CARBON ISOTOPE PROFILES AND THEIR CORRELATIO ACROSS THE NEOPROTEROZOIC-CAMBRIA BOUNDARY INTERVAL ON THE YANGTZE PLATFORM, CHINA

Analysis of the stable carbon isotope profiles of the Xiaoran, Meishucun, Maidiping and Tianzhushun sections through the Neoproterozoic-Cambrian boundary interval indicates that there are two sharp drops and two rises in δ^(13)C values between the top of the Upper Sinian Dengying Formation and the Lower Cambrian Yu'anshan Formation . Listed in ascending order, the four carbon isotope excursions are: 1. negative shift in δ^(13)C values at the base of the Daibu Member; 2. rapid increase in δ^(13)C values from the upper Zhongyicun Member to the Dahai Member; 3. sharp decrease in δ^(13)C (from positive to negative) at the base of the Shiyantou Formation; and 4. positive δ^(13)C excursion through the Yu'anshan Formation. These four pronounced excursions respectively, correlate with the biostratigraphical markers A, B, C and D respectively in the Neoproterozoic-Cambrian boundary section at Meishucun. The positive δ^(13)C excursion from the upper Zhongyicun Member to the Dahai Member is equivalent to the positive excursion through the Nemarkit-Daldynian or pre-Tommotiun δ^(13)C rise on the Siberian Platform. The Dahai positive excursion event suggests that the Meishucun Formation (including the Daibu, Zhongyicun, and Duhai Members) predates the Tommotian.

關鍵字

Stable carbon isotope stratigraphy ； Ncoproterozoic-Cambrian boundary ； Yangtze Platform

並列摘要

通過雲南省肖灘與梅樹村、四川峨嵋麥地坪和峽東天柱山末元古系－寒武系界線剖面同位素地層學對比表明，從震旦系燈影組頂部至下寒武統節竹寺組玉案山段碳酸鹽岩δ^13C值出現二次突降和二次上升：1. 小歪頭山段底負漂移；2. 中宜村段至上部大海段δ^13C値大幅度上升；3. 石岩頭段底快速下降，向負値漂移；4. 玉案山段出現上升趨勢。這四次δ^13C值突然變化與早期骨骼化石生物地層分帶一致，它們分別出現在相當於梅樹村剖面末元古系－寒武系界線參考點：A、B、C、D點位置附近。其中，中宜村段上部（B點）至大海段頂（C點之下）δ^13C值上升相當於俄羅斯西伯利亞早寒武世Nemakit - Daldyn正漂移或前托莫特階δ^13C上升。大海正漂移事件表明湞東地區梅樹村組（包括小歪頭山段、中宜村段和大海段）的時代老於托莫特階。

並列關鍵字

碳同位素地層學；末元古系－韓五系界線；揚子地台

國際替代計量

CARBON ISOTOPE PROFILES AND THEIR CORRELATIO ACROSS THE NEOPROTEROZOIC-CAMBRIA BOUNDARY INTERVAL ON THE YANGTZE PLATFORM, CHINA

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