北羌塘盆地沃若山地区中—下侏罗统雀莫错组一段沉积环境分析

A sedimentary environment analysis of the first member of the Quemo Co Formation in Woruo Mountain area of the North Qiangtang Basin

北羌塘盆地沃若山地区中—下侏罗统雀莫错组一段主要为一套碎屑岩沉积,主要岩性包括紫红色含砾砂岩、中—细砂岩和泥质粉砂岩,形成于氧化环境。通过对雀莫错组一段碎屑岩岩性特征、沉积构造、概率累积曲线、萨胡判别式、粒度参数散点图和C-M图等分析表明,雀莫错组一段砂岩分选性较差,在概率直方图上多表现为双峰或多峰,概率累积曲线主要为"两段式",少见"三段式",跳跃总体含量较高,滚动总体和悬浮总体较少。在Sk-σi散点图中,雀莫错组一段的砂岩均落入河砂范围内;在C-M图上表现为PQ段发育,QR段次之,为一套典型的河流相沉积。雀莫错组的沉积从河流-冲积扇相开始,之上为三角洲相和局限台地相沉积,总体上表现为逐渐变深的海侵序列。

The first member of the Quemo Co Formation in the Woruo Mountain area of the North Qiangtang Basin is mainly composed of purplish red pebbly sandstone, medium to fine sandstone, and argillaceous siltstone, deposited in an oxidation environment. The lithologic characters, sedimentary structures, probability cumulative grain size curves, Sahu formula, grain-size parameters scattergram, and C-M pattern of the sandstones of the first member of the Quemo Co Formation all show that the sandstones are of bad sorting, and the frequency histogram is bimodal or multimodal, the probability cumulative curve of the sandstones mostly represents two-stage and a few three-stage, the percentage of the traction populations is high, and the percentage of the saltation and suspension populations is relatively low. In the Sk-~i diagram, the sandstones of the first member of the Quemo Co Formation fall into the river sand area. Its C-M pattern has the typical feature of fluvial deposit, with the PQ section richly developed but the QR section poorly developed. The deposition of the Quemo Co Formation started with fluvial-alluvial facies, and then these strata were overlain by delta and restricted platform deposition, thus overall displaying a deepening-upward transgressive sequence.