Geologic map of the Styx River area, Lime Hills C-1 Quadrangle, Western Alaska Range, Alaska

Beryllium-10 chronology of early and late Wisconsinan moraines in the Revelation Mountains, Alaska: Insights into the forcing of Wisconsinan glaciation in Beringia

This report presents isotopic age data from mineralized granitic plutons in an area of the Alaska Range located approximately 200 kilometers to the west-northwest of Anchorage in southwestern Alaska. Uranium-lead isotopic data and trace element concentrations of zircons were determined for 12 samples encompassing eight plutonic bodies ranging in age from approximately 76 to 57.4 millions of years ago (Ma). Additionally, a rhenium-osmium age of molybdenite from the Miss Molly molybdenum occurrence is reported (approx. 59 Ma). All of the granitic plutons in this study host gold-, copper-, and (or) molybdenum-rich prospects.

From 1977-84, DGGS completed 1:63,360-scale geologic mapping of the McGrath quadrangle in western Alaska. Rock units in the study area range in age from lower Paleozoic to recent. The geologic history of this region has integrated stratigraphy, igneous activity, and mineral resources. From Cambro-Ordovician to Middle Devonian time, the Nixon Fork and Dillinger assemblages were deposited as coeval platform continental margin facies. Upper Devonian through Lower Jurassic shallow to deep-water sedimentary-volcanic facies of the Mystic assemblage overlie both older sequences. All three may have been offset right laterally from the Selwyn basin in northwestern Canada along the Tintina and other faults in central Alaska. Upper Jurassic to Lower Cretaceous flysch of the Black Clastic sequence was structurally juxtaposed against the Dillinger and Mystic assemblages, probably during mid-Cretaceous compression related to terrane accretion in southern Alaska. Upper Cretaceous Kuskokwim Group flysch was deposited over Nixon Fork assemblage rocks in an extensional environment in the westernmost portion of the quadrangle. A series of calc-alkaline intrusive and extrusive rocks ranging in age from Late Cretaceous to middle Tertiary intrude and overlie older, layered lithologies. Significant metalliferous epigenetic, stockwork, and skarn deposits are related to these igneous rocks near Farewell and McGrath. Middle Tertiary coal-bearing arenaceous sediments have been deposited in structural troughs related to the Farewell fault system. Offset solutions along the Farewell fault suggest up to 60 km of right-lateral offset since the Cretaceous. At least four Pleistocene and one late Tertiary(?) glaciations have advanced northward from the Alaska Range. The DGGS efforts have resulted in the release of eight geologic maps and an extensive geochemistry survey of the entire quadrangle. A comprehensive summary of the geology and mineral resources of the entire quadrangle is in process. The poster session will also summarize university graduate studies of mineral deposits, igneous petrology, and stratigraphy. End_of_Article - Last_Page 658------------

Because landslide regimes are likely to change in response to climate change in upcoming decades, the need for mechanistic understanding of landslide initiation and up-to-date landslide inventory data is greater than ever. We conducted surficial geologic mapping and compiled a comprehensive landslide inventory of the Denali National Park road corridor to identify geologic and geomorphic controls on landslide initiation in the Alaska Range. The supplemental geologic map refines and improves the resolution of mapping in the study area and adds emphasis on surficial units, distinguishing multiple glacial deposits, hillslope deposits, landslides, and alluvial units that were previously grouped. Results indicate that slope angle, lithology, and thawing ice-rich permafrost exert first-order controls on landslide occurrence. The majority (84%) of inventoried landslides are <0.01 km2 in area and occur most frequently on slopes with a bimodal distribution of slope angles with peaks at 18° and 28°. Of the 85 mapped landslides, a disproportionate number occurred in unconsolidated sediments and in felsic volcanic rocks. Weathering of feldspar within volcanic rocks and subsequent interactions with groundwater produced clay minerals that promote landslide initiation by impeding subsurface conductivity and reducing shear strength. Landslides also preferentially initiated within permafrost, where modeled mean decadal ground temperature is −0.2 ± 0.04 °C on average, and active layer thickness is ∼1 m. Landslides that initiated within permafrost occurred on slope angles ∼7° lower than landslides on seasonally thawed hillslopes. The bimodal distribution of slope angles indicates that there are two primary drivers of landslide failure within discontinuous permafrost zones: (1) atmospheric events (snowmelt or rainfall) that saturate the subsurface, as is commonly observed in temperate settings, and (2) shallow-angle landslides (<20° slopes) in permafrost demonstrate that permafrost and ice thaw are also important triggering mechanisms in the study region. Melting permafrost reduces substrate shear strength by lowering cohesion and friction along ice boundaries. Increased permafrost degradation associated with climate change brings heightened focus to low-angle slopes regionally as well as in high-latitude areas worldwide. Areas normally considered of low landslide potential will be more susceptible to shallow-angle landslides in the future. Our landslide inventory and analyses also suggest that landslides throughout the Alaska Range and similar climatic zones are most likely to occur where low-cohesion unconsolidated material is available or where alteration of volcanic rocks produces sufficient clay content to reduce rock and/or sediment strength. Permafrost thaw is likely to exacerbate slope instability in these materials and expand areas impacted by landslides.

