Shallow gas features in incised-valley fills (Rı́a de Vigo, NW Spain): a case study

García‐Gil, Soledad; Vilas, F.; García‐García, A.

doi:10.1016/s0278-4343(02)00057-2

Cited by 141 publications

(69 citation statements)

References 20 publications

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“…The formation of these gas structures results from their sedimentary environment, which may be due to recent sedimentation or human activity, among the evolutionary processes responsible for the characterization of the sedimentary deposition environment (GARCIA-GIL et al, 2002;BALTZER et al, 2005). The accumulation of these gases occurred in former geological periods (i.e., thousands of years before the present), due to the intense oxidization of organic matter in a sedimentary environment (GARCIA-GIL et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…The accumulation of these gases occurred in former geological periods (i.e., thousands of years before the present), due to the intense oxidization of organic matter in a sedimentary environment (GARCIA-GIL et al, 2002). Transgressive and regressive events over geological time may have changed this sedimentary environment in various ways, so as to have altered the distribution and quantity of the organic matter available at the site, which could thus provide traps to shape various types of gas (GARCIA-GIL et al, 2002). The sandy pockets may create aquifers and/or gas reservoirs, while the finer, mainly muddy sediments may form aquitards and/or sealing layers (GARCIA-GIL et al, 2002;WESCHENFELDER et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

“…The accumulation of these gases may occur on or beneath the surface of the sedimentary column, as well as dissolved in the water column (GARCÍA-GIL et al, 2002). The shallow gas structures occur in various geomorphological features in the form of an Acoustic Blanket (Acoustic Blanking), Acoustic Curtains, Acoustic Columns, Acoustic Turbidity, Turbidity Pinnacles and Intra-sedimentary Plumes, among others types of seismic reflectors (GARCIA-GIL et al, 2002;FRAZÃO;VITAL, 2007;WESCHENFELDER et al, 2006;WESCHENFELDER et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…The shallow gas structures occur in various geomorphological features in the form of an Acoustic Blanket (Acoustic Blanking), Acoustic Curtains, Acoustic Columns, Acoustic Turbidity, Turbidity Pinnacles and Intra-sedimentary Plumes, among others types of seismic reflectors (GARCIA-GIL et al, 2002;FRAZÃO;VITAL, 2007;WESCHENFELDER et al, 2006;WESCHENFELDER et al, 2016). The seepage may also occur in the form of Acoustic Plumes and Pockmarks, among others (GARCIA-GIL et al, 2002;FRAZÃO;VITAL, 2007;WESCHENFELDER et al, 2006;WESCHENFELDER et al, 2016). The spatial distribution of the different types of gas accumulation depends on the grain size, porosity and type of sediment and rock in which the gases are trapped (FRAZÃO;VITAL, 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Shallow gas features can be formed in diverse environments such as in sea-beds and on continental shelves (SCHROOT; SCHÜTTENHELM, 2003;EMEIS et al, 2004, respectively), loughs (LAFFERTY et al, 2006) or bays BENNIKE, 2009;KARNAUKH et al, 2016) and rías (DIEZ et al, 2007;GARCIA-GIL et al, 2002;DUARTE et al, 2007;IGLESIAS;, since these environments provide favorable conditions for their formation. In Brazil, the presence of these features has been described by various authors such as VITAL and STATTEGGER (1997) in the lowest stretch of the Amazon River; FIGUEIREDO and NITTROUER (1995) and FIGUEIREDO et al (1996) in the Amazon submarine delta and COSTA and FIGUEIREDO (1998) on the Amazon Continental Shelf; BAPTISTA NETO et al (2011) in Rodrigo de Freitas Lagoon -Rio de Janeiro; BENITES et al (2015) in Saco do Mamangua, Rio de Janeiro; BAPTISTA NETO et al (1996), QUARESMA et al (2000) and CATANZARO et al (2004) in Guanabara Bay, Rio de Janeiro; WESCHENFELDER et al (2006) in Patos Lagoon -Rio Grande do Sul associated with low-lying paleotopographical features such as paleo river channels and/or valleys; SCHWARZER et al (2006) in the Rio Açu Canyon and FRAZÃO and VITAL (2007) in the Potengy estuary, both in Rio Grande do Norte; FÉLIX (2012) in the Bertioga Channel, São Paulo;andSOUZA et al (2011), DEMARCO et al (2012), GUESSER et al (2012) andWESCHENFELDER et al (2016) presented preliminary results for the North Bay and the Conceição Lagoon -on the Santa Catarina Coast (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

