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USGS2019

Non-anthropogenic diet-based oiling of predatory birds

Oiling of wildlife can have important consequences to individual animals and populations (Kingston 2002). Individual birds that are heavily oiled lose their ability to fly and may become ill or die from hypothermia, starvation, exhaustion, or drowning (Clark 1984, Rocke 1999). For example, large-scale oiling from the Exxon Valdez spill caused local declines in populations of many avian taxa (Irons et al. 2000). Although most oiling reports involve marine wildlife exposed to oil leaked from vessels or oil rigs, oiling also can occur in terrestrial environments, for example, via birds drinking water in puddles on asphalt roadways (Clark and Gorney 1987) or landing in oil field wastewater disposal facilities (Trail 2006, Ramírez 2010).

Journal of Raptor Research↗

USGS1996

The 1992 M=7 Cape Mendocino, California, earthquake: Coseismic deformation at the south end of the Cascadia megathrust

We invert geodetic measurements of coseismic surface displacements to determine a dislocation model for the April 25, 1992, M = 7 Cape Mendocino, California, earthquake. The orientation of the model slip vector, which nearly parallels North America-Juan de Fuca relative plate convergence, and the location and orientation of the model fault relative to the offshore Cascadia megathrust, suggest that the 1992 Cape Mendocino earthquake is the first well-recorded event to relieve strain associated with the Cascadia subduction zone. We use data from three geodetic techniques: (1) the horizontal and vertical displacements of 13 monuments surveyed with the Global Positioning System, corrected for observed horizontal interseismic strain accumulation, (2) 88 section-elevation differences between leveling monuments, and (3) the uplift of 12 coastal sites observed from the die-off of intertidal marine organisms. Maximum observed displacements are 0.4 m of horizontal movement and 1.5 m of uplift along the coast. We use Monte Carlo techniques to estimate an optimal uniform slip rectangular fault geometry and its uncertainties. The optimal model using all the data resolves 4.9 m of slip on a 14 by 15 km fault that dips 28° SE. The fault extends from 1.5 to 8.7 km in depth and the main-shock hypocenter is close to the downdip projection of the fault. The shallowly dipping fault plane is consistent with the observed aftershock locations, and the estimated geodetic moment is 3.1 × 10 19 N m, 70% of the seismic moment. Other models that exclude leveling data collected in 1935 and 1942 are more consistent with seismological estimates of the fault geometry. If the earthquake is characteristic for this segment, the estimated horizontal slip vector compared with plate convergence rates suggests a recurrence interval of 140 years, with a 95% confidence range of 100–670 years. The coseismic uplift occurred in a region that also has high Quaternary uplift rates determined from marine terrace studies. If repeated ruptures of this southernmost segment of the Cascadia megathrust are responsible for the Quaternary uplift, a comparison of the coseismic uplift with coastal uplift rates suggests a recurrence interval of 200–400 years. Thus comparing horizontal and vertical coseismic to long-term deformation suggests a recurrence interval of about 100–300 years for M = 7 events at the south end of the Cascadia megathrust.

Journal of Geophysical Research B: Solid Earth↗

USGS2013

The variability of California summertime marine stratus: impacts on surface air temperatures

This study investigates the variability of clouds, primarily marine stratus clouds, and how they are associated with surface temperature anomalies over California, especially along the coastal margin. We focus on the summer months of June to September when marine stratus are the dominant cloud type. Data used include satellite cloud reflectivity (cloud albedo) measurements, hourly surface observations of cloud cover and air temperature at coastal airports, and observed values of daily surface temperature at stations throughout California and Nevada. Much of the anomalous variability of summer clouds is organized over regional patterns that affect considerable portions of the coast, often extend hundreds of kilometers to the west and southwest over the North Pacific, and are bounded to the east by coastal mountains. The occurrence of marine stratus is positively correlated with both the strength and height of the thermal inversion that caps the marine boundary layer, with inversion base height being a key factor in determining their inland penetration. Cloud cover is strongly associated with surface temperature variations. In general, increased presence of cloud (higher cloud albedo) produces cooler daytime temperatures and warmer nighttime temperatures. Summer daytime temperature fluctuations associated with cloud cover variations typically exceed 1°C. The inversion-cloud albedo-temperature associations that occur at daily timescales are also found at seasonal timescales.