Analysis of late Mesozoic and Cenozoic sedimentary basins, metamorphic rocks, and major faults in the eastern and central Alaska Range documents the progressive development of a suture zone that formed as a result of collision of an island-arc assemblage (the Wrangellia composite terrane) with the former North American continental margin. New basin-analysis, structural, and geochronologic data indicate the following stages in the development of the suture zone: (1) Deposition of 3–5 km of Upper Jurassic–Upper Cretaceous marine strata (the Kahiltna assemblage) recorded the initial collision of the island-arc assemblage with the continental margin. The Kahiltna assemblage exposed in the northern Talkeetna Mountains represents a Kimmeridgian–Valanginian backarc basin that was filled by northwestward-flowing submarine-fan systems that were transporting sediment derived from Mesozoic strata of the island-arc assemblage. The Kahiltna assemblage exposed in the southern Alaska Range represents a Valanginian–Cenomanian remnant ocean basin filled by west-southwestward–flowing submarine-fan systems that were transporting sediment derived from Paleozoic continental-margin strata uplifted in the along-strike suture zone. A belt of retrograde metamorphism and a regional anticlinorium developed along the continental margin from 115 to 106 Ma, roughly coeval with the end of widespread deposition in the Kahiltna sedimentary basins. (2) Metamorphism of submarine-fan deposits of the Kahiltna ba sin, located near the leading edge of the island-arc assemblage, occurred at ca. 74 Ma, as determined from a new U-Pb zircon age for a synkinematic sill. Coeval with metamorphism of deposits of the Kahiltna basin in the southern part of the suture zone was development of a thrust-top basin, the Cantwell basin, in the northern part of the suture zone. Geologic mapping and compositional data suggest that the 4 km of Upper Cretaceous nonmarine and marginal marine sedimentary strata in this basin record regional subaerial uplift of the suture zone. (3) Shortening and exhumation of the suture zone peaked from 65 to 60 Ma on the basis of metamorphic and geochronologic data. In the southern part of the suture zone, submarine-fan deposits of the Kahiltna basin, which had been metamorphosed to kyanite schists at ∼25 km depth and ∼650 °C, were exhumed and cooled through the biotite closure temperature (∼300 °C) by ca. 62 Ma. In the northern part of the suture zone, this time period was marked by shortening, uplift, and erosion of sedimentary strata of the Cantwell basin. (4) From 60 to 54 Ma, ∼3 km of volcanic strata were deposited over deformed sedimentary strata of the Cantwell basin, and several granitic plutons (the McKinley sequence) were emplaced along the suture zone. (5) Following igneous activity, strike-slip displacement occurred from ca. 54 to 24 Ma along the Denali fault system, which had developed in the existing suture zone. Late Eocene–Oligocene strike-slip displacement resulted in the formation of several small sedimentary basins along the Denali fault system. (6) Regional transpressive shortening characterized the suture zone from ca. 24 Ma to the present. Flexural subsidence, related to regional shortening, is represented by late Eocene to Holocene nonmarine deposits of the Tanana foreland basin. Regional subsidence resulted in Miocene coal seams up to 20 m thick and well-developed lacustrine deposits. Overlying the Miocene deposits are ∼1.2 km of Pliocene and Holocene conglomeratic deposits. Compositional and paleocurrent data from these younger deposits record regional Neogene uplift of the suture zone and recycling of detritus from older basins to the south that had become incorporated into the uplifted suture zone. Geologic mapping of major thrust faults along the northern and southern margins of the suture zone documents Paleozoic strata thrust over both Pliocene fluvial deposits and Quaternary glacial deposits of the Tanana basin. These mapping relationships provide evidence that regional shortening continues to the present in the eastern and central Alaska Range.

