西藏喜马拉雅瑞替阶和赫塘阶菊石组合及其生物年代学对比

基于西藏聂拉木拉弄拉地区的格米格剖面新近逐层采集的菊石及缝合线研究,已识别出晚三叠世瑞替阶Choristoceras marshi组合,过渡带Neophyllites-Choristoceras组合,下赫塘阶Psiloceras calliphyllum组合和中赫塘阶Discamphiceras pleuronotum组合。作为东特提斯唯一的三叠系-侏罗系界线地层剖面,格米格菊石组合序列提供了特提斯范围内三叠/侏罗系界线菊石组合(或菊石带)以及地层对比的基础:Choristoceras marshi组合可以和欧洲,南美的秘鲁和智利的MARSHI菊石带,北美的内瓦达,不列颠哥伦比亚(加拿大)等地CRICKMAYI菊石带比较。Neophyllites-Choristoceras组合可和北美的内瓦达侏罗系底部TILMANNI菊石带Neophyllites和Choristoceras共生动物群比较。Psiloceras calliphyllum组合能够和北阿尔卑斯地区CALLIPHYLLUM菊石带比较, 证明北阿尔卑斯地区三叠系和侏罗系之间存在地层缺失。

Rhaetian and Hettangian Ammonoid Assemblages from the Tibetan Himalayas and Their Pan-Tethyan Correlation

On the basis of new collections from the Lanongla area, Nyalam county, Tibet, Rhaetian and Hettangian ammonoid assemblages are recognized, including the Choristoceras marshi, Neophyllites-Charistoceras, Psiloceras calliphyllum and Discamphiceras pleuronotum assemblages. As the only Triassic and Jurassic boundary section known in the East Tethys, the Germig section provides a biochronological correlation in term of ammonoid assemblage, or zonation in the Tethyan domain; the Choristoceras marshi assemblage is comparable with the MARSHI, or CRICKMAYI Zones of Europe, Peru and Chile, Nevada, British Columbia. Neophyllites and Chorstoceras co-occur in a transitional interval between the Choristoceras marshi and Psiloceras calliphyllum assemblages, which can be likely comparable with that in Nevada of North America where both Neophyllites and Choristoceras appear in the basal Jurassic TILMANNI Zone. The Psiloceras calliphyllum assemblage is most likely equivalent to the CALLIPHYLLUM Zone of North Alps and the PLANORBIS Subzone of Northwest European Province.