晚泥盆世弗拉斯期—法门期之交海水温度变化的同位素证据

Isotopic Evidence for the Temperature Change of the Paleo-Ocean between Late Devonian Fransnian Period and Famennian Period in South China

位于我国湖南省冷水江地区锡矿山矿区的老江冲剖面为发育良好的浅水台地相沉积 ,出露著名的上泥盆统弗拉斯—法门阶 (Fr/Fa)界线 ,多年的地层古生物学工作已详细地了解了该区的古生物面貌。本研究采用了基本保存完好的腕足动物Cyrospirifervernemili壳体进行了稳定C、O同位素地球化学分析 ,δ18O值为 - 8.4‰～- 9.6‰ ;δ13C值为 - 2 .2‰～ 0 .5‰ ,二值在弗拉斯—法门阶交界处均发生了异常波动 ,将此值与其他地区的研究结果进行比较 ,可以认为 ,弗拉斯—法门期交界时所发生的剧烈而大范围的事件所造成的同位素波动可以作为大区域地层对比的标志。经过计算 ,推断从弗拉斯期末至法门期初 ,我国华南地区的古海洋发生了降温事件。

The shallow platform sedimentary facies is well developed along the Laojiangchong section in Xikuangshan mine,Lengshuijiang area,Hunan Province,which includes the well known Upper Devonian Fransian Famennian(Fr/Fa) boundary.Long period of field studies and researches led the authors to reveal the palaeotnologyaswellassedimentaryassociationsandcharacteristics.TheshellsofbrachiopodCyrospirifer vernemili were analysed isotopically and by SEM in this study.The carbon and oxygen isotopic analyses ( δ 18 O:-8.4‰～-9.6‰; δ 13 C: -2.2‰～0.5‰) show an abnormal shift around the boundary of Fr/Fa in South China,which can serve as a standard of regional stratigraphic correlation.Depending on the calculation of oxygen isotopes within the well preserved brachiopods,the authors drew the inference about temperature decreasing from late Fransian to early Famennian.