Geophysical studies of mass transport deposits on the slope canyon floor with high-resolution autonomous underwater vehicle (AUV) in the Shenhu area and its implications for sediment transportation
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摘要:
海底峡谷是陆源物质向深海运移的重要通道。对于远离陆地的海底峡谷，通常认为浊流是物质搬运的主要营力。受限于探测精度和复杂作业环境影响，使用常规地球物理资料对深水海底峡谷尤其是对谷底沉积体的形态和结构特征的刻画不够精细。基于水下自主航行器（AUV, Autonomous Underwater Vehicle）采集的高分辨率多波束、旁扫声呐和浅地层剖面资料，对神狐峡谷群中的一条峡谷的谷底表面及部分浅部地层的沉积特征进行了分析。结果表明，峡谷谷底浅部地层并不像它平滑的表面那么简单，而是由大量内部杂乱弱反射、厚度在8.4 m及以下的块体搬运沉积体组成。峡谷中下游块体搬运沉积体大都沿峡谷走向整体呈条带状展布，不是直接来源于相邻的峡谷脊部。研究认为在特定沉积环境下（例如高海平面时期），陆坡限定性峡谷谷底的块体搬运沉积过程的重复进行是峡谷谷底物质输运的重要途径，与浊流共同雕刻了峡谷的地形地貌。基于AUV的地球物理探测技术将是研究海底浅表层沉积过程和保障海底工程施工的重要手段。
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关键词:
- 海底峡谷 /
- 物质输运 /
- 水下自主航行器（AUV） /
- 块体搬运沉积 /
- 神狐峡谷群
Abstract:Submarine canyons are important pathways for terrestrial sediment moving to the deep water far away from the land, and turbidity current is considered as the primary agent. Detailed sedimentary features of the canyon floor are not clear so far due to the low resolution of conventional geophysical data and complicated operating setting in deep water. Here, in this program, high-resolution autonomous underwater vehicle (AUV) based multi-beam bathymetry data, side-scan sonar data and chirp sub-bottom profiles are jointly used to map the floor of a canyon and image its shallow strata in the Shenhu area. The canyon floor looks quite flat. However, the underlying shallow strata are composed of widespread mass transport deposits (MTDs) which are a little less than 8.4 meters with weak and chaotic acoustic reflections. They are distributed along the canyon floor in an elongated shape and show little direct links with adjacent steep canyon ridges at the middle and lower segments of the canyon. Thus, we suggest the repeated mass wasting downslope on the canyon floor is an effective mechanism for sediment transportation in addition to turbidity currents. The AUV based geophysical exploration is a efficient tool for further studies of marine sedimentation and seabed installation under deep water.
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表 1 峡谷谷底MTDs的几何参数
Table 1. Geometric parameters of MTDs on the canyon floor
编号 宽度/m 长度/km 长宽比 厚度/m 面积/km2 体积/km3 MTD1 80～500 5.00 10.00～62.50 1.30～8.40 0.90 4.37 MTD2 260～350 0.75 2.14～2.88 0.90～3.20 0.28 0.58 MTD3 70～600 2.00 3.33～28.57 1.20～3.00 1.10 2.31 
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