Channel-like features created by erosive submarine debris flows: Field evidence from the Middle Eocene Ainsa Basin,Spanish Pyrenees |
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| Institution: | 1. Instituto Geológico y Minero de España, c/Rios Rosas 23, 28003 Madrid, Spain;2. Instituto Geologico y Minero de España, Unidad de Zaragoza, c/Manuel Lasala 44, 50006 Zaragoza, Spain;3. Departamento de Ciencias de la Tierra, Universidad de Zaragoza, c/Pedro Cerbuna 12, 50009 Zaragoza, Spain;1. Stratigraphy Group, School of Earth and Environment, University of Leeds, LS2 9JT, UK;2. Stratigraphy Group, School of Earth, Atmospheric and Environmental Science, University of Manchester, M13 9PL, UK;1. Earth and Environmental Sciences Division, Los Alamos National Laboratory, 87545 Los Alamos, NM, USA;2. Ciencias de la Tierra, Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain;3. Desert Research Institute, 2215 Raggio Parkway, Reno, NV, USA;4. Geografía y Ordenación del Territorio, Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain;5. Instituto Geológico y Minero de España, Unidad de Zaragoza, Manuel Lasala 44, 50006 Zaragoza, Spain;6. Unidad Asociada en Ciencias de la Tierra IGME-Universidad de Zaragoza, Spain;7. Department of Geography, The University of Sheffield, Sheffield S10 2TN, UK;8. Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, 28006 Madrid, Spain;1. Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, Ministry of Natural Resources, Qingdao, Shandong 266061, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210093, China;4. Departamento de Geología, Universidad Nacional del Sur, Av. Alem 1253, cuerpo B´- 2° Piso, 8000 Bahía Blanca, Argentina.;5. State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China |
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| Abstract: | We present field evidence from the Middle Eocene deep-marine Ainsa Basin, Spanish Pyrenees, to show channel-like features likely created by erosive subaqueous debris flows. Evidence from this basin suggests that the most erosive subaqueous debris-flows may create megascours removing up to ～35 m thickness of sandy submarine-fan deposits from base-of-slope and lower-slope settings. This study suggests that individual debris flows may have been more erosive than turbidity currents, an observation that is opposed to many previous studies from the Ainsa Basin and other ancient deep-water clastic systems. In the Ainsa Basin, many of the debris flows deposited pebbly mudstones immediately above the basal erosion surfaces into which gouging flow-parallel grooves and pebble scours left isolated pebbles embedded in the immediately underlying sandstones. In one particularly well-exposed case, the sandstones immediately below the eroding debris flow were incorporated into it and preserved as sheared, disaggregated, brecciated, and partially liquefied sandstone beds within the pebbly mudstone. Our study suggests that erosion by large-volume debris flows in base-of-slope settings can be at least as important, if not more so, than turbidity currents in producing submarine megascours (probably chutes that, in cross section, superficially resemble submarine channels). This has important implications for understanding the erosivity of debris flows versus turbidity currents in modern and ancient environments, and it has significant implications for hydrocarbon reservoir continuity and heterogeneity, including the origin and recognition of mudstone-filled chutes or channels. |
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