保山盆地湖相泥岩微量元素分布与古盐度定量评价

QUANTITATIVE EVALUATION OF PALEOSALINITES AND DISTRIBUTION OF TRACE ELEMENTS IN THE LACUSTRINE MUDSTONE OF BAOSHAN BASIN

于1994—1995年间，在云南保山盆地第三系地层采集泥岩样品，用中子活化分析方法和化学分析方法测定了泥岩的微量元素和氧化物含量；用X－射线衍射（XRD）分析和扫描电镜（SEM）分析方法测试了泥岩的粘土矿物成分和含量；应用科奇和亚当斯理论计算了湖盆古盐度。结果表明，该湖盆羊四段盐度最高达15.70，羊三段盐度为12．79,羊一段盐度为13．35，南林组盐度为13．26。随着沉积介质盐度的增大，微量元素硼（B）、相当硼含量逐渐增大，Sr／Ba，B／Ga比值也逐渐增加，它们之间呈线性正相关关系。

In 1994- 1995,mudstone samples were collected from the Baoshan Neogene basin,Yunnan. The content of trace elements and oxide in the mudstone was determined by chemical and neutron activation analyses. The content and composition of clay minerals in the mudstone were determined by X-ray diffraction analysis and scanning electron microscope analysis. Based on a comprehesive study on the contents of trace elements and clay minerals in the mudstone, equivalent boron was calculated using adjusted boron and departur curves. The equivalent boron can be used as a reliable criterion for the identification of water-body salinlty. The content of equivalent boron in the fourth section of Yangyi Formation is 208 ×10-6-235 ×10-6;it is 46 ×10 -6-205 ×10-6 in the third section and 180 × 10-6-220 ×10-6 in the first section of the Formation, and 210 ×10-6in Nanlin Formation. The result shows tha the third section of Yangyi Formation represents fresh water deposits; the remainder are fresh water deposits containing salt water.Paleosalinities have been calculated with the equations proposed by Adams et al. (1965) and by Couch (1971), in ascordance with the data of clay minerals and boron contents. The result shows tha salinity in some strata of the fourth section of Yangyi Formation reaches as high as 15.70; it is 6.57-12.79 in the third section and 13.35 in the first section of Yangyi Formation, and 13.26 in Nanlin Fomation. On the basis of relationships betwen salinity and trace element content, the trace element boron and equivalent boron, the ratio of B / Ga and Sr / Ba mny be used as a reliable criterion for water body paleosalinity. They increase in response to an increase in the paleosalinity.Howevef, although they indicate the chages in water-body salinity, they may not be used as geochemical criteria for differentiating marine and continental sedimentary fasies.