The Marnoso-arenacea turbidite succession outcropping in northern Italy is one of the most studied deep-water systems worldwide due to its excellent exposure. Despite the well-established sedimentology of the arenaceous succession, the origin of fine-grained intervals within the Marnoso-arenacea Fm is reconsidered in the light of methane-rich fluid expulsion, in particular as seep-carbonates are present. Fine-grained intervals are marked by limited vertical and lateral extent, in the order of 10² m and 10³ m respectively, and are often associated with small-scale sediment deformation. In this study, we conduct a detailed sedimentological and stratigraphic investigation of the well-exposed Prati Piani fine-grained interval (Serravallian in age) with particular focus on the characterization of trace fossils and seep-carbonates. Trace fossils interpreted as Thalassinoides are widespread throughout the interval and form a complex network testifying long-lasting burrowing activity of decapod crustaceans. Seep-carbonates crop out at different stratigraphic levels and form meter-sized blocks with δ¹³C from −33.2‰ to −18.2‰. The occurrence of aragonite cements and fossil chemosymbiotic fauna indicates episodic carbonate precipitation close to the paleo-seafloor. Although crustaceans have been frequently reported grazing microbial mats at modern seeps and leaving a ¹³C-depleted isotopic signature in trace fossils, in our study we found only one slightly depleted δ¹³C value (−9.5‰,) allowing us to exclude preferential authigenesis. Moreover, burrows are filled by detrital fine-grained sediments and hemipelagic micrite that may have diluted the methane-related signature. The association between in situ seep-carbonates and well-preserved trace fossils is of use to interpret the interval as formed by fine-grained sedimentation draping a thrust-related anticline. In this model, the stratigraphically- and laterally-confined deformed zones affecting the Prati Piani interval reflect in-situ soft-sediment deformation and small-scale slumping induced by fluid seepage along the ridge, consistent with present-day observations from several continental margins worldwide.

意大利北部出露的 Marnoso-arenacea 浊积岩序列因其极好的暴露度而成为全球研究最多的深水系统之一。尽管砂质层序的沉积学已经确立，但考虑到富含甲烷的流体排出，特别是当渗出碳酸盐存在时，重新考虑了 Marnoso-arenacea Fm 内细粒层段的起源。细粒度间隔以有限的垂直和横向范围为标志，数量级为 10 ²  m 和 10 ³ m ，并且通常与小尺度沉积物变形有关。在这项研究中，我们对出露良好的 Prati Piani 细粒层段（Serravallian 年代）进行了详细的沉积学和地层调查，特别关注痕量化石和渗出碳酸盐岩的表征。被解释为Thalassinoides 的痕量化石在整个区间广泛分布，并形成了一个复杂的网络，证明了十足目甲壳类动物的长期穴居活动。渗碳岩在不同地层层位出土并形成 δ ^{13 的}米级块体C从-33.2‰到-18.2‰。文石胶结物和化石化学共生动物群的出现表明在古海底附近有偶发性碳酸盐沉淀。尽管经常有报道称甲壳类动物在现代渗漏处放牧微生物垫，并在痕量化石中留下¹³ C 耗尽的同位素特征，但在我们的研究中，我们只发现了一种轻微耗尽的 δ ¹³C 值 (-9.5‰,) 允许我们排除优先自生。此外，洞穴中充满了碎屑细粒沉积物和半远洋泥晶，它们可能稀释了与甲烷相关的特征。原位渗出碳酸盐岩与保存完好的痕迹化石之间的关联可用于解释由细粒沉积覆盖与逆冲相关的背斜形成的层段。在该模型中，影响 Prati Piani 层段的地层和侧向限制变形带反映了原位软沉积物变形和沿山脊流体渗漏引起的小规模坍塌，与当今世界多个大陆边缘的观测结果一致.