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Mud volcanoes as a window into the deep biosphere?
Depreiter, D.; Vasconcelos, C.; Mauclaire, L.; McKenzie, J.; Van Rensbergen, P.; Henriet, J.-P. (2004). Mud volcanoes as a window into the deep biosphere?, in: 32nd International Geological Congress, Florence, Italy, August 20-28, 2004. Abstract Volume. pp. 1406 (Abstract 315-12)
In: (2004). 32nd International Geological Congress, Florence, Italy, August 20-28, 2004. Abstract Volume. IGC: Florence. 2 vols pp., more

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Author keywords
    mud vulcanoes carbonate crust microbial ecosystem Moroccan Margin

Authors  Top 
  • Depreiter, D., more
  • Vasconcelos, C.
  • Mauclaire, L.
  • McKenzie, J.
  • Van Rensbergen, P., more
  • Henriet, J.-P., more

    Mud volcanoes are often regarded as a source of geological information about the subsurface, through the mineralogical and/or isotopic composition of expelled mud, clasts and fluids. Here, we propose that mud volcanoes might also be considered as a window into the deep biosphere. We present results obtained using different methods to investigate microbial abundance and community structure. The microbial community structure in mud volcano sediments from Captain Arutyunov mud volcano on the Moroccan Margin was studied by fluorescent in situ hybridation (FISH) using four general oligonucleotide probes, targeting all organisms, Eubacteria, Archea, and sulphate reducers. Also, TOC and TC analyses of these sediments were measured, and the carbon and oxygen isotopic composition of carbonate crusts from a fault-bounded cliff in a nearby region was analysed.The total bacterial count of the samples averaged 1.2 10^8 cells per g of sediment, with the highest abundance at 10 cm below the sediment surface. This high density indicates that the mud volcano sediments are a suitable environment for microbial growth. This is confirmed by a relatively high percentage of hybridization obtained with the general probe, which showed that about 50% of the cells were metabolically active. The highest relative activity (62% at 10 cm below the sediment surface) also coincides with the highest abundance.The isotopic analysis has been carried out on separate components of a crust sample. The lithified carbonate matrix shows a carbon isotopic value of about -25‰. The other components, nonlithified mud, corals and bioclasts, display values of about -5‰. These results indicate that carbonate crust formation may occur within the methanogenesissulphate reduction transition zone (MST), which is located at a very shallow depth. This implies an upward migration of methane, possibly driven by fluid flow.Our results suggest that some of the microorganisms, present in the shallow subsurface on and around mud volcanoes, are brought to the surface together with fluids and/or mud breccia from the deep source layers. With further phylogenetic analysis of microorganisms living in mud volcano sediments and involved in the carbonate precipitation, we propose to identify some of these deep-dwelling organisms which are apparently able to adapt to a shallow sedimentary environment.

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