Characteristics of mineral matter in the lignite from Mile Basin,Eastern Yunnan:New evidence for the seawater input during the peat accumulation process into the inland basin

X-Ray Diffractometer (XRD),X-Ray Fluorescence Spectrometer (XRF),Inductively Coupled Plasma Mass Spectrometer (ICP-MS) and Thermal Ionization Mass Spectrometer (TI-MS) have been applied on the Miocene lignite of Mile Basin,Eastern Yunnan,for the geochemical,mineralogy and strontium isotope analysis,and new evidence for the seawater input during the peat accumulation process into the terrestrial coal basin have been identified. Besides the consistence of strontium isotope 87Sr/86 Sr of gypsum,which is abundant in the Mile coals,with the value of contemporary seawater,the occurrence modes of gypsum and authigenic pyrite in the coals also indicate the peat was influenced by seawater during its accumulation process. The ratios of sediment environment sensitive element Ca/Mg,Sr/Ba,Th/U and V/Ni,the percentage of P2O5,and the anomalous of rare earth element La and Gd,as well as the variety of Y/Ho along the seam profile,indicate the peat was suffering a decreasing seawater influence,while an increasing fresh water influence and supply of terrigenous debris with the peat accumulation. During the peat accumulation process,the Mile Basin which located in multiple-stage-active deformed zone,connected the Tethys with the Ailao Shan-Red River fault,providing an access for the transformation of seawater into the peat pile;meanwhile,the uplift of north area of the deformed zone,contributed to the decreasing influence of seawater on the peat during the Mile coal basin.