Val Verde Basin
The Cook Inlet Basin (Northern Alaska)
The Cook Inlet Basin is a northeast-trending collisional forearc basin that stretches from the Gulf of Alaska into South central Alaska, just east of the Matanuska Valley. [1]. It is located in the arc-trench gap between the Alaska-Aleutian Range batholith. The western portion of the basin lies dierectly above the Aleutian subduction zone[1], while the eastern side of the basin overlays the subduction of the Yakutat microplate beneath the North American plate.
Tectonic Evolution
The geology of Alaska is characterized by the collision and accretion of terranes over the last 100Ma[2]
Depositional History and Stratigraphy
Late Triassic and Early Jurassic
The Upper Triassic lithology, known as the Kamishak Formation, and the Lower Jurassic lithology, known as the Talkeetna Formation, are both part of an oceanic island arc [3]. These formations are present along the East-West margin of the Burin Bay Fault zone and are intruded by igneous plutons originating from dehydration melt produced by Pacific Plate subduction. The Kamishak Formation is reflective of a shallow reef environment that graded into deeper marine sediments that were deposited during a transgressive ocean sequence[4]. During the late Triassic, the pacific plate was subducting beneath the North American Plate causing plutons, dikes and sills to intrude into the country rock, especially near the Burin Bay Fault zone. Triassic sediments within the Kamishak sit atop a 7775 ft layer of Permian volcanic rocks[5].
The Jurassic Talkeetna formation sits unconformably on top of the Kamishak formation, although some disconformities are seen throughout the peninsula [1]. The Talkeetna is comprised mostly of volcanic material interbedded with characteristic lava flows and tuffs. Geochemical analysis of the lava flows indicate the formation was once at great depths within the ocean[6]. The formation records periods of shallow, intermediate and deep crustal levels originating in an oceanic island arc environment.
Middle and Upper Jurassic
During the middle to late Jurassic, the collision between an amalgamated superterrane of Tertiary, Quartenary and Mesozoic sediments collided into the continental margin of Alaska[7]. The collision caused the shallow crust to be uplifted and eroded causing the exposure of igneous dike intrustions. The stratigraphy of this time period records the synorogenic sedimentation of marine Jurassic and Cretaceous sandstone, shale and limestone. Three major unconformities are present, the lower Tuxendi Group, the upper Tuxedni Group-Chinitna Formation and the Naknek Formation[1].
The lower Texendi Group
This unconformity is comprised of deep water marine sediments that indicate two instances of a transgressive and regressive oceanic sequence. Between each sequence the grading of the sediments reflect a deltaic environment[1].
Upper Tuxedni Group
The Upper Tuxendi Group is comparable to the lower Tuxendi Group in that it reflects a marine environment consistent with deltaic facies. There are also interbedded deposits of shale, siltstone, sandstone and conglomerates[8] However this marine sequence is not see throughout the group. Nonmarine debris flows are also present but they eventually grade into fine, sandy marine deposits.
Naknek Formation
Cretaceous
Major Faults
Bruin bay Fault System
The Burin Bay fault system is system of steeply dipping, northeast-striking faults which extend roughly 498km along the western region of the basin. It extends from the south of Becharof Lake on the Alaskan Peninsula up to its termination point against the Castle-Mountain Lake fault system.[9]. The system separates Mesosoic and Cenozoic volcanic sediments and Upper Triassic and Lower Jurassic volcanic rocks of the arc from Mesozoic marine and non-marine strata within the forearc basin [1]. Faults within the system are generally high angle and westward dipping, but due to the accumulation of sediments on the surface over time, the Burin Bay Fault system is present predominantly within the subsurface. The fault system was believed to have been active during Naknek deposition, and intrusive volcanic plutons indicate fault activity occurring before the Oligocene epoch [10].
Border Ranges Fault System
Castle Mountain Fault System
References
- ^ a b c d e http://archives.datapages.com/data/specpubs/memoir104/data/37_aapg-sp1940037.htm.
- ^ Fuis, G.S., T.E. Moore, G. Plafker, T.M. Brocher, M.A. Fisher, W.D. Mooney, W.J. Nokleberg, R.A. Page, B.C> Beaudoin, N.I. Chrisetnsen, W.J. Lutter, R.W> Saltus, and N.A. Ruppert, 2008, Trans-Alaska Crustal Transect and continental evolution involving underplating and synchronous foreland thrusting, Geology, v. 36, pp. 267-270.
- ^ Clift, P.D., A.E. Draut, P.B. Kelemen, J. Bluzatajn, and A. Greene, 2005a, Stratigraphic and geochemical evolution of an oceanic arc upper crustal section: The Jurassic Talkeetna volcanic formation, south-central Alaska: GSA Bulletin, v. 117, p. 902–925.
- ^ Decker, P.L., 2008, Mesozoic and Cenozoic source rock-characteristics, Puale Bay outcrops and North Aleutian Shelf COST #1 Well, in Reifenstuhl, R. R., and Decker, P. L., eds., Bristol Bay-Alaska Peninsula region, overview of 2004-2007 geologic research: Alaska Division of Geological & Geophysical Surveys Report of Investigation 2008-1B, p. 11–33.
- ^ Blodgett, R.B., and B. Sralla, 2008, A major unconformity between Permian and Triassic strata at Cape Kekurnoi, Alaska Peninsula; old and new observations on stratigraphy and hydrocarbon potential, in Haeussler, P. J., and Galloway, J. P., eds., Studies by the USGS in Alaska, 2006: USGS Professional Paper 1739-E, 13 p., available at http://pubs.usgs.gov/pp/pp1739/e/.
- ^ Draut, A.E., and P.D. Clift, 2006, Sedimentary processes in modern and ancient arc settings: Evidence from the Jurassic Talkeetna Formation of Alaska and the Mariana and Tonga arcs, western Pacific: Journal of Sedimentary Research, v. 76, p. 493–514.
- ^ Plafker, G., Gilpin, L.M., and Lahr, J.C., 1994a, Geology of the southern Alaska margin, in Plafker, G., and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 389–449.
- ^ Detterman, R.L., and J.K. Hartsock, 1966, Geology of the Iniskin-Tuxedni Peninsula region, Alaska: USGS Professional Paper 512, 78 p., 7 plates.
- ^ Detterman, R.L., T. Hudson, G. Plafker, R.G. Tysdal, and J.M. Hoare, 1976, Reconnaissance geologic map along Bruin Bay and Lake Clark faults in Kenai and Tyonek Quadrangles, Alaska: USG Open-file Map 76-477, scale 1:250,000.
- ^ Detterman, R.L., and B.L. Reed, 1980, Stratigraphy, structure, and economic geology of the Iliamna Quadrangle, Alaska: USGS Bulletin 1368-B, 86 p., scale 1:250,000, 1 plate.