Frontal and Lateral Submarine Lobe Fringes: Comparing Sedimentary Facies, Architecture and Flow Processes
Frontal and Lateral Submarine Lobe Fringes: Comparing Sedimentary Facies, Architecture and Flow Processes
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DOI：
10.2110/jsr.2017.2
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发表时间：
2017
影响因子：
2
通讯作者：
Yvonne T. Spychala;D. Hodgson;A. Prélat;I. Kane;S. Flint;N. Mountney
中科院分区：
文献类型：
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作者：
Yvonne T. Spychala;D. Hodgson;A. Prélat;I. Kane;S. Flint;N. Mountney
海底瓣缘沉积形成了可能包含高比例混合层的异石器序列。叶缘序列的识别有助于古地理背景和盆地围限程度的解释。在这里，首次研究了前缘和侧叶边缘沉积的沉积学和构造学差异。来自南非Karoo盆地Skoorsteenberg组Fan 4的大量露头和岩心数据，使得下倾(正面)和跨走向(横向)的扇体和扇体复合体从轴线到边缘的相变化速度和样式可以在800 km2的研究区内得到严格限制。扇4由三个易砂分区组成，形成补偿叠加的扇体复合体，由厚厚的薄层粉砂岩和砂岩与(泥质)粉砂岩夹层隔开，解释为扇体复合体的边缘。瓣缘相组合包括：i)挤压膨胀的厚层无构造或平面叠层砂岩，并与下伏的碎屑岩伴生；ii)泥质和富含泥屑的混合层；iii)水流涟漪叠层砂岩和粉砂岩。通常，前缘含有高比例的混合层，并从长度为1-2公里的厚层砂岩过渡而来。相反，侧缘沉积往往由水流波纹层状砂岩组成，这些砂岩在叶轴上转换为厚层砂岩，绵延数公里。解释了原生流动过程的可变性，以控制记录的相组合差异。前缘混合层的优先沉积与流动的高密度核心的主要下游动量有关。相反，横向边缘位置的波纹层状薄层被解释为由更稀薄的低密度(部分)流动沉积。建立区分前缘和侧缘层序的识别标准对于改进露头和地下海底扇的古地理重建至关重要，并将有助于减少油气田评价和开发过程中的不确定性。
Submarine lobe-fringe deposits form heterolithic successions that may include a high proportion of hybrid beds. The identification of lobe-fringe successions aids interpretation of paleogeographic setting and the degree of basin confinement. Here, for the first time, the sedimentological and architectural differences between frontal and lateral lobe-fringe deposits are investigated. Extensive outcrop and core data from Fan 4, Skoorsteenberg Formation, Karoo Basin, South Africa, allow the rates and style of facies changes from axis to fringe settings of lobes and lobe complexes in both down-dip (frontal) and across-strike (lateral) directions to be tightly constrained over an 800 km2 study area. Fan 4 comprises three sand-prone divisions that form compensationally stacked lobe complexes, separated by thick packages of thin-bedded siltstone and sandstone intercalated with (muddy) siltstone, interpreted as the fringes of lobe complexes. Lobe-fringe facies associations comprise: i) thick-bedded structureless or planar-laminated sandstones that pinch and swell, and are associated with underlying debrites; ii) argillaceous and mudclast-rich hybrid beds; and iii) current-ripple-laminated sandstones and siltstones. Typically, frontal fringes contain high proportions of hybrid beds and transition from thick-bedded sandstones over length scales of 1 to 2 km. In contrast, lateral fringe deposits tend to comprise current-ripple-laminated sandstones that transition to thick-bedded sandstones in the lobe axis over several kilometers. Variability of primary flow processes are interpreted to control the documented differences in facies association. Preferential deposition of hybrid beds in frontal fringe positions is related to the dominantly downstream momentum of the high-density core of the flow. In contrast, the ripple-laminated thin beds in lateral fringe positions are interpreted to be deposited by more dilute low-density (parts of the) flows. The development of recognition criteria to distinguish between frontal and lateral lobe-fringe successions is critical to improving paleogeographic reconstructions of submarine fans at outcrop and in the subsurface, and will help to reduce uncertainty during hydrocarbon field appraisal and development