To better understand the sedimentary facies of tide-dominated deltas, a core dataset from the Ba Lai palaeochannel in the Mekong River Delta was obtained and studied. Nine sedimentary facies were identified and interpreted as representing the Late Holocene evolution of the Ba Lai palaeochannel, including its pre-abandonment and post-abandonment phases, as well as pre-channel phases. The channel formed at 2.6 ka as a distributary channel connected to the deltaic network and was abruptly abandoned and rapidly infilled with sediment at 0.7 ka. The channel deposits are up to ca 11 m thick and overlie shelfal shell layers, which, in turn, overlie Mid-Holocene and Pleistocene deposits. The active-channel fill and mouth-bar deposits consist of sand and mud with cyclical patterns, bidirectional lenses and abundant mud layers, suggesting deposition mainly driven by river and tidal processes. The abandoned-channel fill consists entirely of organic-rich mud, suggesting a predominance of tidal processes. Other sedimentary facies include tidal-flat and marsh deposits; they mostly consist of mud and formed in shallow to subaerial areas near the channel margins or on barforms. Depending on the exact location of the core in this depositional setting, three possible stratigraphic successions and facies models are presented herein. Near channel margins, the deposits show an upward gradual change from heterolithic to mud with a well-developed fining-upward trend. Away from the channel margins, the deposits show an upward sharp change from heterolithic to mud due to the channel abandonment. The mouth-bar-area facies model shows an upward gradual change from heterolithic to heterolithic/sand to mud deposits with a coarsening-upward to fining-upward trend. Although differences among systems likely exist, the authors suggest that the sedimentary facies described in this study and the resulting facies models should be used to better understand tide-dominated deltaic systems and to improve their interpretation in the geological record.

中文翻译：

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一个活跃至废弃的潮控分流河道及其口坝晚全新世地层演化与沉积相

为了更好地了解潮汐三角洲的沉积相，获得并研究了湄公河三角洲巴莱古河道的核心数据集。九个沉积相被识别并解释为代表巴莱古河道的晚全新世演化，包括其弃前和弃后阶段，以及河道前阶段。该河道在 2.6 ka 时形成，作为与三角洲网络相连的分流河道，在 0.7 ka 时突然被废弃并迅速充满沉积物。通道存款高达ca11 m 厚，覆盖陆架壳层，而陆壳层又覆盖中全新世和更新世沉积物。活动河道充填和河口坝沉积物由砂泥组成，具有周期性、双向透镜体和丰富的泥层，表明沉积主要由河流和潮汐过程驱动。废弃河道填充物完全由富含有机物的泥浆组成，表明潮汐过程占主导地位。其他沉积相包括滩涂和沼泽沉积；它们主要由泥浆组成，形成于靠近河道边缘或条形的浅层至地下区域。根据该沉积环境中岩心的确切位置，本文提出了三种可能的地层序列和相模型。接近通道边缘，矿床呈由异质向泥质逐渐向上变化，呈细化向上的趋势。远离河道边缘，由于河道废弃，沉积物显示出从异质岩到泥浆的急剧上升变化。河口-坝区相模式呈现出由异质岩向异质岩/砂岩向泥质沉积的向上渐变变化，呈现粗化向上向细化向上的趋势。尽管系统之间可能存在差异，但作者建议应使用本研究中描述的沉积相和由此产生的相模型来更好地了解以潮汐为主的三角洲系统并改进其在地质记录中的解释。河口-坝区相模式呈现出由异质岩向异质岩/砂岩向泥质沉积的向上渐变变化，呈现粗化向上向细化向上的趋势。尽管系统之间可能存在差异，但作者建议应使用本研究中描述的沉积相和由此产生的相模型来更好地了解以潮汐为主的三角洲系统并改进其在地质记录中的解释。河口-坝区相模式呈现出由异质岩向异质岩/砂岩向泥质沉积的向上渐变变化，呈现粗化向上向细化向上的趋势。尽管系统之间可能存在差异，但作者建议应使用本研究中描述的沉积相和由此产生的相模型来更好地了解以潮汐为主的三角洲系统并改进其在地质记录中的解释。