云南富宁地区泥盆系—石炭系界线碳、氧同位素特征及对海平面变化的响应

    Carbon and oxygen isotopes across Devonian and Carboniferous boundary in the Funing area of Yunnan Province and the response to sea-level changes

    • 摘要: 右江盆地沉积连续的泥盆纪—石炭纪岩石地层,是中国泥盆纪与石炭纪之交Hangenberg生物大灭绝事件的重点研究区域。选取右江盆地西缘云南富宁地区晚泥盆世—早石炭世地层,在岩石地层学研究的基础上对碳酸盐岩进行系统的碳、氧同位素组成研究。富宁地区晚泥盆世—早石炭世地层存在不同幅度的δ13C、δ18O负向偏移,尤其在泥盆系—石炭系界线附近负偏移明显,δ13C、δ18O值偏移层位与层序地层学转换及古生物灭绝事件发生层位一致,反映了晚泥盆世法门期海平面下降和早石炭世的海侵事件。研究区泥盆系—石炭系界线附近δ13C值负偏趋势与右江盆地内δ13C值演化偏移相似,华南其他典型剖面δ13C值亦呈现不同幅度的负向偏移,泥盆纪与石炭纪之交的碳同位素演化序列与欧洲、北美地区δ13C值负向偏移反映的海平面下降事件一致,具全球性对比意义。

       

      Abstract: Youjiang Basin in which continuous strata from Devonian to Carboniferous were deposited is the key area for the study of Hangenberg biological extinction event between Devonian and Carboniferous in China. The Upper Devonian to Lower Carboniferous strata of Funing area in the western margin of the Youjiang Basin were selected to systematically study carbon and oxygen isotopic compositions of carbonate rocks based on the litho-stratigraphic research. Negative shifts of δ13C and δ18O with different amplitudes exist in the Upper Devonian to Lower Carboniferous in the Funing area, especially near the Devonian-Carboniferous boundary. The layers in which δ13C and δ18O shifts are consistent with the sequence of stratigraphic transformation and paleontological extinction events, which reflected the decline of sea level during the Famennnian stage of the Late Devonian and the transgression events in the Early Carboniferous. The negative δ13C shift near the Devonian-Carboniferous boundary in the study area is similar to the evolutionary shift of δ13C values in Youjiang Basin. The δ13C values in other typical sections in South China all show negative shifts of different magnitudes. The evolutionary sequence of carbon isotopes near the Devonian-Carboniferous boundary is consistent with the sea-level decline events reflected by the offset of δ13C values in Europe and North America, which shows global correlation significance.

       

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