峡东地区陡山沱组三段硅质条带中的微体化石分布特征及其控制因素OA北大核心

In this study,we perform paleontological and sedimentary research of three sections,Tianjiayuanzi,Jiulongwan,and Qinglinkou,located within the carbonate platform of the Huangling Anticline in the eastern Three Gorges area,Yichang City,Hubei Province.The aim is to investigate the spatial distribution patterns of microfossils in silicified bands from the lower Member Ⅲ of the Doushantuo Formation and their potential controlling factors.The results show that silicified bands and nodules in the Tianjiayuanzi section contain abundant acritarch fossils,tubular fossils,and cyanobacteria,along with oolitic grains and intraclasts.The Jiulongwan section contains sparse acritarch fossils and fragmented tubular fossils,with localized accumulations of oolitic sandy clasts,occasional gravel clasts,and minor thrombolites.The Qinglinkou section is dominated by lithified microbial mats and fine sandy grains,with rare thrombolites observed.Based on these findings,it is inferred that during the deposition of the lower Member Ⅲ of the Doushantuo Formation(1)the Tianjiayuanzi section had an intertidal flat environment,(2)the Jiulongwan section occupied an upper subtidal zone,and(3)the Qinglinkou section was situated between a lower subtidal zone and normal wave base.The variations in microfossil assemblage diversity and abundance among these study sections may reflect taphonomic influence;that is,fossils in shallow-water sections are preserved due to the rapid formation of siliceous nodules during early burial.Lower biodiversity in deeper water environments could be attributed to rapid microbial decomposition of planktonic acritarchs in the water column or during early burial in sediments,which is an important source of marine dissolved organic carbon.