Stratigraphic Expression of Intra-Point-Bar Erosion and Rotation
Stratigraphic Expression of Intra-Point-Bar Erosion and Rotation
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DOI：
10.2110/jsr.2015.78
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发表时间：
2015-10
影响因子：
2
通讯作者：
P. Durkin;S. Hubbard;R. Boyd;D. Leckie
中科院分区：
文献类型：
--
作者：
P. Durkin;S. Hubbard;R. Boyd;D. Leckie
曲流带的特征是由点坝及其伴生的沉积元素（如牛轭湖填充物）组成的复杂混合体。点坝沉积物是一种复合元素，通常以复杂的滚动条模式为特征，这些模式是在蜿蜒弯曲的膨胀、旋转和平移过程中形成的。在现代河流系统中经常观察到点坝内侵蚀，但其产物很少在古代记录中被描述。加拿大阿尔伯塔中南部出现了晚白垩世由点坝向反点坝过渡而成的曲流带沉积及其伴生的废弃河道充填体。地层的特点是广泛存在点内砂坝沉积侵蚀和间断旋转的证据。在地层记录中，点内砂坝沉积侵蚀和间断旋转表现为陡倾不协调面（最高达20°），截断了先前沉积的侧向增生包体。在这些侵蚀表面上，沙洲迁移的方向经常显著旋转，可达50°。随后的吸积面覆盖在点坝内沉积物侵蚀面上。分析表明，点坝面是由沿其长度的侵蚀作用和沉积作用的复杂相互作用形成的，其地层表面可能是高度复合的。该研究改变了将沉积物视为连续侧向增生的简单点坝过程模型，因此对古环境重建和地下储层表征具有重要意义。
Abstract Meander belts are characterized by a complex amalgam of point bars and associated depositional elements, such as oxbow-lake fills. Point-bar deposits are composite elements often characterized by complex scroll-bar patterns formed in response to processes of expansion, rotation, and translation of a meander bend. Intra-point-bar erosion is commonly observed in modern river systems, yet its product is rarely described from the ancient record. Late Cretaceous meander-belt deposits, consisting of a transition from a point-bar to counter-point-bar deposit, as well as an associated abandoned channel fill, crop out in south central Alberta, Canada. The strata are characterized by widespread evidence for intra-point bar deposit erosion and punctuated rotation. In the stratigraphic record, intra-point bar deposit erosion and punctuated rotation is expressed by steeply dipping discordant surfaces (up to 20°), which truncate previously deposited lateral-accretion packages. Across these erosion surfaces the direction of bar migration often rotates significantly, up to 50°. Subsequent accretion surfaces onlap intra-point-bar-deposit erosion surfaces. The analysis reveals that point-bar surfaces are formed through a complex interplay of erosional and depositional processes along their length, resulting in stratigraphic surfaces that may be highly composite. This study departs from more simplistic process models of point bars that consider deposits to be the product of continuous lateral accretion, and as such has important implications for paleoenvironmental reconstructions and subsurface reservoir characterization.