California↗

USGS2024

Reconstructing half a century of coregonine recruitment reveals species-specific dynamics and synchrony across the Laurentian Great Lakes

Understanding how multiple species and populations vary in their recruitment dynamics can elucidate the processes driving recruitment across space and time. Lake Whitefish ( Coregonus clupeaformis ) and Cisco ( C. artedi ) are socioecologically important fishes across their range; however, many Laurentian Great Lakes populations have experienced declining, poor, or sporadic recruitment in recent decades. We integrated catch and age data from 38 long-term surveys across each of the Great Lakes and Lake Simcoe, resulting in a combined time series spanning 1960–2019. We estimated Lake Whitefish and Cisco year-class strength (YCS) in each lake using longitudinal mixed-effects regressions of relative cohort abundance. We subsequently quantified interspecific, spatial, and temporal synchrony in YCS using correlation and dynamic factor analyses. Lake Whitefish YCS was positively spatially synchronous on average, and YCS in all six lakes was elevated during the 1980s–1990s. In contrast, Cisco YCS was sporadic, not spatially synchronous, and highly variable around long-term, lake-specific means. YCS was not synchronous between species in any lake. Collectively, our analyses demonstrate that these species exhibit differential recruitment dynamics that may be regulated by species-specific factors. Results from this study can be leveraged in future research on the causes and consequences of cross-species, cross-basin recruitment variability.

Laurentian Great Lakes↗

USGS2005

Impact of longer-term modest climate shifts on architecture of high-frequency sequences (Cyclothems), Pennsylvanian of midcontinent U.S.A

Pennsylvanian glacioeustatic cyclothems exposed in Kansas and adjacent areas provide a unique opportunity to test models of the impact of relative sea level and climate on stratal architecture. A succession of eight of these high-frequency sequences, traced along dip for 500 km, reveal that modest climate shifts from relatively dry-seasonal to relatively wet-seasonal with a duration of several sequences (???600,000 to 1 million years) had a dominant impact on facies, sediment dispersal patterns, and sequence architecture. The climate shifts documented herein are intermediate, both in magnitude and duration, between previously documented longer-term climate shifts throughout much of the Pennsylvanian and shorter-term shifts described within individual sequences. Climate indicators are best preserved at sequence boundaries and in incised-valley fills of the lowstand systems tracts (LST). Relatively drier climate indicators include high-chroma paleosols, typically with pedogenic carbonates, and plant assemblages that are dominated by gymnosperms, mostly xerophytic walchian conifers. The associated valleys are small (<2 km wide and <11 m deep) and are commonly filled with locally derived limestone clasts, which indicate small drainage networks. Relatively wetter climates are indicated by locally preserved paleosols exhibiting both low-chroma and high-chroma variants, common coals, and plant assemblages that are dominated by fern foliage, seed ferns, and sphenopsids. The incised-valley fills associated with these facies are large (>4 km wide and >20 m deep), and dominated by quartz sandstones derived from distant source areas, reflecting large drainage networks. Transgressive systems tracts (TST) in all eight sequences gen erally are characterized by thin, extensive limestones and thin marine shales, suggesting that the dominant control on TST facies distribution was the sequestration of siliciclastic sediment in updip positions. Highstand systems tracts (HST) were significantly impacted by the intermediate-scale climate cycle in that HSTs from relatively drier climates consist of thin marine shales overlain by extensive, thick regressive limestones, whereas HSTs from relatively wetter climates are dominated by thick marine shales. Previously documented relative sea-level changes do not track the climate cycles, indicating that climate played a role distinct from that of relative sea-level change. These intermediate-scale modest climate shifts had a dominant impact on sequence architecture. This independent measure of climate and relative sea level may allow the testing of models of climate and sediment supply based on modern systems. Copyright ?? 2005, SEPM.

