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RISS 인기검색어
- 검색키워드
- 저자 : Dallimore, S.R. (검색결과 2 건)
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Riedel, M.,Brent, T.A.,Taylor, G.,Taylor, A.E.,Hong, J.-K.,Jin, Y.-K.,Dallimore, S.R. Elsevier 2017 Marine and petroleum geology Vol.81 No.-
<P><B>Abstract</B></P> <P>The presence of a wedge of offshore permafrost on the shelf of the Canadian Beaufort Sea has been previously recognized and the consequence of a prolonged occurrence of such permafrost is the possibility of an underlying gas hydrate regime. We present the first evidence for wide-spread occurrences of gas hydrates across the shelf in water depths of 60–100 m using 3D and 2D multichannel seismic (MCS) data. A reflection with a polarity opposite to the seafloor was identified ∼1000 m below the seafloor that mimics some of the bottom-simulating reflections (BSRs) in marine gas hydrate regimes. However, the reflection is not truly bottom-simulating, as its depth is controlled by offshore permafrost. The depth of the reflection decreases with increasing water depth, as predicted from thermal modeling of the late Wisconsin transgression. The reflection crosscuts strata and defines a zone of enhanced reflectivity beneath it, which originates from free gas accumulated at the phase boundary over time as permafrost and associated gas hydrate stability zones thin in response to the transgression. The wide-spread gas hydrate occurrence beneath permafrost has implications on the region including drilling hazards associated with the presence of free gas, possible overpressure, lateral migration of fluids and expulsion at the seafloor. In contrast to the permafrost-associated gas hydrates, a deep-water marine BSR was also identified on MCS profiles. The MCS data show a polarity-reversed seismic reflection associated with a low-velocity zone beneath it. The seismic data coverage in the southern Beaufort Sea shows that the deep-water marine BSR is not uniformly present across the entire region. The regional discrepancy of the BSR occurrence between the US Alaska portion and the Mackenzie Delta region may be a result of high sedimentation rates expected for the central Mackenzie delta and high abundance of mass-transport deposits that prohibit gas to accumulate within and beneath the gas hydrate stability zone.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Discovery of permafrost related gas hydrate regime in Beaufort shelf region. </LI> <LI> Base of gas hydrate stability zone follows trend predicted by thermal modelling. </LI> <LI> Permafrost-associated gas hydrate regime poses geo-hazards to drilling. </LI> <LI> Deep-water marine hydrate regime appears irregular across Beaufort margin. </LI> </UL> </P>
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