Age of some Pleistocene interglacial beds and associated fossils in eastern Beringia defined by fission tracks in glass shards of Chester Bluff tephra

2017 ◽  
Vol 88 (1) ◽  
pp. 152-159 ◽  
Author(s):  
John A. Westgate ◽  
Nicholas J.G. Pearce
Keyword(s):  
Fission Track ◽  
Yukon Territory ◽  
East Central ◽  
Oxygen Isotope Stage ◽  
Yukon River ◽  
Dating Method ◽  
The Mean ◽  
Loess Deposits ◽  
The Rich

AbstractApplication of the glass fission-track dating method to Chester Bluff tephra (CBt), exposed in loess deposits at Chester Bluff along the Yukon River in east-central Alaska, has clarified the age of the immediately underlying fossiliferous interglacial bed. Surprise Creek tephra (SZt), at site CRH47 in the northern Old Crow basin of the Yukon Territory, is a correlative of CBt so that the new age information on CBt can also be applied to the interglacial sediments below SZt. Two independent age determinations were obtained on CBt, 243±28 ka and 249±26 ka, giving a weighted mean age and error of 246±19 ka. Therefore, the closely associated interglacial bed belongs to the early part of Marine Oxygen Isotope Stage (MIS) 7. The stratigraphy and paleoenvironmental setting of SZt show that deposition of the tephra occurred soon after interglacial conditions, when the climate became colder, probably between MIS 7.5 and 7.4, that is, slightly younger than the mean fission-track age, but within the 1σ uncertainty. This result tightly constrains the age of the rich mammalian faunal assemblage found at and just below SZt at the CRH47 site.

Recurring middle Pleistocene outburst floods in east-central Alaska

2003 ◽  
Vol 60 (1) ◽  
pp. 50-62 ◽  
Author(s):  
Duane G. Froese ◽  
Derald G. Smith ◽  
John A. Westgate ◽  
Thomas A. Ager ◽  
Shari J. Preece ◽  
...  
Keyword(s):  
Fission Track ◽  
Magnetic Polarity ◽  
Middle Pleistocene ◽  
Pleistocene Glaciation ◽  
Flood Events ◽  
East Central ◽  
Yukon River ◽  
Outburst Floods ◽  
Minimum Age ◽  
Age Constraints

AbstractRecurring glacial outburst floods from the Yukon-Tanana Upland are inferred from sediments exposed along the Yukon River near the mouth of Charley River in east-central Alaska. Deposits range from imbricate gravel and granules indicating flow locally extending up the Yukon valley, to more distal sediments consisting of at least 10 couplets of planar sands, granules, and climbing ripples with up-valley paleocurrent indicators overlain by massive silt. An interglacial organic silt, occurring within the sequence, indicates at least two flood events are associated with an earlier glaciation, and at least three flood events are associated with a later glaciation which postdates the organic silt. A minimum age for the floods is provided by a glass fission track age of 560,000 ± 80,000 yr on the GI tephra, which occurs 8 m above the flood beds. A maximum age of 780,000 yr for the floods is based on normal magnetic polarity of the sediments. These age constraints allow us to correlate the flood events to the early-middle Pleistocene. And further, the outburst floods indicate extensive glaciation of the Yukon-Tanana Upland during the early-middle Pleistocene, likely representing the most extensive Pleistocene glaciation of the area.

Northern Alaska–Kuskokwim Mountains, Domain 10

2007 ◽  
Author(s):  
Earl B. Alexander ◽  
Roger G. Coleman ◽  
Todd Keeler-Wolfe ◽  
Susan P. Harrison
Keyword(s):  
Marine Sediments ◽  
Strike Slip ◽  
Yukon Territory ◽  
Mean Annual Precipitation ◽  
Thrust Faults ◽  
Brooks Range ◽  
Yukon River ◽  
Interior Alaska ◽  
The Mean ◽  
Northern Alaska

