摘要
1998—2004年间在西藏聂拉木、林周、墨竹工卡和洛扎等地进行的三叠系/侏罗系界线地层研究表明,西藏隆子县和洛扎县尚未发现具有连续菊石层序的三叠系/侏罗系界线地层剖面。拉萨以北地区广泛分布的火山岩时代确定为晚三叠世—早侏罗世早期,这有助于解释晚三叠世末期生物绝灭与晚三叠世岩浆侵入和大规模的火山活动有关,但T/J界线尚待精确限定。聂拉木县格米格剖面是特提斯地区唯一未曾“压缩”的三叠系/侏罗系界线地层剖面,具有瑞替阶MARSHI菊石带、赫塘阶Tibeticum、Callyphyllum和Pleuro-notum菊石带。格米格剖面三叠系/侏罗系界线碳稳定同位素曲线记录了晚三叠世瑞替阶末期(Marshi菊石带)突然的负偏移,它很有可能和晚三叠世末期的由超级温室效应所产生的生物绝灭事件相对应。
Study of the latest Triassic extinction is required to define the Triassic and Jurassic boundary; the field work has recently been carried out in the Nyalam, Linzhou, Muzugongka, Longzi and Lhoza areas, Tibet during the years from 1998-2004. No continuous ammonoid-biostratigraphic sequence across the Triassic and Jurassic boundary has been known from the Longzi and Lhoza areas. Data from the Lhasa block indicate that the late Triassic magmatlc and volcanic activities were likely the cause of the mass extinction, however, the Triassic and Jurassic boundary there requires to exactly define. The ammonoid succession from the Germig section which is the only uncondensed Triassic and Jurassic boundary section in the Tethyan realm, allows to the establishment of the latest Triassic Marshi zone of the Rhaetian, the earliest Jurassic Tibeticum zone of the Hettangian, as well as the Hettangian Calliphyllum and Pleuronotum zones; the end-Triassic mass extinction is coupled with a carbon isotope negative excursion. The relationship implies that the biotic crisis is related to the changes in the global carbon cycle. A pronounced negative excursion is recognized at the T-J boundary between Triassic and Jurassic in coincidence with the end-Triasslc extinction, caused likely by a ＂super greenhouse＂ effect.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2006年第4期244-254,共11页
Earth Science Frontiers
基金
国家自然科学基金资助项目(40072001
40320120168
40572013)
