福州盆地第四纪钻孔XRF连续扫描的元素特征及沉积相指示意义

摘要

对福州盆地河口地区一个39 m钻孔岩芯进行 X-Ray Fluorescence(XRF)扫描,通过 XRF元素连续扫描结果探讨福州盆地海陆交互地层在不同沉积单元中各元素的变化特征及其沉积相指示意义。钻孔岩芯从晚更新世晚期至全新世共经历了5个沉积阶段：湖泊相—河流冲积相—淤泥质滨海潮滩相—河口潮滩相—河流冲积相。XRF扫描结果表明：元素Co,Fe,Ti,Si及其与 Rb的比值受到沉积物粒度影响较大,对陆相(河流相)和海相(潮滩相)中粒度特征相近的层位进行了元素均值统计显示,近岸河口湾海相沉积物中的Ca,Ti,Mn,Fe,Co等元素是陆相地层中的3~10倍,Si元素则在陆相层中相对富集。说明除了粒度因素,海-陆沉积环境的变化对元素的富集也起到了重要作用。Ca,Ti,Mn,Fe,Co 等元素是较好的海相沉积指示元素,而Si则是较好的陆相沉积指示元素,K,Rb,Sr对陆相沉积具有一定的指示意义。研究结果表明XRF元素连续扫描可以识别沉积物的元素变化细节,并根据元素的强度变化进一步判断沉积相,可以作为沉积相划分的重要辅助手段。该研究为 XRF连续扫描方法在海陆交互带的应用提供了实例。%This paper focuses on the study on continuous XRF (X-Ray Fluorescence)scanning elements of a 3 9 m core from Fuzhou Basin.The XRF scanning result is used to recognize the different sedimentary environment before the discussion of the element variation of different deposit in transitional zone between land and ocean.There are five sedimentary facies in the study area from the late Pleistocene:lacustrine-fluvial-estuary (mud tidal flat)-mixed tidal flat-fluvial.The XRF result from the 5 sedi-mentary stages shows that the high concentration of Co,Fe,Ti,Si are controlled largely by grain size.The average element in-tensity of layers with similar grain size indicates that Ca,Ti,Mn,Fe and Co from the marine (tidal flat)deposit is 3~10 times bigger than those from terrestrial (fluvial)deposit,with higher content of Si coinciding with terrestrial deposit.It is indicated that except grain size,the deposit environment is an important factor for element concentration.In this study,Ca,Ti,Mn,Fe and Co are relatively better indicator elements for marine sediments while Si is good and K,Rb and Sr have some indication for terrestrial sediments.The study result shows XRF continuous scanning can help to identify the subtle variation of elements,as to the determination of the sediment facies.Thus,XRF scanning is an important supplement to sediment facies identification. This study also provides an application example of XRF in a typical transitional zone between land and ocean.