日喀则弧前盆地昂仁组海底扇朵叶体构型研究

白垩系昂仁组是藏南日喀则弧前盆地的主体, 沉积于深水盆地、海底扇、海底峡谷、斜坡等环境, 是研究海底扇朵叶体沉积的理想对象。文章选取交通方便、出露良好的恩贡寺剖面进行剖面实测和沉积学观察, 基于岩石组合和沉积构造识别出砾岩相、无构造砂岩相、砂岩相、条带砂岩相、泥石流沉积相、砂岩/粉砂岩组合相、粉砂岩相、泥岩/灰岩相等岩相, 根据岩相的组合确定恩贡寺剖面昂仁组为深水海底扇朵叶复合体沉积, 是7期朵叶体叠置的产物。不同的微相组合关系表明, 不同期次的朵叶体沉积过程不同, 可能主要受控于源区的构造活动。

The Cretaceous Ngamring Formation constitutes the main body of the Xigaze forearc basin, southern Xizang. It was deposited in deep-water basin, submarine fan, submarine canyon and slope environments, which provides a good opportunity to study the architecture of submarine lobe. This study conducts stratigraphic and sedimentologic analyses on the easily-accessible, well-outcropped Engongsi section of the Ngamring Formation. Different lithofacies have been described based on lithologies and sedimentary structures, including conglomerate, structureless sandstone, structured sandstone, banded sandstone, debrites, heterolithic packages, siltstone and claystone/limestone. Microfacies of lobe axis, off-axis, fringe and distal fringe have been identified according to assemblages of lithofacies, indicating that the strata were deposits of submarine lobe complex with seven periods of superposed lobes. Different arrangements of microfacies suggest sedimentological variability of each lobe, probably due to the tectonic activities in the source areas.