Journal of Sedimentary Research↗

USGS2007

Spatial trends in marsh sediment deposition within a microtidal creek system, Waccasassa Bay, Florida

Marsh surface deposition, suspended sediment concentrations, tidal hydrodynamics, and marsh surface characteristics were measured within a tidal creek system of a west-central Florida, microtidal, open marine Juncus roemerianus marsh to examine the depositional relationship between a creek system and the surrounding marsh during nonstorm conditions. Results suggest that short-term marsh deposition is highly episodic with deposition showing an inverse relationship with marsh surface inundation. Deposition was greatest at marsh sites adjacent to secondary creek segments over all examined timescales. Variations in hydroperiod, time–velocity asymmetry, vegetation density, and sediment availability could not explain the observed differences in short-term deposition.

Florida↗

USGS2010

USGS perspectives on an integrated approach to watershed and coastal management

The writers discuss three critically important steps necessary for achieving the goal for improved integrated approaches on watershed and coastal protection and management. These steps involve modernization of monitoring networks, creation of common data and web services infrastructures, and development of modeling, assessment, and research tools. Long-term monitoring is needed for tracking the effectiveness approaches for controlling land-based sources of nutrients, contaminants, and invasive species. The integration of mapping and monitoring with conceptual and mathematical models, and multidisciplinary assessments is important in making well-informed decisions. Moreover, a better integrated data network is essential for mapping, statistical, and modeling applications, and timely dissemination of data and information products to a broad community of users.

Marine Technology Society Journal↗

USGS2012

Dust deposition in southern Nevada and California, 1984–1989: Relations to climate, source area, and source lithology

Dust samples collected annually for 5 years from 55 sites in southern Nevada and California provide the first regional source of information on modern rates of dust deposition, grain size, and mineralogical and chemical composition relative to climate and to type and lithology of dust source. The average silt and clay flux (rate of deposition) in southern Nevada and southeastern California ranges from 4.3 to 15.7 g/m 2 /yr, but in southwestern California the average silt and clay flux is as high as 30 g/m 2 /yr. The climatic factors that affect dust flux interact with each other and with the factors of source type (playas versus alluvium), source lithology, geographic area, and human disturbance. Average dust flux increases with mean annual temperature but is not correlated to decreases in mean annual precipitation because the regional winds bring dust to relatively wet areas. In contrast, annual dust flux mostly reflects changes in annual precipitation (relative drought) rather than temperature. Although playa and alluvial sources produce about the same amount of dust per unit area, the total volume of dust from the more extensive alluvial sources is much larger. In addition, playa and alluvial sources respond differently to annual changes in precipitation. Most playas produce dust that is richer in soluble salts and carbonate than that from alluvial sources (except carbonate‐rich alluvium). Gypsum dust may be produced by the interaction of carbonate dust and anthropogenic or marine sulfates. The dust flux in an arid urbanizing area may be as much as twice that before disturbance but decreases when construction stops. The mineralogic and major‐oxide composition of the dust samples indicates that sand and some silt is locally derived and deposited, whereas clay and some silt from different sources can be far‐traveled. Dust deposited in the Transverse Ranges of California by the Santa Ana winds appears to be mainly derived from sources to the north and east.

