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首页> 外文期刊>Journal of Asian earth sciences >Acoustical facies analysis at the Ba Lat delta front (Red River Delta, North Vietnam)
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Acoustical facies analysis at the Ba Lat delta front (Red River Delta, North Vietnam)

机译：Ba Lat三角洲前缘（北越南红河三角洲）的声相分析

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A shallow penetrating, high-resolution acoustic study was performed in the Ba Lat delta, the major distributary of the Red River System in Northern Vietnam. An acoustic facies map was constructed and the various facies types were validated through analysis of bottom sediments, by a study of gravity cores collected at 22 stations. Analysis of the acoustic profiles and gravity cores revealed the presence of an asymmetrical, S to SW prograding prodelta lobe, in accordance with the prevailing longshore currents to the S. The southern part of this prodelta is detached from the protruding Ba Lat delta front. The prodelta is dominated by muddy sediments with minor thin (< 5 cm) sandy and silty layers. The coarser-grained layers decrease in abundance away from the Ba Lat river mouth. Offshore, the modern delta deposits are characterized by an off-lapping contact over a semi-prolonged bottom reflector lacking any sub-bottom reflectors. This semi-prolonged bottom reflector is correlated with sandy deposits of presumably Early Holocene age. Bottom and coastal erosion is restricted to two areas N and SW of the Ba Lat. Erosion in the North is inferred to be due to reduced sediment supply as a result of shifting in 1971 of the main outlet to its present, more southern location. The erosional area along the Hai Hau coast SW of the Ba Lat also has experienced a reduction in sediment supply in the course of the 20th century, when the local Song Vop distributary channel became less active and was completely dammed in the 1970s. Most sediment supplied by the Ba Lat at present bypasses the Hai Hau erosional coastal zone, as the active part of the Ba Lat prodelta is detached from the coast SW of the Ba Lat. An active, NNE-SSW trending fault system with surface expression is located along the offshore edge of the prodelta, and is linked to deeper fault structures in this active neotectonic region. Subsurface reflectors are folded in the vicinity of the fault.
机译：在越南北部红河系统的主要分支Ba Lat三角洲进行了浅层，高分辨率的声学研究。通过研究在22个站点收集的重力岩心，构造了声相图，并通过分析底部沉积物验证了各种相类型。对声学剖面和重力核心的分析表明，与通向S的主要近岸海流相一致，存在从S到SW的不对称S到SW推进的三角洲前凸。该三角洲的南部与突出的Ba Lat三角洲前缘分离。前三角洲以泥质沉积物为主，泥沙层较薄（<5 cm）。较粗颗粒的层在远离Ba Lat河口的地方大量减少。在近海，现代三角洲沉积物的特征是在半延长的底部反射器上缺乏重叠接触，该底部反射器缺少任何底部反射器。这种半延长的底部反射层与大概是全新世早期的砂质沉积物有关。底部和沿海侵蚀仅限于Ba Lat的N和SW两个区域。据推测，北部的侵蚀是由于主要出口在1971年转移到现在的更南部的位置而导致的泥沙供应减少。在20世纪期间，Ba Lat沿海口海岸西南海岸的侵蚀区的沉积物供应也减少了，当时当地的Song Vop分流河道变得不那么活跃，并在1970年代被完全筑坝。由于Ba Lat三角洲的活跃部分与Ba Lat的西南海岸脱离，目前Ba Lat提供的大多数沉积物绕过了海口侵蚀沿海地区。一个活跃的，具有表面表达的NNE-SSW趋势断层系统沿着三角洲的近海边缘定位，并与这个活跃的新构造区的较深断层结构相连。地下反射器在断层附近折叠。

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