关键词: 豫西, 早二叠世, 碳酸盐台地, 稀土元素, 演化

Abstract:

This paper presents the study of the sedimentary facies of Taiyuan Formation in typical sections from Jiaozuo area to Yuzhou area, mainly focusing on the platform sedimentary characteristics and evolution of epicontinental sea. Sedimentary facies of Taiyuan Formation, which is mainly featured by limestones along with interlayered siltstones, mud shales and coal seams, can be divided into five facies including open carbonate platform, limited carbonate platform, barrier island, lagoonswamp and tidalflat facies. The storm depositional events widely developed in the carbonate platform, which can be divided into several sedimentary cycles. Open carbonate platform (mainly in Yuzhou area) mainly contain amount of bioclastic, featured by substantial broken fossils, high content of trace elements and rare earth elements, much higher content of LREE than that of HREE, the respectively positive correlations between the value of ∑REE and the content of Fe as well as between that of LREE/HREE and Fe. Compared with open carbonate platform, restricted carbonate platform (mainly in Jiaozuo area) is featured by the widespread micrite, which infer that the ancient ocean in the restricted carbonate platform contained less fossils and colloids, and became much more restricted and quieter than that of open carbonate platform. The bottom limestones of the Lower Limestone Section of Taiyuan Formation, which is formed in transgressive systems tract(TST) during the early phase of first transgression, are featured by high content of biodetritus, Sc, Ba and ∑REE, low value of Sr/Ba, low differentiation between LREE and HREE. The top limestones of the Lower Limestone Section formed in highstand systems tract (HST), which reflected the sedimentary environment of the limited carbonate platform in the research area evolving from the previous turbulent water into confined and quite surroundings with biodetritus and collides diminishing and evaporation strengthening. It aims to put implications on the research of the characteristics and evolution by comparing with the sedimentary characteristics of Taiyuan Formation limestones in different stage of the system tracts in restricted carbonate platform.

Key words: western Henan, Early Permian, carbonate platform, rare earth element, evolution