贵州省兴义地区中三叠世兴义动物群化石储集层古环境初步分析

Preliminary Analysis of Environment of Fossils Reservoir of Xingyi Fauna in Guizhou Province

通过野外剖面观察、测量、取样和室内工作,对贵州省兴义市乌沙镇泥麦古村爆竹厂剖面中三叠统法郎组竹杆坡段兴义动物群化石储集层碳酸盐岩的沉积微相、碳氧同位素进行初步分析,探讨其沉积环境及其变化。识别出5种微相类型:均质泥质微晶灰岩、含少量生物碎屑的泥质微晶灰岩、含丰富破碎生物碎屑的泥质微晶灰岩、含丰富完整生物碎屑的泥质微晶灰岩以及水平纹层状泥晶灰岩。结合前人的工作,推断该地区在拉丁期经历局限海、开阔海、台内盆地3种环境,整体为一个海进过程。δ13C和δ18O普遍偏低,δ13C在化石层出现明显负漂移。综合微相、沉积相及碳氧同位素特征,推断兴义动物群生活在局限海且海水温度相对偏高的环境中。

Based on the field investigation on the Zhuganpo Member of Falang Formation at Wusha of Xingyi, Guizhou Province, lithofacies analysis in the laboratory, and the analysis of values of the δ13C and δ18O were conducted to reconstruct the paleoenvironmental background of the Xingyi Fauna. Five microfacies for this carbonate bed were recognized： homogeneous argillaceous micrite, muddy microcrystalline limestone containing a small amount of bioclastic, muddy microcrystalline limestone containing a mass of broken bioclastic, muddy microcrystalline limestone containing a mass of intact bioclastic, and horizontal laminated micrite. Combined with previous research, three sedimentary facies： restricted sea, open sea and interplatform basin can be reconstructed, which indicates a transgression in Ladinian age in this region. The values of the δ13C and δ18O are generally low in the whole of the carbon and oxygen isotope curves, and δ13C value appears obvious negative drift in the fossil bed. Combined with the features of the microfacies, sedimentary facies and the carbon and oxygen isotope curves, it can be found that the environment where the Xingyi Fauna lived in was restricted sea and relatively high seawater temperature