Devonian-Carboniferous Boundary in the Neritic Facies Areas of South China from the Viewpoint of Integrative Stratigraphy

摘要

In regard to isochroneity of stratigraphical unit boundaries, the present stratigraphical methods may be divided into two types. One is biostratigraphy, which is based on the irreversible evolution of life and is basic in stratigraphy, although its unit boundaries are in most cases diachronous. The other includes event stratigraphy, sequence stratigraphy, ecuslratigraphy, magnetostratigraphy, seismic stratigraphy, and stable isotope stratigraphy, in which the unit boundaries are by definition isochronous and correlatable over a considerable extent, even all over the world. However, these units lack unique signals and are recurrent in geological history. Their age can not be decided without biostratigraphy or isotope dating. Integrative stratigraphy attempts to make full use of stratigraphic data, including physical, chemical and biological, and specially emphasizes a combined use of all stratigraphical methods. Within the stratigraphic framework established by means of biostratigraphy, event stratigraphic and other isochronous stratigraphic unit boundaries are used for more detailed division and precise correlation. It provides an effective method in high-resolution stratigraphy. In the present paper an attempt is made to discuss the Devonian -Carboniferous Boundary (DCB) in the neritic facies areas of South China from the viewpoint of integrative stratigraphy. A combined study of biostratigraphy, event stratigraphy, sequence stratigraphy, and ecostratigraphy shows that in the neritic facies areas of South China, the DCB, matching the boundary between Siphanodelia praesulcata Zone and S. sidcata Zone in pelagic facies areas, is not only higher than the top of the Cystophrentis Range Zone, but also higher than the top of the event beds which caused the extinction of Cystophrentis. We may here define the Devonian-Carboniferous Boundary by the most distinct transgressive surface within the CystophrenlisPseudouraUna Interval Zone in the neritic facies areas of South China. This boundary is the base of transgress systems tract of a Sloss sequence, which coincides with the top surface of the DCB event beds, and approximately corresponds to the bottom of Pseudouralinia Assemblage Zone. In cyclic stratigraphy, this boundary is also the basal boundary of a T-R cycle. Remarkable changes in palaeoeeologic pattern and sudden variation in magnetic susceptibility of limestones and stable isotope took place at the boundary, which seems therefore to be a ideal natural boundary between Devonian and Carboniferous.