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Julie A. Dumoulin

Publications and source records attributed to Julie A. Dumoulin.

At least 91 records · Page 5Linked to original sources
USGS1992

Correlation of pre-Carboniferous carbonate successions of northern Alaska

Fault-bounded successions of pre-Carboniferous (meta)carbonate rocks occur throughout northern Alaska. Successions studied in detail are those in the York Mountains (Seward Peninsula), the western and eastern Baird Mountains (western Brooks Range), the Snowden Mountain area (central Brooks Range), and the Sublik and Sadlerochit Mountains (eastern Brooks range); they are correlated on the basis of the lithofacies and conodont biostratigraphy. Available lithologic and biogeographic data are best explained by postulating that these successions accumulated on a single continental margin or platform that had faunal exchange with both Siberia and North America, rather than on a series of discrete platforms juxtaposed by later tectonic events.

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USGS1992

Deep-water facies of the Lisburne Group, west-central Brooks Range, Alaska

Deep-water lithofacies of the Lisburne Group (chiefly Carboniferous) occur in thurst sheets in the western part of the foreland fold-and-thrust belt of the Brooks Range and represent at least three discrete units. The Kuna Formation (Brooks Range allochthon) consists mostly of spiculitic mudstone and lesser shale; subordinate carbonate layers are chiefly diagenetic dolomite. The Akmalik Chert (Picnic Creek allochthon) is mostly radiolarian-spiculitic chert; rare limy beds are calcitized radiolarite. The Rim Butte unit (Ipnavik river allochthon) consists chiefly of calcareous turbidites, derived from shallow- and deep-water sources, interbedded with spiculitic mudstone. Much of the material in the turbidites came from a contemporaneous carbonate platform and margin, but some fossils and lithic clasts were eroded from older, already lithified carbonate-platform rocks. All three units appear to be roughly coeval in the Howard Pass area and are chiefly late Tournaisian and early Viséan (late Early Mississippian) in age. Shallow-water lithofacies of the Lisburne Group exposed in the Howard Pass area (Brooks Range allochthon) are mostly of Viséan and younger (Late Mississippian) age. Thus, these carbonate-platform rocks were not the source of the calcareous turbidites in the Rim Butte unit. Rim Butte turbidites could have been derived from older carbonate-platform rocks such as the Utukok Formation of Tournaisian age (Kelly River allochthon) exposed mainly to the west of the Howard Pass quadrangle.

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USGS1989

The Resurrection Peninsula ophiolite

The Resurrection Peninsula forms the east side of Resurrection Bay (fig. 3). Relief ranges from 437 m (1,434 ft) at the southern end of the peninsula to more than 1,463 m (4,800 ft) opposite the head of the bay. All rock units composing the informally named Resurrection Peninsula ophiolite of Nelson and others (1987) are visible or accessible by boat. "Ophiolite" has been a geologic term since 1827 (Coleman, 1977). The term "ophiolite" initially referred to the rock serpentinite; the Greek root "ophi" (meaning snake or serpent) alluded to the greenish, mottled, and shiny appearance of serpentinites. In 1927, Steinmann described a rock association in the Alps, sometimes known as the "Steinmann Trinity', consisting of serpentine, diabase and spilitic lavas, and chert. Recognition of this suite led to the idea that ophiolites represent submarine magmatism that took place early in the development of a eugeosyncline. In the early 1970s the Steinmann Trinity was reconsidered in light of the plate tectonic theory, new petrologic studies, and the recognition of abducted oceanic lithosphere in orogenic belts of the world. In 1972 at a Geological Society of America Penrose Conference (Anonymous, 1972) the term "ophiolite" was defined as a distinctive assemblage of mafic to ultramafic rocks, with no emphasis on their origin. A complete ophiolite should contain, from bottom to top: 1) Tectonized ultramafic rocks (more or less serpentinized) 2) Gabbro complex containing cumulus textures and commonly cumulus peridotites 3) Mafic sheeted-dike complex, grading upward into; 4) Submarine pillow lavas of basaltic composition. Common associated rock types include plagiogranite (Na-rich) and an overlying sedimentary section typically dominated by chert.

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USGS1988

Sandstone petrographic evidence and the Chugach-Prince William terrane boundary in southern Alaska

The contact between the Upper Cretaceous Valdez Group and the Paleocene and Eocene Orca Group has been inferred to be the boundary between the Chugach and the Prince William tectonostratigraphic terranes. Sandstone petrographic data from the Prince William Sound area show no compositional discontinuity across this contact. These data are best explained by considering the Valdez and Orca Groups to be part of a single terrane - a thick flysch sequence derived primarily from a progressively unroofing magmatic arc with increasing input from subduction-complex sources through time.

