The arrival of bison in North America marks one of the most successful large-mammal dispersals from Asia within the last million years, yet the timing and nature of this event remain poorly ...determined. Here, we used a combined paleontological and paleogenomic approach to provide a robust timeline for the entry and subsequent evolution of bison within North America. We characterized two fossil-rich localities in Canada’s Yukon and identified the oldest well-constrained bison fossil in North America, a 130,000-y-old steppe bison, Bison cf. priscus. We extracted and sequenced mitochondrial genomes from both this bison and from the remains of a recently discovered, ∼120,000-y-old giant long-horned bison, Bison latifrons, from Snowmass, Colorado. We analyzed these and 44 other bison mitogenomes with ages that span the Late Pleistocene, and identified two waves of bison dispersal into North America from Asia, the earliest of which occurred ∼195–135 thousand y ago and preceded the morphological diversification of North American bison, and the second of which occurred during the Late Pleistocene, ∼45–21 thousand y ago. This chronological arc establishes that bison first entered North America during the sea level lowstand accompanying marine isotope stage 6, rejecting earlier records of bison in North America. After their invasion, bison rapidly colonized North America during the last interglaciation, spreading from Alaska through continental North America; they have been continuously resident since then.
This paper presents estimates of the potential health-related economic benefits of providing universal access to in-home water and sanitation services to households in rural Alaska. In particular, we ...use data on disease incidence rates, health care costs, and local estimates of the impact of piped water on disease reduction to estimate the potential health-related economic benefits of providing universal access to piped water in the Yukon Kuskokwim (Y.K.) Delta region of Alaska. We include estimates of avoided treatment and diagnosis costs as well as private benefits associated with reduced morbidity and mortality associated with improved access to in-home piped water. To our knowledge, these are the first estimates of the economic benefits of improved access to water and sanitation in rural Alaska and the Arctic. Our analysis suggests increased access to in-home piped water in the region may yield substantial reductions in direct medical expenses incurred by public agencies and families, as well as reductions in time and travel costs associated with improved health outcomes. These benefits, along with the array of health and non-health-related benefits not included in our analysis, may provide new impetus to expanding access to high-quality water and sanitation services in the region.
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The rise of eukaryotic macroalgae in the late Mesoproterozoic to early Neoproterozoic was a critical development in Earth's history that triggered dramatic changes in biogeochemical cycles and ...benthic habitats, ultimately resulting in ecosystems habitable to animals. However, evidence of the diversification and expansion of macroalgae is limited by a biased fossil record. Non-mineralizing organisms are rarely preserved, occurring only in exceptional environments that favor fossilization. Investigating the taphonomy of well-preserved macroalgae will aid in identifying these target environments, allowing ecological trends to be disentangled from taphonomic overprints. Here we describe the taphonomy of macroalgal fossils from the Tonian Dolores Creek Formation (ca. 950 Ma) of northwestern Canada (Yukon Territory) that preserves cm-scale macroalgae. Analytical microscopy, including scanning electron microscopy and tomographic x-ray microscopy, was used to investigate fossil preservation, which was the result of a combination of pyritization and aluminosilicification, similar to accessory mineralization observed in Paleozoic Burgess Shale-type fossils. These new Neoproterozoic fossils help to bridge a gap in the fossil record of early algae, offer a link between the fossil and molecular record, and provide new insights into evolution during the Tonian Period, when many eukaryotic lineages are predicted to have diversified.
Apatite is a common U- and Th-bearing accessory mineral in igneous and metamorphic rocks, and a minor but widespread detrital component in clastic sedimentary rocks. U–Pb and Th–Pb dating of apatite ...has potential application in sedimentary provenance studies, as it likely represents first cycle detritus compared to the polycyclic behavior of zircon. However, low U, Th and radiogenic Pb concentrations, elevated common Pb and the lack of a U–Th–Pb apatite standard remain significant challenges in dating apatite by LA-ICPMS, and consequently in developing the chronometer as a provenance tool.
