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首页> 外文期刊>Sedimentology: Journal of the International Association of Sedimentologists >Organic-facies determination: a key for understanding facies distribution in the basal peat layer of the Holocene Rhine-Meuse delta, The Netherlands
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Organic-facies determination: a key for understanding facies distribution in the basal peat layer of the Holocene Rhine-Meuse delta, The Netherlands

机译：有机相确定：了解全新世莱茵-默兹三角洲基底泥炭层中相分布的关键

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摘要

Peat and gyttja (organic lake sediment) are important indicators for past environmental conditions; they form in areas where the supply of clastic sediment is insufficient to fill the accommodation space. Previous studies of delta sediments, however, have focused mainly on clastic deposits, whereas organics have received only minimal attention. Identification of organic facies can be of value for understanding delta formation as it provides insight into, for example, palaeoenvironmental conditions and compaction susceptibility of these layers. Currently, however, field characteristics of organics are not welldocumented for the full range of facies present in delta plains. In this study, a field method – a classification key – for identifying organic facies in delta plains was developed based on concisely described organic facies in selected cores from the Rhine-Meuse delta, The Netherlands. This method was tested on archived borehole descriptions of the diachronous basal peat layer in the distal Holocene Rhine-Meuse delta; this was done by means of a semi-automated procedure to select and classify samples from a database. The resulting data set was used for mapping organic facies in the basal peat layer by means of indicator kriging and inverse distance weighting. The resulting facies distribution map shows consistent and geologically meaningful patterns, which were interpreted in terms of hydrological regimes. The formation of the basal peat layer, which marks the onset of Holocene aggradation, has been controlled by marinedominated, fluvial-dominated and seepage-dominated environments. Before 9000 cal yr bp, marine processes influenced the initial stage of organic accumulation in the western part of The Netherlands. After 9000 cal yr bp, on the flanks of topographical higher regions, seepage-dominated mesotrophic organic facies characterized the onset of accumulation. Simultaneously, nutrient-rich organic facies could develop in the Rhine-Meuse valley: gyttja formed in the sediment-limited Meuse realm, whereas reed peat accumulated in the Rhine realm, indicating lower water depths and thus a higher elevated surface level. It is concluded that the classification key for identifying organic facies is a strong tool to better recognize peat and gyttja types on the basis of macroscopic field characteristics. Application of the key on archived boreholes also proved to be feasible. Identification of organic facies and determination of their spatial distribution at delta scale, as is shown in this study, contributes to understanding delta evolution.
机译：泥炭和gyttja（有机湖沉积物）是过去环境条件的重要指标;它们形成在碎屑沉积物供应不足以填满居住空间的区域。但是，以前对三角洲沉积物的研究主要集中在碎屑沉积物上，而有机物仅受到很少的关注。有机相的识别对于理解三角洲的形成可能是有价值的，因为它可以洞悉例如古环境条件和这些层的压实敏感性。但是，目前，对于三角洲平原地区存在的全部相，有机物的田间特征还没有得到充分证明。在这项研究中，基于荷兰莱茵河默兹三角洲选定岩心中简洁描述的有机相，开发了一种用于识别三角洲平原有机相的现场方法（分类键）。该方法已在全新世莱茵河-默兹河三角洲远侧基底泥炭层的钻孔描述中进行了测试。这是通过半自动程序从数据库中选择和分类样本来完成的。所得数据集用于通过指示剂克里金法和反距离权重法绘制基层泥炭层中的有机相。生成的相分布图显示出一致且具有地质意义的模式，这些模式是根据水文状况来解释的。基层泥炭层的形成，标志着全新世的开始聚集，已经受到海洋为主，河流为主和渗流为主的环境的控制。在9000 cal yr bp之前，海洋过程影响了荷兰西部有机积累的初始阶段。在9000 cal yr bp之后，在地形较高区域的侧面，以渗流为主的中营养有机相表征了聚集的开始。同时，莱茵-默兹河谷可能会形成营养丰富的有机相：在沉积物有限的默兹域中形成gyttja，而芦苇泥炭在莱茵河域中积累，表明水深较低，因此地表水位较高。结论是，基于宏观领域特征，用于识别有机相的分类关键字是更好地识别泥炭和gyttja类型的有力工具。将密钥应用于已归档的钻孔也被证明是可行的。如本研究所示，有机相的识别及其在三角洲尺度上的空间分布确定，有助于理解三角洲的演化。

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