Rock-magnetic signature of gas hydrates in accretionary prism sediments

Housen, Bernard A.; Musgrave, R. J.

doi:10.1016/0012-821x(95)00245-8

Cited by 85 publications

(113 citation statements)

References 21 publications

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“…The magnetic index D JH characterizes the occurrence of fine-grained (single domain-pseudo single domain) magnetic iron sulfides (Housen and Musgrave 1996). It is defined as the hysteresis parameters ratio (M rs /M s )/ (B cr /B c ) with M rs is the remanence at saturation, M s is the magnetization at saturation, B c is the coercive field, and B cr is the remanent coercive field.…”

Section: Introductionmentioning

confidence: 99%

“…It is defined as the hysteresis parameters ratio (M rs /M s )/ (B cr /B c ) with M rs is the remanence at saturation, M s is the magnetization at saturation, B c is the coercive field, and B cr is the remanent coercive field. In the Cascadia Margin marine sediments, D JH displays high values within low chlorinity zones and indicates the occurrence of gas hydrates (Housen and Musgrave 1996). Widespread occurrence of greigite (Fe 3 S 4 ) and pyrrhotite (Fe 7 S 8 ), associated with gas hydrates has later been reported in the Cascadia Margin (e.g., Musgrave et al 2006;Larrasoaña et al 2006;Larrasoaña et al 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Gas hydrates dissociate rapidly during drill core recovery, and their identification is mostly indirect. Various analytical approaches on cores and during drilling are indicative of gas hydrate occurrences such as isotopic and pore water anomalies (essentially chlorinity anomalies) (Hesse 2003), lower core temperature, well logging data (Collett 2001), heat flow and thermal anomalies (Yamano et al 2014;Kinoshita et al 2015), and characteristic rock magnetic variations (e.g., Housen and Musgrave 1996;Larrasoaña et al 2007).…”

Section: Introductionmentioning

confidence: 99%

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Rock magnetic characterization of ferrimagnetic iron sulfides in gas hydrate-bearing marine sediments at Site C0008, Nankai Trough, Pacific Ocean, off-coast Japan

Kars

Kodama

2015

Earth Planet Sp

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A high-resolution rock magnetic study was carried out in Integrated Ocean Drilling Program (IODP) Expedition 316 Hole C0008A located in the Megasplay Fault Zone of the Nankai Trough, SW offshore Japan, in order to document changes in magnetic properties throughout gas hydrate-bearing horizons. A total of 169 Pleistocene discrete samples were collected from~110 to 153 m core depth below sea floor (CSF), and their magnetic minerals concentration, grain size, composition, and rock magnetic parameters were estimated. Results showed the presence of iron oxides ((titano)-magnetite), iron sulfides (greigite and pyrrhotite), and their mixture, among which single-domain greigite is the most major magnetic mineral present in the samples. Two horizons containing ferrimagnetic iron sulfides (114.5-127.5 and 129.5-150 m CSF) covering almost the entire studied interval were identified, both associated with slight local pore water anomalies, suggesting occurrence of gas hydrates and anoxic conditions. These results are different from the neighboring Hole C0008C (215 m away from Hole C0008A) where four pore water anomalies and six iron sulfide-rich intervals were identified for the same time slice. Comparison of the lithology, physical properties, and geochemical data of the two boreholes at Site C0008 suggests that a combination of processes (e.g., availability of reactive iron, microbial activity) is responsible for such laterally varying distribution of the ferrimagnetic iron sulfides.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Rock magnetic characterization of ferrimagnetic iron sulfides in gas hydrate-bearing marine sediments at Site C0008, Nankai Trough, Pacific Ocean, off-coast Japan

Kars

Kodama

2015

Earth Planet Sp

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“…As at Site 994, this interval corresponds to a zone of downhole-decreasing interstitialwater chlorinity (see "Inorganic Geochemistry" section, this chapter) in a manner closely analogous to Sites 889 and 890 from Leg 146 (Shipboard Scientific Party, 1994). High SIRM/k in the interval of downhole-decreasing chlorinity at Sites 889 and 890 was associated with the presence of substantial proportions of greigite, which was demonstrated through a variety of shore-based rock-magnetic analyses (Housen and Musgrave, 1996). Alkalinity at both Sites 994 and 995 also exhibits an inflection between two distinct trends at -250-260 mbsf.…”

