Relating seafloor geomorphology to subsurface architecture: How mass‐transport deposits and knickpoint‐zones build the stratigraphy of the deep‐water Hikurangi Channel
Relating seafloor geomorphology to subsurface architecture: How mass‐transport deposits and knickpoint‐zones build the stratigraphy of the deep‐water Hikurangi Channel
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DOI：
10.1111/sed.12890
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发表时间：
2021-05
期刊：
影响因子：
3.5
通讯作者：
Daniel E. Tek;A. McArthur;M. Poyatos‐Moré;L. Colombera;Marco Patacci;Benjamin Craven;W. McCaffrey
中科院分区：
文献类型：
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作者：
Daniel E. Tek;A. McArthur;M. Poyatos‐Moré;L. Colombera;Marco Patacci;Benjamin Craven;W. McCaffrey
对现代深水水道的监测揭示了迁移的水道底部地貌如何形成和消除地层，增进了对水道形态与其沉积物之间关系的理解。在此，通过对高分辨率测深和三维地震数据的综合研究，对新西兰近海希库朗伊海沟轴部约150公里长的一段水道进行成像，使海底和地下数据相互印证。在海底，阶梯状的水道壁环绕着一个平坦、宽阔的水道底部，其上有三种尺度的地貌，它们在下游的纵向坡度先增大后减小，且在下游变宽：旋回阶地、裂点和裂点带（尺寸依次增大）。源自水道壁坍塌的块体搬运沉积物，在上游由宽阔平坦的水道底部区域环绕，在下游由裂点带（包含多个裂点的区域）环绕。在地下，对十种地震相和五种界面类型的识别能够确定四种沉积单元：水道充填物、席状或阶地、天然堤和块体搬运沉积物。地下和海底解释的综合表明，裂点带始于阻塞水道的块体搬运沉积物的下游边缘；随着水道趋于平衡，它们迁移并切割穿过块体搬运沉积物以及在上游形成的弱限制沉积物。在裂点带的下游，一个平坦的水道底部由新形成的阶地环绕。裂点通过在上游侵蚀和在下游沉积而迁移，在其后方形成充填的上凹（横截面）面。在裂点带内，由裂点产生的面会被随后经过的裂点再次切割，从而形成一个复合边界面；该面并不能描绘任何古水道的形态。希库朗伊水道的地下结构记录了通过裂点带迁移对块体搬运沉积物就位的局部侵蚀响应，展示了瞬时的海底地貌如何构建成水道化地层。该模型为通过长段水道的“切割 - 充填”形成水道沉积物的传统模型提供了一种额外的机制。这些发现可能有助于在缺乏当代相似体或数据覆盖较差的系统中进行地下解释。
Monitoring of modern deep‐water channels has revealed how migrating channel‐floor features generate and remove stratigraphy, improving understanding of how channel morphologies relate to their deposits. Here, seafloor and subsurface data are reconciled through an integrated study of high‐resolution bathymetry and three‐dimensional seismic data imaging a ca 150 km stretch of the trench‐axial Hikurangi Channel, offshore New Zealand. On the seafloor, terraced channel‐walls bound a flat, wide, channel‐floor, ornamented with three scales of features that increase then decrease in longitudinal gradient downstream, and widen downstream: cyclic‐steps, knickpoints and knickpoint‐zones (in increasing size). Mass‐transport deposits derived from channel‐wall collapse, are bordered by wide and flat reaches of channel‐floor upstream and by knickpoint‐zones (reaches containing multiple knickpoints) downstream. In the subsurface, recognition of ten seismofacies and five types of surface enables identification of four depositional elements: channel‐fill, sheet or terrace, levée, and mass‐transport deposits. Integration of subsurface and seafloor interpretations reveals that knickpoint‐zones initiate on the downstream margins of channel‐damming mass‐transport deposits; they migrate and incise through the mass‐transport deposits and weakly‐confined deposits formed upstream, as the channel tends towards equilibrium. Downstream of a knickpoint‐zone, a flat channel‐floor is bounded by newly‐formed terraces. Knickpoints migrate by eroding upstream and depositing downstream, generating filled concave‐up (cross‐sectional) surfaces in their wake. Within knickpoint‐zones, knickpoint‐generated surfaces are re‐incised by subsequently‐passing knickpoints to produce a composite bounding surface; this surface does not delineate the morphology of any palaeo‐conduit. The Hikurangi Channel’s subsurface architecture records the localized erosional response to mass‐transport deposit emplacement via knickpoint‐zone migration, showcasing how transient seafloor features can build channelized stratigraphy. This model provides an additional mechanism to conventional models of channel deposit formation through ‘cut‐and‐fill’ over long stretches of channel. These findings may aid subsurface interpretation in systems lacking a contemporary self‐analogue or with poor data coverage.