Landform development on moraines of the Klutlan Glacier,Yukon Territory,Canada

The landform evolution of the Klutlan moraines is described and explained primarily with respect to processes that cause voids in which debris is deposited. Morainal deposits of different ages provide examples of landforms at different stages of development, so that continuous ideal evolutionary sequences can be inferred. Specific features are classified as those on material of the same depositional age that develop mostly in a vertical direction with numerous topographic reversals, and those cross-cutting materials of different depositional age that develop primarily in a horizontal direction. The evolution of slopes is often terminated by their destruction as the underlying ice melts, but former slopes on morainal debris are traceable to ice-ridge slopes on the original glacier surface. The general process of evolution is one of downwasting by surficial icemelt, in which a grand topographic reversal takes place as the original ice mass with a gently convex surface melts to leave a basin floored by a concave mantle of morainal debris. The primary glacial process of melting differs from the primary karst process of solution, but many minor glacial processes and major glacial forms are similar to minor karst processes and major karst forms.     

Limnology of the Klutlan moraines,Yukon Territory,Canada

Lakes of the Klutlan moraines originate by down-melting of stagnant ice under a mantle of rock debris and vegetation ranging from scattered herbs and shrubs on the younger moraines to multiple-generation closed spruce forest on the oldest moraines, which are 600–1200 yr old. Lakes on the youngest moraines are temporary, turbid with glacial silt, and marked by unstable ice-cored slopes. On older moraines most lakes have clear water and stable slopes. On the oldest moraines many lakes have brown water caused by dissolved humic materials derived from the thick forest floor, but even here some slopes are unstable because of continued melting of buried ice. Morainic lakes contain bicarbonate waters of moderate alkalinity and conductivity and low levels of nutrients. The highly diverse phytoplankton is dominated by chrysophytes and cryptomonads, with few diatoms. Extremely low values for phytoplankton biomass place most of the lakes in an “ultraoligotrophic” category. Zooplankton is dominated by copepods, which were found even in ice ponds only a few years old, and by the cladoceran Daphnia pulex. Surface-sediment samples contained a total of 16 species of chydorid Cladocera. Of these, Alonella excisa and Alona barbulata are apparently the pioneer species in the youngest lakes. Chydorus sphaericus only appears in lakes of the oldest moraines. A successional pattern is not conspicuous, however, partly because some of the lakes on the older moraines originated by recent collapse over buried ice. Lakes on the upland outside the dead-ice moraines yielded 39 species in the zooplankton. The distinctive assemblage on upland lakes may relate more to different water chemistry than to age.     

Formation of the Neoglacial surge moraines of the Klutlan Glacier,Yukon Territory,Canada

The Klutlan Glacier is a valley glacier 82-km long emerging from the Icefield Ranges of the St. Elias Mountains. It is one of at least 200 surging glaciers identified in western North America. During about the past 1200 yr, the glacier has deposited at its terminus a series of at least 7 surge-related Neoglacial ice-cored moraines. Lithologic characteristics of the Klutlan moraines suggest that they have resulted principally from the surging of the tributary Nesham Glacier, which periodically injects a lobe of medial and lateral moraines and the underlying ice into a more slowly moving Klutlan ice stream. Subsequent surges of the main ice carry the Nesham surge lobes to the Klutlan terminus as discrete geomorphic features. For the past 400 yr a Nesham lobe has reached the Klutlan terminus at approximately 80-yr intervals.     

Soil development on recent end moraines of the Klutlan Glacier,Yukon Territory,Canada

Data on soils with six Neoglacial moraines of the Klutlan Glacier have been compared with those from moraines at the warm, moist coastal site of Glacier Bay, 160 km south. Percentage organic matter increases rapidly for the first 100 to 150 yr of soil development and then continues to rise gradually for the next 100 yr. Soil pH falls from 8.0 in recent till to approximately 6.0 in 200-yr-old soils. Nitrogen levels in the mineral soil increase from near zero in recent tills to 0.7% in soils 175–200 yr old; organic horizons of soils associated with spruce forests in later successional stages contain approximately 1% nitrogen. Concentrations of certain inorganic phosphate ions in the different-aged soils increase continually throughout the succession. Data for nine chemical variables were subjected to a principal components analysis; the major pattern in the data reflects the differences between soils of low organic content and high pH present in early successional stages, and nutrient-rich soils with high organic content and low pH present after succession has progressed toward the spruce forest. These trends in soil development with time are strikingly similar to those reported from Glacier Bay, except that the changes in soil properties appear to be delayed by 50–100 yr at the Klutlan terminus. Although numerous signs of nitrogen deficiency have been identified in plants growing on new soils at Glacier Bay, none was observed visually in living plants or in nutrients measured in samples of foliage from three plant taxa (Epilobium latifolium, Salix spp., and Populus balsamifera) taken from the Klutlan moraines. Concentrations of nitrogen and other nutrients (Ca, Mg, K, total P) in the foliage samples show no clear trends with increasing soil development. Low temperatures, a short growing season, and very low mean annual precipitation probably limit plant growth and account for the delayed soil development on the Klutlan moraines.     

