Preliminary report on the geology of the continental slope adjacent to OCS Lease Sale 55, eastern Gulf of Alaska: Petroleum resource implications

Plafker, George; Winkler, Gary R.; Coonrad, W.L.; Claypool, George E.

doi:10.3133/ofr801089

Cited by 10 publications

(5 citation statements)

References 3 publications

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“…The Yakutat Group is interpreted as a metamorphosed, remnant accretionary prism consisting of both coherent greywacke‐argillite assemblages and mélange of greywacke, argillite, marble, and metachert [ Plafker , 1987; Plafker et al , 1994]. Offshore, rocks dredged off the continental slope at the Fairweather Ground uplift (Figure 2) have been correlated to the Yakutat Group [ Plafker et al, 1980 ]. These onshore and offshore observations of the Yakutat Group influenced the original interpretation of the Dangerous River Zone as a crustal scale boundary separating ‘continental’ Yakutat basement on the east and oceanic Yakutat basement on the west [e.g., Plafker , 1987].…”

Section: Discussionmentioning

confidence: 99%

“…The cover sequence is primarily composed of the glacially derived Yakataga Formation of marine mudstones and interbedded sandstones and siltstones [ Plafker , 1987; Trop and Ridgway , 2007]. The Yakataga Formation ranges in thickness up to ∼10 km [ Worthington et al , 2010] and overlies the pre‐glacial Poul Creek and Kultieth Formations [ Plafker et al , 1994; Trop and Ridgway , 2007]. These sedimentary units may be differentiated within the velocity model between OBS 110 and OBS 119.…”

Section: Discussionmentioning

confidence: 99%

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Crustal structure of the Yakutat terrane and the evolution of subduction and collision in southern Alaska

et al. 2012

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[1] We present a two-dimensional velocity model to constrain crustal thickness and composition of the Yakutat terrane in the northern Gulf of Alaska. The model was constructed using seismic reflection and refraction data along a $455 km onshore-offshore profile. Our model shows that the crystalline crust composing the Yakutat terrane is wedge-shaped, with crustal thickness increasing west to east from $15 km to $30 km. Crustal velocity and structure are continuous across the terrane, with lower crustal velocities >7 km/s, suggesting that the Yakutat terrane is an oceanic plateau across its entire offshore extent rather than a composite oceanic-continental terrane as previously proposed. The thickest Yakutat crust is entering the adjacent St. Elias orogen where elevated exhumation rates and concentrated seismicity in this vicinity are likely influenced by incipient Yakutat-North America collision. Our model includes a $8 km thick low-velocity crustal cap extending across the eastern portion of the profile where shallow basement is imaged on marine seismic reflection data. We interpret this cap as a lithified, metamorphosed remnant accretionary prism, providing evidence of a previous attempt at Yakutat subduction along its eastern margin prior to current emplacement at the southern Alaska margin.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Crustal structure of the Yakutat terrane and the evolution of subduction and collision in southern Alaska

et al. 2012

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“…The source terrain for the Yakutat block Paleogene strata is indeed a problem; the sandstone lithologies reported by Plafker et al (1980) for the Yakutat rocks are not well matched to lithologies of Oregon and Washington. However, Plafker's conclusion (Comment above) that the offshore Yakutat Paleogene strata were derived from "a remarkably homogeneous and distinctive ... source terrane" is based on modal analysis of only ten dredge samples from a poorly controlled position within the Yakutat block stratigraphic section by Plafker et al (1980); they also noted that "in several places, glauconitic tuffaceous sandstones ... were dredged from the continental slope"; modal analyses were not done of these "volcaniclastic" sandstones. Thus, on the basis of the few samples studied, it is perhaps premature to restrict the source terrain for a section up to 5 km thick to a single area.…”

Section: Replymentioning

confidence: 99%

Comments and Replies on “Model for the origin of the Yakutat block, an accreting terrane in the northern Gulf of Alaska”

Bruns¹,

Keller²

1984

Geol

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“…There is complete coverage by multichannel reflections seismic data with 10 km line spacing. Seismic refraction data is presented in Bayer and others, 1978. Sections from equivalent strata onshore ( Figure 56) have been described by Stonely (1967) and Plafker (1971).…”