California, Nevada↗

USGS2000

Responses of stable bay-margin and barrier-island systems to Holocene sea-level highstands, western Gulf of Mexico

The microtidal, wave-dominated coast of the western Gulf of Mexico displays a variety of Holocene geomorphic features indicating higher-than-present water levels that were previously attributed to storm processes while geoidal sea level was at its present position. Field and aerial-photograph examinations of bay margins, barrier islands, and beach-ridge plains following major hurricanes show that the elevated features are inundated periodically by high storm surge. Despite their inundation, these highstand features are not modified by modern storm processes. Instead, storm-related erosion and deposition are always seaward of and lower than the highstand features and are always limited to the extant shorezone, where elevations typically are less than 1.5 m above present sea level. Bay-margin and lagoonal highstand indicators include raised marshes and subtidal flats, wave-cut benches, abandoned wave-cut scarps with fringing marshes and/or beach ridges, and accretionary islands and recurved spits. Other emergent marine features include abandoned compound flood-tidal delta and washover fan complexes attached to barrier islands and anomalously high beach ridges within both the barrier-island complexes and beach-ridge plains. The highest beach ridges, raised marshes and flats, and erosional scarps and benches are manifestations of one or more rising phases and highstands in sea level, whereas the lower marshes and accretionary topography are mainly products of the falling phases and shoreface adjustment to present sea level. Different elevations of beach-ridge sets, discordant truncation of beach ridges, and elevated marine- and brackish-water faunal assemblages preserved in beach ridges, raised marshes and flats, and natural levees are compelling evidence of sea-level fluctuations of ±1 to 1.5 m from about 5500 to 1200 cal yr BP. Independent evidence from studies of geodynamic, climatic, and glacio-eustatic processes can explain the mid-Holocene highstands and late Holocene lowering of sea level that is observed in tectonically stable coastal regions far from former centers of glaciation.

Journal of Sedimentary Research↗

USGS2005

Quaternary geomorphology and modern coastal development in response to an inherent geologic framework: An example from Charleston, South Carolina

Coastal landscapes evolve over wide-ranging spatial and temporal scales in response to physical and biological processes that interact with a wide range of variables. To develop better predictive models for these dynamic areas, we must understand the influence of these variables on coastal morphologies and ultimately how they influence coastal processes. This study defines the influence of geologic framework variability on a classic mixed-energy coastline, and establishes four categorical scales of spatial and temporal influence on the coastal system. The near-surface, geologic framework was delineated using high-resolution seismic profiles, shallow vibracores, detailed geomorphic maps, historical shorelines, aerial photographs, and existing studies, and compared to the long- and short-term development of two coastal compartments near Charleston, South Carolina. Although it is clear that the imprint of a mixed-energy tidal and wave signal (basin-scale) dictates formation of drumstick barriers and that immediate responses to wave climate are dramatic, island size, position, and longer-term dynamics are influenced by a series of inherent, complex near-surface stratigraphic geometries. Major near-surface Tertiary geometries influence inlet placement and drainage development (island-scale) through multiple interglacial cycles and overall channel morphology (local-scale). During the modern marine transgression, the halo of ebb-tidal deltas greatly influence inlet region dynamics, while truncated beach ridges and exposed, differentially erodable Cenozoic deposits in the active system influence historical shoreline dynamics and active shoreface morphologies (block-scale). This study concludes that the mixed-energy imprint of wave and tide theories dominates general coastal morphology, but that underlying stratigraphic influences on the coast provide site-specific, long-standing imprints on coastal evolution.

Journal of Coastal Research↗

USGS1973

Permian paleogeography of the Arctic

Three large land areas were dominant in the Arctic during the Permian: Fennoscandia, central and southern Siberia (Angara), and Canada. Smaller landmasses were in China, the Seward-Chukotskiy region, northern and eastern Siberia, and near Alaska. Coal deposits and strata bearing land plants covered a large area in central Siberia; saline basins containing red beds formed in the Zechstein, Perm, and West Texas basins as the seas withdrew, generally in the later Permian. Eugeosynclinal troughs, apparently limited to the Pacific border regions, were marked by volcanism and deposition of predominantly clastic sediments in many areas. Platform and miogeosynclinal deposits, dominated by carbonate rocks, preceded saline deposition in the basins and persisted on shallow shelves adjacent to the geosynclines. The Arctic Permian marine fauna evolved in middle Permian time because of partial isolation of the Arctic areas from the southern ocean. Endemism, latitudinal temperature controls, and the effect of ocean currents explain in large part the faunal patterns in Permian seas. Post-Permian tectonic movements account for anomalies in the present positions of some rock sequences and fossils. Northeasterly drift and counterclockwise rotation of the northern landmasses are suggested. Right-lateral shear along the southern edge of Asia is supported, followed by northward movement of peninsular India.

