Intertidal meanders developed on salt marshes are known to expand and produce inclined heterolithic stratification rich in fine-grained sediments and to bear evidence for rhythmic deposition in the upper part of the inner meander bend (i.e. the upper part of the point bar). This occurs because the lower point-bar deposits are washed by strong currents, which remove mud drapes and develop discontinuous record of tidal cycles. Although these criteria are widely accepted, facies models for tidal point bars still lack a three-dimensional perspective and overlook the along-bend variability of sediment distribution. The present study focuses on a hypertidal point bar belonging to the upper-intertidal domain of the Mont-Saint-Michel Bay (France), and it analyses the sedimentology of a 3D time-framed accretionary package formed between 28 March 2012 and 29 November 2012 by means of lidar topographic data, geomorphological field surveys and sedimentological core data. To define the 3D time-framed accretionary package, data from thirteen lidar (light detection and ranging) topographic surveys were used to create the point-bar synthetic stratigraphy. Data show that over the study period the point bar expanded alternating deposition along its seaward and landward sides, pointing out the occurrence of depositional patterns more complex than a simple progressive expansion of the bend. The thickest deposits were accumulated in the point-bar-apex zone, where the largest amount of mud was also stored. High sediment accretion in the bend-apex zone is ascribed to the development of low-energy conditions due to flow and bed configuration. High accretion rate of the point-bar-apex zone promoted also a better preservation of rhythmites, which are almost missing from deposits accumulated along the point-bar sides. This study remarks that preservation of mud and tidal rhythmites within intertidal-point-bar deposits is controlled, not only by their elevation with respect to the tidal range, but also by their location along the point bar.

中文翻译：

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结合激光雷达时间序列和沉积岩心数据揭示的超潮点坝（法国西北部圣米歇尔山湾）的沉积学

已知在盐沼上发育的潮间带曲流会扩展并产生富含细粒沉积物的倾斜异石分层，并证明内曲折弯的上部（即点坝的上部）有节奏的沉积。这是因为较低的点坝沉积物被强水流冲刷，从而去除了泥浆并形成了不连续的潮汐循环记录。尽管这些标准被广泛接受，但潮点坝的相模型仍然缺乏三维视角，并且忽略了沉积物分布的沿弯变化。本研究的重点是属于圣米歇尔山湾（法国）上潮间带域的潮汐点条，它通过激光雷达地形数据、地貌实地调查和沉积岩芯数据分析了 2012 年 3 月 28 日至 2012 年 11 月 29 日期间形成的 3D 时间框架增生包的沉积学。为了定义 3D 时间框架增生包，来自 13 个激光雷达（光探测和测距）地形调查的数据用于创建点条合成地层学。数据显示，在研究期间，点杆沿其向海和向陆两侧交替沉积扩展，指出沉积模式的发生比简单的弯曲渐进扩展更复杂。最厚的沉积物堆积在尖顶带，那里也储存了最多的泥浆。弯曲顶点区域的高沉积物增加归因于由于流动和床配置而导致的低能量条件的发展。点棒顶带的高吸积率也促进了节律石的更好保存，这些节律石几乎从点棒两侧堆积的沉积物中丢失。这项研究指出，潮间带点坝沉积物中泥浆和潮汐韵律石的保存受到控制，不仅取决于它们相对于潮差的高度，而且还取决于它们沿点坝的位置。