Plate S1: 1:24,000 scale map of the surficial geology of the Denali National Park road corridor. Table S1: Landslide inventory data, including coordinates of the initiation site and slope characteristics of the landslides evaluated.

The Platte River of south-central Nebraska was studied at three scales to place the river in its geological context and to trace its evolution through geologic time.At the largest scale the Elm Creek West and the Newark 7.5 minute quadrangles were mapped.These quadrangles are located just west and just east of Kearney and serve to illustrate the main geomorphic elements of the present Platte River Valley.The central elements of the quadrangles are the Platte River channels, islands, and bottomlands, which are fl anked by terraces that step up away from the river to the north and south.Significant other elements of the landscape are eolian sand and loess deposits.The geologic maps are supplemented by topographic profi les of the mapped terraces and graphical representations of subsurface units in test wells that occur within the quadrangles.An intermediate-scale study consisted of examining descriptions of well cuttings in a 17 county area in southcentral Nebraska, which includes the Platte River Valley, and building a database of information about sediment lithology and thickness.The wells penetrated a sequence of gravel, sand, silt, and clay beds from the ground surface to the top of the subsurface Tertiary Ogallala Group or Cretaceous formations.The sequence consists of Pliocene-, Pleistocene-, and Holocene-age strata that document the deposition of a veneer of alluvium by late Tertiary and Quaternary streams intermixed with and overlain by wind-blown loess.Various isopleth and structure maps illustrate the distribution and alluvial architecture of the sedimentary sequence, and support the interpretation of former positions of the Platte River.A regional-scale study consisted of documenting the geologic history

The Overthrust Belt extends for 5000 mi (8000 km) from the Brooks Range in Alaska to the Sierra Madre Oriental in Mexico. It consists of northeastward vergent thrust and fold structures involving late Precambrian to early Tertiary sedimentary section. These sediments represent deposition off the western rift margin, formed in late Precambrian time, of the North American Precambrian craton. The northeastward thrusting continued throughout the Mesozoic as a response to the convergence of the East Pacific Plate with the North American Plate. This convergence resulted in subduction beneath the North American Plate except at the northwest end (the Brooks Range) where the result was obduction. Convergence ceased when the west edge of the East Pacific Plate reached the subduction zone. The sedimentary section involved in the Thrust Belt contains good Devonian to Cretaceous hydrocarbon source rocks, and Ordovician to traps related to the thrusting (simple thrust sheets, imbricate thrust sheets, folded thrust sheets, step anticlines, footwall cutoffs, footwall anticlines, etc.). Field methods involved in exploration for hydrocarbons include field geological mapping, remote sensing (aerial photography and Landsat imagery), various seismic refraction and seismic reflection techniques (including modern detailed three dimension surveys) and potential field methods such as gravity and magneticmore » surveying. Studies of the field data include paleontology, source rock and hydrocarbon migration studies, structural and stratigraphic analyses, and the processing of geophysical data. This work has succeeded in two major areas: the Western Canadian Rocky Mountain Foothills, a major gas province producing mainly from Paleozoic reservoirs; and the Wyoming-Idaho-Utah portion of the thrust belt, also a major gas producer from Paleozoic reservoirs and, in addition, a major oil producer from the Jurassic Nugget Sandstone.« less

Permafrost, or perennially frozen ground, covers 9×105km2 or 55% of the landmass of Alaska. The continuous zone of permafrost encompasses the physiographic subdivisions of the Arctic Coastal Plain, the Arctic Foothills, the northern Norton Sound Highlands, and the Brooks Range. The zone of discontinuous permafrost encompasses the physiographic subdivisions of the Interior Alaska Lowlands, the Interior Alaska Highlands, the Alaska Range, the Copper River Plateau, the Kuskokwin Highlands, the southern Norton Sound Highlands, and the Western Alaska Coastal Plains and Deltas (Wahrhaftg, 1965; Pewe, 1975) (see Figure 2.2.1).