Journal of Research of the U.S. Geological Survey↗

USGS2012

Book review: The requisite reference for the study of Sirenia

Sirenians often are given little or no notice in texts on marine mammals; whales, dolphins, and seals are what come to mind for most when a marine mammal is imagined. An order of only four extant species, the Sirenia is indeed the “other” frequently overlooked group of marine mammals. Dugongs and manatees remain unknown by much of the world, but to those that study these species, the members are extraordinarily unique and fascinating. The three highly respected authors of this newly published volume are all distinguished researchers, with more than a century of combined expertise in the study of this mammalian order. Their collective experience and insight make this book a captivating and valuable read for students, professionals, and anyone interested in having an all-inclusive reference for learning about the Order Sirenia. Review info: Ecology and conservation of the Sirenia-dugongs and manatees . By H. Marsh, T. J. O'Shea, and J. E. Reynolds, III, 2012. ISBN: 978-0521888288, 521 pp.

Journal of Mammalian Evolution↗

USGS2010

Modeling migratory energetics of Connecticut River American shad ( Alosa sapidissima ): implications for the conservation of an iteroparous anadromous fish

We present a simulation model in which individual adult migrant American shad ( Alosa sapidissima ) ascend the Connecticut River and spawn, and survivors return to the marine environment. Our approach synthesizes bioenergetics, reproductive biology, and behavior to estimate the effects of migratory distance and delays incurred at dams on spawning success and survival. We quantified both the magnitude of effects and the consequences of uncertainty in the estimates of input variables. Behavior, physiology, and energetics strongly affected both the distribution of spawning effort and survival to the marine environment. Delays to both upstream and downstream movements had dramatic effects on spawning success, determining total fecundity and spatial extent of spawning. Delays, combined with cues for migratory reversal, also determined the likelihood of survival. Spawning was concentrated in the immediate vicinity of dams and increased with greater migratory distance and delays to downstream migration. More research is needed on reproductive biology, behavior, energetics, and barrier effects to adequately understand the interplay of the various components of this model; it does provide a framework, however, that suggests that provision of upstream passage at dams in the absence of expeditious downstream passage may increase spawning success — but at the expense of reduced iteroparity.

Connecticut, Massachusetts, New Hampshire, Vermont↗

USGS1975

Early Ordovician gastropod opercula and epicontinental seas

Collections made for some years from Lower Ordovician rocks by many geologists have established that the heavy calcareous operculum of the gastropod Ceratopea is almost never found associated with a shell and that commonly this operculum is secondarily silicified. Ceratopea may have lived in a stressed habitat and may have been essentially the only shelled invertebrate present. Presumably these animals grazed on algal mats and mounds growing in areas of water slightly more saline than open marine water and were killed by an influx of hypersaline water. Subsequent decay of soft parts would permit the operculum to rot off and would also lighten the shell so that it could float away. Pene-contemporaneous silicification of calcareous opercula on the Ordovician sea bottom is postulated. Some Middle Ordovician opercula of the Middle to Late Ordovician genus Maclurites serve to test this speculation. These opercula also occur in geologic settings which may be interpreted in terms of kill of animal, wafting away of shell, and secondary silicification of operculum.

