中国洞穴石笋铀含量分布及其影响因素研究OA

The uranium content of stalagmites is the foundation of stalagmite chronology research.It directly determines whether a stalagmite sample is suitable for paleoclimate research and affects the accuracy and precision of stalagmite dating results.Currently,two uranium-series dating techniques are commonly used for stalagmites:U-Th dating and U-Pb dating.The U-Th method can date samples up to approximately 690,000 years old,while the U-Pb method extends the dating range to the Paleozoic or even earlier geological periods.However,the reliability of both methods is highly dependent on the uranium concentration in the stalagmites.Stalagmite samples with low uranium content often result in large age uncertainties,which can lead to significant misinterpretations of the timing and duration of past abrupt climatic events,thereby compromising the accuracy of paleoclimate reconstructions.Therefore,investigating the factors that influence uranium concentrations in stalagmites is of great significance both theoretically and practically.Such understanding can help identify high-uranium stalagmite samples,enhance dating precision,and ultimately support the establishment of more robust chronological frameworks.Nevertheless,current knowledge of the mechanisms controlling uranium content in stalagmites remains limited.Most existing studies focus on the climatic significance of uranium concentration and initial(234U/238U)ratios in stalagmites.Previous studies have shown that the uranium content in stalagmites is influenced by factors such as soil,surrounding rock,the infiltration path of karst water,and the duration of water-rock interaction;While,systematic large-scale studies that integrate these factors are still lacking.In China,karst landscapes are widely distributed,and stalagmite records have played a vital role in high-resolution paleoclimate studies.However,there are relatively few comprehensive analyses on the temporal and spatial distribution characteristics of uranium content in cave stalagmites,as well as the influencing factors.This study aims to explore the temporal and spatial distribution characteristics of uranium content in cave stalagmites in China and the key influencing factors.The goal is to provide a scientific basis for selecting suitable stalagmite samples with adequate uranium concentrations,thereby minimizing unnecessary use and waste of valuable stalagmite resources. This study collects and analyzes the data from 114 published cave stalagmite samples in China.By examining the spatial distribution and temporal evolution of uranium concentrations,the study explores the roles of regional tectonic background,host rock lithology,mineralogy of the stalagmite,and the hydroclimatic conditions under which the stalagmites formed.The main research objectives are:(1)Clarifying the spatial distribution pattern and temporal variation characteristics of uranium content in Chinese stalagmites;(2)Identifying the primary controlling factors,including geological settings,mineral composition,and environmental parameters;(3)Providing scientific criteria for selecting suitable samples for uranium-series dating,thereby avoiding unnecessary waste of stalagmite resources. The analysis of the research results indicates:(1)The spatial distribution of karst caves in China is regionally distinct.Although they are widely distributed,most caves develop on the second geomorphic step and in tectonically active zones such as the Qinling-Dabie orogenic belt and the monsoon-affected regions east of the Hu Line.The warm and humid climate conditions are conducive to the development of karst caves;(2)Based on published Chinese stalagmite records,uranium concentrations typically range from 0.5×10-6 to 10× 10-6.High-uranium stalagmites(1× 10-6to 10×10-6)are mainly found in karst caves developed in Mesozoic or older limestone formations located in the junction regions of Guizhou,Chongqing,Hubei,and Hunan;(3)The lithology of host rocks is a critical factor influencing uranium enrichment.When stalagmites are composed of calcite,those formed in dolomite tend to have higher uranium contents than those formed in limestone.This may be attributed to differences in rock weathering processes,inter-crystalline porosity,and water-rock interaction time;(4)The presence of dolomite within the host rock or geological strata appears to be an important contributor to elevated uranium levels in aragonite stalagmites;(5)Uranium concentrations are significantly correlated with regional hydroclimate conditions.There is a positive relationship between uranium content and stalagmite growth rate:stalagmites formed under warm and humid conditions generally contain higher uranium levels,whereas those formed under cold and arid conditions tend to have lower uranium concentrations;(6)In general geological settings,the primary source of uranium in sedimentary strata is ancient seawater,thus creating a link between uranium content in stalagmites and that in paleo-seawater.However,in certain specialized geological environments,such as coal-bearing formations or areas with magmatic intrusions,localized uranium enrichment in bedrock can lead to abnormally high uranium levels in stalagmites. This study enhances our understanding of the variability and controlling mechanisms of uranium concentration in stalagmites under different lithological,stratigraphic,and climatic conditions.The findings provide both theoretical insights and practical guidelines for selecting high-uranium stalagmite samples,thereby supporting the continued advancement of stalagmite-based paleoclimate reconstructions.