Physical processes controlling mud depocenter development on continental shelves – Geological, oceanographic, and modeling concepts
Physical processes controlling mud depocenter development on continental shelves – Geological, oceanographic, and modeling concepts
复制标题
DOI：
10.1016/j.margeo.2020.106402
复制
发表时间：
2021-02
期刊：
影响因子：
2.9
通讯作者：
L. Porz;Wenyan Zhang;T. Hanebuth;C. Schrum
中科院分区：
文献类型：
--
作者：
L. Porz;Wenyan Zhang;T. Hanebuth;C. Schrum
泥沉积中心（MDC）代表了现代大陆架上细粒陆源物质、碳和污染物的主要近海相汇。在过去的几十年中，一些研究揭示了控制MDC发展的物理过程，在不同的时间尺度，从受控水槽实验和现场海洋监测，以地震声学和沉积物岩心数据的基础上，最近和古代存款的地层分析。因此，已经发现了与MDC的形成和维持动力学相关的关键机制：a）悬浮泥浆通过重力流的跨岸底输运，B）泥浆与海洋锋相关密度梯度的相互作用，c）内波对泥浆再悬浮和扩散的控制，d）在高能流条件下泥浆形成层压层理的底沙沉积，在已确定或提出的物理过程中，MDC的发展可分为三种概念模式：1.连续供应，与稳定的沉积物供应和相对平静条件下的半远洋沉降有关; 2.连续的再悬浮-沉积循环，其中MDC区域的部分在最终掩埋之前经受再悬浮、再沉积和再加工的多个循环;以及3.偶发性沉积和侵蚀，其中诸如河流洪水和大气风暴等极端事件主导总的长期沉积物通量。虽然这些范例中的每一个在一个单一的MDC中的主导地位在很大程度上取决于所考虑的时间尺度，案例研究往往强调与这三个范例中的一个相关的过程。因此，相对的，长期的贡献，个别过程仍然在很大程度上不确定的许多MDC.The数值模型的能力，以准确地预测中期到长期的泥浆积累不仅受到计算成本，但也不充分的参数化的泥浆沉积过程。由于影响泥浆内聚特性的因素的多样性和复杂性，包括其固结状态以及存在的有机物质的数量和类型，这些因素仍然具有约束力。弥合单个事件和长期积累之间的差距是更全面地了解MDC沉积过程的关键。
Mud depocenters (MDCs) represent major proximal-marine sinks for fine-grained terrigenous material, carbon, and contaminants on modern continental shelves. Throughout the past decades, several studies have shed light on the physical processes controlling MDC development at various timescales, ranging from controlled flume experiments and in-situ oceanographic monitoring, to stratigraphic analyses of recent and ancient deposits based on seismo-acoustic and sediment-core data. Thereby, key mechanisms related to the formation and maintenance dynamics of MDCs have been discovered: a) cross-shore bottom transport of suspended mud throughgravity flows, b) interaction of mud with density gradients associated withoceanic fronts, c) resuspension and dispersal control of mud byinternal waves, d)bedloaddeposition of mudforming laminated bedding under energetic flow conditions, and e) mud resuspension resulting fromchronicbottom trawling.Among the physical processes identified or proposed, three conceptual paradigms for MDC development can be distinguished: 1.continuous supply, associated with a steady sediment supply and hemipelagic settling in relatively calm conditions; 2.continual resuspension-deposition cycles, wherein parts of an MDC area are subject to multiple cycles of resuspension, redeposition and reworking before ultimate burial; and 3.episodic sedimentation and erosion, in which extreme events such as riverine floods and atmospheric storms dominate the total, long-term sediment flux. Although the predominance of each of these paradigms within a single MDC depends to a large degree on the timescales considered, case studies tend to emphasize processes associated with only one of these three paradigms. As a result, the relative, long-term contribution of individual processes remains largely uncertain for many MDCs.The ability of numerical models to accurately predict medium to long-term mud accumulation is restricted not only by computational costs, but also by insufficient parametrizations of the muddy sedimentation process. These remain challenging to constrain due to the multiplicity and complexity of factors affecting the cohesive properties of mud, including its state of consolidation, and the amount and type of organic matter present. Bridging the gap between individual events and long-term accumulation is the key to a more complete understanding of sedimentation processes in MDCs.