Alabama, Arkansas, Colorado, Georgia, Maryland, Ne↗

USGS2013

Integrating satellite observations and modern climate measurements with the recent sedimentary record: An example from Southeast Alaska

Assessments of climate change over time scales that exceed the last 100 years require robust integration of high-quality instrument records with high-resolution paleoclimate proxy data. In this study, we show that the recent biogenic sediments accumulating in two temperate ice-free fjords in Southeast Alaska preserve evidence of North Pacific Ocean climate variability as recorded by both instrument networks and satellite observations. Multicore samples EW0408-32MC and EW0408-43MC were investigated with 137 Cs and excess 210 Pb geochronometry, three-dimensional computed tomography, high-resolution scanning XRF geochemistry, and organic stable isotope analyses. EW0408-32MC (57.162°N, 135.357°W, 146 m depth) is a moderately bioturbated continuous record that spans AD ∼1930–2004. EW0408-43MC (56.965°N, 135.268°W, 91 m depth) is composed of laminated diatom oozes, a turbidite, and a hypopycnal plume (river flood) deposit. A discontinuous event-based varve chronology indicates 43MC spans AD ∼1940–1981. Decadal-scale fluctuations in sedimentary Br/Cl ratios accurately reflect changes in marine organic matter accumulation that display the same temporal pattern as that of the Pacific Decadal Oscillation. An estimated Sitka summer productivity parameter calibrated using SeaWiFS satellite observations support these relationships. The correlation of North Pacific climate regime states, primary productivity, and sediment geochemistry indicate the accumulation of biogenic sediment in Southeast Alaska temperate fjords can be used as a sensitive recorder of past productivity variability, and by inference, past climate conditions in the high-latitude Gulf of Alaska.

Alaska↗

USGS2003

Seabird tissue archival and monitoring project: Egg collections and analytical results 1999-2002

In 1998, the U.S. Geological Survey Biological Resources Division (USGS-BRD), the U.S. Fish and Wildlife Service (USFWS) Alaska Maritime National Wildlife Refuge (AMNWR), and the National Institute of Standards and Technology (NIST) began the Seabird Tissue Archival and Monitoring Project (STAMP) to collect and cryogenically bank tissues from seabirds in Alaska for future retrospective analysis of anthropogenic contaminants. The approach of STAMP was similar to that of the Alaska Marine Mammal Tissue Archival Project (AMMTAP). AMMTAP was started in 1987 by NIST and the National Oceanic and Atmospheric Administration (NOAA) as part of the Outer Continental Shelf Environmental Assessment Program sponsored by the Minerals Management Service. Presently sponsored by the USGS-BRD, AMMTAP continues its work as part of a larger national program, the Marine Mammal Health and Stranding Response Program. AMMTAP developed carefully designed sampling and specimen banking protocols. Since 1987, AMMTAP has collected tissues from marine mammals taken in Alaska Native subsistence hunts and has cryogenically banked these tissues at the NIST National Biomonitoring Specimen Bank (NBSB). Through its own analytical work and working in partnership with other researchers both within and outside Alaska, AMMTAP has helped to develop a substantial database on contaminants in Alaska marine mammals. In contrast, data and information is limited on contaminants in Alaska seabirds, which are similar to marine mammals in that they feed near the top of the food chain and have the potential for accumulating anthropogenic contaminants. During its early planning stages, STAMP managers identified the seabird egg as the first tissue of choice for study by the project. There is a relatively long history of using bird eggs for environmental monitoring and for investigating the health status of bird populations. Since 1998, protocols for collecting and processing eggs, and cryogenically banking egg samples have been developed by STAMP (see York et al. 2001). Eggs are being collected on an annual basis for several species at nesting colonies throughout Alaska. Aliquots of these egg samples are being analyzed on a regular basis for persistent organic pollutants and mercury. Results of this work have been published in scientific journals (Christopher et al. 2002) and in conference proceedings (Kucklick et al. 2002; Vander Pol et al. 2002a, 2002b). The intent of this report is to provide an up-to-date description of STAMP. The report contains the most recent egg collection inventory, analytical data, preliminary interpretations based on these data, and a discussion of possible future directions of the project.

