| Summary: | About 97 400km of the coastal and offshore areas of the Beaufort-Mackenzie Basin were studied in the region from 68° to 71°N, and 130° to 137°30′W. Salinity of formation waters ranges up to 46 000mg/l at depths of 4km and shows evidence of extensive flushing by meteoric waters. Statistical multi-response permutation procedures demonstrate that, despite this deep flushing, it is also possible to distinguish formation waters from geopressure zones that had their composition modified by the membrane effects of shales. The top of the main geopressure zone lies at depths of about 2km beneath Richards island and increases in depth basinward to ~5km/ It is suggested that the main geopressure zone was already in existence sometime during the middle of the Tertiary, with its top lying at about 2km depth. Basinal uplift and erosion in the period from 6 to 5Ma was associated with extensive influx of meteoric water, which biodegraded the earlier formed hydrocrabons. Pliocene to Recent sediments of the Iperk sequence were deposited during a major basinal downwarp, with up to 3.5km being deposited far offshore. The geothermal regime has been able to adjust to this downwarping but the pre-Pliocene geopressure zone has not, and as a result still lies about 2km below the base of the Iperk sequence. Hydrocarbons, in the Mackenzie Bay and Kugmallit sequences (Miocene and Oligocene, respectively) occur above the main geopressure zone. -from Authors
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