广西中-上泥盆统界线附近的化学地层学特征

中国广西是世界上泥盆系发育最好的地区之一 ,沉积相齐全、出露良好 ,是进行地层学及沉积相研究的理想地区。大乐剖面与马鞍山剖面直线距离约为 7km,根据生物地层学的研究 ,两剖面中 -上泥盆统 (D2 - D3 )界线附近发生了明显的穿时现象。化学地层学的研究表明在这两条剖面上的界线附近 disparilis带内碳同位素组成发生了明显的两次负向波动 ,波动幅度分别可达 1.1‰和 0 .8‰ (马鞍山军田剖面 )和 1.5‰和 1.3‰ (大乐剖面 ) ;两条剖面上该牙形石化石带内及上下地层中元素锶 (Sr)的含量波动趋势同样可以很好地对比 ,本研究结果显示了岩石地层学界线的穿时现象并纠正了以往用岩石地层学特征划定 D2 - D3 界线的错误

CHEMOSTRATIGRAPHIC CHARACTERS OF THE MIDDLE-UPPER DEVONIAN BOUNDARY IN GUANGXI,SOUTH CHINA

Guangxi in South China is one of the best areas in the world where the Devonian with various sedimentary facies is excellently developed. It is an ideal region for studying stratigraphy and facies. The two studied sections, named Maanshan (Juntian) and Dale (Baqi), are several kilometers apart. In the conodont disparilis Zone carbon isotopic compositions shift negatively twice times on both sections, and the Sr content can also be a good correlation marker within this zone 1.1 ‰ and 0.8‰ on the Maanshan (Juntian) section and 1.5‰ and 1.3‰ on the Dale section, respectively. Based on the palaeotonlogi-cal and chemostratigraphic studies, an obviously stratigraphic diachronism near the Middle-Upper Devonian boundary is proved. This result corrects the mistake of the lithological boundary between the M-U Devonian in Guangxi, and suggests that the South China Plate be at a quite stable position around this period.