The ultramafic rocks in this domain are in the western part of the Brooks Range, the interior Alaska lowlands of the Koyukuk–Yukon Basin, the interior Alaska highlands of the Tanana–Yukon Upland, and the Kuskokwim Mountains. This domain extends east to the Seventymile River, a tributary of the Yukon River that is near the Canadian border, and presumably to the Clinton Creek area in the Yukon Territory. Although the highest elevations in the Brook Range are near 2700 m, those in the western mountains of the range are mostly <1400 m. Flatlands, hills, and low mountains dominate the Koyukuk–Yukon Basin and Tanana–Yukon Uplands, Elevations in the Kuskokwim Mountains are mostly <1000 m. Some of the mountains in uplands of the Tanana–Yukon Uplands are higher than 1600 m. Although the Brooks Range was glaciated during the Pleistocene, there was no glaciation in the Koyukuk–Yukon Basin, and only the higher elevations in the Tanana-Yukon Upland were glaciated during the Quaternary. Today, permafrost prevails throughout the Brooks Range, but it is discontinuous in the Koyukuk–Yukon Basin and Tanana–Yukon Upland and in the Kuskokwim Mountains (Ferrians 1965). Loess is extensive in the basins of interior Alaska and at lower elevations in the Kuskokwim Mountains, with some deposits >60 m thick (Péwé 1975). The climate is very cold throughout the domain, with severe winters and relatively short summers, although mean maximum summer (July) temperatures are >20°C (up to 24°C or 25°C) in the interior basins. With latitudes from 61°N to 68°N, days are very long during summers and very short during winters. The mean annual precipitation is 15–45 cm, with the greatest precipitation during summers. Even though the precipitation is low, the climate is not arid because evapotranspiration is limited by short and relatively cool summers. The freeze-free period is on the order of 60–90 days. The northern and interior Alaska ultramafics (serpentine) consist of Paleozoic and Mesozoic thrust slices emplaced onto Precambrian and Paleozoic marine sediments. They all belong to well-defined belts and are related to low-angle thrust faults or to later high strike–slip faults.

Pleistocene volcanic damming of Yukon River and the maximum age of the Reid Glaciation, west-central Yukon

2004 ◽  
Vol 41 (2) ◽  
pp. 151-164 ◽  
Author(s):  
Crystal A Huscroft ◽  
Brent C Ward ◽  
René W Barendregt ◽  
Lionel E Jackson Jr. ◽  
Neil D Opdyke
Keyword(s):  
Flood Plain ◽  
Yukon Territory ◽  
Early Pleistocene ◽  
Middle Pleistocene ◽  
Pillow Basalt ◽  
Oxygen Isotope Stage ◽  
Yukon River ◽  
River Flood ◽  
Normal Magnetization ◽  
Eruptive Period

Stratigraphic, paleomagnetic, and radioisotope investigations of the Selkirk Volcanic Group have identified a new eruptive period and constrained the age of the Reid Glaciation, the most extensive middle Pleistocene cordilleran advance recognized in central Yukon. Downstream from Fort Selkirk, a complex of valley-filling compound pahoehoe basalt flows and pillow basalt is exposed for 10 km along the Yukon River and is overlain by outwash deposited during the Reid Glaciation. The flows have an 40Ar/39Ar age of 311 ± 32 ka. This age is consistent with the normal magnetization of the flows and their termination below the level of the contemporary Yukon River flood plain. Taken with the ca. 190 ka Sheep Creek tephra, which overlies Reid drift elsewhere in Yukon Territory, the Reid Glaciation is constrained to oxygen isotope stage 8, not stage 6 as previously thought. The presence of thick foreset-bedded pillow breccia units intercalated with the subaerial flows indicates that this eruption caused damming of the Yukon River. Reevaluation of the stratigraphy of early Pleistocene basalt flows and pillow lavas in the Fort Selkirk area indicates that volcanic damming of the Yukon River has occurred at least once previously.

The Dawson Cut Forest Bed in the Fairbanks area, Alaska, is about two million years old☆

2003 ◽  
Vol 60 (1) ◽  
pp. 2-8 ◽  
Author(s):  
John A. Westgate ◽  
Shari J. Preece ◽  
Troy L. Péwé
Keyword(s):  
Fission Track ◽  
Chemical Properties ◽  
Late Cenozoic ◽  
Yukon River ◽  
Direct Association ◽  
Loess Deposits ◽  
Tephra Beds ◽  
And Chemical Properties ◽  
Glass Shards

AbstractThe Dawson Cut Forest Bed lies in the lower part of thick, late Cenozoic loess deposits in the Fairbanks area. It is associated with several distal tephra beds that provide age control and offer the opportunity of its recognition elsewhere in central Alaska. EC tephra (named herein) occurs in the uppermost part of the Dawson Cut Forest Bed and its petrographic and chemical properties point to a co-magmatic relationship with PA tephra, which has not been found in direct association with the forest bed. Both tephra beds are pink and have unusually high Cl in their glass shards, which readily separates them from all other tephra beds in the Fairbanks area. They were produced by discrete eruptions, closely spaced in time. PA tephra has a glass-fission-track age of 2.02 ± 0.14 myr, indicating that the Dawson Cut Forest Bed must be about 2 million years old. The Palisades tephra (named herein) has very similar properties to these two tephra beds, suggesting that the buried forest bed just above it at the Palisades site on the Yukon River, about 250 km west of Fairbanks, correlates with the Dawson Cut Forest Bed.

The Date and Circumstances of Olympiodorus of Thebes

Traditio ◽  
1993 ◽  
Vol 48 ◽  
pp. 1-29 ◽  
Author(s):  
Andrew Gillett
Keyword(s):  
Roman Empire ◽  
Late Antiquity ◽  
Fifth Century ◽  
Imperial Court ◽  
Political Narrative ◽  
History Of ◽  
The Rich ◽  
The Relationship ◽  
Western Half

Olympiodorus of Thebes is an important figure for the history of late antiquity. The few details of his life preserved as anecdotes in hisHistorygive glimpses of a career which embraced the skills of poet, philosopher, and diplomat. A native of Egypt, he had influence at the imperial court of Constantinople, among the sophists of Athens, and even outside the borders of the empire. HisHistory(more correctly, his “materials for history”) is lost, surviving only as fragments in the narratives of Zosimus, Sozomen, and Philostorgius, and in the rich summary given by the ninth-century Byzantine patriarch Photius. These remains comprise the most substantial narrative sources for events in the western Roman Empire in the early fifth century. Besides its value as a source, theHistoryis important as a monument to the vitality of the belief in the unity of the Roman Empire under the Theodosian dynasty. Olympiodorus wrote in Greek, and knowledge of his work is attested only in Constantinople, yet his political narrative, from 407 to 425, concerns only events in the western half of the empire. To understand the significance of these facts, it is necessary to set the composition of Olympiodorus's work in its proper context. Clarifying the date of publication is the first step toward this goal. Internal and external evidence suggests that the work was written in 440 or soon after, more than a decade later than the date of composition usually accepted. Taken with thematic emphases evident in the structure of theHistory, this revised dating explains why an eastern writer should have written a detailed account of western events in the early part of the century. Olympiodorus's account is a characteristic product of the highly literate class of eastern imperial civil servants, and of their genuine preoccupation with the relationship between the eastern and western halves of the Roman Empire at a time when both were threatened by the rise of the new Carthaginian power of the Vandals.

scholarly journals Thermal annealing of implanted <sup>252</sup>Cf fission tracks in monazite

Geochronology ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 89-102
Author(s):  
Sean Jones ◽  
Andrew Gleadow ◽  
Barry Kohn
Keyword(s):  
Thermal Annealing ◽  
Fission Track ◽  
Closure Temperature ◽  
Fission Tracks ◽  
Temperature Ranges ◽  
Best Fitting ◽  
The Mean ◽  
Oriented Parallel ◽  
Increasing Temperature ◽  
Ambient Surface

Abstract. A series of isochronal heating experiments were performed to constrain monazite fission track thermal annealing properties. The 252Cf fission tracks were implanted into monazite crystals from the Devonian Harcourt granodiorite (Victoria, Australia) on polished surfaces oriented parallel to (100) pinacoidal faces and perpendicular to the crystallographic c axis. Tracks were annealed over 1, 10, 100 and 1000 h schedules at temperatures between 30 and 400 ∘C. Track lengths were measured on captured digital image stacks and then converted to calculated mean lengths of equivalent confined fission tracks that progressively decreased with increasing temperature and time. Annealing is anisotropic, with tracks on surfaces perpendicular to the crystallographic c axis consistently annealing faster than those parallel to the (100) face. To investigate how the mean track lengths decreased as a function of annealing time and temperature, one parallel and two fanning models were fitted to the empirical dataset. The temperature limits of the monazite partial annealing zone (MPAZ) were defined as length reductions to 0.95 (lowest) and 0.5 (highest) for this study. Extrapolation of the laboratory experiments to geological timescales indicates that for a heating duration of 107 years, estimated temperature ranges of the MPAZ are −44 to 101 ∘C for the parallel model and −71 to 143 ∘C (both ±6–21 ∘C, 2 standard errors) for the best-fitting linear fanning model (T0=∞). If a monazite fission track closure temperature is approximated as the midpoint of the MPAZ, these results, for tracks with similar mass and energy distributions to those involved in spontaneous fission of 238U, are consistent with previously estimated closure temperatures (calculated from substantially higher energy particles) of < 50 ∘C and perhaps not much higher than ambient surface temperatures. Based on our findings we estimate that this closure temperature (Tc) for fission tracks in monazite ranges between ∼ 45 and 25 ∘C over geological timescales of 106–107 years, making this system potentially useful as an ultra-low-temperature thermochronometer.

scholarly journals ‘Hardcastle Hollows’ in loess landforms: Closed depressions in aeolian landscapes – in a geoheritage context

2018 ◽  
Vol 10 (1) ◽  
pp. 58-63
Author(s):  
Roger Fagg ◽  
Ian Smalley
Keyword(s):  
Monte Carlo ◽  
Random Processes ◽  
Ground Subsidence ◽  
Shape Classification ◽  
Random Shape ◽  
Side Ratio ◽  
Landscape Processes ◽  
Stage Process ◽  
The Mean ◽  
Loess Deposits

Abstract Loess landscapes sometimes contain isolated depressed areas, which often appear as lakes. The outline shape (and distribution) of these depressions could be controlled by random processes, particularly if the depressions are caused by loess hydroconsolidation and ground subsidence. By applying the Zingg system of shape classification it is possible to propose a mean random shape for the closed depressions. A Zingg rectangle with a side ratio of about 2:1 is produced by a very simple Monte Carlo method, which had been used previously to calculate the mean random shape of a loess particle. The Zingg rectangle indicates the basic shape of the mean closed depression. A simple four stage process for the formation of the depressions is proposed. They might be called ‘Hardcastle Hollows’ in honour of John Hardcastle who first reported them, in New Zealand. Studies on Ukrainian deposits suggest that there might be some stratigraphic value in the observation of closed depressions; they are often not superimposed in successive depositions of loess. Hydroconsolidation is important in landscape processes. The hollows provide interesting habitats and enlarge the ecological interest of loess deposits; the geoheritage scene is enhanced.

Timber Harvest in Interior Alaska

2006 ◽  
Author(s):  
Tricia L. Wurtz ◽  
Robert A. Ott
Keyword(s):  
Timber Harvest ◽  
Timber Harvesting ◽  
Yukon Territory ◽  
Private Land ◽  
Yukon River ◽  
Timber Sales ◽  
History Of ◽  
Dawson City ◽  
Electrical Generation ◽  
The Town

The most active period of timber harvesting in the history of Alaska’s interior occurred nearly a century ago (Roessler 1997). The beginning of this era was the year 1869, when steam-powered, stern-wheeled riverboats first operated on the Yukon River (Robe 1943). Gold was discovered in Alaska in the 40-Mile River area in 1886, a find that was overshadowed 10 years later by the discovery of gold in the Klondike, Yukon Territory. By 1898, Dawson City, Yukon Territory, was reported to have 12 sawmills producing a total of 12 million board feet of lumber annually (Naske and Slotnick 1987). Over the next 50 years, more than 250 different sternwheeled riverboats operated in the Yukon drainage, covering a large part of Alaska and Canada’s Yukon Territory (Cohen 1982). This transportation system required large amounts of fuel. Woodcutters contracted with riverboat owners to provide stacked cordwood at the river’s edge, at a cost of $7.14 in 1901 (Fig. 18.1; Cohen 1982). Between 100 and 150 cords of wood were required to make the 1400-km round trip from the upper Yukon to Dawson City (Trimmer 1898). Over time, woodcutters moved inland from the rivers’ edges, significantly impacting the forest along many rivers of the Yukon drainage (Roessler 1997). The growth of the town of Fairbanks required wood for buildings and flumes as well as for fuel. In Fairbanks’s early days, all electrical generation was by wood fuel at the N.C. Company’s power plant. From the founding of the town in 1903 through the 1970s, white spruce harvested in the Fairbanks area was used exclusively by local sawmills, which produced small amounts of green and air-dried lumber. In 1984, however, the Alaska Primary Manufacturing Law was struck down by the U.S. Supreme Court, removing the legal barrier to round-log export of timber harvested from State lands. During the late 1980s and 1990s, many high-quality logs from State and private land timber sales were exported, primarily to Pacific Rim countries. Declining markets ended this trend in the late 1990s, and there have been no significant exports since the market collapse.

Sign in / Sign up

Export Citation Format

Share Document