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Recent discovery of thermogenic gaseous hydrocarbons seeping from the seafloor 45 km south of Nome, Alaska, suggests that the underlying Norton basin may be an important future petroleum province. The results of 38 sonobuoy refraction profiles obtained in 1977 and 1978 show that Norton Sound and Chirikov basin are underlain by a single sedimentary trough approximately 130 km wide and 350 km long; the basin axis trends west-northwest and extends from Stuart Island to a point 100 km west-southwest of King Island. Although average depth to basement is only 2.5 km, two deeper areas, containing up to 5.5 km of sedimentary section, were discovered 75 to 90 km northwest of the Yukon River delta.
Norton basin is floored by an acoustic basement whose compressional velocity is 5.5 to 6.5 km/sec. The basin fill consists of three major units distinguishable on the basis of their compressional velocities; unconformities probably separate each of these units. The basal unit, with a velocity of 4.9 km/sec, is present only in the deeper parts of the basin. A thick (2 to 3 km) section has velocities ranging from 2.3 to 3.7 km/sec and lies on this lower unit and on acoustic basement. Compressional velocities in the 1.2 km-thick upper unit range from 1.6 to 2.1 km/sec. The lower two units are probably Cretaceous and lower to middle Tertiary marine and nonmarine rocks lying on a basement complex of Paleozoic and Mesozoic igneous, metamorphic, and sedimentary rocks similar to those mapped n Seward Peninsula and St. Lawrence Island. The upper unit probably consists of upper Tertiary and Quaternary sedimentary rocks and sediment.
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