Wastage of the Klutlan ice-cored moraines,Yukon Territory,Canada

A series of ice-cored Neoglacial moraines at the terminus of the Klutlan Glacier covers an area of 90 km². Studies were made to determine empirically how long ice persisted in the Klutlan moraines and to develop models that can accurately predict wastage rates under current climatic conditions. A meltout curve based on climatological data reflects the sum of three melting processes: surficial melting, melting by lake water, and melting by geothermal heat. About 950 yr are required to melt 180 m of ice with a debris concentration of 1%, or about 1200 yr for a 1.5% debris load. Another meltout curve, based on seismic data, suggests total meltout in about 875 yr. When all geologic factors are considered, the empirical meltout curve is remarkably similar to that derived by considering the major heat-flux parameters. Meltout rates can be predicted if (1) the fundamental climatic parameters can be ascertained, and (2) the sediment concentration in the ice is known.     

Surge moraines of the Klutlan Glacier,Yukon Territory,Canada: Origin,wastage, vegetation succession,lake development,and application to the late-glacial of Minnesota

The Klutlan Glacier in the St. Elias Mountains of the Yukon Territory has surged repeatedly during the last few hundred years, and its drift-covered stagnant ice provides an analog for the downwastage, landform development, vegetational succession, and lake formation on Late Wisconsin moraines of Minnesota. Melting of the buried ice caused collapse of the drift mantle and the formation of lakes, which become filled with sediment that slumps in from receding ice walls. Topographic reversals are common, as the sediment cover of drained lakes inhibits local under-melting, and collapse occurs elsewhere. As the drift mantle thickens the land surface becomes stabilized and pioneer herbs are succeeded by shrubs and then by white spruce. The oldest moraines (600–1200 yr old) have a multiple-generation spruce forest, yet melting of buried ice still locally forms young lakes. Cores of organic sediment from the oldest lakes contain a stratigraphic sequence of pollen, diatoms and cladocerans that record the early stages in lake and landscape succession.     

Modern pollen assemblages and vegetational history of the moraines of the Klutlan Glacier and its surroundings,Yukon Territory,Canada

Modern pollen assemblages have been studied from surficial lake muds and moss polsters collected from five vegetated ice-cored moraines of the Klutlan Glacier. The youngest vegetated moraine (K-II) is characterized by high pollen values for Salix and Hedysarum, K-III by high Salix and Shepherdia canadensis and low Hedysarum and Picea, K-IV by high Betula, Salix, and Shepherdia, and K-V and the Harris Creek moraine (HCM) by high Picea. Variations are summarized by canonical variates analysis. A percentage pollen diagram from Gull Lake on the upland east of the glacier records vegetational development since the deposition of the White River volcanic ash 1220 ¹⁴C yr ago. An initial species-rich treeless vegetation was replaced by birch-alder-willow shrub-tundra, and this by open Picea glauca forest similar to present vegetation around the lake. Sites on HCM show two basic stratigraphies. Triangle Lake reflects vegetational succession from Salix-Shepherdia canadensis scrub similar to that on K-III today, through open Picea woodland of K-IV type, to closed Picea forests of K-V and HCM. Heart Lake and Cotton Pond reflect vegetational development following melting of ice underlying the spruce forests of HCM. These two types are summarized by positioning the fossil spectra on the first two canonical variate axes of the modern surface spectra.     

