HR: 1340h
AN: PP43B-1283    [Abstracts]
TI: Characterization of the Paleoenvironmental Evolution of the Mallik Area From Gas Geochemistry Data
AU: * Wiersberg, T
EM: wiers@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473, Germany
AU: Erzinger, J
EM: erz@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473, Germany
AB: During drilling of the JAPEX/JNOC/GCS et al. Mallik Gas Hydrate Production Research wells (NWT, Canada), up to 35 vol-% CH₄ were found in drill mud gas at 106 m depth within the permafrost. The carbon isotope composition of CH₄ implies that this gas is of microbial origin (δ¹³C from -75‰ to - 77‰ PDB). Surprisingly, noble gas data suggest that at least some of this gas could be trapped in gas hydrates, at a depth distinctly shallower than the predicted gas hydrate stability field. Although microbes are capable of some metabolic activities at subzero temperatures, it is unlikely that production of methane under permafrost conditions can account for that amount of natural gas at this depth. Therefore, we suggest that the formation of this gas must have occurred under non-permafrost conditions. Furthermore, this gas reservoir was sealed from mixing with thermogenic gas, migrating from depth, which could be identified at the base of the permafrost at approx. 620m depth (δ¹³C=-42.5‰). We interpret the observed features by partially thawing of existing permafrost at least down to 106 m depth during a period of warming where the area was covered by a lake or by the ocean through inundation of the shoreline. Once the lake was drained or the shoreline was uplifted, the surface became again exposed to air and permafrost again developed on top of the unfrozen ground. As the permafrost gradually advanced downward, the water below was pressurized due to freezing and expansion of the newly formed ice, leading to pressure conditions that stabilize gas hydrates.
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
DE: 0702 Permafrost (0475)
DE: 0704 Seasonally frozen ground
DE: 1055 Organic and biogenic geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting