Anomalously deep BSR related to a transient state of the gas hydrate system in the western Black Sea

Type Article
Date 2019-01
Language English
Author(s) Ker StephanORCID1, Thomas Yannick1, Riboulot VincentORCID1, Sultan NabilORCID1, Bernard Céline1, 2, Scalabrin CarlaORCID1, Ion G3, Marsset Bruno1
Affiliation(s) 1 : IFREMER, REM GM, Plouzane, France
2 : ENSTA Bretagne, 2 rue François Verny, 29806 Brest Cedex 6, France
3 : GeoEcoMar, 23-25 Dimitrie Onciul Street, RO-024053, Romania
Source Geochemistry Geophysics Geosystems (1525-2027) (American Geophysical Union), 2019-01 , Vol. 20 , N. 1 , P. 442-459
DOI 10.1029/2018GC007861
WOS© Times Cited 3
Keyword(s) gas hydrate, BSR, excess pore pressure, Black Sea
Abstract

A comprehensive characterization of the gas hydrate system offshore the western Black Sea was performed through an integrated analysis of geophysical data. We detected the Bottom Simulating Reflector (BSR), which marks, in this area, the base of gas hydrate stability. The observed BSR depth does not fit the theoretical steady-state base of gas hydrate stability zone (BGHSZ). We show that the disparity between the BSR and predicted BGHSZ is the result of a transient state of the hydrate system due to the ongoing re-equilibrium since the Last Glacial Maximum. When gas hydrates are brought outside the stability zone due to changes in temperature and sea level, their dissociation generates an increase in interstitial pore pressure. This process is favorable to the re-crystallization of gas hydrates and delays the upward migration of the hydrate stability zone explaining the anomalously deep BSR. The BSR depth, which is commonly used to derive geothermal gradient values by assuming steady state conditions, is used here to derive the maximum excess pore pressure at the base of the gas hydrate stability zone. Derived excess pore pressure values of 1-2 MPa are probably the result of the low permeability of hydrate-bearing sediments. Higher pore pressure values derived at the location of a fault system could cause hydro-fracturing enabling the free gas to cross the gas hydrate stability zone and emerge at the seafloor, forming the flares observed in close vicinity to where the shallow gas hydrates were sampled.

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Ker Stephan, Thomas Yannick, Riboulot Vincent, Sultan Nabil, Bernard Céline, Scalabrin Carla, Ion G, Marsset Bruno (2019). Anomalously deep BSR related to a transient state of the gas hydrate system in the western Black Sea. Geochemistry Geophysics Geosystems, 20(1), 442-459. Publisher's official version : https://doi.org/10.1029/2018GC007861 , Open Access version : https://archimer.ifremer.fr/doc/00474/58531/