This study has determined U–Pb and Th–Pb ages for seven well known apatite occurrences (Durango, Emerald Lake, Kovdor, Mineville, Mud Tank, Otter Lake and Slyudyanka) by LA-ICPMS. Analytical procedures involved rastering a 10
μm spot over a 40
×
40
μm square to a depth of 10
μm using a Geolas 193
nm ArF excimer laser coupled to a Thermo ElementXR single-collector ICPMS. These raster conditions minimized laser-induced inter-element fractionation, which was corrected for using the back-calculated intercept of the time-resolved signal. A Tl–U–Bi–Np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias. External standards (Plešovice and 91500 zircon, NIST SRM 610 and 612 silicate glasses and STDP5 phosphate glass) along with Kovdor apatite were analyzed to monitor U–Pb, Th–Pb, U–Th and Pb–Pb ratios
Common Pb correction employed the
207Pb method, and also a
208Pb correction method for samples with low Th/U. The
207Pb and
208Pb corrections employed either the initial Pb isotopic composition or the Stacey and Kramers model and propagated conservative uncertainties in the initial Pb isotopic composition. Common Pb correction using the Stacey and Kramers (1975) model employed an initial Pb isotopic composition calculated from either the estimated U–Pb age of the sample or an iterative approach. The age difference between these two methods is typically less than 2%, suggesting that the iterative approach works well for samples where there are no constraints on the initial Pb composition, such as a detrital sample. No
204Pb correction was undertaken because of low
204Pb counts on single collector instruments and
204Pb interference by
204Hg in the argon gas supply.
Age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common Pb-corrected ages, a Tera–Wasserburg Concordia intercept age and a Tera–Wasserburg Concordia intercept age anchored through common Pb. The samples in general yield ages consistent (at the 2σ level) with independent estimates of the U–Pb apatite age, which demonstrates the suitability of the analytical protocol employed. Weighted mean age uncertainties are as low as 1–2% for U- and/or Th-rich Palaeozoic–Neoproterozoic samples; the uncertainty on the youngest sample, the Cenozoic (31.44
Ma) Durango apatite, ranges from 3.7–7.6% according to the common Pb correction method employed. The accurate and relatively precise common Pb-corrected ages demonstrate the U–Pb and Th–Pb apatite chronometers are suitable as sedimentary provenance tools. The Kovdor carbonatite apatite is recommended as a potential U–Pb and Th–Pb apatite standard as it yields precise and reproducible
207Pb-corrected,
232Th–
208Pb, and common Pb-anchored Tera–Wasserburg Concordia intercept ages.
► Rapid, accurate U–Pb and Th–Pb apatite dating is possible by single collector LAICPMS. ► Apatite standards yield ages consistent with independent estimates of the U–Pb age. ► Th–Pb dating yields much promise, particularly in high Th samples. ► Accurate common Pb correction can be achieved without measuring 204Pb. ► This study opens the possibility of detrital apatite dating for sedimentary provenance analysis.
Boreal forest and tundra biomes are key components of the Earth system because the mobilization of large carbon stocks and changes in energy balance could act as positive feedbacks to ongoing climate ...change. In Alaska, wildfire is a primary driver of ecosystem structure and function, and a key mechanism coupling high-latitude ecosystems to global climate. Paleoecological records reveal sensitivity of fire regimes to climatic and vegetation change over centennial–millennial time scales, highlighting increased burning concurrent with warming or elevated landscape flammability. To quantify spatiotemporal patterns in fire-regime variability, we synthesized 27 published sediment-charcoal records from four Alaskan ecoregions, and compared patterns to paleoclimate and paleovegetation records. Biomass burning and fire frequency increased significantly in boreal forest ecoregions with the expansion of black spruce, ca. 6,000–4,000 years before present (yr BP). Biomass burning also increased during warm periods, particularly in the Yukon Flats ecoregion from ca. 1,000 to 500 yr BP. Increases in biomass burning concurrent with constant fire return intervals suggest increases in average fire severity (i.e., more biomass burning per fire) during warm periods. Results also indicate increases in biomass burning over the last century across much of Alaska that exceed Holocene maxima, providing important context for ongoing change. Our analysis documents the sensitivity of fire activity to broad-scale environmental change, including climate warming and biome-scale shifts in vegetation. The lack of widespread, prolonged fire synchrony suggests regional heterogeneity limited simultaneous fire-regime change across our study areas during the Holocene. This finding implies broad-scale resilience of the boreal forest to extensive fire activity, but does not preclude novel responses to 21st-century changes. If projected increases in fire activity over the 21st century are realized, they would be unprecedented in the context of the last 8,000 yr or more.
