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C.E. Kirschner

Publications and source records attributed to C.E. Kirschner.

7 recordsLinked to original sources
USGS1992

Impact origin of the Avak Structure, Arctic Alaska, and genesis of the Barrow gas fields

Geophysical and subsurface geologic data suggest that the Avak structure, which underlies the Arctic Coastal Plain 12 km southeast of Barrow, Alaska, is a hypervelocity meteorite or comet impact structure. The structure is a roughly circular area of uplifted, chaotically deformed Upper Triassic to Lower Cretaceous sedimentary rocks 8 km in diameter that is bounded by a ring of anastomosing, inwardly dipping, listric normal faults 12 km in diameter. A zone of gently outward-dipping sedimentary country rocks forms a discontinuous ring of "rim anticlines" within the peripheral ring of normal faults. Beyond these anticlines, the sedimentary rocks are almost flat-lying. Basement consists of strongly deformed Ordovician and Silurian argillite. Density and acoustic impedance con rasts between the argillite and the overlying strata produce gravity and seismic-reflection signatures that define a ring of anticlines around the disturbed zone and a structural high surrounded by an annular structural low at its center. In the adjacent Barrow gas fields, the tops of the informally named Neocomian "pebble shale" unit and the gas-producing Lower Jurassic Barrow sand (local usage) lie at average subsea depths of 488 m and 670 m, respectively. In the Avak 1 well, drilled on the central high, the pebble shale and the Barrow sand lie near the surface, documenting more than 500 m of relative uplift at the high. The cores in this well have steep dips (30-90 degrees), mixed breccia with Franklinian argillite clasts 10 and 90 m above basement, quartz grains with shock mosaicism and multiple sets of shock lamellae, oriented concussion fractures in sand-size quartz grains, and shatter cones resembling those found in the peripheral zones of well-documented impact structures. In addition, above-background levels o fractured quartz grains in Barrow sand were found as far as 19 km beyond the rim of the Avak structure. Data concerning the age of the Avak structure are not definitive. If submarine landslide deposits in the upper part of the Aptian and Albian Torok Formation, in the subsurface 200 km to the east, were triggered by the Avak event, then the Avak meteorite struck a submerged marine shelf about 100 + or - 5 Ma. However, the impact features found at Avak (shatter cones, concussion fractures, shock lamellae and shock mosaicism in quartz grains, and widespread cataclasis) characterize the distal zones of meteorite impact structures. Fused rocks, plastic deformation, and shock-metamorphic minerals found in more proximal zones of impact structures are apparently missing. These observations, and the lack of Avak ejecta in cuttings and cores from the Torok Formation and Nanushuk Group (Albian to middle Cenomanian) in surrounding test wells, indicate that the impact event postdated these beds. In this case, the Avak meteorite struck a Late Cretaceous or Tertiary marine shelf or coastal plain between the Cenomanian (ca. 95 Ma), and deposition of the basal beds of the overlying late Pliocene and Quaternary Gubik Formation (ca. 3 Ma).