Report↗

USGS2006

Submarine geology of Hana Ridge and Haleakala Volcano's northeast flank, Maui

We present a morphostructural analysis of the submarine portions of Haleakala Volcano and environs, based upon a 4-year program of geophysical surveys and submersible explorations of the underwater flanks of Hawaiian volcanoes that was conducted by numerous academic and governmental research organizations in Japan and the U.S. and funded primarily by the Japan Agency for Marine–Earth Science and Technology. A resulting reconnaissance geologic map features the 135-km-long Hana Ridge, the 3000 km 2 Hana slump on the volcano's northeast flank, and island-surrounding terraces that are the submerged parts of volcanic shields. Hana Ridge below 2000 m water depth exhibits the lobate morphology typical of the subaqueously erupted parts of Hawaiian rift zones, with some important distinctions: namely, subparallel crestlines, which we propose result from the down-rift migration of offsets in the dike intrusion zone, and an amphitheater at its distal toe, where a submarine landslide has embayed the ridge tip. Deformation of Haleakala's northeast flank is limited to that part identified as the Hana slump, which lies downslope from the volcano's submerged shield, indicating that flank mobility is also limited in plan, inconsistent with hypothesized volcanic spreading driven by rift-zone dilation. The leading edge of the slump has transverse basins and ridges that resemble the thrust ramps of accretionary prisms, and we present a model to describe the slump's development that emphasizes the role of coastally generated fragmental basalt on gravitational instability of Haleakala's northeast flank and that may be broadly applicable to other ocean-island slumps.

Hawai'i↗

USGS2012

Tectonic setting of the Yukon-Koyukuk basin and its borderlands, western Alaska

The Yukon-Koyukuk basin of western Alaska is composed of an arcuate belt of Jurassic and Early Cretaceous subduction-related volcanic and plutonic rocks (Koyukuk terrane) flanked by deep subbasins filled with mid-Cretaceous terrigenous sedimentary rocks. The basin is bordered on three sides by metamorphosed Proterozoic and Paleozoic continental rocks (Seward, Arctic Alaska, and Ruby terranes) and is separated from the metamorphic borderlands by a narrow, highly tectonized belt of oceanic crust and mantle rocks (composite Angayucham-Tozitna terrane). The oceanic and mantle rocks, which dip inward beneath the basin and are thrust outward onto the borderlands, are divided into three separate thrust panels: (1) a structurally lowest panel (Slate Creek) composed of phyllite and metagraywacke of probable Devonian age, (2) a middle panel (Narvak) composed of imbricated basalt, chert, and gabbro of Devonian to Early Jurassic age, and (3) a structurally highest panel (Kanuti) composed of gabbro and peridotite of probable Middle and Late Jurassic age. The three thrust panels appear to represent a reversely stacked sequence that progresses from continental slope deposits in the lower panel to cumulus and mantle peridotites in the upper. Metamorphic mineral K-Ar ages from garnet amphibolite on the sole of the upper panel suggest that the upper panel was emplaced on the middle panel in the Middle to Late Jurassic. Subsequent accretion of all three panels to the continental rocks of the borderlands occurred in the latest Jurassic and Early Cretaceous, synchronous with arc volcanism within the basin. Arc volcanism waned and the accretionary phase ended in the middle of Early Cretaceous time. Uplift and erosion of the metamorphic borderlands and the obducted oceanic rocks began in late Early Cretaceous and was accompanied by the rapid filling of two flanking subbasins with turbiditic sediments. In the latest Early Cretaceous and early Late Cretaceous, shallow marine and nonmarine conglomerates were deposited around the margins of the basin, and a prograding delta was built out from the southeast margin of the basin across the turbiditic subbasins and the remnant volcanic arc. In the Late Cretaceous, western Alaska was subjected to strong east-west compression which severely deformed both the Yukon-Koyukuk basin and the borderlands. Several widespread magmatic episodes in the mid- and Late Cretaceous and in early Tertiary transgress the basin boundaries and stitch together the accreted arc and oceanic terranes and the continental borderlands.

Journal of Geophysical Research Solid Earth↗