Sedimentary Characteristics And Origin Of High Natural Gamma Abnormal Layers Of Late Permian Coal Measures In Panxian Area Of Western Guizhou Province

Based on the theory and method of petrology,mineralogy,geochemistry,geophysics,etc.,through the comprehensive analysis of 16 drilling geology data,and the experimental test results of J901 well and J301 well samples,the spatial distribution characteristics,sedimentary characteristics and geochemical characteristics of the Late Permian coal-series natural gamma-high abnormal layer of Pan Area in western Guizhou Province were discussed and their cause and geological significance were studied and analyzed.In this study,the identification principle of natural gamma high abnormal layer in the study area was established by collating and analyzing the geophysical logging data in the area,and the abnormal layer was divided into sub-high abnormal layer and significantly high abnormal layer according to the relative size and absolute size of the natural gamma log data,and the lateral and plane distribution characteristics of the abnormal layer were comprehensively analyzed,then the abnormal layer with stable development in the lateral direction(contrast layer)was named;the sedimentary characteristics of the abnormal layer sample were detailedly analyzed.Special or rare minerals such as berthierine,rutile,illite and boehmite were found in the key research samples by mineralogical analysis.According to the geochemical test result and referencing the content of radioactive element.After analyzing the characteristics of major,trace and rare earth elements of anomalous layer samples other than GR-a layer,it is found that the rare earth element distribution curves of most anomalous layer samples have certain similarities with rhyolite and high-titanium basalt.It is indicated that the source of anomalous layer material has duality.It is believed that the Th element may come from a variety of clay minerals.The enrichment of U element is mainly related to organic matter.Potassium element is mainly present in the clay mineral of the mixed layer of Illite-montmorillonite.Test results show that the Th element mainly comes from berthierine,and the enrichment of U elements is also related to organic matter,while K elements are mainly from illite.In addition,titanium minerals also contain much radioactive elements.The minerals in the layer are mainly volcanic genesis,and the radioactive elements and their occurrence minerals are mostly derived from acidic volcanic rocks.Comparing the key layer(GR-a layer)in this study with the high natural gamma abnormal layer at the bottom of the Xuanwei Formation in eastern Yunnan Province,the mineral combination of them has a high degree of similarity and inheritance.It is believed that its genesis is basically consistent with the material source,and its formation mechanism is proposed.It is believed that the falling volcanic debris(volcanic ash)is its main formation mechanism.