Open AccessControls on the formation and stability of gas hydrate‐related bottom‐simulating reflectors (BSRs): A case study from the west Svalbard continental slope
Author(s) -
Haacke R. Ross,
Westbrook Graham K.,
Riley Michael S.
Publication year - 2008
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007jb005200
Subject(s) - clathrate hydrate , geology , continental shelf , continental margin , flux (metallurgy) , seabed , hydrate , fluid dynamics , flow (mathematics) , petrology , geomorphology , mineralogy , mechanics , oceanography , tectonics , materials science , chemistry , physics , organic chemistry , metallurgy , paleontology
The growth and stability of the free‐gas zone (FGZ) beneath gas‐hydrate related bottom‐simulating seismic reflectors (BSRs) is investigated using analytical and numerical analyses to understand the factors controlling the formation and depletion of free gas. For a model based on the continental slope west of Svalbard (a continental margin of north Atlantic type), we find that the FGZ is inherently unstable under a wide range of conditions because upward flow of under‐saturated liquid depletes free gas faster than it is produced by hydrate recycling. In these scenarios, the 150‐m‐thick FGZ that presently exists there would deplete within 10 5 –10 6 years. We suggest the FGZ is in a stable state, however, that is formed by a diffusion‐dominated mechanism that produces low concentrations of gas in a FGZ of steady state thickness. Gas forms across a thick zone because the upward fluid flux is relatively low and because the gas–water solubility decreases to a minimum several hundred meters below the seabed. This newly understood solubility‐curvature effect is complementary to hydrate recycling, but becomes the most important factor controlling the presence and properties of the BSR in environments where the rate of upward fluid flow and the rate of hydrate recycling are both relatively low (i.e., rifted continental margins). If the present‐day FGZ is in steady state, we estimate that the upward fluid flux in the west Svalbard site must be less than 0.15 mm a −1 .