贵州新民石门坎三叠系关岭组底部火山凝灰岩锆石U-Pb年龄及意义

华南地区三叠系地层发育,安尼阶底界（即下—中三叠统界线）附近广泛发育浅绿色火山凝灰岩或凝灰质碎屑岩,俗称 “绿豆岩”。国际安尼阶底界界线层型候选剖面——位于南盘江盆地内的贵州关刀剖面和广西湾头剖面,已获得可对比的“绿豆岩”锆石U-Pb年龄,但在相邻的上扬子台地上尚缺少对安尼阶底界测年的可对比数据。本研究采集了贵州省盘州市新民镇石门坎剖面三叠系关岭组底部的多层“绿豆岩”,利用LA-ICP-MS获得锆石的U-Pb年龄。结果显示,石门坎剖面关岭组底部的锆石结晶年龄为246.9±1.1 Ma,可与南盘江盆地内及上扬子台地区出露安尼阶底界的剖面相对比。其绝对年龄为上扬子台地区内的安尼阶底界年龄对比提供了参照,有助于限定中三叠世海生爬行动物群所代表的海洋生态系统的复苏时间。石门坎剖面地层沉积连续,未来有望继续开展综合地层学的研究。     

Biodiversity and Sequence of the Middle Triassic Panxian Marine Reptile Fauna, Guizhou Province, China

Abstract: The Middle Triassic Panxian fauna is a physical marker and representative record of the rapid recovery of the Triassic marine ecosystem following the Early Triassic stagnant stage after the end-Permian mass extinction. Ten marine reptile taxa have been found from the 1.82–2.10 m-thick fossiliferous level in the Upper Member of the Guanling Formation, which can be subdivided into three marine reptile beds through the analysis on the stratigraphic distributions of fossil reptiles. The Lower Reptile Bed yields the sauropterygians Placodus inexpectatus Jiang et al., 2008 and Lariosaurus hongguoensis Jiang et al., 2006, the ichthyopterygians Xinminosaurus catactes Jiang et al., 2008 and Phalarodon cf. Phalarodon fraasi Merriam, 1910, associated with Mixosaurus panxianensis Jiang et al., 2006, representing a stage of predominance of durophagous taxa. In this bed, the large complete skeletons may reach up to 2.3 m in length, and lithofacies and chemostratigraphic analyses indicate a relatively deep carbonate platform with an oxic water environment near the bottom, as well as a rising sea level. The Middle Reptile Bed yields the sauropterygian Nothosaurus yangjuanensis Jiang et al., 2006 and the archosaur Qianosuchus mixtus Li et al., 2006, associated with Mixosaurus panxianensis Jiang et al., 2006. The fossils in this bed are characterized by its pincering dentition and large overall body size, with the largest possibly exceeding 3 m in length. This bed might represent a time of deepest basin with relatively anoxic condition near the bottom. The Upper Reptile Bed yields the sauropterygians Wumengosaurus delicatomandibularis Jiang et al., 2008, Keichousaurus sp., the protorosaur Dinocephalosaurus orientalis Li, 2003, and the ichthyopterygian Mixosaurus panxianensis Jiang et al., 2006. In this bed, reptilian taxa characterized by suction feeding appeared, and most are less than 1 m long. This bed corresponds to a period of decreasing water depth.     

湖北省南漳/远安动物群特征及其意义初探

通过资料整理和野外调查,本文认为南漳/远安动物群是产自于嘉陵江组三段顶部纹层状灰岩、微晶灰岩中,以海生爬行动物为特色,伴有大量菌藻类和软体动物的早三叠世奥伦尼克期Spathian晚期的动物群落。该动物群中的海生爬行动物为幻龙类-鱼龙类-汉江蜥-贵州龙-湖北鳄类的组合特征。湖北鳄类相对其他海生爬行动物类型,数量最多,多样性最为丰富。独特的骨骼特征暗示其位于脊椎动物食物链的最低层。大量分异度较高的海生爬行动物在同一群落中出现,暗示在Spathian晚期,海洋生态系统可能已经开始恢复。     

