Geologic map of the Chandalar quadrangle, Alaska

Brosge, W.P.; Reiser, H.N.

doi:10.3133/ofr6214

Cited by 11 publications

(26 citation statements)

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“…In the northern part of east-central Alaska, the Lower Jurassic is poorly exposed but is reported to consist of about 1000 feet (305 m) of sandstone, siltstone, shale, and quartzite that are part of the Glenn Shale Reiser 1964, 1969;Imlay and Detterman, 1973, p. 13, 14). The basal 120 feet (37 m) exposed on Spike Mountain about 30 miles (48 km) north of Old Rampart, consists of sandy beds, rests on granite, and contains the Hettangian ammonites Psiloceras (Psiloceras) and R. 15 W. R. 14 W. …”

Section: East-central Alaskamentioning

confidence: 99%

Early Jurassic ammonites from Alaska

Imlay¹

1981

Professional Paper

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Section: East-central Alaskamentioning

confidence: 99%

Early Jurassic ammonites from Alaska

Imlay¹

1981

Professional Paper

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“…Nappe N3 and overlying nappes N4, N5, and N6 are folded in a post-imbrication, eastnortheast-trending synform whose northern flank is cut by the Foggytop thrust that divides the Skajit allochthon into two structural domains. Nappe N3 is composed of a complex imbricate stack dominated by exposures of the Skajit marble with subordinate siliciclastic units (Brosgé and Reiser, 1964;Dillon et al, 1988). The structure and lithology of nappe N3 was not studied in detail but based on the results of previous work (Brosgé and Reiser, 1964;Dillon et al, 1988) and our reconnaissance, clearly contains the same lithologies as those in nappe N1 (Fig.…”

Section: Thrust Nappe N3mentioning

confidence: 92%

“…Collections from the uppermost Skajit marble in the Wiseman and Chandalar Quadrangles indicate a Frasnian (early Late Devonian) age ( Fig. 1; location 4) that may serve as an upper age limit for the unit (Brosgé and Reiser, 1964;Dillon et al, 1987).…”

Section: Thrust Nappe N1mentioning

confidence: 98%

“…Several klippen of the Skajit allochthon are found tens of kilometers to the east of the Chandalar River, where they overlie the Endicott Mountains allochthon. Southwest of the Chandalar River, the Skajit allochthon overlies the Schist belt on a northeast-striking thrust fault originally recognized by Brosgé and Reiser (1964) that dips moderately to the northwest. To the south, the basal thrust of the allochthon is truncated by the south-dipping Minnie Creek thrust ( Fig.…”

Section: Structural Settingmentioning

confidence: 99%

“…Fossil suites collected from the marble of nappe N3 consist of solitary corals, brachiopods, pelecypods, stromatoporoids, and conodonts (Brosgé and Reiser, 1964;Dillon et al, 1988;Oldow, unpublished data). Recovered conodont fragments yield little useful age constraint and have an allowable range of Ordovician to Triassic (Dillon et al, 1988).…”

Section: Thrust Nappe N3mentioning

confidence: 99%

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Stratigraphy and paleogeographic setting of the eastern Skajit allochthon, central Brooks Range, Arctic Alaska