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USGS1988

Off-platform Silurian sequences in the Ambler River quadrangle: A section in Geologic studies in Alaska by the U.S. Geological Survey during 1987

Lithofacies changes in coeval upper Paleozoic rocks have been used to unravel the tectonic history of northern Alaska (for example, Mayfield and others, 1983). Conodont biostratigraphy and detailed petrologic studies are now revealing facies differences in lower Paleozoic rocks that can also be used to constrain their tectono-sedimentary framework (Dumoulin and Harris, 1987). A basic element of basin analysis is the discrimination of shallow-water shelf and platform sequences from deeper water slope and basinal deposits. This report documents several new localities of deeper water, off-platform Silurian deposits in the Ambler River quadrangle and briefly outlines some of their paleogeographic implications.

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USGS1988

Stromatolite- and coated-grain-bearing carbonate rocks of the western Brooks Range: A section in Geologic studies in Alaska by the U.S. Geological Survey during 1987

Carbonate rocks characterized by locally abundant stromatolites and coated grains have been found at several localities in the Baird Mountains and Ambler River quadrangles (fig. 1). These rocks are part of a belt of metasedimentary and metaigneous rocks that constitutes the southwestern flank of the Brooks Range; all are included in the parautochthon (Schwatka sequence) of Mayfield and others (1983). The rocks have been deformed and metamorphosed to blueschist and greenschist facies, but primary textures and sedimentary structures are locally well preserved.

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USGS1987

Resurrection Peninsula and Knight Island ophiolites and recent faulting on Montague Island, southern Alaska

The Resurrection Peninsula forms the east side of Resurrection Bay (Fig. 1 ). The city of Seward is located at the head of the bay and can be reached from Anchorage by highway (127 mi;204 km). Relief ranges from 1,434 ft (437 m) at the southern end of the peninsula to more than 4,800 ft (1,463 m) 17 mi (28 km) to the north. All rock units composing the informally named Resurrection Peninsula ophiolite are visible and (or) accessible by boat.The eastern half of the peninsula is located within the Chugach National Forest; the western half is mainly state land, but there is some private land with recreational cabins. The Seward A6 and A7 and Blying Sound D6 and D7 maps at 1:63,360 scale (mile-to-the-inch) cover the entire Resurrection Peninsula. Knight Island is located 53 mi (85 km) east of Seward (Fig. 1 ). Numerous fiords indent the 31-mi-long (50 km) by 7.4-mi-wide (12 km) island and offer excellent bedrock exposures. The island is rugged and has a maximum elevation of 3,000 ft (914 m). It has numerous mineral prospects (Tysdal, 1978; Nelson and others, 1984; Jansons and others, 1984; Koski and others, 1985), and several abandoned canneries are located on the island. Knight Island lies entirely within the Chugach National Forest—state and private inholdings constitute less than five percent of its total land area. The Seward A2, A3, B2, B3, and C2, 1:63,360-scale U.S. Geological Survey topographic maps cover the entire island. Montague Island, 50 mi (80 km) long and up to 11 mi (18 km) wide, lies 10.6 mi (17 km) southeast of Knight Island. It belongs to an island group that forms the southern margin of Prince William Sound (Fig. 1 ). Montague Island is less rugged and less heavily vegetated than either the Resurrection Peninsula or Knight Island. Rock exposures are excellent along the beaches, and ground disruption due to recent fault movements is clearly visible. The Seward Al and A2 and Blying Sound Dl, D2, and D3 maps cover the areas of interest on Montague Island. In all areas, access is by float-equipped aircraft, helicopter, or boat. Wheel-equipped aircraft can land on the beaches or at several landing strips on Montague Island.

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USGS1987

Lower Paleozoic carbonate rocks of the Baird Mountains quadrangle, western Brooks Range, Alaska

Lower Paleozoic carbonate rocks in the Baird Mountains quadrangle form a relatively thin, chiefly shallow-water succession that has been thrust-faulted and metamorphosed to blueschist and greenschist facies. Although this succession was thought to be mostly Devonian until recently, a large part of it is in fact pre-Silurian in age. Middle and Upper Cambrian rocks - the first confirmed in the western Brooks Range - occur in the northeastern quarter of the quadrangle, south of Mt. Angayukaqsraq. These rocks consist of massive marble that grades upward into thin-bedded metalimestone/dolostone couplets and contain pelagiellid mollusks, acrotretid brachiopods, and agnostids. Sedimentologic features and the Pefagiellas indicate a shallow-water depositional environment. Overlying these Cambrian rocks is a thin sequence of Lower arid Middle Ordovician metalimestone and phyllite containing graptolites and cool-water, mid-shelf to basinal conodonts. Upper Ordovician rocks in the Mt. Angayukaqsraq area are bioturbated to laminated dolostone containing conodonts of warm-, shallow-water biofacies. In the Omar and Squirrel Rivers area to the west, the Lower Ordovician carbonate rocks are thicker and quite different in lithofacies and biofacies. These rocks are mainly dolostone with locally well-developed fenestral fabric and evaporite molds, and bioturbated to laminated orange- and gray-weathering dolomitic marble and metalimestone. Conodonts and sedimentary structures indicate deposition in restricted to normal marine, shallow to very shallow water platform environments. Exposures of Upper Silurian rocks occur near Mi. Angayukaqsraq and on the middle fork of the Squirrel River, and consist mostly of thinly laminated dolomitic mudstones. Conodonts in these rocks indicate deposition in a somewhat restricted, shallow-water environment. Devonian carbonate rocks are widely distributed in the western Baird Mountains quadrangle; at least two distinct sequences have been identified. In the Omar and Squirrel Rivers area, Lower and Middle Devonian dolostone, metalimestone and marble are locally cherty and rich in megafossils. To the north, in the Nakolik River area, Middle and Upper Devonian marble and metalimestone are interlayered with planar- to cross-laminated quartz-carbonate metasandstone and phyllite. Baird Mountains carbonate rocks show some striking similarities in biofacies and lithofacies to lower Paleozoic carbonate rocks of the Seward Peninsula to the southwest and the central Brooks Range to the east.

