贵州兴义地区下三叠统嘉陵江组牙形石生物地层及碳同位素记录

CONODONT BIOSTRATIGRAPHY AND CARBON ISOTOPE RECORD OF THE LOWER TRIASSIC JIALINGJIANG FORMATION IN XINGYI COUNTY, GUIZHOU PROVINCE

扬子地台嘉陵江组的海相碳酸盐岩地层记录了当时海水的碳同位素变化。贵州兴义地区位于扬子地台西南缘,根据岩性、岩相,嘉陵江组划分为四段,以开阔-局限台地相碳酸盐岩沉积为特点,牙形石生物地层可划分出Parachirognathus-Pachycladina和Neospathodus homeri-N. triangularis牙形石组合带,时代归属于早三叠世奥伦尼克期。该区坝佑和龙广2条典型嘉陵江组剖面上采集的25件碳酸盐岩样品进行碳同位素测试表明,δ13C值介于-1.7‰~5.9‰,包括2个完整的下降-上升旋回,其高频率的震荡变化是二叠纪生物大灭绝之后生物复苏延迟的直观体现,表现为海洋环境的不稳定性对全球碳循环的影响。

The lower Triassic carbonates of the Jialingjiang Formation preserve carbon isotopic record of coeval seawater of the Yangtze Platform, China. The Jialingjiang Formation from the southwestern margin of Yangtze Platform in Xingyi of Guizhou Province is characterized by carbonate deposits of an open-restricted platform facies dduring the Olenekian of the Early Triassic, and can be subdivided into four parts. Two conodont zones are recognized in ascending order as follows: Parachirognathus-Pachycladina Zone and Neospathodus homeri-N.triangularis Zone. Carbon isotope data were obtained from 25 carbonate samples from the Jialingjiang Formation of the Bayou and Longguang sections. The values of the ?13 C include two complete cycles from downtrend to uptrend, changing from –1.7‰ to 5.9‰. Fluctuation of the carbon isotope can be attributed to the instability of marine environment that resulted in the delay biotic recovery from the end-Permian extinction.