Section: Petroleum Geologymentioning

confidence: 99%

“…Cross sections and stratigraphic columns are also shown in Bruns, 1982b. Stratigraphic columns appear in Plafker, 1971.…”

Section: Petroleum Geologymentioning

confidence: 99%

Analytical results and sample locality maps of skarn, porphyry, and vein samples from the Dillon, Butte, and Dubois 1° x 2° quadrangles, Idaho-Montana

Leatham-Goldfarb¹,

Siems²,

Welsch³

et al. 1986

Open-File Report

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Plate 1. Sample locality map of quartz vein samples from the Oil Ion, Butte, and Dubois 1° x 2° quadrangles, Idaho-Montana...in pocket This report presents the results of analyses of rock samples that were collected in a geochemical survey of the Oil Ion 1° x 2° quadrangle, Montana-Idaho. Geochemical samples were collected as one of several multidisciplinary studies associated with the Conterminous United States Mineral Appraisal Program (CUSMAP). INTRODUCTION Rock samples were collected as part of a reconnaissance geochemical survey that was conducted in the Oil Ion, Montana-Idaho, 1° x 2° quadrangle from 1978 through 1981. Additional rock samples were collected from the adjacent Butte and Dubois 1° x 2° quadrangles. The Oil Ion quadrangle comprises about 11,000 mi 2 (17,700 km 2) in Montana and Idaho. Oil Ion is located from 45°00'00" to 46°00'00" latitude and 112°00 I 00" to 114°00'00" longitude. Additional samples were collected from the Butte 1° x 2° quadrangle to a northernmost latitude of 46°15 I 00". Likewise, samples were collected from the Dubois 1° x 2° quadrangle to a southernmost latitude of 44°30'00". Access to the study area is provided on the north by Interstate 90 and by Interstate 15 on the south. The Oil Ion quadrangle contains complex thrust-faulted terranes of Precambrian and Phanerozoic sedimentary rocks on a Precambrian crystalline basement. These terranes were intruded by calc-alkaline batholithic rocks in the Mesozoic. Mesozoic-Tertiary volcanic rocks are also found in the area. During the Tertiary, large grabens were formed that are presently filled with volcanic rocks and fluvial sedimentary rocks. The topographic relief in the Oil Ion quadrangle varies from about 3,900 ft (1,182 m) to approximately 11,000 ft (3,333 m). METHODS OF STUDY Sample Media Analyses of unaltered or unmineralized rock samples provide background geochemical data for individual rock units. On the other hand, analyses of altered or mineralized rocks, where present, may provide useful geochemical information about the major-and trace-element assemblages associated with a mineralizing system. Sample Collection Rock samples were collected at 2,219 sites (Plates 1-4). However, the data in this report represent only those rocks collected from quartz veins, wall rocks, porphyries, and skarns. Sampling density varied with the spatial distribution of the outcrops. Sample Preparation Rock samples were crushed using a "chimpmunk-jaw crusher" and then pulverized to less than 0.15 mm using a "vertical pulverizer" with ceramic plates. Sample Analysis Spectrographlc method The prepared rock samples were analyzed for elements using a semiquantitative, direct-current arc emission spectrographic method (Grimes and Marranzino, 1968). The elements analyzed and their lower limits of determination are listed in Table 1. Spectrographic results were obtained by visual comparison of spectra derived from the sample against spectra obtained from standards made from pure oxides and carbonates. Standard concentrations are geometrically spaced...

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Preliminary report on the geology of the continental slope adjacent to OCS Lease Sale 55, eastern Gulf of Alaska: Petroleum resource implications

Cited by 10 publications

References 3 publications

Crustal structure of the Yakutat terrane and the evolution of subduction and collision in southern Alaska

Crustal structure of the Yakutat terrane and the evolution of subduction and collision in southern Alaska

Comments and Replies on “Model for the origin of the Yakutat block, an accreting terrane in the northern Gulf of Alaska”

Analytical results and sample locality maps of skarn, porphyry, and vein samples from the Dillon, Butte, and Dubois 1° x 2° quadrangles, Idaho-Montana

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