Abstract
The natural emission of methane-rich fluids from the seafloor, known as cold seepage, is a widespread process at modern continental margins. The studies on present-day cold seepages provide high-resolution datasets regarding the fluid plumbing system, biogeochemical processes in the sediment, seafloor seepage distribution and ecosystems. However, the long-term (hundreds of thousands to millions of years) evolution of cold seepage remains elusive. The identification and study of outcrop analogous now exposed on land represent a valuable method for better understanding the effects of geological processes and climate forcing on the development of cold seepage systems. Here, we provide an overview on Miocene seep-carbonate deposits of the northern Apennines (from Emilia to the Umbria-Marchean sector, Italy), based on decades of field research integrated with detailed sedimentological and geochemical investigations. We report a total of 13 seep-carbonate outcrops, which formed in three different structural settings of the paleo-accretionary wedge corresponding to wedge-top basins, outer slope and intrabasinal highs at the deformational front. We discuss the recurring lithostratigraphic occurrence of seep deposits and the main compositional features (carbonate facies, carbon and oxygen stable isotopes) in order to interpret the seepage dynamics, duration and infer the contribution of methane-rich fluids released by paleo-gas hydrates. The datasets presented in this study represent a valuable complete record of cold seepage spanning ~12 Myr, that can be used to better understand factors controlling the regional-scale spatial and temporal evolution of cold seepage systems at modern active continental margins.
Highlights
The seepage of methane-rich fluids at the seafloor, known as cold seeps, has been frequently observed in accretionary wedges, where active tectonics generate pore-fluid overpressures and induce fluid migration through the sediments [1,2,3,4,5]
Spectacular seep-carbonate examples have been reported from Miocene outer shelf and upper slope deposits at Hikurangi Margin, New Zealand [10,19,20] and in Cretaceous deposits linked to cold seepage in forebulge setting (Tepee Buttes carbonate mounds) cropping out in Colorado, USA [21]
In this paper we provide an overview of the main geochemical, sedimentological and stratigraphical features of the northern Apennine seep-carbonates located in the Emilia to Umbria-Marchean area (Figure 1), included in Burdigalian to Messinian successions
Summary
The seepage of methane-rich fluids at the seafloor, known as cold seeps, has been frequently observed in accretionary wedges, where active tectonics generate pore-fluid overpressures and induce fluid migration through the sediments [1,2,3,4,5]. Spectacular seep-carbonate examples have been reported from Miocene outer shelf and upper slope deposits at Hikurangi Margin, New Zealand [10,19,20] and in Cretaceous deposits linked to cold seepage in forebulge setting (Tepee Buttes carbonate mounds) cropping out in Colorado, USA [21] It is worth mentioning the well-exposed and widely-studied. The extraordinary dataset reported here, covers ~10,000 km area and the examined carbonate outcrops are representative of different structural settings along the paleo-Apennine wedge, serving as a record of the regional-scale spatial and temporal evolution of cold seepage systems which can be used to better understand analogous systems in other modern convergent geo-settings.
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