Reconnaissance geologic map of the Kuskokwim Bay region, southwest Alaska

Wilson, Frederic H.; Hults, Chad P.; Mohadjer, Solmaz; Coonrad, W.L.

doi:10.3133/sim3100

Cited by 18 publications

(44 citation statements)

References 27 publications

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“…Geology from Wilson et al . []. (a) The Tyonek, Beluga, and Sterling Formations (shades of orange) occur as isolated outcrops on the Kenai Peninsula.…”

Section: Methodssupporting

confidence: 86%

“… Maps showing the location of the subducted Yakutat microplate [ Eberhart‐Phillips et al ., ], major basin‐bounding faults [ Wilson et al ., ], mapped subsurface anticlines [ Bruhn and Haeussler , ], inferred sediment dispersal patterns (this study; size of arrow indicates relative contribution), and isopach contours for the (a) Tyonek, (b) Beluga, and (c) Sterling plus Quaternary strata [ Hartman et al ., ], modern seismicity >50 km deep beneath the Cook Inlet basin (d) from the Alaska Earthquake Information Center catalog, and (e) the mean annual precipitation in south‐central Alaska [ Gibson , ] and extent of modern glaciers.…”

Section: Paleogeographic and Tectonic Implicationsmentioning

confidence: 98%

“…The problem still remains, however, that the primary sediment source as reflected in the detrital zircon populations, and supported by exhumation and paleoflow patterns, was the eastern region where magmatism has not occurred during late Cenozoic time. Although the volcanoes of the modern arc are active along the western margin of the Cook Inlet basin as far north as the northern western Alaska Range today (Figure ), Pliocene volcanic rocks have not been mapped in that region [ Wilson et al ., ]. Pliocene zircons are found in ashes in the Sterling Formation [ Triplehorn et al ., ; Turner et al ., ], so if Pliocene bedrock is beneath the modern glaciers in the Alaska Range, then modern rivers should contain Pliocene zircons.…”

Section: Paleogeographic and Tectonic Implicationsmentioning

confidence: 98%

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Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Finzel

Enkelmann

2017

Geochem Geophys Geosyst

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The Cook Inlet in south‐central Alaska contains the early Oligocene to Recent stratigraphic record of a fore‐arc basin adjacent to a shallowly subducting oceanic plateau. Our new measured stratigraphic sections and detrital zircon U‐Pb geochronology and Hf isotopes from Neogene strata and modern rivers illustrate the effects of flat‐slab subduction on the depositional environments, provenance, and subsidence in fore‐arc sedimentary systems. During the middle Miocene, fluvial systems emerged from the eastern, western, and northern margins of the basin. The axis of maximum subsidence was near the center of the basin, suggesting equal contributions from subsidence drivers on both margins. By the late Miocene, the axis of maximum subsidence had shifted westward and fluvial systems originating on the eastern margin of the basin above the flat‐slab traversed the entire width of the basin. These mud‐dominated systems reflect increased sediment flux from recycling of accretionary prism strata. Fluvial systems with headwaters above the flat‐slab region continued to cross the basin during Pliocene time, but a change to sandstone‐dominated strata with abundant volcanogenic grains signals a reactivation of the volcanic arc. The axis of maximum basin subsidence during late Miocene to Pliocene time is parallel to the strike of the subducting slab. Our data suggest that the character and strike‐orientation of the down‐going slab may provide a fundamental control on the nature of depositional systems, location of dominant provenance regions, and areas of maximum subsidence in fore‐arc basins.

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“…Geology from Wilson et al . []. (a) The Tyonek, Beluga, and Sterling Formations (shades of orange) occur as isolated outcrops on the Kenai Peninsula.…”

Section: Methodssupporting

confidence: 86%

Section: Paleogeographic and Tectonic Implicationsmentioning

confidence: 98%

Section: Paleogeographic and Tectonic Implicationsmentioning

confidence: 98%

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Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Finzel

Enkelmann

2017

Geochem Geophys Geosyst

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“…The Upper Cretaceous Kuskokwim Group (Cady et al, 1955) covers a large portion of southwestern Alaska (Fig. 1) and consists of marine turbiditic argillite, graywacke, and conglomerate, as well as marginal marine and nonmarine sandstone and conglomerate, which locally contains coal (Hoare and Coonrad, 1959;Box et al, 1993;Miller and Bundtzen, 1994;Kalbas, 2006;Wilson et al, 2006Wilson et al, , 2008. Based on fossil ages and geologic relationships, the age of the Kuskokwim Group is well constrained to early Late Cretaceous (Fig.…”

Section: Kuskokwim Groupmentioning

confidence: 99%

Two flysch belts having distinctly different provenance suggest no stratigraphic link between the Wrangellia composite terrane and the paleo-Alaskan margin

