Migration–aggradation history and 3-D seismic geomorphology of submarine channels in the Pleistocene Benin-major Canyon, western Niger Delta slope
Migration–aggradation history and 3-D seismic geomorphology of submarine channels in the Pleistocene Benin-major Canyon, western Niger Delta slope
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DOI：
10.1016/j.marpetgeo.2007.01.005
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发表时间：
2007-06
影响因子：
4.2
通讯作者：
M. Deptuck;Z. Sylvester;C. Pirmez;C. O’Byrne
中科院分区：
文献类型：
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作者：
M. Deptuck;Z. Sylvester;C. Pirmez;C. O’Byrne
贝宁大峡谷 54 公里长的一段内包含数条横向偏移和加剧的蜿蜒海底通道。轴向河道沉积物在三维 (3-D) 地震剖面上产生高振幅反射。一些地震反射具有 U 形或 V 形横截面图案，这些图案与沿线性到蜿蜒路径长达 70 公里的置信度相关。它们在这里被称为河道形态（CF），并且被认为是在整个河道底板加蚀过程中保留下来的海底河道的轴向部分。总共绘制了 15 个独立的 CF，以便在空间和时间上研究海洋梯度、尺寸和形态，从而深入了解海底峡谷如何填充。它们的平面几何形状主要通过交替的切割和填充周期以逐步方式演变，但也观察到更渐进的通道迁移。连续河道底板位置的最大偏移发生在显着的垂直 CF 填充期之后（“thalweg 堵塞”——沉积物通常由较低振幅组成，对混沌地震反射透明）。充填期后侵蚀流的通过导致河道位置突然发生变化，特别是在曲流弯曲处，形成伪曲流环路截止的可能性增加。碳纤维堆积结构的显着空间差异归因于局部斜坡变形，也可能归因于研究区域西部最近发生的河道撕脱。西部研究区域的河道突然变直，与谷地梯度增加的时期相一致，而谷地梯度增加与底层背斜褶皱的放大有关。该区域最年轻的CF表现出有限的加蚀作用，其特点是反复发生的溯源侵蚀导致了拐点迁移，因为最近的河道底部试图建立平滑的分级深度剖面，但没有成功。这与东部研究区的时间当量主要是加积性 CF 形成鲜明对比，东部研究区显示出蜿蜒度随时间逐渐增加。
Several laterally offset and aggradational sinuous submarine channels are contained within a 54km long segment of the Benin-major Canyon. Axial channel deposits produce high amplitude reflections on three-dimensional (3-D) seismic profiles. Some seismic reflections have U- or V-shaped cross-sectional motifs that were correlated with confidence along linear to meandering paths for distances up to 70km. They are referred to here as channel-forms (CFs), and are believed to be the axial parts of submarine channels preserved during overall channel floor aggradation. A total of 15 separate CFs were mapped allowing thalweg-gradients, dimensions, and morphology to be studied spatially and through time, providing insight into how submarine canyons fill. Their planform geometry evolved predominantly in a stepwise fashion through alternating periods of cut-and-fill, but more gradual channel migrations are also observed. The largest offsets in successive channel floor position occur after periods of significant vertical CF fill (‘thalweg plugging’—with deposits commonly consisting of lower amplitude, transparent to chaotic seismic reflections). The passage of erosive flows after such periods of fill caused abrupt shifts in channel position, particularly at meander bends, with increased potential for the formation of pseudo meander loop cut-offs. Significant spatial differences in the stacking architecture of CFs are attributed to local slope deformation and perhaps also to a recent channel avulsion just west of the study area. Abrupt channel straightening in the western study area coincides with a period of increased valley-gradient associated with amplification of an underlying anticlinal fold. The youngest CFs in this area show limited aggradation and are characterized by repeated episodes of headward erosion causing knickpoint migration as the recent channel floor tried, unsuccessfully, to establish a smooth graded depth profile. This is in stark contrast to the time-equivalent predominantly aggradational CFs in the eastern study area that show a progressive increase in sinuosity through time.