色灰质泥岩/燧石组成。最顶部的卡匹敦期牙形石带缺失；然而，茅口组不整合地被260±4百万年的火山灰（王坡层）和含有植物的含煤泥岩及浅海碳酸盐岩（粘结灰岩）的洛平世早期吴家坪组覆盖。新确定的相变表明，四川北部在瓜德鲁普晚期经历了快速的海平面变化，即在卡匹敦期中段首先是海侵，然后在瓜德鲁普 - 洛平世边界发生海退。由于瓜德鲁普末期以全球海退为特征，这种剧烈的海平面波动，特别是海平面上升，在华南特提斯洋一侧是独特的。新识别出的相对深水的瓜德鲁普晚期层序增加了新的古环境信息，并进一步为瓜德鲁普末期大灭绝前夕低纬度东特提斯洋边缘提供了古构造解释。
