The enigma of double BSRs: indicators for changes in the hydrate stability field?

Posewang, Jörg; Mienert, Jürgen

doi:10.1007/s003670050103

Cited by 85 publications

(68 citation statements)

References 5 publications

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“…To convert travel-time in depth, we considered minimum and maximum velocity values of 1600 and 1800 m/s, respectively, in agreement with velocity analysis in similar environments (Posewang and Mienert, 1999;Lüdmann et al, 2004).…”

Section: Methodsmentioning

confidence: 98%

“…While the upper BSR is generally interpreted to represent the current BGHSZ, the origin of the lower BSR has remained controversial. Several interpretations have been proposed, such as a relic of a former position of the BGHSZ (Posewang and Mienert, 1999;Matsumoto et al, 2000;Foucher et al, 2002;Baba and Yamada, 2004;Bangs et al, 2005), a current equilibrium feature associated with layers of gas hydrates with distinct compositions (Posewang and Mienert, 1999;Andreassen et al, 2000), or the lower boundary of a transitional zone between gas hydrates and free gas (Baba and Yamada, 2004). Alternatively, other processes not associated with gas hydrates such as transition from opal-A to opal-CT may create a normal-polarity diagenesis-related BSR (Hein et al, 1978;Berndt et al, 2004).…”

Section: Introductionmentioning

confidence: 93%

“…Uncommon double BSRs have been reported on the Norwegian margin (Posewang and Mienert, 1999;Andreassen et al, 2000), in the Nankai Trough off central Japan (Matsumoto et al, 2000;Foucher et al, 2002;Baba and Yamada, 2004) and at Hydrate Ridge on Cascadia continental margin (Shipboard Scientific Party ODP Leg 204, 2002;Bangs et al, 2005). While the upper BSR is generally interpreted to represent the current BGHSZ, the origin of the lower BSR has remained controversial.…”

Section: Introductionmentioning

confidence: 95%

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Multiple bottom-simulating reflections in the Black Sea: Potential proxies of past climate conditions

et al. 2006

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A previously unknown pattern of multiple bottom-simulating reflections (BSRs) occurs on high-resolution reflection seismic data in the Danube deep-sea fan, associated with acoustic features indicating free gas. Our study provides evidence that this pattern is developed in relation with the architecture of distinct channel-levee systems of the Danube fan. Channel-levee systems hosting multiple BSRs act as relatively sealed gas-bearing systems whose top is situated above the base of the gas hydrate stability zone (BGHSZ). Inside these systems, free gas accumulates below the BGHSZ under a combined lithological, structural and stratigraphical control.The uppermost BSR marks the current equilibrium BGHSZ, for a gas composition of more than 99% methane. Model-derived depths of the BGHSZ for different gas compositions and pressure-temperature conditions show that multiple BSRs would correspond to the BGHSZ either for (1) layers of gas hydrates with high contents of heavy hydrocarbons or hydrogen sulphide, or (2) stable climatic episodes with temperatures between glacial values and the present-day conditions. As the gas hydrate compositions required by hypothesis (1) are in sharp contradiction with the general background of the gas composition in the study area, we suggest that multiple BSRs are most probably relics of former positions of the BGHSZ, corresponding to successive steps of climate warming. In this case, they can provide sea-bottom paleotemperature values for these episodes, and hence they are potential new proxies for deciphering past climate conditions.

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Section: Methodsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 95%

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Multiple bottom-simulating reflections in the Black Sea: Potential proxies of past climate conditions

et al. 2006

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“…Gas and gas hydrate. While a well-defined bottom-simulating reflection (BSR) was identified on seismic profiles from the northern flank of the Storegga Slide (Bugge, 1983;Mienert and Bryn, 1997;Mienert et al, 1998;Posewang and Mienert, 1999;Bouriak et al, 2000, among others), there is no physical evidence of gas hydrates in the area. According to the NGI report No.…”

Section: Geotechnical Characterisationmentioning

confidence: 97%

Triggering mechanisms of slope instability processes and sediment failures on continental margins: a geotechnical approach

et al. 2004

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The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment.In the second part of the paper, the geotechnical properties of the sediment from different Costa areas are presented. Comparison between observed geotechnical properties and the theoretical behaviour was done in order to improve our understanding of the origin of the different observed slides. D

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“…They hypothesized that the lower level could correspond to a paleo-BSR, a former BSR, that now lies below the BGHS because of sediment deposition which led to an upward shift of the BGHS. A BSR that splits into two levels representing an actual BSR and a paleo-BSR has been observed before by Gorman et al (2002) at the Blake Ridge, where this splitting was caused by erosion, and also by Posewang and Mienert (1999b) near Norway, as well as by Foucher et al (2002) on the Nankai Slope. Foucher et al (2002) also offer an explanation for the observation of a Paleo-BSR.…”

Section: Paleo-bsrmentioning

confidence: 88%

Seismic velocities from the Yaquina forearc basin off Peru: evidence for free gas within the gas hydrate stability zone

Netzeband

Hübscher

Gajewski

et al. 2005

Int J Earth Sci (Geol Rundsch)

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Multichannel seismic (MCS) data from the Yaquina forearc basin off Peru reveal a complex distribution of gas and gas hydrate related reflections. Lateral variations of the reflection pattern at the assumed base of the gas hydrate stability zone in terms of continuity, amplitude, and signal attenuation underneath are observed, as well as the possible occurrence of paleobottom simulating reflectors (BSRs). Phase reversed reflections above the bottom simulating reflector point to free gas within the gas hydrate stability zone (GHSZ). To constrain the interpretation of the observed reflection pattern we calculated the velocity distribution along the MCS line from high-resolution ocean bottom hydrophone recordings with two independent methods. Heat flux values estimated on the basis of the velocity-depth functions increase with decreasing amplitude of the BSR and peak near chemoherms. These results suggest a model of the Yaquina Basin where free gas is trapped under parts of the BSR, and within the GHSZ, particularly under the seafloor and under an erosional unconformity. The hypothesis of a paleo-BSR that reflects the uplift of the base of the hydrate stability zone caused by the deposition of a particular sediment sequence is supported by the estimated heat flux values.

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The enigma of double BSRs: indicators for changes in the hydrate stability field?

Cited by 85 publications

References 5 publications

Multiple bottom-simulating reflections in the Black Sea: Potential proxies of past climate conditions

Multiple bottom-simulating reflections in the Black Sea: Potential proxies of past climate conditions

Triggering mechanisms of slope instability processes and sediment failures on continental margins: a geotechnical approach

Seismic velocities from the Yaquina forearc basin off Peru: evidence for free gas within the gas hydrate stability zone

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