Geochemical processes associated with gas hydrate formation lead to the growth of iron
sulphides which have a geophysically-measurable magnetic signature. Detailed magnetic
investigation, complemented by petrological observations, were undertaken on cores from a
permafrost setting, the Mackenzie Delta (Canadian Northwest Territories) Mallik region, and
two marine settings, IODP Expedition 311 cores from the Cascadia margin off Vancouver
Island and the Indian National Gas Hydrate Program Expedition 1 from the Bengal Fan.
Stratigraphic profiles of the fine scale variations in bulk magnetic measurements correspond to
changes in lithology, grain size and pore fluid geochemistry which can be correlated on local to
regional scales. The lowest values of magnetic susceptibility are observed where iron has been
reduced to paramagnetic pyrite, formed in settings with high methane and sulphate or sulphide
flux, such as at methane vents. High magnetic susceptibility values are observed in sediments
which contain detrital magnetite, for example from glacial deposits, which has survived
diagenesis. Other high magnetic susceptibility values are observed in sediments in which the
ferrimagnetic iron-sulphide minerals greigite or smythite have been diagenetically introduced.
These minerals are mostly found outside the sediments which host gas hydrate. The mineral
textures and compositions indicate rapid disequilibrium crystallization. The unique physical
and geochemical properties of the environments where gas hydrates form, including the
availability of methane to fuel microbiological activity and the concentration of pore water
solutes during gas hydrate formation, lead to iron sulphide precipitation from solute-rich brines.
Magnetic surveying techniques help delineate anomalies related to gas hydrate deposits and the
diagenesis of magnetic iron minerals related to their formation. Detailed core logging
measurements and laboratory analyses of magnetic properties provide direct ties to original
lithology, petrophysical properties and diagenesis caused by gas hydrate formation.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/1046 |
| Date | 07 1900 |
| Creators | Esteban, Lionel, Enkin, Randolph J., Hamilton, Tark. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
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