Paleolimnology of two lakes in the Klutlan Glacier region,Yukon Territory,Canada

Lakes developed on progressively younger end moraines of the Klutlan Glacier were initially assumed to have originated shortly after moraine emplacement and to have persisted to the present. Limnological differences between lakes on old vs young moraines were thought to result from limnological maturation within the lakes and ponds themselves and in response to the development of soils and vegetation on moraine surfaces. This study represents a paleolimnological test of this hypothesis. If true, the first-formed sediments of lakes on old moraines should be comparable to sediments presently forming in lakes on young moraines. Geochemical and paleontological studies of surface sediment to a series of lakes on progressively older moraines provide baseline information for comparing successive levels of lake sediment cores from older moraines. Results indicate that the time of lake initiation seldom reflects moraine age. Even on the oldest moraine (Harris Creek), lake basins are presently forming. Their sediment character more closely relates to the rapidity of basin formation due to melting of buried ice than to age of the lake itself or of the moraine on which it is situated. Vegetation and soil development play an important but secondary role in determining the character of lake sediments; rapid subsidence can convert humic-water lakes surrounded by second-generation spruce forests into turbid-water lakes with unstable, slumping margins. A detailed paleolimnological study of two lakes, one on the unglaciated upland and another in an outwash channel penetrating the oldest moraine, revealed progressive limnologic changes through time, suggesting that their basins were stable for 1200 and 400 yr, respectively. The changes in diatom stratigraphy of these lakes appear to relate to natural limnological changes associated with lake maturation and accumulation of nutrients as well as to changes in the surrounding vegetation and soils.     

Late Holocene moisture balance variability in the southwest Yukon Territory,Canada

Analyses of sediment cores from Marcella Lake, a small, hydrologically closed lake in the semi-arid southwest Yukon, provides effective moisture information for the last ∼4500 years at century-scale resolution. Water chemistry and oxygen isotope analyses from lakes and precipitation in the region indicate that Marcella Lake is currently enriched in ¹⁸O by summer evaporation. Past lake water values are inferred from oxygen isotope analyses of sedimentary endogenic carbonate in the form of algal Charophyte stem encrustations. A record of the δ¹⁸O composition of mean annual precipitation at Jellybean Lake, a nearby evaporation-insensitive system, provides data of simultaneous δ¹⁸O variations related to decade-to-century scale shifts in Aleutian Low intensity/position. The difference between the two isotope records, Δδ, represents ¹⁸O-enrichment in Marcella Lake water caused by summer effective moisture conditions. Results indicate increased effective moisture between ∼3000 and 1200 cal BP and two marked shifts toward increased aridity at ∼1200 and between 300 and 200 cal BP. These prominent late Holocene changes in effective moisture occurred simultaneously with changes in Aleutian Low circulation patterns over the Gulf of Alaska indicated by Jellybean Lake. The reconstructed climate patterns are consistent with the topographically controlled climatic heterogeneity observed in the coastal mountains and interior valleys of the region today.     

Natural acid rock drainage associated with black shale in the Yukon Territory,Canada

Investigated herein are water and sediment geochemistry, and metal attenuation processes associated with natural acid rock drainage originating from black shale formations in the Macmillan Pass area, Clear Lake prospect and Engineer Creek by the Dempster Highway in the Yukon Territory, Canada. The most metalliferous water having pH 3.0, 150 mg/L Zn, 39 mg/L Ni, 2.8 mg/L Cu and 9.1 mg/L As was found in a tributary stream of Engineer Creek with no known mineral deposits occurring in the vicinity. For all three study areas, the water and sediment geochemistry is significantly affected by the local lithology and prevailing metal attenuation processes. Despite their anomalous acidity and metal contents, the natural acid streams contribute only a small fraction of the contaminant loadings to the major water courses because of their low flows. Dilution, neutralization, sorption and co-precipitation are identified as the major mechanisms attenuating aqueous transport of potentially deleterious metals. However, microbial mediation in metal attenuation is also evident in low-flow systems. The wide variation of water and sediment geochemistry along a flow path renders the establishment of background metal values difficult. In assessing environmental impacts, it may be more practical to consider metal loadings on a watershed scale than to rely on a comparison with operationally defined background concentrations.     

The geochemistry of the sedimentary rocks in the vicinity of the Tom Pb-Zn-Ba deposit, Yukon Territory, Canada

A total of 138 samples of the Devonian sediments in the vicinity of the Tom stratiform Pb-Zn-Ba deposit were analysed for major elements and 16 minor and trace elements by X-ray fluorescence.The geochemistry of the footwall argillites is characterised by a concentration of elements that are typically associated with the detrital resistate minerals and feldspars (e.g. Al₂O₃, Na₂O, K₂O, TiO₂, Ce, Nb, Zr), which are contained within the interbedded silty layers of probable distal turbidite origin.The hanging-wall shales are characterised by high V concentrations. The C-organic data and the V/Cr ratios suggest that sapropelic conditions may have been locally developed in the vicinity of the West zone mineralisation and in the hanging-wall shales. Very high concentrations of Ba were found to be present in the hanging-wall shales (>0.5% Ba).Zn is more widely dispersed than Pb in the sediments around the mineralisation. There is no marked enrichment of Fe, Mn or Cu in the sediments close to the mineralisation.     

