ABSTRACT

Deep-water channels can be bound by overbank deposits, resulting from overspilling flows, which are often ornamented with sediment waves. Here, high-resolution bathymetry, backscatter, and 2D and 3D seismic data are integrated to discern the controls on flow processes on the overbank areas of the Hikurangi Channel. Qualitative seismic interpretation and quantitative analyses of sediment wave morphologies and distributions are conducted through the shallowest 600 m of stratigraphy up to the seafloor. Four outer-bend wave fields are present throughout the studied stratigraphy on the landward margin (left margin looking down-channel) only. Originally closely spaced or combined, these fields evolved to become spatially separated; two of the separate wave fields became further subdivided into distinct outer- and inner-bend fields, whose constituent waves developed distinct differences in morphology and distribution. Sediment wave character is used to interpret the direction and strength of overbank flow. Nine controls on such flow and associated deposition are identified: flow versus conduit size, overbank gradient, flow tuning, Coriolis forcing, contour current activity, flow reflection, centrifugal forcing, interaction with externally derived flows, and interaction of overspill from different locations. Their relative importance may vary across parts of overbank areas, both spatially and temporally, controlling wave field development such that: (1) outer-bend wave fields only develop on the landward margin; (2) the influence of centrifugal force on outer-bend overbanks has increased through time, accompanying a general increase in channel sinuosity; (3) inner-bend wave fields on the landward margin form by the interaction of Coriolis-enhanced inner-bend overbank flow, and outer-bank flow from up-channel bends; (4) inner-bend fields on the oceanward margin form by the interaction of axial flow through wave troughs, and a transverse, toward-channel flow component. This work has implications for interpreting overbank flow from seafloor and seismic data, and for palaeogeographic reconstructions from outcrop data.

摘要

深水河道可能会被越岸沉积物所束缚，这些沉积物是由溢出的水流造成的，这些水流通常饰有沉积物波。在这里，高分辨率测深、反向散射以及 2D 和 3D 地震数据被整合在一起，以识别对 Hikurangi 海峡上岸区域流动过程的控制。沉积物波形态和分布的定性地震解释和定量分析是通过最浅的 600 m 地层直到海底进行的。仅在向陆边缘（左边缘向下看通道）的整个研究地层中存在四个外弯曲波场。这些场最初是紧密间隔或组合的，后来演变为空间分离。两个独立的波场进一步细分为不同的外弯场和内弯场，其组成波在形态和分布上产生了明显的差异。泥沙波特征用于解释越岸流的方向和强度。确定了对此类流量和相关沉积的九种控制：流量与管道尺寸、溢流坡度、流量调整、科里奥利强迫、等高线电流活动、流动反射、离心强迫、与外部衍生流动的相互作用以及来自不同位置的溢出的相互作用。它们的相对重要性可能在空间和时间上在跨岸地区的各个部分有所不同，从而控制波场的发展，使得：（1）外弯波场仅在向陆边缘发展；(2) 离心力对外弯越岸的影响随时间增加，河道弯曲度普遍增加；(3) 向陆边缘的内弯波场是由科里奥利增强的内弯越岸流与上游河道弯道的外岸流相互作用形成的；(4) 向洋边缘的内弯场由通过波槽的轴向流和横向的、朝向航道的流分量的相互作用形成。这项工作对解释海底和地震数据中的溢流以及从露头数据中重建古地理具有重要意义。