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The Navarin basin consists of three en echelon subbasins filled with more than 26,000 ft of layered Tertiary sedimentary rock. The subbasins initially formed as a result of extensional deformation associated with oblique subduction of the Kula plate beneath the North American plate in the Late Cretaceous to early Tertiary. By the late Eocene, the fragment of the Kula plate, which now floors the Aleutian basin, was isolated by initiation of subduction at the present Aleutian arc. Active graben growth and major faulting ceased by the late Oligocene. Regional subsidence, controlled primarily by crustal cooling, initiated a second phase of sedimentation within and beyond structurally defined subbasins of pre-late Oligocene. The Navarin basin COST 1 well suggests that since th late Eocene, sedimentation within the three subbasins consisted of predominantly marine mudstone and siltstone and minor amounts of sandstone. Regressive events in the middle and late Oligocene, however, exposed older Tertiary and Mesozoic basement highs to wave-base erosion, which may have formed aprons of coarser grained detritus along the subbasins flanks. Eocene and early Oligocene marine sediments with good liquid hydrocarbon source potential and favorable levels of thermal maturity were present at the well site. This marine sequence thickens toward the deeper parts of the basin, indicating that a significant amount of source rock may be present next to traps associated with basement highs.
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