Section: Summary Of Rock-magnetic Analysismentioning

confidence: 81%

“…The alkalinity trend between 250 and 100 mbsf shows a positive anomaly above a linear gradient, which may imply bacterial activity over this interval. Bacterial authigenesis of greigite in response to the availability of methane (both as hydrate and as free gas or in solution) has been proposed previously (Musgrave et al, 1995;Housen and Musgrave, 1996).…”

Section: Summary Of Rock-magnetic Analysismentioning

confidence: 99%

Site 995

1996

Proceedings of the Ocean Drilling Program

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Coring totals:Type Nannofossil biostratigraphy indicates that the sequence recovered at Site 995 is mostly continuous except for a short hiatus within the uppermost Miocene between 570 and 580 mbsf. The sedimentation rates for the Quaternary (60 m/m.y.) and lower Pliocene (150 m/m.y.) sequences are almost identical to those at Site 994. However, the rate for the upper Pliocene (110 m/m.y.) is -17% higher than at Site 994. Because of the presence of a hiatus, we could not obtain a sedmintation rate for the upper Miocene sequence. The age of the oldest sediments cored at Site 995 (704.6 mbsf) is estimated to be 6.1 Ma. A magnetostratigraphy was determined for Hole 995A, despite remanences of <0.5 mA/m. Major chron boundaries were recognized as follows: C2An/C2r (Gauss/ Matuyama) at 136 mbsf, C2Ar/C2An (Gilbert/Gauss) at 295-320 mbsf, C3n/C2Ar at 320-350 mbsf, C3r/C3n at 545-580 mbsf, and C3An/C3r (Anomaly 5/Gilbert) at 620-635 mbsf.Methane/ethane ratios decrease with depth and reach a minimum of 146 at 699.4 mbsf. Higher molecular weight hydrocarbons are present in

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Authigenesis of magnetic minerals in gas hydrate-bearing sediments in the Nankai Trough, offshore Japan

Kars

Kodama

2015

Geochem. Geophys. Geosyst.

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Gas hydrate occurrence is one of the possible mechanisms invoked for iron sulfide formation.A high-resolution rock magnetic study was conducted in IODP Expedition 316 Hole C0008C located in the Megasplay Fault Zone of the Nankai Trough, offshore Japan. In this particular zone, no bottom simulating reflectors (BSR), indicating the base of the gas hydrate stability field, have been identified. Two hundred and eighteen Pleistocene samples were collected from 70 to 110 m CSF in order to document the changes in the concentration, grain size, and rock magnetic parameters of magnetic minerals, through the gas hydrate-bearing horizons. Two different populations of magnetic grains are recognized in the pseudosingle domain range. Three types of magnetic mineral assemblages are identified: iron oxides (magnetite), ferrimagnetic iron sulfides (greigite and pyrrhotite), and their mixture. Greigite and pyrrhotite are authigenic and constitute six layers, called IS1-IS6. IS1, IS3, IS4, and IS6 are associated with pore water anomalies, suggesting the occurrence of gas hydrates and anoxic conditions. IS2 and IS5 are probable gas hydrates horizons, although there is no independent data to confirm it. The remaining intervals are mainly composed of detrital iron oxides and paramagnetic iron sulfides. Two scenarios based on different diagenetic stages are proposed to explain the variations in the magnetic properties and mineralogy over the studied interval. The results suggest that rock magnetism appears useful to better constrain the gas hydrate distribution in Hole C0008C, and counterbalances the low resolution of pore water analyses and the absence of a BSR.

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Rock-magnetic signature of gas hydrates in accretionary prism sediments

Cited by 85 publications

References 21 publications

Rock magnetic characterization of ferrimagnetic iron sulfides in gas hydrate-bearing marine sediments at Site C0008, Nankai Trough, Pacific Ocean, off-coast Japan

Rock magnetic characterization of ferrimagnetic iron sulfides in gas hydrate-bearing marine sediments at Site C0008, Nankai Trough, Pacific Ocean, off-coast Japan

Site 995

Authigenesis of magnetic minerals in gas hydrate-bearing sediments in the Nankai Trough, offshore Japan

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