Ultramafic Gabbro massive Fe-Ni-Cu sulfide (+PGE) Possible global analog: Norilsk/Talnakh Hosted in feeders to Siberian Traps

the 1 63 360 kavik river geologic map area consists of 620 square miles and ties together previous dggs mapping in the sadlerochit and shublik mountains area of the western arctic national wildlife refuge anwr on the east and the structurally complex foothills and mountain front near the kemik gas accumulation on the west the map area exposes a unique intersection of north slope stratigraphy where all three major depositional megasequences are mappable in close association ellesmerian beaufortian and brookian

Three distinct intrusive phases have been identified in the Pool Creek map area (95C/5), southeast Yukon, during geological mapping as part the Central Foreland NATMAP project: a nepheline syenite and associated dykes (Pool Creek syenite), a biotite syenite, and an intrusive breccia. All intrusive units are exposed in the core of a large anticline in the transition zone between Early Paleozoic MacDonald Platform carbonates to the southeast and Selwyn Basin basinal shales to the northwest. U-Pb isotopic dating of zircons from the different intrusive phases resulted in a cluster of ages of 640-650 Ma for the Pool Creek syenite and associated dykes, and an age of 51.8 ± 0.2 Ma for the biotite syenite. An age could not be assigned to the intrusive breccia on the basis of the analytical data. Similar-age Neoproterozoic igneous rocks are rare in the North American Cordillera. The Pool Creek syenite may be related to prolonged syn-Winderemere age rifting on the western margin of Laurentia. The superposition of Eocene and Neoproterozoic intrusive activity is rare and cannot be readily explained, but may be related to focused magmatism along the Liard Line, which is interpreted as a Neoproterozoic transfer fault structure.

Geologic mapping and geochemical sampling in the central Alaska Range have identified several mineralized areas near the headwaters of the Wood River, Edgar Creek, and a t the head of the West Fork Glacier. Geochemical samples collected from these sites contain significant concentrations of copper, silver, and gold. Metalliferous zones include: (1) all rocks adjacent t o gabbro sills and granodiorite plutons, ( 2 ) the interior of gabbro sills, and ( 3 ) subsidiary fracture zones related t o the Hines Creek Fault. This report provides Locations and a general description of these mineral occurrences as well as elemental analyses of selected samples.

Steller sea lion (Eumetopias jubatus) populations have undergone precipitous declines through their western Alaskan range over the last four decades with the leading hypothesis to explain this decline centering around changing prey quality, quantity, or availability for this species (i.e., nutritional stress hypothesis). Under chronic conditions of reduced food intake sea lions would conserve energy by limiting energy expenditures through lowering of metabolic rate known as metabolic depression. To examine the potential for nutritional stress, resting metabolic rate (RMR) and body composition were measured in free-ranging juvenile Steller sea lions (N = 91) at three distinct geographical locations (Southeast Alaska, Prince William Sound, Central Aleutian Islands) using open-flow respirometry and deuterium isotope dilution, respectively. Average sea lion RMR ranged from 6.7 to 36.2 MJ d−1 and was influenced by body mass, total body lipid, and to a lesser extent, ambient air temperature and age. Sea lion pups captured in the Aleutian Islands (region of decline) had significantly greater body mass and total body lipid stores when compared to pups from Prince William Sound (region of decline) and Southeast Alaska (stable region). Along with evidence of robust body condition in Aleutian Island pups, no definitive differences were detected in RMR between sea lions sampled between eastern and western populations that could not be accounted for by higher percent total body lipid content, suggesting that that at the time of this study, Steller sea lions were not experiencing metabolic depression in the locations studied.

130 : Biostratigraphy and Lower Permian Fusulinidae of the Upper Delta River Area, East-Central Alaska Range