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Potential for generation of natural gas in sediments of the convergent margin of the Aleutian Trench Area
Sediment being subducted in the eastern part of the convergent margin of the Aleutian Trench has a potential to generate large volumes of natural gas, perhaps as much as 2.8 x 10/sup 6/ m/sup 3/ of methane per km/sup 3/ of sediment, even though the content of organic carbon in the sediment is very low, averaging about 0.4%. This high potential for gas generation results primarily from the enormous volume of sediment undergoing subduction. Along the eastern Aleutian Arc-Trench system a 3-km thick sheet of sediment is being subducted at a rate of about 60 km per million years. We estimate, based on considerations of the stability requirements for gas hydrates observed as anomalous reflectors in some of our seismic records, and on one measurement in a deep well, that the geothermal gradient in this region is about 30/sup 0/C/km. Such a gradient suggests a temperature regime in which the maximum gas generation in the subducting sediment occurs beneath the upper slope. Thus the sediment of the upper slope, as opposed to that of the shelf and lower slope, could be the most prospective for gas accumulation if suitable reservoirs are present. 40 refs., 11 figs., 3 tabs