Post-lease sale exploraton of the Navarin Basin, Bearing Sea, Alaska
Although the basin had optimistic beginnings, interest in further exploration of the Navarin Basin is waning because of disappointing d r i g results. Eight exploratory wells were drilled in the Navarin Basin in the year following Lease Sale 83 in 1984. All of these wells tested Tertiary fill that drapes or folds over simple, broad basement highs. Significant reservoir rocks were absent in all of these wells. Immature to mature Eocene kerogen with possible hydrocarbon-generating characteristics was found in a stratigraphic test well and two exploratory wells located on the flanks of the Pervenets subbasin. However, no signs of oil or oil migration were evident. A third exploratory well d r i ed on the southeast flank of the Pinnacle Island subbasin encountered thermogenic gas from a thin, probably lenticular Paleocene sandstone. The gas was probably sourced from interbedded, resinous coal. The geologic information collected from seven of the eight exploratory wells has now been released to the public. Of the leases acquired in Sale 83, 74 percent have been relinquished as of January 1988.
Review of Petroleum Geology of Anadyr and Khatyrka Basins, USSR
Two sedimentary basins bordering the Bering Sea in northeastern Siberia, the Anadyr and the Khatyrka, have been the targets of recent Soviet exploration for oil and gas. Drilling in the Anadyr basin has produced noncommercial quantities of gas and condensate from Tertiary volcaniclastic rocks. The Anadyr basin lies due west of Norton basin, a large unexplored sediment-filled Tertiary basin that underlies Norton Sound. Geologically, Anadyr basin lies between a late Mesozoic belt of volcanic and plutonic rocks similar to the Sierra Nevada of California and a complex foldbelt on the south that is structurally and lithologically similar to Franciscan terrane of the California Coast Ranges. Less extensive exploration in the Khatyrka basin has discovered only noncommercial quantities of oil and gas. The Khatyrka basin extends offshore between Capes Rubicon and Navarin near the northwest end of the Navarin basin on the Bering Shelf, and contains Tertiary sediment deposited within a structurally complex Mesozoic foldbelt that parallels the edge of the continental shelf.
Uyak Complex, Kodiak Islands, Alaska: A Cretaceous subduction complex
The Uyak Complex is a chaotic assemblage of gray chert and argillite, wacke, greenstone, radiolarian chert, and gabbroic and ultramafic rocks. The simplest interpretation of these rocks is that the gabbroic and ultramafic rocks and greenstone represent basal oceanic crust upon which the radiolarian chert, gray chert and argillite, and wacke were deposited, respectively, at a mid-ocean rise, on the abyssal ocean floor, and in an oceanic trench. Fossils are scarce in the complex and range in age from mid-Permian to mid–Early Cretaceous. The Uyak Complex was emplaced by underthrusting to the northwest beneath lower Mesozoic metamorphic, igneous, and sedimentary rocks. During underthrusting, brittle rock types were broken into phacoids of all sizes and suspended in the less competent matrix of gray chert and argillite with their longest dimensions aligned subparallel to cataclastic foliation. Prehnite and pumpellyite developed extensively in lithologies of suitable composition. The Uyak Complex correlates to the northeast with a similar assemblage of deep-sea rocks on the Barren Islands and with the McHugh Complex on the Kenai Peninsula and near Anchorage. The Uyak-McHugh belt defines a probable subduction complex trending northeast for at least 600 km along the margin of southwestern Alaska. The time of emplacement of this melange is uncertain, but fossils present indicate that it occurred after mid–Early Cretaceous time. To the southeast, the Uyak is underthrust by deformed turbidites of the Kodiak Formation, which are interpreted to have been deposited in an oceanic trench and accreted to the Alaskan margin in Late Cretaceous time. The relationship between the Uyak Complex and Kodiak Formation is uncertain, but they may represent two phases, or two facies, of Late Cretaceous accretion. Two large bodies of schist, referred to as the Kodiak Islands schist terrane, occur along the northwest border of the Uyak. The Kodiak Islands schist terrane is a blueschist-bearing metamorphic belt that has yielded mainly Early Jurassic K-Ar mineral ages. Similarities in K-Ar ages, metamorphism, and tectonic setting support a correlation between the Kodiak Islands schists and the Seldovia schist terrane on southern Kenai Peninsula. The Upper Triassic Shuyak Formation structurally overlies the Kodiak Islands schist terrane and Uyak Complex but is separated from them by a long, narrow pluton emplaced in Early Jurassic time. The Shuyak is a little-deformed formation of volcanic and volcaniclastic rocks. It correlates with similar rocks on the Alaska and Kenai Peninsulas, which together outline a lower Mesozoic forearc basin; K-Ar ages show that much of the Alaska-Aleutian Range batholith was intruded coeval with deposition in this forearc basin. A likely interpretation of these rocks is that the Kodiak-Seldovia schists are the only vestige of a subduction complex emplaced along the margin of southwestern Alaska during the prominent early Mesozoic volcanoplutonic activity recorded on the Alaska and Kenai Peninsulas and the Kodiak Islands.