Mud dominates volumetrically the fraction of sediment delivered and deposited in deep-water environments, and mudstone is a major component of basin-floor successions. However, studies of basin-floor deposits have mainly focused on their proximal sandstone-prone part. A consequent bias therefore remains in the understanding of depositional processes and stratigraphic architecture in mudstone-prone distal settings beyond the sandstone pinchouts of basin-floor fans. This study uses macroscopic and microscopic descriptions of over 500 m of continuous cores from research boreholes from the Permian Skoorsteenberg Formation of the Karoo Basin, South Africa, to document the sedimentology, stratigraphy, and ichnology of a distal mudstone-prone basin-floor succession. Very thin- to thin-bedded mudstones, deposited by low-density turbidity currents, stack to form bedsets bounded by thin packages (< 0.7 m thick) of background mudstones. Genetically related bedsets stack to form bedset packages, which are bounded by thicker (> 0.7 m thick) background mudstones. Stratigraphic correlation between cores suggests that bedsets represent the distal fringes of submarine fan lobe elements and/or lobes, and bedset packages represent the distal fringes of lobe complexes and/or lobe complex sets. The internal stacking pattern of bedsets and bedset packages is highly variable vertically and laterally, which records dominantly autogenic processes (e.g., compensational stacking, avulsion of feeder channels). The background mudstones are characterized by remnant tractional structures and outsize particles, and are interpreted as deposited from low-density turbidity currents and debris flows before intense biogenic reworking. These observations challenge the idea that mud accumulates only from hemipelagic suspension fallout in distal basin-floor environments. Thin background mudstones separating bedsets (< 0.7 m thick) are interpreted to mainly represent autogenically driven lobe abandonment due to up-dip channel avulsion. The thicker background mudstones separating bedset packages (> 0.7 m thick) are interpreted to dominantly mark allogenically driven regional decrease of sand supply to the basin floor. The recognition of sandstone-prone basin-floor fans passing into genetically linked distal fringe mudstones suggests that submarine lobes are at least ∼ 20 km longer than previously estimated. This study provides sedimentological, stratigraphic, and ichnological criteria to differentiate mudstones deposited in different sub-environments in distal deep-water basin-floor settings, with implications for the accurate characterization of basin-floor fan architecture, and their use as archives of paleoenvironmental change.

中文翻译：

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边缘或背景：表征盆底扇形砂岩夹层以外的深水泥岩

在深水环境中，泥浆在体积上占主导地位，而沉积物在泥盆中占主导地位，而泥岩是盆地底层演替的主要组成部分。但是，盆底沉积物的研究主要集中在其近端砂岩易发部分。因此，在盆底扇形砂岩夹层以外的泥岩多发的远侧环境中，对沉积过程和地层构造的理解仍然存在偏见。这项研究使用了来自南非Karoo盆地二叠纪Skoorsteenberg地层研究钻孔的500 m以上连续岩心的宏观和微观描述，记录了易发泥岩的盆地底部地层演替的沉积学，地层学和岩石学。低密度浊流沉积的非常薄至薄层的泥岩，堆叠以形成由薄包裹（<0.7 m厚）的背景泥岩为边界的床组。遗传相关的床叠成床叠，并由较厚（> 0.7 m厚）的背景泥岩界定。岩心之间的地层学相关性表明，床组代表海底扇形叶要素和/或波瓣的远侧边缘，床组组合代表波瓣复合体和/或波瓣复合体组的远侧边缘。床组和床套件的内部堆叠模式在垂直和水平方向上都高度可变，这记录了主要的自生过程（例如，补偿性堆叠，馈线通道的破坏）。背景泥岩的特征是残余的牵引结构和超大颗粒，并被解释为在密集的生物重做之前是由低密度浊流和泥石流沉积而成。这些观察结果挑战了这样一种观念，即泥浆仅在近海盆地地面环境中由半海相悬浮物的沉降物积累。分隔床层的薄背景泥岩（<0.7 m厚）被解释为主要代表由于上倾通道撕脱而引起的自发驱动的叶遗弃。分离床套件的较厚背景泥岩（> 0.7 m厚度）被解释为主要标志着由异源作用驱动的向盆地底板供砂的区域性减少。易于砂岩的盆地底扇进入遗传连锁的远缘条纹泥岩，这表明海底裂隙比以前的估计至少长了约20 km。这项研究提供了沉积学，