Sediment dispersal and accumulation off the Ayeyarwady delta – Tectonic and oceanographic controls
Sediment dispersal and accumulation off the Ayeyarwady delta – Tectonic and oceanographic controls
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DOI：
10.1016/j.margeo.2019.106000
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发表时间：
2019-11
期刊：
影响因子：
2.9
通讯作者：
S. Kuehl;Joshua R. Williams;J. Liu;C. Harris;D. W. Aung;D. Tarpley;Mary Goodwyn;Y. Aye
中科院分区：
文献类型：
--
作者：
S. Kuehl;Joshua R. Williams;J. Liu;C. Harris;D. W. Aung;D. Tarpley;Mary Goodwyn;Y. Aye
利用2017年12月收集的海底、水柱和高分辨率地震数据，研究了伊洛瓦底江（Irrawaddy）和Thanlwin （sal温江）附近安达曼海北部大陆架近期沉积物的扩散和积聚。210在Martaban坳陷中部大陆架区域，pb和137cs沉积沉积速率最高（高达10 cm y - 1），该盆地形成于N-S走向的实均断裂东侧。在那里，一个泥泞的水下三角洲正在迅速淤积。在最高堆积带的内陆，在Martaban浅海湾内，是一个高度浑浊的带，在那里海底经常混合到沉积物水界面以下~1 m的深度。该地区频繁的再悬浮可能导致水柱中形成广泛的流体泥浆，因此浅层海底的再氧化可能降低了河流向海洋提供大量陆地碳的地区的碳埋藏效率。来自马尔班湾的沉积物岩心具有独特的红棕色，而x射线照片显示泥沙沉积物中的细粉砂层状沉积结构，这表明强烈的潮汐影响。现代水下三角洲附近的马尔塔班坳陷向海部分覆盖着残留沉积物，现代沉积物与近海马尔塔班峡谷之间没有明显的联系。在实皆断裂带的西侧，“伊洛瓦底河口”是一个巨大的海岬，自全新世最大海侵以来，陆上三角洲沿着印度-缅甸山脉的东侧向海推进了约200 公里。“伊洛瓦底河口”陆架区域目前表现出较低的沉积物堆积速率（~1 cm y - 1）和相对粗糙的（砂质）质地。目前西部陆架地区的堆积减少和粗糙结构是由于频繁的波浪再悬浮和随后在西南季风期间将较细的河流沉积物向东（进入马尔塔班坳陷）输送所致。三角洲西北部存在泥幔（沉积速率<1 cm/yr），在那里一些沉积物可能从陆架逃逸到孟加拉湾深处。与Martaban湾相比，该泥层的沉积物呈橄榄灰色，而沉积结构以斑驳的带壳砂泥为主，偶有砂层。泥幔可能来自于从印度-缅甸山脉向西流出的当地河流的混合物，以及东北季风期间伊洛瓦底河系统的贡献。综上所述，伊洛瓦底江和檀云江陆架是一个由海洋和构造因素共同控制的复合型水下三角洲，由东向西差异明显。
Recent sediment dispersal and accumulation on the Northern Andaman Sea continental shelf, off the Ayeyarwady (Irrawaddy) and Thanlwin (Salween) Rivers, are investigated using seabed, water column, and high-resolution seismic data collected in December 2017.210Pb and137Cs derived sediment accumulation rates are highest (up to 10 cm y−1) in the mid-shelf region of the Martaban Depression, a basin that has formed on the eastern side of the N-S trending Sagaing fault, where rapid progradation of a muddy subaqueous delta is occurring. Landward of the zone of highest accumulation, in the shallow Gulf of Martaban, is a highly turbid zone where the seabed is frequently mixed to depths of ~1 m below the sediment water interface. Frequent resuspension in this area may contribute to the formation of extensive fluid muds in the water column, and consequent re-oxidation of the shallow seabed likely reduces the carbon burial efficiency for an area where the rivers are supplying large amounts of terrestrial carbon to the ocean. Sediment cores from the Gulf of Martban have a distinctive reddish brown coloration, while x-radiographs show sedimentary structures of fine silt laminations in mud deposits, which indicates strong tidal influences. The seaward part of the Martaban Depression off the modern subaqueous delta is covered by relict sediment, with no apparent connection between the modern sediment deposit and the offshore Martaban canyon. On the western side of the Sagaing fault, the “Mouths of the Ayeyarwady” represent a large promontory where the subaerial delta has prograded seaward some ~200 km along the eastern flank of the Indo-Burman range since the Holocene maximum transgression. The shelf area off the “Mouths of the Ayeyarwady” presently exhibits low sediment accumulation rates (~1 cm y−1) and a relative coarse (sandy) texture. The reduced accumulation and coarse texture in the western shelf region at the present time is attributed to frequent wave resuspension, and subsequent transport of finer river-derived sediment eastward (into the Martaban Depression) during the SW Monsoon. A mud drape (accumulation rates <1 cm/yr) is present on the northwestern part of the delta, where some sediment likely escapes the shelf to the deeper Bay of Bengal. In contrast with the Gulf of Martaban, sediments in this mud drape show olive grey coloration, while sedimentary structures are dominated by mottled sandy mud with shells, and occasional sand layers. The mud drape is likely derived from a mixture of local rivers draining westward from the Indo-Burman range, and a contribution from the Ayeyarwady system delivered during the NE monsoon. Overall, the shelf offshore the Ayeyarwady and Thanlwin rivers represents a compound subaqueous delta with marked differences from east to west that are controlled by a combination of oceanographic and tectonic factors.