陆相湖泊深水砂质碎屑流与浊流的微观沉积特征及区分方法——以鄂尔多斯盆地延长组长7段为例

基于薄片观察、粒度分析、环境扫描电镜和全岩矿物定量分析、荧光光谱元素分析等测试结果，对鄂尔多斯盆地旬邑、瑶曲地区三叠系延长组长7段中的砂质碎屑流和浊流的微观沉积特征进行了研究。结果表明:（1）砂质碎屑流沉积的碎屑颗粒呈杂乱无序排列，而浊流沉积（鲍马序列A段）则有较明显的定向排列特征，反映出前者为整体快速搬运特征，而后者具有部分牵引流特征，表明其密度偏低，而二者均具有黄铁矿；（2）砂质碎屑流砂岩概率曲线具明显的两段式，反映牵引流特征，结合镜下观察，其来源应为浅水或陆上河流，而浊流砂岩则为单段式，反映重力流特征；（3）瑶曲长7沉积期古环境为干冷气候，砂质碎屑流相对浊流而言，其古环境大部分时期淋滤作用较弱；（4）砂质碎屑流砂岩及伴生泥岩的Sr/Ba值均小于浊流，表明其对湖水的稀释作用更强，注入速度更快，瑶曲整体Sr/Cu值低于旬邑，相对降雨量更丰富，此外，砂质碎屑流砂岩中重矿物Zr含量整体要高于浊流，表明其具有更强的碎屑搬运能力；（5）砂质碎屑流沉积和浊流沉积的黏土组成及混层比无明显差异，但全岩矿物成分组成有差别，通过差异性较大的石英与黏土含量制订划分模板，可将砂质碎屑流沉积、浊流沉积及两者过渡段进行定量划分。 

Microscale sedimentary characteristics and distinguishing methods for deep-water sandy debris flow and turbidity flow in continental lakes: a case study of seventh member of Yanchang Formation,Ordos Basin

Based on the results of thin section observation, grain size analysis, environmental scanning electron microscopy, whole rock mineral quantitative analysis and fluorescence element analysis, the microscale sedimentary characteristics of sedimentary sand debris flow and turbidity flow were studied in details after a systematic sampling of the seventh member of Yanchang Formation (Chang 7) of Xunyi and Yaoqu areas of Ordos Basin. The results showed that: (1) The clastic particles deposited in the sand debris flow were in a disordered arrangement, while the turbid flow deposition(section A of the Bouma sequence) has a more obvious directional arrangement, indicating the former is characterized by overall rapid transport, while the latter is characterized by traction flow, indicating a low density. Both of them contain pyrites. (2) The probability curve of the sand debris flow sandstones showed a two-stage pattern, reflecting the characteristics of traction and drainage. According to microscopic observation, its source could be shallow water or land river. The probability curve of the turbid flow sandstones shows a single stage pattern, reflecting the characteristics of gravity flow. (3) The paleoenvironment of the Chang 7 sedimentary period of Yaoqu area is dry and cold. The eluviation of sandy debris flow is weaker than that of turbid flow in most periods. (4) For elemental compositions, the Sr/Ba ratios of both sandy debris flow sandstonesand associated mudstones were lower than those of turbidity current, which indicates that it has stronger dilution effect on lake water and faster injection speed. The Sr/Cu ratios of Yaoqu area were lower than those of Xunyi area, and the relative rainfall is more abundant. In addition, the Zr content in sandy debris flow sandstones is higher than that in turbidity flow sandstones, which indicates that it had stronger debris transport capacity. (5) Through the quantitative analysis of the whole rock and clay by X-ray diffraction, there is no obvious difference in clay composition and mixed layer ratio between them, but there were differences in mineral composition of the whole rock. Since the contents of quartz and clay showed great difference, a division template of them has been established, which can quantitatively distinguish sandy debris flow sandstones, turbidity flow sandstones and the transition section.