广西弗拉阶—法门阶之交碳同位素与分子地层对比研究

对广西 7条碳酸盐台地、斜坡和盆地相剖面的碳同位素与分子地层的对比研究表明 ,在牙形石生物地层带或偏心率轨道旋回层建立的等时地层格架内 ,跨越弗拉阶—法门阶 (F—F)之交的碳同位素组成在 1 4Ma内不具一致性 ,表现为正偏、负偏和无偏 3种模式。主要的分子化石包括正构烷烃、类异戊二烯烃、萜类、甾类 ;其母体生物源主要为海源浮游植物、浮游动物、底栖非光合作用的菌类和陆源高等植物。其中浮游植物和浮游动物是构成F—F事件期碳酸盐台地、斜坡和盆地相生物量的主体。分子地层参数及其与碳同位素的关系显示 ,F—F之交广西海域高温、高盐、缺氧、多风 ;Pr Ph与δ1 3C曲线的变化表现为负相关。地层的加积方式 (加积、进积和退积 )、堆积速率、缺氧程度、分子化石类型和丰度是影响广西F—F之交碳同位素组成变化的主要因素。退积序列、快速堆积、缺氧程度和有机质埋藏量增加通常对应δ1 3C值增加。由于分子地层参数能提供生物与环境这两大直接影响碳同位素组成的量化信息 ,因此 ,碳同位素与分子地层的对比研究对正确解释碳同位素的特征和成因具有重要意义

AN INTEGRATED STUDY OF CARBON ISOTOPE AND MOLECULAR STRATIGRAPHY IN THE FRASNIAN-FAMENNIAN TRANSITION OF GUANGXI, SOUTH CHINA

Studies of carbon isotope and molecular stratigraphy on seven sections of carbonate platform slope and basin facies show that there are positive, negative and vertical δ 13 C excursions spanning the Frasnian Famennian boundary within the isochronous chronostratigraphic framework established by conodont biostratigraphy and orbital cyclostratigraphy, and that molecular fossils are dominated by n alkanes, isoprenoids, terpanes and steranes in the Frasnian Famennian transition of Guangxi Province, South China. Molecular fossils are supposed to be derived from marine phytoplankton, zooplankton, benthic bacteria with no photosynthesis and continental higher plants. Dominant marine biomasses are composed of the phytoplankton and zooplankton in the Frasnian Famennian transition. Molecular stratigraphic parameters and their relations to δ 13 C indicate that the marine basin would have higher temperature and hypersalinity; and would be of anoxia and windy; and that there are the negative correlation between Pr/Ph and δ 13 C in the Frasnian Famennian transition of Guangxi Province, South China. Stratigraphic architecture model (aggradation, progradation and retrogradation), sedimentation rates, anoxic degree, types and abundance of molecular fossils are believed to be main influential factors on δ 13 C. Retrogradation sequence, higher sedimentation rate, anoxia and increment of organic carbon burials correspond to positive δ 13 C excursion. Molecular stratigraphic parameters can provide quantitative information on both organism and its environment, which directly influence on δ 13 C, therefore, an integrative study of both carbon isotope and molecular stratigraphy is significant for correct explanation of δ 13 C.