Using cryogenic SEM, we investigated the physical states of gas-hydrate-bearing samples
recovered by drill core from several localities including the SE India margin (NGHP Expedition
01), Cascadia margin (IODP Leg 311), Gulf of Mexico (RV Marion Dufresne 2002), and
Mackenzie River Delta (Mallik site, well 5L-38). Core material with a significant fraction of
preserved hydrate has only been obtained for cryogenic SEM investigation from relatively few
sites worldwide to date, yet certain consistent textural characteristics, as well as some clear
differences between sites have been observed. Gas hydrate in cores recovered from Cascadia,
Gulf of Mexico, and Mallik often occurs as a dense substrate with typical grain size of 30 to as
large as 200 μm. The hydrate often contains a significant fraction of isolated macropores that are
typically 5–100 μm in diameter and occupy 10-30 vol. % of the domain. In fine-grained sediment
sections of marine samples, gas hydrate commonly forms small pods or lenses with clay platelets
oriented sub-parallel around them, or as thin veins 50 to several hundred microns in thickness. In
some sections, hydrate grains are delineated by a NaCl-bearing selvage that forms thin rinds
along hydrate grain exteriors, presumably produced by salt exclusion during original hydrate
formation. Preliminary assessment of India NGHP-01 samples shows some regions consistent
with the observations described above, as well as other regions dominated by highly faceted
crystals that line the walls or interior of cavities where the hydrate grows unimpeded. Here, we
focus on gas hydrate grain morphology and microstructures, pore characteristics and distribution,
and the nature of the hydrate/sediment grain contacts of the recovered samples, comparing them
to each other and to laboratory-produced gas hydrates grown under known conditions.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/1109 |
| Date | 07 1900 |
| Creators | Stern, Laura A., Kirby, Stephen H. |
| 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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