Introduction

Gas hydrate in onshore arctic environments is typically closely associated with permafrost. It is generally believed that thermal conditions conducive to the formation of permafrost and gas hydrate have persisted in the Arctic since the end of the Pliocene (about 1.88 Ma). Maps of present day permafrost reveal that about 20 percent of the land area of the northern hemisphere is underlain by permafrost (Fig. 1). Geologic studies (MacKay, 1972; Lewellen, 1973; Molochushkin, 1978) and thermal modeling of subsea conditions (Osterkamp and Fei, 1993) also indicate that permafrost and gas hydrate may exist within the continental shelf of the Arctic Ocean. Subaerial emergence of portions of the Arctic continental shelf to current water depths of 120 m (Bard and Fairbanks, 1990) during repeated Pleistocene glaciations, subjected the exposed shelf to temperature conditions favorable to the formation of permafrost and gas hydrate. Thus, it is speculated that "relic" permafrost and gas hydrate may exist on the continental shelf of the Arctic Ocean to present water depths of 120 m. In practical terms, onshore and nearshore gas hydrate can only exist in close association with permafrost, therefore, the map in Figure 1 that depicts the distribution of onshore continuous permafrost and the potential extent of "relic" sub-sea permafrost also depicts the potential limit of onshore and nearshore gas hydrate.

The primary objective here is to assess the occurrence and distribution of permafrost-associated gas hydrate accumulations within the circumarctic of the northern hemisphere. Regions examined (Fig. 2) include northern Alaska, the Mackenzie Delta-Beaufort Sea region and Sverdrup Basin of Canada; and four physiographic provinces of Russia: West Siberian Basin, Lena-Tunguska, Timan-Pechora and several sedimentary basins in northeastern Siberia and the

Pewe, 1983).
Figure 2. Location of sedimentary basins in the Northern Hemisphere that may contain gas hydrate.

Kamchatka area. The potential occurrence of gas hydrate on Svalbard and under the Greenland ice cap is also considered. Each regional discussion contains a brief description of the regional geology and a comprehensive review of the geologic parameters controlling the stability (formation temperature, pore-pressure, gas chemistry, and pore-water salinity) of gas hydrate accumulations. When available, each regional review contains descriptions of confirmed and/or inferred gas hydrate occurrences.

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