手持X射线衍射仪(ED-XRF)在旋回地层学中的应用:以酒泉盆地青西凹陷早白垩世下沟组为例

The Application of the Handheld Energy-Dispersive X-Ray Fluorescence(ED-XRF)in the Cyclostratigraphy Research——A Case Study from the Xiagou Formation of the Lower Cretaceous in the Qingxi Sag,Jiuquan Basin

在旋回地层学研究中,高分辨率地球化学数据作为一重要的替代指标,其一般获取方式(ICP-MS或WD-XRF)较耗费时间和经费,而手持X射线衍射仪(ED-XRF)能够高效的解决这一问题,目前将ED-XRF运用在沉积地层研究中,尤其是旋回地层学研究领域中较少.以酒泉盆地青西凹陷早白垩世下沟组深湖相泥岩、白云质泥岩为研究对象,将连续采集的岩心样品通过ED-XRF测试,该测试方法能够保证在不破坏样品的前提下,并在误差允许的范围内的条件下,短时间内(5min)完成对单一样品的测试.通过测试精确得出24种主量及微量元素的含量,将得出的地球化学特征作为旋回地层学研究的替代指标,并针对K/Al,Ca/Al,Si/Al,Fe/Al,Ti/Al,Mn/Al,Ni/Al,Zn/Al和Pb/Al的比值进行频谱分析.数据表明W2井下沟组一段(SQK1g1)地层旋回性表现出与天文旋回明显的对应关系.沉积地层中的旋回厚度比值为20.25∶4.75∶1.75∶1.00,与米兰科维奇旋回中长偏心率、短偏心率、斜率和岁差的周期比值:400ka∶95ka∶37ka∶20ka相对应.该地区的沉积记录受天文轨道周期的影响得到了证明,与此同时,为手持X射线衍射仪在旋回地层学中的应用开辟了新领域.

The high resolution geochemical data are used as important proxies in cyclostratigraphy,which cost a lot of time and money to obtain the data in the usual way（ICP-MS or WD-XRF）.And the handheld energy-dispersive X-ray fluorescence（EDXRF）can obtain the high resolution geochemical data efficiently.Currently,the handheld energy-dispersive X-ray fluorescence（ED-XRF）was few used in the study of sedimentary strata,especially in cyclostratigraphy research field.Continuous core samples of deep lacustrine mudstone and dolomitic mudstone were selected from the Xiagou Formation of the Lower Cretaceous in the Qingxi Sag,Jiuquan Basin.Content of 24 major elements and trace elements which can be used as important proxies in cyclostratigraphy were accurately measured under the Handheld energy-dispersive X-ray fluorescence（ED-XRF）testing,a nondestructive,direct method with high precision in an efficiency way which can test one single sample in five minutes.Ratios of obtained geochemical data（K/Al,Ca/Al,Si/Al,Fe/Al,Ti/Al,Mn/Al,Ni/Al,Zn/Al and Pb/Al）were analyzed by spectral methods further.Such results presented cycle wavelengths in the stratigraphic units show a value of 20.25∶4.75∶1.75∶1.00,corresponding with those of Milankovitch cycle periods（400 ka（long eccentricity）∶95 ka（short eccentricity）∶37 ka（obliquity）∶20 ka（precession）,respectively）in Well W2.The correspondences between the sedimentary cycle ratios and the Milankovitch cycle periods indicates controlling effect of astronomical factors on sedimentation.ED-XRFprovide the new possibilities in detection and quantification of geological processes,and have great significance in establishing geological time series.