•Hematite slip surfaces mark subsidiary damage along eastern Denali fault zone (EDFZ).•Foliated hematite microfabrics indicate aseismic or subseismic slip.•Hematite (U-Th)/He dates capture ...hydrothermal-strain events at ∼8 Ma, 6 Ma, and 4 Ma.•Data highlight fault networks that partially accommodate regional surface uplift.•Slip coeval with regional Miocene deformation and plate interactions.
Unraveling complex slip histories in fault damage zones to understand relations among deformation, hydrothermal alteration, and surface uplift remains a challenge. The dextral eastern Denali fault zone (EDFZ; southwest Yukon, Canada) bounds the Kluane Ranges and hosts a variety of fault-related rocks, including hematite fault surfaces, which have been exhumed through the brittle regime over a protracted period of geologic time. Scanning electron microscopy-based microtextural observations and hematite (U-Th)/He (hematite He) thermochronometry from these surfaces indicate multiple generations of foliated, high-aspect ratio hematite plates. Single-aliquot hematite He dates (n=38) from 11 samples range from 11.5 ± 3.2 Ma (2σ) to 3.4 ± 2.1 Ma and exhibit moderate inter- and intrasample dispersion. A subset of dates is 15-20 Myr younger than previously published apatite (U-Th)/He dates from collocated host rocks, despite similar closure temperatures, precluding a simple ambient cooling interpretation for our hematite He data. Mixture modeling defines hematite He date populations at ∼8 Ma, ∼6 Ma, and ∼4 Ma, and when combined with microtextural observations, supports episodes of hydrothermal alteration and fault reactivation at aseismic to subseismic slip rates. There is no evidence that hematite experienced deformation- or hydrothermal fluid-related He loss. Hematite He dates overlap previously documented Kluane Ranges surface uplift and shifting dynamics of the Yakutat microplate, pinpointing fault networks and deformation processes that accommodate regional deformation in response to far-field plate boundary processes.
The Aleutian Arc-Alaska Peninsula and Wrangell volcanic field are the main source areas for tephra deposits found across Alaska and northern Canada, and increasingly, tephra from these eruptions have ...been found further afield in North America, Greenland, and Europe. However, there have been no broad scale reviews of the Late Pleistocene and Holocene tephrostratigraphy for this region since the 1980s, and this lack of data is hindering progress in identifying these tephra both locally and regionally. To address this gap and the variable quality of associated geochemical and chronological data, we undertake a detailed review of the latest Pleistocene to Holocene tephra found in interior Alaska and Yukon. This paper discusses nineteen tephra that have distributions beyond southwest Alaska and that have the potential to become, or already are, important regional markers. This includes three ‘modern’ events from the 20th century, ten with limited data availability but potentially broad distributions, and six that are widely reported in interior Alaska and Yukon. Each tephra is assessed in terms of chronology, geochemistry and distribution, with new Bayesian age estimates and geochemical data when possible. This includes new major-element geochemical data for Crater Peak 1992, Redoubt 1989–90, and two andesitic tephra from St Michael Island (Tephra D), as well as revised age estimates for Dawson tephra, Oshetna, Hayes set H, Aniakchak CFE II, and the White River Ashes, northern and eastern lobes.
•Late Pleistocene-Holocene tephra found within interior Alaska & Yukon are reviewed.•Geochemical and chronological information are summarised for 19 tephra.•New Bayesian age estimates and major element EPMA glass datasets are detailed.•The potential for a North American tephrostratigraphic framework is demonstrated.•This supports future work on volcanic hazards, and correlating sedimentary records.
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