Hults

Wilson

Donelick³

et al. 2013

Lithosphere

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The provenance of Jurassic to Cretaceous fl ysch along the northern boundary of the allochthonous Wrangellia composite terrane, exposed from the Lake Clark region of southwest Alaska to the Nutzotin Mountains in eastern Alaska, suggests that the fl ysch can be divided into two belts having different sources. On the north, the Kahiltna fl ysch and Kuskokwim Group overlie and were derived from the Farwell and Yukon-Tanana terranes, as well as smaller related terranes that were part of the paleo-Alaskan margin. Paleocurrent indicators for these two units suggest that they derived sediment from the north and west. Sandstones are predominantly lithic wacke that contain abundant quartz grains, lithic rock fragments, and detrital mica, which suggest that these rocks were derived from recycled orogen and arc sources. Conglomerates contain limestone clasts that have fossils matching terranes that made up the paleo-Alaskan margin. In contrast, fl ysch units on the south overlie and were derived from the Wrangellia composite terrane. Paleocurrent indicators for these units suggest that they derived sediment from the south. Sandstones are predominantly feldspathic wackes that contain abundant plagioclase grains and volcanic rock fragments, which suggest these rocks were derived from an arc. Clast compositions in conglomerate south of the boundary match rock types of the Wrangellia composite terrane.The distributions of detrital zircon ages also differentiate the fl ysch units. Flysch units on the north average 54% Mesozoic, 14% Paleozoic, and 32% Precambrian detrital zircons, refl ecting derivation from the older Yukon-Tanana, Farewell, and other terranes that made up the paleo-Alaskan margin. In comparison, fl ysch units on the south average 94% Mesozoic, 1% Paleozoic, and 5% Precambrian zircons, which are consistent with derivation from the Mesozoic oceanic magmatic arc rocks in the Wrangellia composite terrane. In particular, the fl ysch units on the south contain a large proportion of zircons ranging from 135 to 175 Ma, corresponding to the age of the Chitina magmatic arc in the Wrangellia terrane and the plutons of the Peninsular terrane, which are part of the Wrangellia composite terrane. Flysch units on the north do not contain signifi cant numbers of zircons in this age range. The fl ysch overlying the Wrangellia composite terrane apparently does not contain detritus derived from rocks of the paleo-Alaska margin, and the fl ysch overlying the paleo-Alaskan margin apparently does not contain detritus derived from the Wrangellia composite terrane.The provenance difference between the two belts helps to constrain the location of the northern boundary of the Wrangellia composite terrane. Geophysical models place a deep, through-going, crustal-scale suture zone in the area between the two fl ysch belts. The difference in the provenance of the two belts supports this interpretation. The youngest fl ysch is Late Cretaceous in age, and structural disruption of the fl ysch units is constrained to the Late Cretaceous, so it ap...

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“…Democrat Lode geologic setting Loess, reworked loess/colluvium (> 1m) deeply oxidized bedrock Wilson et al (2015) after Weber et al (1978) 9…”

mentioning

confidence: 99%

Geologic mapping in the Richardson-Uncle Sam area, interior Alaska (presentation): Alaska Miners Association Annual Convention, Anchorage, Alaska, November 7-12, 2017

Twelker¹,

Werdon²,

Sicard³

et al. 2017

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During the 2017 field season, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling of part of the Richardson Mining District southeast of Fairbanks. The project area is about 30 miles west of the Pogo gold mine and covers gold exploration activity at the Montecristo and Uncle Sam properties. The goal of this work is to build an improved understanding of the area geology and controls on gold mineralization for purposes of exploration targeting and mineral resource assessment.The 260-square-mile map area lies between the Salcha River and Shaw Creek and is bounded by the Trans-Alaska Pipeline access road to the southwest (figure 1). The area is characterized by forested, moderate-relief hills blanketed by vegetation, loess, and locally, sand dunes. Rock outcrop is less than one percent, consequently, the map interpretation relies heavily on the DGGS East Richardson airborne magnetic and electromagnetic survey (Burns and others, 2006) as well as rocks collected from pits dug into rocky colluvial deposits below the surficial loess or sand.Metamorphic rocks form a map-scale upright synform plunging gently northwest (figure 1). Sillimanitebearing paragneiss displaying migmatitic textures (unit mpg) forms the lowest structural level. The overlying unit is characterized by similar paragneiss but lacks migmatitic texture (unit pg). The structurally highest rock package (unit sg) is a mixed unit comprised of similar sillimanite-bearing paragneiss, biotite and muscovite schist, quartzite, calc-silicate rock, and graphitic schist and quartzite. This unit also contains small, discontinuous bodies of granitic orthogneiss, amphibolite, and serpentinite. These subsidiary units are mapped separately where possible.The map area is intruded by abundant dikes and several small stocks of muscovite ± tourmaline ± garnetbearing granite (unit tmg), as well as biotite granite. Whole-rock geochemical analyses indicate both are peraluminous granites of arc character (Twelker and others, 2017). They most closely resemble the early Cretaceous (105-114 Ma) peraluminous felsic dikes documented in the southeastern Richardson district (Graham and others, 2002). Altered hypabyssal quartz-feldspar porphyry dikes found south of the study area may correlate with ca. 90 Ma dikes of similar composition and texture at the Democrat prospect.Shallowly dipping, brittle-ductile-style shearing is evident in drill core, and these structures are an important host for gold mineralization at the Naosi and other prospects in the area. At map scale, faultbounded and discontinuous bodies of serpentinite offer evidence of a broader, layer-parallel shear zone affecting the structurally uppermost mixed schist-gneiss unit. A similar broad shear zone cutting a similar mixed lithologic package hosts the low-angle veins at Pogo gold mine.Two sets of high-angle faults cut the area; these are mappable as lineaments and offsets in airborne magnetic and electromagnetic survey data. Northwest-trending high-angl...

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Reconnaissance geologic map of the Kuskokwim Bay region, southwest Alaska

Cited by 18 publications

References 27 publications

Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Two flysch belts having distinctly different provenance suggest no stratigraphic link between the Wrangellia composite terrane and the paleo-Alaskan margin

Geologic mapping in the Richardson-Uncle Sam area, interior Alaska (presentation): Alaska Miners Association Annual Convention, Anchorage, Alaska, November 7-12, 2017

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