et al. 2016

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This paper presents the spatial distribution of shallow gas structures and classifies them on the basis of two different data sets of CHIRP seismic records, one from the Conceição Lagoon (CL) and the other from North Bay (NB), both on Santa Catarina Island, Southern Brazil. Side scan sonar data from the CL were used to facilitate the understanding. The sub bottom (SB) seismic data were processed and interpreted by means of the SeisPrho software, the side scan sonar (SSS) data by SonarWiz5 software and the spatial extension being measured with the help of GIS. The shallow gas structures were defined in accordance with their shapes in the seismic recordings (echo-character). At the CL, shallow gas accumulations were found in the form of seepages and features presenting shallow gas structures between the surface and 8.20 ms (around 12.3 m). Accumulations of gas were found in the form of Acoustic Blanking with Acoustic Plume, and also Black Shadows. Pockmarks were found on the lagoon floor and associated with gas seepages (average size diameter 0.97 ± 0.19 m and density from 54 to 242 units per 50 m2). In the NB three types of shallow gas features were found in the seismic profile, namely Acoustic Blanking, Turbidity Pinnacles and Intra-sedimentary plumes. The depth varied from the surface to 12.10 ms (around 18.15 m). In both environments, the gas is escaping from the sediment into the water column. The Pockmarks in the CL and the Acoustic Plume features and sediment rich in total sulfur in the NB validate these findings.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

et al. 2016

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A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

Luo

Dale

Haffert

et al. 2016

Geochem Geophys Geosyst

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Takahe seep, located on the Opouawe Bank, Hikurangi Margin, is characterized by a well-defined subsurface seismic chimney structure $80,500 m 2 in area. Subseafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure. Reaction-transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m. Model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas.

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Sulfur, Iron, and Manganese Speciation in Anoxic Sediments with Methane (Ría de Vigo, NW Spain)

Ramírez-Pérez

Blas

García‐Gil

2017

CLEAN Soil Air Water

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High sedimentation rates and high organic matter contents promote the development of anoxic conditions in the Ría de Vigo (NW Spain). In these anoxic environments, elements such as S, Fe, and Mn are involved in redox processes affecting the CH4 dynamic. In this work, speciation of S, Fe, and Mn was evaluated through a five‐step sequential extraction procedure (exchangeable form and bound to carbonate, present in the reductive phase bound to Fe/Mn oxides, weakly bound to organic matter, strongly bound to organic matter, and residual fractions) in order to identify the origin of S, Fe, and Mn, distinguishing between fractions bound to organic compounds from those in the sulfide phase in these anoxic sediments. The study was conducted on samples from three gravity cores retrieved in the inner and outer zones of the ría in November 2012. S was mainly found in the fraction strongly bound to organic matter, showing that S is incorporated in the organic matter. However, the S in this fraction was associated with total organic carbon only in the inner zone (r = 0.833). More than 65% of total Fe and Mn was found in the residual fraction at all zones, being the highest in the outer zone, and showing an intense diagenesis in the ría, where precipitation of these elements as sulfides is favored by anoxic conditions. SO42− reduction, Fe and Mn reduction processes coexist in the same area within the cores.

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Shallow gas features in incised-valley fills (Rı́a de Vigo, NW Spain): a case study

Cited by 141 publications

References 20 publications

Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

Sulfur, Iron, and Manganese Speciation in Anoxic Sediments with Methane (Ría de Vigo, NW Spain)

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