华北盆地西部太原组遗迹化石组合对古水深变化的响应

Responses of ichnoassemblages to paleo-water-depth of the Taiyuan Formation in western North China Basin

通过对豫西-晋中南地区上石炭统-下二叠统太原组碳酸盐岩中遗迹化石的组成、产状及分布特征的研究,结合部分生物潜穴中Sr含量、Sr/Ba值、1000×(Sr/Ca)值和δ13C值,得到不同地区太原组沉积期古水深的变化曲线,建立了3种不同水深的遗迹组合:(1) Nereites-Chondrites遗迹组合,产生于氧化还原界面附近水体相对较深的浅海下部环境;(2) Zoophycos-Teichichnus遗迹组合,形成于浪基面至氧化还原界面之间的浅海中部沉积环境;(3) Zoophycos-Thalassinoides遗迹组合,出现在平均海平面至浪基面之间的浅海上部或较为闭塞的海湾潟湖沉积环境。依据这3种遗迹组合在各剖面上的变化特征和古水深,认为在豫西-晋中南地区太原组沉积期发生过2次较大规模的海侵。这一成果为精细研究华北西部地区太原期沉积环境演变规律及对比地层提供了生物遗迹学方面的依据。

In this paper,we studied composition,appearance and distribution of ichnofossils in the carbonates of the Upper Carboniferous-Lower Permian Taiyuan Formation in the western North China Basin,and analyzed the relationships between Sr contents,Sr/Ba values,1000×(Sr/Ca),and δ13 C in some ichnofossils burrow and paleo-water-depth. Three types of ichnoassemblages with different water-depths were established:(1) Nereites-Chondrites ichnoassemblage occurred in the lower zone of the shallow sea below the redox interface;(2) Zoophycos-Teichichnus ichnoassemblage formed in the middle zone of the shallow sea between the wave base and redox interface;(3) Zoophycos-Thalassinoides ichnoassemblage occurred in the upper zone of the shallow sea(between the sea level and wave base) or lagoonal environments. Based on various characteristics of these ichnoassemblages in different sections,and paleo-waterdepth changes in different area,two major transgressions can be identified in the Taiyuan Formation in the study area. This research provides ichnology basis for detailed studies on evolution of depositional environments and stratigraphic correlation of the Taiyuan Formation in the western North China.