Electromagnetic surveying of seafloor mounds in the northern Gulf of Mexico

Ellis, Michelle; Evans, Robert; Hutchinson, Deborah R.; Hart, Patrick E.; Gardner, J. M.; Hagen, Rick A.

doi:10.1016/j.marpetgeo.2007.12.006

Cited by 36 publications

(26 citation statements)

References 38 publications

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“…During the R/V Pelican cruise, researchers collected several controlled-source electromagnetic profiles over the mounds and more than 6000 bottom photographs (Evans, 2004;Evans et al, 2004;Ellis et al, 2008). Fornari (2003) gives a detailed description of the deep-towed digital camera system.…”

Section: Methodsmentioning

confidence: 99%

“…This study area contains several seafloor mounds that may be vent features with associated accumulations of gas hydrate (Snyder et al, 2004). Prior to the 2005 JIP drilling, several research cruises, led by the U.S. Geological Survey, the Naval Research Laboratory, and the Woods Hole Oceanographic Institution, have investigated this site and collected high-resolution seismic reflection data , piston cores, heat flow measurements , electromagnetic readings (Ellis et al, 2008), near-bottom photographs , side-scan sonar, and multibeam bathymetry data. WesternGeco has also provided recently reprocessed 3D seismic data coverage of the area to the JIP, giving an excellent picture of the deep geologic framework beneath the mounds.…”

Section: Introductionmentioning

confidence: 99%

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A photographic and acoustic transect across two deep-water seafloor mounds, Mississippi Canyon, northern Gulf of Mexico

Hart

Hutchinson

Gardner

et al. 2008

Marine and Petroleum Geology

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a b s t r a c tIn the northern Gulf of Mexico, a series of seafloor mounds lie along the floor of the Mississippi Canyon in Atwater Valley lease blocks 13 and 14. The mounds, one of which was drilled by the Chevron Joint Industry Project on Methane Hydrates in 2005, are interpreted to be vent-related features that may contain significant accumulations of gas hydrate adjacent to gas and fluid migration pathways. The mounds are located w150 km south of Louisiana at w1300 m water depth.. New side-scan sonar data, multibeam bathymetry, and near-bottom photography along a 4 km northwest-southeast transect crossing two of the mounds (labeled D and F) reveal the mounds' detailed morphology and surficial characteristics. Mound D, w250 m in diameter and 7-10 m in height, has exposures of authigenic carbonates and appears to result from a seafloor vent of slow-to-moderate flux. Mound F, which is w400 m in diameter and 10-15 m high, is covered on its southwest flank by extruded mud flows, a characteristic associated with moderate-to-rapid flux. Chemosynthetic communities visible on the bottom photographs are restricted to bacterial mats on both mounds and mussels at Mound D. No indications of surficial gas hydrates are evident on the bottom photographs.Published by Elsevier Ltd.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A photographic and acoustic transect across two deep-water seafloor mounds, Mississippi Canyon, northern Gulf of Mexico

Hart

Hutchinson

Gardner

et al. 2008

Marine and Petroleum Geology

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show abstract

“…Geochemical and electromagnetic observations show significant lateral variability on and near Mound F (Coffin et al, 2008;Ellis et al, 2008). However, despite the assumed presence of dispersed advective conduits, the most intense instantaneous flux to the ocean appears to occur at mounds, where the mounds themselves, as well as a mudflow visible in side-scan data suggest flux energetic enough to mobilize sediment.…”

Section: Methane Distribution and Transportmentioning

confidence: 98%

Gas and gas hydrate distribution around seafloor seeps in Mississippi Canyon, Northern Gulf of Mexico, using multi-resolution seismic imagery

Wood

Hart

Hutchinson

et al. 2008

Marine and Petroleum Geology

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a b s t r a c tTo determine the impact of seeps and focused flow on the occurrence of shallow gas hydrates, several seafloor mounds in the Atwater Valley lease area of the Gulf of Mexico were surveyed with a wide range of seismic frequencies. Seismic data were acquired with a deep-towed, Helmholz resonator source (220-820 Hz); a high-resolution, Generator-Injector air-gun (30-300 Hz); and an industrial air-gun array (10-130 Hz). Each showed a significantly different response in this weakly reflective, highly faulted area. Seismic modeling and observations of reversed-polarity reflections and small scale diffractions are consistent with a model of methane transport dominated regionally by diffusion but punctuated by intense upward advection responsible for the bathymetric mounds, as well as likely advection along pervasive filamentous fractures away from the mounds.Published by Elsevier Ltd.

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“…Further details of the system are given by Evans [2007]. The system has been used previously across an area of gas discharge in the Gulf of Mexico [Ellis et al, 2008]. In this instance, extremely high conductivities within the subsurface were observed, resulting from the advection of warm briny fluids from depth toward the seafloor.…”

Section: Towed Electromagnetic Datamentioning

confidence: 99%

Geophysical and geochemical survey of a large marine pockmark on the Malin Shelf, Ireland

Szpak

Monteys

O’Reilly

et al. 2012

Geochem Geophys Geosyst

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[1] Marine pockmarks are a specific type of seabed geological setting resembling craters or pits and are considered seabed surface expressions of fluid flow in the subsurface. A large composite pockmark on the Malin Shelf, off the northern coast of Ireland was surveyed and ground truthed to assess its activity and investigate fluid related processes in the subsurface. Geophysical (including acoustic and electromagnetic) data confirmed the subsurface presence of signatures typical of fluids within the sediment. Shallow seismic profiling revealed a large shallow gas pocket and typical gas related indicators such as acoustic blanking and enhanced reflectors present underneath and around the large pockmark. Sulphate profiles indicate that gas from the shallow reservoir has been migrating upwards, at least recently. However, there are no chimney structures Copyright 2012 by the American Geophysical Union 1 of 18 observed in the sub-bottom data and the migration pathways are not apparent. Electromagnetic data show slightly elevated electrical conductivity on the edges of the pockmarks and a drop below regional levels within the confines of the pockmark, suggesting changes in physical properties of the sediment. Nuclear Magnetic Resonance (NMR) experiments were employed to characterize the organic component of sediments from selected depths. Very strong microbial signatures were evident in all NMR spectra but microbes outside the pockmark appear to be much more active than inside. These observations coincide with spikes in conductivity and the lateral gas bearing body suggesting that there is an increase in microbial activity and biomass when gas is present.

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Electromagnetic surveying of seafloor mounds in the northern Gulf of Mexico

Cited by 36 publications

References 38 publications

A photographic and acoustic transect across two deep-water seafloor mounds, Mississippi Canyon, northern Gulf of Mexico

A photographic and acoustic transect across two deep-water seafloor mounds, Mississippi Canyon, northern Gulf of Mexico

Gas and gas hydrate distribution around seafloor seeps in Mississippi Canyon, Northern Gulf of Mexico, using multi-resolution seismic imagery

Geophysical and geochemical survey of a large marine pockmark on the Malin Shelf, Ireland

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