Records of palaeoearthquakes in sedimentary rocks are often debated due to the potential confusion in distinguishing seismic versus aseismic trigger mechanisms causing liquefaction. The present paper documents some unique soft-sediment deformation structures (SSDS), characterized by their extremely large size, complex morphology and preservation in coarse-grained pebbly sandstone. The SSDS are present in the Permian Barren Measures Formation, a syn-rift depositional unit within the Lower Gondwana succession in the Pranhita-Godavari Valley, eastern Peninsular India. The ~ 210 m thick succession is represented by stacked fining-up retrogradational cycles, characterized by coarse-grained trough cross-stratified pebbly sandstones near the base and fine-grained heterolithic sandstones–mudstones at the top. Each cycle signifies a change from fluvial- to tidal-influenced depositional systems. Coarse-grained pebbly sandstone beds near the base of each cycle record most SSDS, including complexly deformed layers, pseudonodules, load and flame structures, various water-escape structures like vertical/inclined sediment columns (sedimentary dykes) and contorted beds, and syn-sedimentary faults. The deformed beds are underlain and overlain by the undeformed beds. Complexly deformed SSDS are often sharply truncated at the top by undeformed beds manifesting syn-sedimentary character, which signifies that deformation took place just after deposition of the affected beds, but before deposition of the overlying beds while sedimentation was continuous. Facies analysis reveals the absence of processes like storms/pounding waves, slumps, rapid dumping (massive beds), impact shaking, volcanisms, tsunami waves or sediment gravity flows in the study area, thus negating their possibility as triggering agents for the liquefaction. The complex nature and large size of the deformation structures imply extensive liquefaction near the sediment–water interface. In addition, the deformed beds comply with most of the criteria of typical seismites. In half-graben type Gondwana basins, such seismites can be linked to palaeoearthquakes, which signify the phases of syn-rift fault reactivation, basinal sagging and associated accommodation changes.

中文翻译：

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印度 Pranhita-Godavari 山谷二叠纪贫瘠措施地层中的大型软沉积物变形结构 (SSDS)：与同裂谷古地震事件的潜在联系

由于在区分引起液化的地震触发机制与抗震触发机制方面可能存在混淆，因此沉积岩中的古地震记录经常受到争论。本文记录了一些独特的软沉积变形结构（SSDS），其特点是尺寸极大，形态复杂，保存在粗粒卵石砂岩中。SSDS 存在于二叠纪贫瘠措施地层中，这是印度半岛东部 Pranhita-Godavari 河谷下冈瓦纳系列中的同裂谷沉积单元。~ 210 m 厚的序列以堆积的精炼回积旋回为代表，其特征是底部附近为粗粒槽交叉层状卵石砂岩，顶部为细粒杂岩砂岩-泥岩。每个循环都意味着从受河流影响的沉积系统到受潮汐影响的沉积系统的变化。每个周期底部附近的粗粒卵石砂岩层记录了大多数 SSDS，包括复杂变形层、假结核、载荷和火焰结构、垂直/倾斜沉积柱（沉积岩脉）和扭曲床等各种逃水结构，以及同步沉积断层。变形层位于未变形层的下方和上方。复杂变形的 SSDS 通常在顶部被未变形层明显截断，表现出同沉积特征，这表明变形发生在受影响层刚刚沉积之后，但在上覆层沉积之前，同时沉积是连续的。相分析显示不存在风暴/冲击波、坍塌、快速倾倒（大床）、撞击震动、火山活动、海啸波或研究区的沉积物重力流，从而否定了它们作为液化触发剂的可能性。变形结构的复杂性和大尺寸意味着在沉积物-水界面附近发生了广泛的液化。此外，变形层符合典型地震岩的大部分标准。在半地堑型冈瓦纳盆地中，这种震积岩可以与古地震联系起来，这标志着同裂谷断层再激活、盆地凹陷和相关的容纳变化阶段。变形结构的复杂性和大尺寸意味着在沉积物-水界面附近发生了广泛的液化。此外，变形层符合典型地震岩的大部分标准。在半地堑型冈瓦纳盆地中，这种震积岩可以与古地震联系起来，这标志着同裂谷断层再激活、盆地凹陷和相关的容纳变化阶段。变形结构的复杂性和大尺寸意味着在沉积物-水界面附近发生了广泛的液化。此外，变形层符合典型地震岩的大部分标准。在半地堑型冈瓦纳盆地中，这种震积岩可以与古地震联系起来，这标志着同裂谷断层再激活、盆地凹陷和相关的容纳变化阶段。