沉积学报2025，Vol.43Issue(3)：1072-1090,19.DOI:10.14027/j.issn.1000-0550.2023.083
早三叠世鲕粒和巨鲕差异成因及其古环境意义
Differential Genesis and Paleoenvironmental Significance of Early Triassic Ooids and Giant Ooids:A case study from the Yuanba area in northern Sichuan
摘要
Abstract
[Objective]The Early Triassic was a special geological period after the mass extinction of organisms,during which oolitic and giant oolitic deposits were widely developed in shallow carbonate platforms worldwide.How-ever,there is still significant controversy regarding the origin and paleomarine environmental significance of oolitic and giant oolitic deposits.[Methods]Based on field and core observations,this study utilized petrological,mineral-ogical,and geochemical analyses to explore the sedimentary characteristics,genesis,and paleoenvironmental signifi-cance of the Early Triassic Feixianguan Formation oolites and giant oolites in the Yuanba area.[Results]Research shows that the oolites and giant oolites of the Feixianguan Formation in the Yuanba area primarily developed in the margin zone of the section 2 of Feixianguan Formation.The types of oolites are concentric and single crystal oolites,which are developed in the middle and upper part of the meter scale sedimentary cycle and are produced in thick lay-ers and blocks,indicating that they were formed in a shallow water environment with strong hydrodynamic forces and easy exposure.Giant ooids are primarily composed of concentric ooids,which are developed in the upper part of the meter scale sedimentary cycle and the lower part of the mud crystal limestone.They are produced in a thin layer and have clear erosion at the bottom,indicating that they were formed under intermittent strong hydrodynamic conditions,mostly due to storm action.Based on geochemical analysis,the Sr content in the concentric layer of oolites is found to be high,and the crystal structure is mostly needle-like or rod-shaped,indicating that the original minerals are arago-nite deposits.However,the Sr content in the concentric layers of giant ooids is relatively low,and their crystal struc-ture is irregularly inlaid,indicating that their original minerals are calcite deposits.In addition,the concentric layer of oolites has characteristics such as high Fe content,weak positive Ce anomaly,clear positive Eu anomaly,enrich-ment of light rare earth element(LREE)relative to heavy rare earth element(HREE),and low Y/Ho values,indicat-ing that it was formed in a reducing environment of iron mineralization.Giant ooids have characteristics such as low Fe content,weak negative Ce anomalies,relative HREE depletion of LREE,and high Y/Ho values,indicating that they were formed in a weakly oxidizing environment.[Conclusions]Comprehensive analysis suggests that during the sedimentary period of the Early Triassic Feixianguan Formation,the seawater was mainly characterized by the anoxic aragonite sea.However,in the context of gradual atmospheric oxidation and strengthened continental weathering,in-termittent storm action increased the input of terrestrial materials(particularly Ca2+)and oxidants,resulting in a de-crease in Mg/Ca in shallow seawater and weak oxidation,as well as the development of a transient weak oxidation cal-cite sea.This may be the cause for the gradual improvement of the marine environment and slow biological recovery in the Early Triassic.关键词
鲕粒/巨鲕/成因机制/古海洋环境/早三叠世/元坝地区Key words
oolites/giant oolites/genetic mechanism/paleomarine environment/Early Triassic/Yuanba district分类
天文与地球科学引用本文复制引用
张风顺,谭谦,施泽进,彭秋,易驰,宁科科,唐劭禹..早三叠世鲕粒和巨鲕差异成因及其古环境意义[J].沉积学报,2025,43(3):1072-1090,19.基金项目
国家自然科学基金项目(41872137)[National Natural Science Foundation of China,No.41872137] （41872137）
