Characterisation and correlation of active hydrocarbon seepage using geophysical data sets: An example from the tropical, carbonate Yampi Shelf, Northwest Australia

Rollet, Nadège; Logan, Graham A.; Kennard, J. M.; O'Brien, P. E.; Jones, Andrew; Sexton, M.

doi:10.1016/j.marpetgeo.2005.10.002

Cited by 80 publications

(63 citation statements)

References 54 publications

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“…The identification and delineation of seep sites on the ocean floor often arises from the detection of anomalously high acoustic backscatter on side scan sonar or multibeam echosounder recordings (Hovland, 1991;Hovland, 1992;Orange et al, 2002;Van Rensbergen et al, 2002;Johnson et al, 2003;Sager et al, 2003;Shoji et al, 2005;Gay et al, 2006;Klaucke et al, 2006;Rollet et al, 2006). High-acoustic backscatter is caused by the enhanced acoustic impedance or roughness contrast between certain regions of the seafloor and their surroundings (Blondel and Murton, 1997).…”

Section: Introductionmentioning

confidence: 99%

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Anomalous sea-floor backscatter patterns in methane venting areas, Dnepr paleo-delta, NW Black Sea

et al. 2008

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The relation between acoustic seafloor backscatter and seep distribution is examined by integrating multibeam backscatter data and seep locations detected by single-beam echosounder. This study is further supported by side scan sonar recordings, high-resolution 5 kHz seismic data, pore-water analysis, grain-size analysis and visual seafloor observations. The datasets were acquired during the 2003 and 2004 expeditions of the EC-funded CRIMEA project in the Dnepr paleo-delta area, northwestern Black Sea.More than 600 active methane seeps were hydro-acoustically detected within a small (3.96 km by 3.72 km) area on the continental shelf of the Dnepr paleo-delta in water depths ranging from -72 m to -156 m. Multibeam and side scan sonar recordings show backscatter patterns that are clearly associated with seepage or with a present dune area. Seeps generally occur within medium-to highbackscatter areas which often coincide with pockmarks.High-resolution seismic data reveal the presence of an undulating gas front, i.e. the top of the free gas in the subsurface, which domes up towards and intersects the seafloor at locations where gas seeps and medium-to high-backscatter values are detected. Pore-water analysis of 4 multi-cores, taken at different backscatter intensity sites, shows a clear correlation between backscatter intensity and dissolved methane fluxes. All analyzed chemical species indicate increasing anaerobic oxidation of methane (AOM) from medium-to high-backscatter locations. This is confirmed by visual seafloor observations, showing bacterial mats and authigenic carbonates formed by AOM. Grain-size analysis of the 4 multi-cores only reveals negligible variations between the different backscatter sites.Integration of all datasets leads to the conclusion that the observed backscatter patterns are the result of ongoing methane seepage and the precipitation of methane-derived authigenic carbonates (MDACs) caused by AOM. The carbonate formation also appears to lead to a gradual (self-)sealing of the seeps by cementing fluid pathways/horizons followed by a relocation of the bubble-releasing locations. KeywordsMethane seeps; acoustic seafloor backscatter; anaerobic oxidation of methane; bacterial mats; pockmarks; methane-derived authigenic carbonates

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Section: Introductionmentioning

confidence: 99%

“…Direct localization of seeps, i.e. locations of bubble release, is performed by echosounders that detect gas bubbles in the water column due to the acoustic impedance contrast between water and the free gas in the bubbles (Egorov et al, 1998;Artemov, 2006;Naudts et al, 2006;Rollet et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Anomalous sea-floor backscatter patterns in methane venting areas, Dnepr paleo-delta, NW Black Sea

et al. 2008

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“…The remaining six study areas were in open shelf and slope regions. The Caswell Sub-basin (CSB) area is situated at water depths of 83-448 m along the northern continental shelf and slope, offshore from the Kimberley coast and downslope from the Yampi Shelf, which is noted for active hydrocarbon seepage (Rollet et al 2006). The survey locations lie between the shallow water areas, including Scott Reef, Ashmore and Cartier Islands and Heywood Shoals .…”

Section: Study Areas Geological Contextmentioning

confidence: 99%

Baseline biogeochemical data from Australia's continental margin links seabed sediments to water column characteristics

Radke

Nicholas

Thompson

et al. 2017

Mar. Freshwater Res.

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Abstract. Surficial marine sediments are an important source of nutrients for productivity and biodiversity, yet the biogeochemistry of these sediments is poorly known in Australia. Seabed samples were collected at .350 locations in Australia's western, northern and eastern continental margins during Federal Government surveys . Parameters analysed included measures of organic matter (OM) source (d 13 C, d 15 N and C : N ratios), concentration (percentage total organic carbon, %TOC, and surface area-normalised TOC, OC : SA) and bioavailability (chlorin indices, total reactive chlorins, total oxygen uptake, total sediment metabolism (TSM), sediment oxygen demand (SOD) and SOD and TSM normalised against TOC). The aim of the present study was to summarise these biogeochemical 'baseline' data and make contextualised inferences about processes that govern the observed concentrations. The OM was primarily from marine sources and the OC : SA broadly reflected water column productivity (based on Moderate Resolution Imaging Spectroradiometer, MODIS). Approximately 40% of sediments were organic poor by global standards, reflecting seawater oligotrophy; ,12% were organic rich due to benthic production, high water column productivity and pockmark formation. OM freshness varied due to pigment degradation in water columns and dilution with refractory OM in reworked sediments. d 15 N values confirmed the importance of N 2 fixation to Timor Sea productivity, and point to recycling of fixed nitrogen within food chains in Western Australia.

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“…Pockmarks have been reported in various depositional systems at water depths ranging from 30 m to over 3000 m (for a detailed review see Rollet et al, 2006;Gay et al, 2007). They generally form in unconsolidated, fine-grained deposits.…”

Section: Seafloor Fluid Seepagementioning

confidence: 99%

Geological fluid flow in sedimentary basins

Migeon

2017

Bull. Soc. géol. Fr.

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Characterisation and correlation of active hydrocarbon seepage using geophysical data sets: An example from the tropical, carbonate Yampi Shelf, Northwest Australia

Cited by 80 publications

References 54 publications

Anomalous sea-floor backscatter patterns in methane venting areas, Dnepr paleo-delta, NW Black Sea

Anomalous sea-floor backscatter patterns in methane venting areas, Dnepr paleo-delta, NW Black Sea

Baseline biogeochemical data from Australia's continental margin links seabed sediments to water column characteristics

Geological fluid flow in sedimentary basins

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