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USGS1985

Sea cliff exposures of metamorphosed carbonate and schist, northern Seward Peninsula: A section in The United States Geological Survey in Alaska: Accomplishments during 1983

Extensive seacliff exposures of marble, metadolostone, and schist occur on the north shore of Seward Peninsula in the Kotzebue A-1 and A-2 Quadrangles (fig. 12). Some of the exposed units have no analogs when compared to rocks mapped to the south in the Bendeleben and Solomon Quadrangles. Others are similar to units exposed to the south, but they differ in metamorphic grade and minor, though significant, compositional characteristics. Carbonate rocks predominate from Ninemile Point westward; schists of varying composition occur with carbonate rocks to the east. The carbonate-dominated section is separated in the vicinity of Ninemile Point from the schist-dominated section by a major fault zone, thought to be the northern extension of the Kugruk fault zone of Sainsbury (1974).

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USGS1985

Summary of data on the age of the Orca Group, Alaska: A section in The United States Geological Survey in Alaska: Accomplishments during 1984

The Orca Group is a widespread, thick, complexly deformed accretionary sequence of flysch and tholeiitic basalt in the Prince William Sound area (Winkler, 1976; Winkler and Plafker, 1981) (fig. 49). Despite a number of extensive field studies of the Orca Group, reliable data on the age of the unit have been elusive. On the basis of sparse paleontologic and radiometric data, the sequence was regarded as Paleocene and early Eocene(?) age (Winkler and Plafker, 1981). New paleontologic data from fossil localities shown in figure 49 suggest that some strata assigned to the Orca Group are of middle Eocene age and possibly as young as late Eocene or Oligocene. However, data suggesting an age younger than about 50 Ma appear to be incompatible with radiometrically determined ages for plutons that intrude the Orca Group.

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USGS1984

A transect of metamorphic rocks along the Copper River, Cordova and Valdez Quadrangles, Alaska: A section in The United States Geological Survey in Alaska: Accomplishments during 1982

The lower Tertiary Orca Group is juxtaposed against the Upper Cretaceous Valdez Group along the Contact fault system (Winkler and Plafker, 1974, 198; Plafker and others, 1977)(fig. 33). In both groups, turbidites are the dominant rock type, with lesser mafic volcanic rocks (table 10). The Valdez Group, on the north, has traditionally been considered to be of higher metamorphic grade than the Orca Group (Moffit, 1954; Tysdal and Case, 1979; Winkler and Plafker, 198; Winkler and others, 1981). In 1982, we made a transect across the regional strike of the rocks and the contact between the two groups. The transect area follows the Copper River for 85 km from the Cordova quadrangle north into the Valdez quadrangle and extends for about 25 km on either side of the river (fig. 33). We planned, by systematic sampling of the area, to examine the metamorphic differences between the Orca and Valdez Groups. We found, however, that a strong thermal metamorphic event has overprinted and obscured regional metamorphic relations. We believe intrusion of Tertiary granite (fig. 33) to be responsible for this metamorphism. (Figures 33 and 34 and tables follow this article.)

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USGS1984

The Jeanie Point complex revisited

The so-called Jeanie Point complex is a distinctive package of rocks within the Orca Group, a Tertiary turbidite sequence. The rocks crop out on the southeast coast of Montague Island, Prince William Sound, approximately 3 km northeast of Jeanie Point (loc. 7, fig. 44). These rocks consist dominantly of fine-grained limestone and lesser amounts of siliceous limestone, chert, tuff, mudstone, argillite, and sandstone (fig. 47). The Jeanie Point rocks also differ from those typical of the Orca Group in their fold style. Thus, the Orca Group of the area is isoclinally folded on a large scale (tens to hundreds of meters), whereas the Jeanie Point rocks are tightly folded on a 1- to 3- m-wavelength scale (differences in rock competency may be responsible for this variation in fold style).

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