Gas and fluid venting at the Makran accretionary wedge off Pakistan

Rad, Ulrich von; Berner, Ulrich; Delisle, G.; Doose-Rolinski, Heidi; Fechner, N.; Линке, Петер; Lückge, Andreas; Roeser, H. A.; Schmaljohann, Ralf; Wiedicke, Michael; Parties, Scientific; Block, M.; Damm, Volkmar; Erbacher, Jochen; Fritsch, J.; Harazim, Bodo; Poggenburg, J.; Scheeder, Georg; Schreckenberger, Bernd; Mirbach, N. von; Drews, Manuela; Walter, Sylvia; Khan, Athar Ali; Inam, Asif; Tahir, Mazlan Md; Tabrez, Ali R.; Cheema, Amjed; Pervaz, M.; Ashraf, Muhammad

doi:10.1007/s003670000033

Cited by 81 publications

(34 citation statements)

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“…Cold seeps off Pakistan and their properties as habitats for chemosynthetic microbial and faunal life were described earlier (Faber et al, 1994;von Rad et al, 1996von Rad et al, , 2000Schmaljohann et al, 2001). Von Rad et al (2000) found signs for gas seepage mostly on the upper slope (<1000 m) which they explained to result from local tectonic uplift and hence a destabilization of gas hydrates trapped within the gas hydrate stability zone at greater depth. These authors found that the occurrence of Thioploca sp.…”

Section: Fischer Et Al: Pore Water Geochemistry Of Cold Seeps Offmentioning

confidence: 87%

“…Kukowski et al (2001) pointed out that sediments above the décollement are being accreted by imbricate thrusting, forming well defined coast-parallel accretionary ridges. This N-S cascade of accretionary ridges was mapped in 1997 ( Kukowski et al, 2000) and a distinct bottom simulating seismic reflector indicative for the phase boundary between free gas below and solid gas hydrates above has been described for the area (Kaul et al, 2000;von Rad et al, 2000;Ding et al, 2010).…”

Section: Geological Setting and Local Oceanographymentioning

confidence: 97%

“…and/or Beggiatoa sp. mats in the area is confined to sites punctually expelling free gas or sites of drift-wood or other large pieces of organic matter on the sea floor (von Rad et al, 2000). It has been suggested that local variations in the spatial distribution of benthic, chemosynthetic macrofauna in the study area may be co-induced by the depth of AOMderived sulfide supply and oxygen availability in the bottom water (von Rad et al, 1995(von Rad et al, , 1996(von Rad et al, , 2000Schmaljohann et al, 2001).…”

Section: Fischer Et Al: Pore Water Geochemistry Of Cold Seeps Offmentioning

confidence: 99%

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Interaction between hydrocarbon seepage, chemosynthetic communities, and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

et al. 2012

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Abstract. The interaction between fluid seepage, bottom water redox, and chemosynthetic communities was studied at cold seeps across one of the world's largest oxygen minimum zones (OMZ) located at the Makran convergent continental margin. Push cores were obtained from seeps within and below the core-OMZ with a remotely operated vehicle. Extracted sediment pore water was analyzed for sulfide and sulfate concentrations. Depending on oxygen availability in the bottom water, seeps were either colonized by microbial mats or by mats and macrofauna. The latter, including ampharetid polychaetes and vesicomyid clams, occurred in distinct benthic habitats, which were arranged in a concentric fashion around gas orifices. At most sites colonized by microbial mats, hydrogen sulfide was exported into the bottom water. Where macrofauna was widely abundant, hydrogen sulfide was retained within the sediment.Numerical modeling of pore water profiles was performed in order to assess rates of fluid advection and bioirrigation. While the magnitude of upward fluid flow decreased from 11 cm yr −1 to <1 cm yr −1 and the sulfate/methane transition (SMT) deepened with increasing distance from the central gas orifice, the fluxes of sulfate into the SMT did not significantly differ (6.6-9.3 mol m −2 yr −1 ). Depth-integrated rates of bioirrigation increased from 120 cm yr −1 in the central habitat, characterized by microbial mats and sparse macrofauna, to 297 cm yr −1 in the habitat of large and few small vesicomyid clams. These results reveal that chemosynthetic macrofauna inhabiting the outer seep habitats below the core-OMZ efficiently bioirrigate and thus transport sulfate down into the upper 10 to 15 cm of the sediment. In this way the animals deal with the lower upward flux of methane in outer habitats by stimulating rates of anaerobic oxidation of methane (AOM) with sulfate high enough to provide hydrogen sulfide for chemosynthesis. Through bioirrigation, macrofauna engineer their geochemical environment and fuel upward sulfide flux via AOM. Furthermore, due to the introduction of oxygenated bottom water into the sediment via bioirrigation, the depth of the sulfide sink gradually deepens towards outer habitats. We therefore suggest thatin addition to the oxygen levels in the water column, which determine whether macrofaunal communities can develop or not -it is the depth of the SMT and thus of sulfide production that determines which chemosynthetic communities are able to exploit the sulfide at depth. We hypothesize that large vesicomyid clams, by efficiently expanding the sulfate zone down into the sediment, could cut off smaller or less mobile organisms, as e.g. small clams and sulfur bacteria, from the sulfide source.