贵州新民石门坎三叠系关岭组底部火山凝灰岩锆石U-Pb年龄及意义

华南地区三叠系地层发育,安尼阶底界（即下—中三叠统界线）附近广泛发育浅绿色火山凝灰岩或凝灰质碎屑岩,俗称 “绿豆岩”。国际安尼阶底界界线层型候选剖面——位于南盘江盆地内的贵州关刀剖面和广西湾头剖面,已获得可对比的“绿豆岩”锆石U-Pb年龄,但在相邻的上扬子台地上尚缺少对安尼阶底界测年的可对比数据。笔者采集了贵州省盘州市新民镇石门坎剖面三叠系关岭组底部的多层“绿豆岩”,利用LA-ICP-MS获得锆石的U-Pb年龄。结果显示,石门坎剖面关岭组底部的锆石结晶年龄为246. 9±1. 1 Ma,可与南盘江盆地内及上扬子台地区出露安尼阶底界的剖面相对比。其绝对年龄为上扬子台地区内的安尼阶底界年龄对比提供了参照,有助于限定中三叠世海生爬行动物群所代表的海洋生态系统的复苏时间。石门坎剖面地层沉积连续,未来有望继续开展综合地层学的研究。     

Guanling Biota: A Marker of Triassic Biotic Recovery from the end-Permian Extinction in the Ancient Guizhou Sea

After a slow recovery from the end-Permian extinction during the Early Triassic and rapid radiation in the Middle Triassic, evolution of organisms reached a new peak phase in the Late Triassic. The Guanling Biota from the Wayao Member （conodont Paragondolella polygnathiformis Zone）, Falang Formation, Xinpu, Guanling County, Guizhou Province, southwestern China corresponds to this peak that marks the full recovery from the end-Permian extinction of marine ecosystems. The biota is of high diversity, containing well preserved and completely articulated skeletons of vertebrates comprising marine reptiles, fishes, and invertebrates including crinoids, ammonites, bivalves, and other fossils, and is one of the best examples of marine ecosystem records in life history. The fossil marine reptiles and crinoids are most significant in this biota, especially the marine reptiles, which provide an important link between the Triassic Pacific and Tethys, and between Triassic basal forms and the Jurassic-Cretaceous marine top predators. The most remarkable fossils are the large completely articulated ichthyosaur skeletons up to and more than 10 m, and the first recorded thalattosaurs and placodonts in China. Following our review, of the 17 named reptilian taxa the eight listed here are considered to be valid： three ichthyosaurs （Qianichthyosaurus zhoui Li, 1999; Guizhouichthyosaurus tangae Cao and Luo in Yin et al., 2000, Guanlingsaurus liangae Yin in Yin et al., 2000）, three thalattosaurs （Anshunsaurus huangguoshuensis Liu, 1999, Xinpusaurus suni Yin in Yin et al., 2000, Xinpusaurus kohi Jiang et al., 2004）, and two placodonts （Sinocyamodus xinpuensis Li, 2000, Psephochelys polyosteoderma Li and Rieppel, 2002）. Mixosaurus guanlingensis Cao in Yin et al., 2000 might be a junior synonym of Qianichthyosaurus zhoui Li, 1999, and Cymbospondylus asiaticus Li and You, 2002 and Panjiangsaurus epicharis Chen and Cheng, 2003 might be junior synonyms of Guizhouichthyosaurus tangae Cao and Luo in Yin et al., 2000. It needs to re-describe the holotypes after a complete preparation for clarifying the taxonomic status of Typicusichthyosaurus tsaihuae Yu in Yin et al., 2000, Xinpusaurus bamaolinensis Cheng, 2003, Neosinosaurus hoangi （Zhou in Yin et al., 2000）, Wayaosaurus geei Zhou in Yin et al., 2000, Wayaosaurus bellus Zhou in Yin et al., 2000 and Placochelys ？ minutus Yin and Luo in Yin et al., 2000.