深水浊积朵叶体构型特征——以爱尔兰克莱尔盆地石炭系露头为例

Architecture of deepwater turbidite lobes: A case study of Carboniferous turbidite outcrop in the Clare Basin, Ireland

通过对爱尔兰西部石炭系RossSandstone组浊积岩露头的精细解剖与岩相分析,建立深海浊积朵叶体沉积模式。研究表明,研究区发育富棱菊石页岩相、薄层页岩相、具层理粉砂岩相、无构造细砂岩相、含泥砾中-细砂岩相、滞留砾岩相、杂乱泥岩相等7种岩相类型;可划分为朵叶体、水道、滑动-滑塌等3种成因单元;可划分为朵叶体复合体、朵叶体、朵叶体单元、单砂层等4级构型层次。朵叶体之间表现出明显的补偿性叠置,朵叶体单元内部呈现"向上变厚"的韵律,构型层次越高,构型界面的保存程度越好。浊积朵叶体沉积整体上表现为板状、平行或类平行的砂泥二元互层结构,由近端的厚层无构造砂岩沿轴向和侧向转变为较薄的砂泥薄互层,砂泥比与砂岩融合程度逐渐减少。

Through lithofacies analysis and architecture anatomy of the Carboniferous Ross Sandstone turbidites outcropped at western Ireland, the depositional model of deepwater turbidite lobes is established. Seven types of lithofacies are recognized including goniatites-rich shale, laminated shale, laminated siltstone, massive sandstone, fine-medium sandstone with mud-gravel, basal gravel, and chaotic mudstone, which can be subdivided into units of three origins, turbidite lobe, turbidite channel, and slide-slump;and four hierarchical levels, lobe complex, lobe, lobe element and single sandstone layer. The lobes show apparent compensational stacking pattern, lobe elements display typical thickening-upward cycles on vertical profile, and the higher the hierarchical level, the better the preservation of the hierarchical boundary is. In general, turbidite lobe deposits appear as tabular, parallel/sub-parallel sandstone and mudstone interbeds, and change from thick, massive sandstone in the proximal end to thinner sandstone and mudstone interbeds from axis to fringe, with the sand-shale ratio and degree of sandstone amalgamation decreasing.