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Section: Fischer Et Al: Pore Water Geochemistry Of Cold Seeps Offmentioning

confidence: 87%

Section: Geological Setting and Local Oceanographymentioning

confidence: 97%

Section: Fischer Et Al: Pore Water Geochemistry Of Cold Seeps Offmentioning

confidence: 99%

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Interaction between hydrocarbon seepage, chemosynthetic communities, and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

et al. 2012

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“…Active mud volcanoes [e.g., Harrison, 1944;Snead, 1964;von Rad et al, 2000;Delisle et al, 2002] may indicate that such décollements take advantage of overpressured shales.…”

Section: Makranmentioning

confidence: 99%

“…The observed segmentation, two wedges separated by a largely undeformed zone, can only take place in the presence of one or more weak décolle-ments. Mud volcanism and seismic profiles [e.g., Harms et al, 1984;von Rad et al, 2000;Delisle et al, 2002;Grando and McClay, 2007;Ellouz-Zimmermann et al, 2007b] indicate the presence of such décollement(s) in the offshore Makran.…”

Section: Application To Makranmentioning

confidence: 99%

Effects of mass waste events on thrust wedges: Analogue experiments and application to the Makran accretionary wedge

Smit

Burg²,

Dolati

et al. 2010

Tectonics

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Geologically controlled intermittent gas eruption and its impact on bottom water temperature and chemosynthetic communities—A case study in the “HaiMa” cold seeps, South China Sea

Wei

et al. 2020

Geological Journal

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In 2018, the Institute of Deep Sea Science and Engineering investigated the “HaiMa” cold seeps in the northwestern part of the South China Sea using R/V “TanSuoYiHao” with manned submersible “ShenHaiYongShi.” Ten dives were conducted to make seafloor observations at six cold seeps (HM‐1 to HM‐6). By combining multibeam echosounder data and seismic profiles, a systematic study was made to understand fluid migration, accumulation, and eruption and their impact on the ecosystem. Location of gas flares observed in the multibeam echosounder data obtained in 2016 and 2018 is different, indicating a year‐level spatiotemporal variation of the cold seep activities. Seafloor observation shows that massive carbonates occur in HM‐1 and HM‐5, indicating two long‐term existed cold seeps (several thousands of years). Mussels covered large areas of HM‐2, HM‐3, and HM‐6, suggesting young active seeps. Elevated seabed with broken edges, mud cones, clay pools, and sudden increased water turbidity and temperature was encountered in multiple areas, which are inferred to be associated with shallow gas accumulation and eruption. Methane content of the headspace gas from shallow sediment at HM‐2 is higher than 99.5% with δ13C‐CH4 of −71.5‰ to 72.3‰, indicating a biogenic gas origin. It is inferred that the gas is sourced by reservoirs at ~1,280 mbsf, which are characterized by low frequency in the seismic profiles. Gas migrates from the gas reservoir to the top of the Basel uplift along the slope. High‐angle faults are widely developed between 800 and 240 mbsf, facilitating gas migration from the top of the Basel uplift to the shallow sediment. Most of the faults did not reach the seafloor; therefore, gas accumulated at shallow depth exhibits bright spots in the seismic profiles. When the pore pressure overcomes the overburden sediment, fractures will be created for gas entering the water column. Gas emission provides a pressure release mechanism; therefore, most fractures did not reach the seafloor as observed in the seismic profiles. However, it is speculated that gas emission will stop with growth of gas hydrates and authigenic carbonates, which continuously decrease the permeability of the original fractures. Pressure will be built up, and new fractures will be generated, leading to the formation of new seeps. This mechanism is inferred to result in the spatiotemporal variation of cold seep activity and affects the development of the cold seep ecosystem.

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Gas and fluid venting at the Makran accretionary wedge off Pakistan

Cited by 81 publications

References 0 publications

Interaction between hydrocarbon seepage, chemosynthetic communities, and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

Interaction between hydrocarbon seepage, chemosynthetic communities, and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

Effects of mass waste events on thrust wedges: Analogue experiments and application to the Makran accretionary wedge

Geologically controlled intermittent gas eruption and its impact on bottom water temperature and chemosynthetic communities—A case study in the “HaiMa” cold seeps, South China Sea

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