Alaska↗
USGS1976

Tectonic framework of petroliferous rocks in Alaska: hydrocarbons

Alaska, which contains about 28% of the land and continental shelf of the United States, is estimated by the U.S. Geological Survey to contain about one third of the nation's undiscovered oil and about one sixth of its undiscovered natural gas. The Survey estimates that fields discovered in Alaska through 1972 ultimately may produce about 26 billion bbl of oil and 68 Tcf of natural gas. In northern Alaska, Paleozoic and Mesozoic shelf and slope carbonate and clastic rocks of the Brooks Range orogen were thrust relatively northward over the depressed south margin of the Paleozoic and Mesozoic Arctic platform. A foredeep, the Colville geosyncline, developed across the depressed margin of the platform in earliest Cretaceous time. Detritus from the Brooks Range filled the foredeep and prograded northward to fill the Cretaceous and Tertiary North Chukchi and Umiat-Camden basins and form the progradational Beaufort shelf. The largest petroleum reserves (Prudhoe Bay and associated fields) and the best prospects for additional large discoveries in Alaska lie in the areally extensive upper Paleozoic to Tertiary carbonate and clastic rocks of northern Alaska. In southern Alaska, a series of arc-trench systems developed on oceanic rocks during Jurassic and Cretaceous time. Between these arcs and the metamorphic (continental) terranes of east-central and northern Alaska, large back-arc and arc-trench gap basins received thick volcanic and detrital deposits. These deposits were extensively, and commonly intensely, deformed and disrupted by mid-Jurassic to Tertiary plutonism, Laramide oroclinal bending, wrench faulting, and arc-related compression. This deformation, coupled with low porosity (in part produced by diagenetic mobilization of labile constituents), has left these rocks with only modest, local prospects for petroleum. Laramide events compressed and consolidated ("continentalized") the late Mesozoic back-arc basin deposits and welded them to the older continental terranes on the north and east. Subsequent sedimentation was localized and nonmarine except in onshore and offshore coastal basins, where thick sections of mixed marine and nonmarine Tertiary sediments accumulated. The Aleutian arc and the associated Queen Charlotte transform-fault system have dominated structural and depositional patterns in southern Alaska, including many of the Tertiary coastal basins, since the early Cenozoic. The Tertiary coastal basins are areally extensive, and in some areas contain many large folds. They are known to be petroliferous in Bristol Bay and the Gulf of Alaska, and to contain major accumulations of oil and gas at Cook Inlet, but they are relatively little explored.

Alaska↗
USGS1975

Tectonic framework of petroliferous rocks in Alaska

Alaska, comprising 3.6 X 10 6 sq km (about 28 percent) of the land, shelf, and upper continental slope of the United States, has been estimated by the U.S. Geological Survey (1974) to contain about 25 percent of the Nation's petroleum resources. Some 11 billion barrels of petroleum liquids and 31 trillion cubic feet of natural gas have been announced as discovered to date. In northern Alaska, Paleozoic and Mesozoic shelf and slope deposits of the Brooks Range orogen were thrust relatively northward over the depressed south margin of the Paleozoic and Mesozoic Arctic platform, upon which a foredeep (the Colville geosyncline) developed in earliest Cretaceous time. Detritus from the Brooks Range filled the foredeep and pro-graded northwest and northeast to fill the Cretaceous and Tertiary North Chukchi and Umiat-Camden basins and form the Beaufort shelf. In southern Alaska, a series of arc-trench systems developed on oceanic rocks during the Jurassic and Cretaceous. Between the arcs and the metamorphic (continental) terranes of east-central and northern Alaska, large back-arc and arc-trench gap basins received thick volcanic and detrital deposits. These deposits were extensively deformed and disrupted by mid-Jurassic to Tertiary plutonism, Laramide oroclinal bending, wrench faulting, and arc-related compression. The Laramide events 'continentalized' the late Mesozoic back-arc basin deposits and welded them to the older continental terranes to the north and east. Subsequent sedimentation was localized and nonmarine except in onshore and offshore coastal basins, where thick mixed marine and nonmarine sections were deposited. The Aleutian arc and associated Queen Charlotte transform fault system have dominated structural and depositional patterns in southern Alaska since the early Cenozoic. The largest petroleum reserves in Alaska (the Prudhoe Bay and associated fields) and the best prospects for additional large discoveries are in northern Alaska, where an extensive terrane is underlain by Upper Paleozoic to Tertiary carbonate and shelf, slope and delta clastic deposits. The pre-Tertiary back-arc and arc-trench gap basins in southern and interior Alaska are too intensely deformed or too low in porosity (because of diagenetic mobilization of labile constituents) to offer more than modest local prospects. The Tertiary coastal basins do, however, offer large tracts of thick marine and nonmarine clastic rocks and in some areas many large folds to exploration. Such basins are known to be petroliferous on Bristol Bay and the Gulf of Alaska and to contain major accumulations of oil and gas at Cook Inlet, but they are relatively little explored.

Alaska↗