Speculations on the petroleum geology of the accretionary body; an example from the central Aleutians

Author(s): McCarthy, Jill; Stevenson, Andrew J.; Scholl, David W.; Vallier, Tracy L.
Author Affiliation(s): Primary:
Stanford Univ., Dep. Geol., Stanford, CA, United States
U. S. Geol. Surv., United States
Volume Title: Marine and Petroleum Geology
Source: in conjunction with the [Marine and Petroleum Geology, 1(2), p.151-167. Publisher: Butterworth] Geological Society, Surrey, United Kingdom. ISSN: 0264-8172
Note: In English. 53 refs.; illus. incl. sects., sketch map
Summary: In the 300 km wide Adak-Amlia sector of the central Aleutian Trench ≈ 36,000 km3 of offscraped trench fill makes up the wedge-shaped mass of the Aleutian accretionary body. Within this wedge, seismic reflection profiles reveal an abundance of potential hydrocarbon-trapping structures. These structures include antiforms, thrust and normal faults, and stratigraphic pinchouts. Maximum closure on these features is 2 km. The silt and possibly sand size sediment within the offscraped turbidite deposits, and the porous diatomaceous pelagic deposits interbedded with and at the base of the wedge, may define suitable reservoirs for the entrapment of hydrocarbons. Potential seals for these reservoirs include diagenetically-altered and -produced siliceous and carbonate sediment. The organic carbon input into the central Aleutian Trench, based on carbon analyses of DSDP Legs 18 and 19 core samples, suggests that the average organic carbon content within the accretionary body is approximately 0.3-0.6%. Heat flow across the Aleutian Terrace indicates that at present the oil generation window lies at a depth of 3-6.5 km. At depths of 8 km (which corresponds to the maximum depth the offscraped sediment has been seismically resolved beneath the lower trench slope), the probable high (170-180°C) temperatures prohibit all but gas generation. The dewatering of trench sediment and subducted oceanic crust should produce an abundance of fluids circulating within the accretionary body. These fluids and gases can conduct hydrocarbons to any of the abundant trapping geometries or be lost from the system through sea floor seepage. The size and ultimate preservation of these deposits, however, are dependent on the deformational history of the prism both during accretion and after the accretion process has been superseded by subsequent tectonic regimes. Modified author abstract.
Year of Publication: 1984
Research Program: DSDP Deep Sea Drilling Project
Key Words: 29 Economic Geology, Energy Sources; Accretion; Adak Island; Alaska; Aleutian Islands; Amlia Island; Carbon; Crust; DSDP Site 186; DSDP Site 187; Deep Sea Drilling Project; Economic geology; Geophysical methods; Geophysical surveys; Leg 18; Leg 19; Oceanic crust; Organic carbon; Organic compounds; Organic materials; Petroleum; Reservoir rocks; Seismic methods; Southwestern Alaska; Stratigraphic traps; Structural traps; Subduction; Surveys; Traps; United States
Coordinates: N510748 N510749 W1740020 W1740021
N510636 N510636 W1735712 W1735712
N290000 N590000 W1220000 W1350000
Record ID: 1984049290
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