Oldow¹,

Boler²,

Lallemant³

et al. 1998

Architecture of the Central Brooks Range Fold and Thrust Belt, Arctic Alaska

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The Skajit allochthon of the south-central Brooks Range is one of the structurally highest units in the late Mesozoic and Cenozoic fold and thrust belt and overlies metasedimentary rocks of the EndicottMountains allochthon on the north and metamorphic tectonites of the Schist belt to the south. The Skajit allochthon is deformed internally in a complex array of folds and thrusts and is composed of two, partially coeval, stratigraphic sequences. The stratigraphic sequences are composed of metamorphosed fine-to coarse-grained siliciclastic, volcanogenic, and volcanic rocks and thin-bedded to massive carbonate units. The two stratigraphic sequences, which constitute numerous imbricate sheets, are spatially segregated into a lower and upper assemblage of thrust nappes. The structurally lower sequence is composed of intercalated shallow-marine to platformal carbonates and fine-to coarse-grained siliciclastic rocks of Middle Cambrian to early Late Devonian age. The clastic and carbonate rocks are conformably overlain by a post-lower Upper Devonian succession of fine-grained siliciclastic and thin-bedded carbonates. The stratigraphic sequence of the structurally higher nappes is composed of fine-to coarse-grained siliciclastic and volcanogenic rocks and subordinate thin-bedded carbonate rocks of Early or Middle Ordovician to early Late Devonian age. The two lower Paleozoic sequences substantially overlap in age but were deposited in distinctly different depositional environments. The Cambrian to Devonian carbonate succession was deposited in a carbonate platform or shelf environment, whereas the partially coeval siliciclastic, carbonate, and volcanic succession is of basin affinity. Paleogeographic restoration of the imbricate thrust sheets places the carbonate succession to the north of the siliciclastic sequence. The carbonate rocks of the shelf succession are the apparent source of fine-grained carbonate mud and occasional carbonate olistoliths found within the basin sequence. Siliciclastic detritus intercalated within the shallow-marine carbonates of the shelf

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Mechanisms and timing of exhumation of collision‐related metamorphic rocks, southern Brooks Range, Alaska: Insights from ⁴⁰Ar/³⁹Ar thermochronology

2002

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[1] New 40 Ar/ 39 Ar thermochronologic data document the spatial distribution of cooling ages and rates across a metamorphic culmination in the south central Brooks Range, providing important constraints on the timing and processes responsible for exhumation of deep-seated metamorphic rocks. The data indicate widespread episodic exhumation-related cooling, with short-lived events in the mid-Albian to early Cenomanian and Paleocene to Eocene. Hornblende ages indicate that cooling from the metamorphic peak began at 105 -103 Ma across the epidoteamphibolite facies core of the culmination. Mica ages, however, increase southward from $90 Ma to $100 Ma, indicating that average cooling rates increased southward. Thermal modeling suggests that Albian cooling is the result of a short-lived exhumation event that ended by the early Cenomanian, and that exhumation rates were between $1 and 8 mm/yr, with higher rates toward the south. The southward increase in cooling/exhumation rates is attributed to a southward increase in the component of tectonic exhumation by normal faulting on the south flank of the range. Rapid erosion, which is recorded by thick molasse deposits in flanking basins that are coeval with rapid cooling, may have been aided by surface uplift in the footwall of these faults. The northward younging of mica ages may not be explained by a simple core complex model involving metamorphic rocks being progressively dragged out from beneath an extensional fault. The overall spatial distribution of metamorphic zones and cooling ages/rates is best explained by a two-step process: (1) a brief episode of extensional faulting producing a regional northward tilt with superimposed doming during the AlbianCenomanian and (2) relative uplift of the core during renewed Tertiary contraction, which enhanced the domal geometry. Diffusion-domain modeling of K-feldspar data indicates a period of little or no cooling that spanned much of the Late Cretaceous followed by rapid increase in cooling rates in the Paleocene to Eocene. Increased Tertiary cooling rates are attributed to renewed contraction leading to surface uplift and erosion.

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Geologic map of the Chandalar quadrangle, Alaska

Cited by 11 publications

References 0 publications

Early Jurassic ammonites from Alaska

Early Jurassic ammonites from Alaska

Stratigraphy and paleogeographic setting of the eastern Skajit allochthon, central Brooks Range, Arctic Alaska

Mechanisms and timing of exhumation of collision‐related metamorphic rocks, southern Brooks Range, Alaska: Insights from ⁴⁰Ar/³⁹Ar thermochronology

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Geologic map of the Chandalar quadrangle, Alaska

Cited by 11 publications

References 0 publications

Early Jurassic ammonites from Alaska

Early Jurassic ammonites from Alaska

Stratigraphy and paleogeographic setting of the eastern Skajit allochthon, central Brooks Range, Arctic Alaska

Mechanisms and timing of exhumation of collision‐related metamorphic rocks, southern Brooks Range, Alaska: Insights from 40Ar/39Ar thermochronology

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Mechanisms and timing of exhumation of collision‐related metamorphic rocks, southern Brooks Range, Alaska: Insights from ⁴⁰Ar/³⁹Ar thermochronology