广西二叠纪菊石生物地层学研究进展

ADVANCES IN BIOSTRATIGRAPHY OF PERMIAN AMMONOID-BEARING FORMATIONS FROM GUANGXI

一广西以其有利的古地理环境和相对连续的沉积及古生物序列。

Two ecologically controlled associations of ammonoids are well-developed in the Permian system of Guangxi. This allows the area to become one of the regions where the uppermost Permian ammonoids of the Restricted Sea have first been studied in detail. Additionally, the area provides sections in which the Lower Permian Open-Sea ammonoids are widely distributed and are represented in the most numerous horizons. Ongoing discoveries of the four horizons with more than 20 ammonoid genera of the Open-Sea ecological pattern represent significant research result bearing on the ecological differentiation theory of Permian ammonoids. Guangxi emerges as one of the ideal areas available for study of the causes, mechanics and results of the ecological differentiation of the Permian ammonoids. It affords us the basis for recognition of two ammonoid sequences, those of the Restricted Sea (platform) and the Open-Sea (basin), and allows their correlation with each other and with those in the world scale. There is a good possibility in the Open-Sea area in Guangxi to look for the representatives, such as Perrinites, Waagenoceras, Timorites, and Cyclolobus from the uppermost Chihsian through Changhsingian Stage. However, there are only a few horizons with the local Restricted Sea ammonoid faunas due to the control from the environment and the exclusive occurrence of these local faunas in silicious, muddy and tuffaceous rocks.Some prominent provincial ammonoids, such as Properrinites and Svetlanoceras are directly associated in Guangxi; this provides the opportunity for regionaI stratigraphic correlation of the different areas where they had lived, and also promotes our understanding of the phenomenon of 'provincialism'. Irrespective of the cause, the ecological differentiation in Permian ammonoids caused by the environment seems to be substantially stronger than that from geographical controls.Discovery of the ammonoids of the Open-Sea ecological pattern from the Middle and Upper Maping Formation and the 'Chihsia Formation' in Guangxi provides an immediate basis for the correlation of these strata with those in the classic areas such as the Urals and other important areas in the world. The middle and upper Maping horizons correlate with at least the Asselian and Sakmarian Stages, and in some areas, may even partially correlate with the earliest Artinskian Stage. Such correlations indicate that the Carboniferous-Permian boundary in South China lies within the Maping Formation.