从综合地层学观点论华南浅海相泥盆系—石炭系的分界

ON THE DEVONIAN-CARBONFEROUS BOUNDARY OF NERITIC FACIES AREAS IN SOUTH CHINA FROM A SYNTHETIC STRATIGRAPHICAL VIEWPOINT

生物地层学、事件地层学和层序地层学综合研究表明,华南浅海相区与Siphon-odella praesulcata带和S.sulcata带之间的界线相当的泥盆系—石炭系的界线不仅高于Cystophrentis带顶界,而且还应高于引起Cystophrentis绝灭的海退事件层的顶界。建议以Cytophrentis-Pseudouraloma间隔带中最明显的一个海进面,即本文的SQ1的海进体系域的底界作为华南浅海相区泥盆系—石炭系界线。这条界线与泥盆纪—石炭纪之交海退事件层的顶界正好一致,大致相当于Pseudouralina组合带底部。

In the present paper an attempt is made to discuss the Devonian-Carboniferous Boundary (DCB) of neritic areas in South China based on a combined study of biostratigraphy, event stratigraphy and sequence stratigraphy.Biostratigraphical data indicate that in the neritic facies areas of South China, the DCB marked by the first appearance of Siphonodella sulcata in the evolutionary series of the conodont Siphonodella praesulcata Zone should be drawn between the rugose coral Cystophrentis Zone and Pseudouralina Assemblage Zone, i. e. the Cystophrentis-Pseudouralina Interval-Zone. The top of the regressive event bed near the DCB is lower than the present boundary between the 5. praesulcata and 5. sulcata, but higher than the top of the regressive event bed causing mass extinction of Cystophrentis . Sequence stratigraphical study shows that the regressive event bed near the DCB constitutes the shelf margin systems tract (SMST) of a depositional sequence (SQ1) in both neritic and pelagic areas. The top of the SMST of SQl is slightly lower than the base of the sulcata Zone in pelagic areas. In neritic areas of South China, therefore, the Devonian - Carboniferous boundary is marked by the most distinct transgressive surface within the Cystiphren-tis-Pseudouralina Interval Zone, i. e. the base of the TST of SQ1. This boundary coincides with the top of the regressive event bed and approximately corresponds to the base of the Pseudouralina Assemblage Zone.