The development of near-surface ground ice during the Holocene at sites near Mayo,Yukon Territory,Canada

An examination of soil thermal and hydrologic regimes at several sites near Mayo, Yukon Territory, and the ground-ice stratigraphy of a thaw-slump headwall close to these sites supports the hypothesis that an ice-rich zone, frequently observed at the base of the active layer, may be due to the annual water balance of permafrost. Observations demonstrate that ice lenses have grown at the top of permafrost in soil tubes installed in 1983. In addition, 90 cm of segregated ice are exposed in the thaw-slump headwall above a thaw unconformity, dated at 8870 ± 200 years BP, but below the base of the present active layer. These data suggest that the rate of water incorporation into permafrost over the last 8000 years in the Mayo area has been at least 0.1 mm yr^?1.     

Factor analysis of stream sediment geochemical data from the Mount Nansen area,Yukon Territory,Canada

Q- and R-mode factor analytical studies were made of 158 stream sediment samples from the Mount Nansen area, Yukon Territory, analyzed for Cu, Pb, Zn, Mo, Ni, Ag, and Sb. R-mode results were more clear-cut than were Q-mode in terms of ease of interpreting geological significance of individual factors, although results of both methods were very comparable. The 3-factor R-mode model accounted for 79.9 percent of the variation in the data. Factor 1, a Pb-Zn-(Ag) factor correlated with Mount Nansen volcanic rocks and particularly with known Pb-Zn-Ag-Au veins within those rocks. Factor 2, a Cu-Mo factor correlated with porphyric intrusions known to contain Cu-Mo mineralized zones. Factor 3, an Sb-(Ag) factor is, as yet, not adequately explained in terms of geology. The main additional contribution of the Q-mode study is the communalities. Samples that depart from the norm (i.e. do not agree well with the 3-factor model) are readily apparent because of low communalities and must be considered anomalous in the general sense until an adequate explanation for this difference is found.     

Holocene paleoenvironmental changes inferred from diatom assemblages in sediments of Kusawa Lake, Yukon Territory, Canada

The southwest Yukon Territory, Canada, is an important region for recovering sensitive records of Holocene paleoclimatic change. More information is needed, however, to constrain the timing of the major Holocene climatic transitions, and to understand associated impacts on different ecosystems. For example, paleolimnological studies have focused on small lakes and ponds, but the history of large lakes has received little study. We analyzed diatom assemblages, species richness, valve concentrations, and biogenic silica, in the sediments of Kusawa Lake (60°16.5'N; 136°10.9'W; 671 m a.s.l.) to reconstruct the responses of this large (surface area = 142 km²), deep (Z_max = 135 m) freshwater ecosystem to Holocene climatic transitions. Diatoms colonized the lake soon after ice retreat, around 11,000 cal yr BP; assemblages throughout the record were dominated by planktonic types. Diatom concentrations and biogenic silica were high during the Holocene Thermal Maximum between 10,700 and 7300 cal yr BP, then began to decrease in response to cooling associated with orbitally driven reductions in insolation. Diatom assemblages shifted towards taxa with lower surface water temperature optima after 8300 cal yr BP, perhaps in response to abrupt and progressive cooling. Our study confirms that diatom assemblages in large lakes are sensitive to regional-scale paleoclimatic changes.     

Structural geology of the eastern Nadaleen trend,Yukon Territory,Canada: Implications for recently discovered sedimentary rock-hosted gold

Recently discovered gold-rich mineral deposits in the eastern Nadaleen trend of northeastern Yukon Territory occur in unmetamorphosed Neoproterozoic carbonate and siliciclastic rocks and their location is partly controlled by structures. Regional deformation largely resulted from mid-Cretaceous NNE-vergent, thin-skinned fold-thrust activity. However, structures in the eastern Nadaleen trend are more complex and include strike-slip and reverse faults, and SSW-, W-, and E-plunging folds. Local structures are cospatial with regional geologic features, including (1) an E-striking structural triangle zone defined by oppositely dipping reverse faults that verge toward the eastern Nadaleen trend, (2) a transition zone between Paleozoic Ogilvie platform rocks in the north to Selwyn basin rocks in the south, and (3) a change in regional deformation character from west to east, whereby to the west, rocks in the south are more deformed than rocks in the north, whereas to the east, rocks show no obvious change in deformation style. The structural complexity within the eastern Nadaleen trend probably resulted from these regional geological features and was further complicated by local competency contrasts between rock units. The cospatial location of the regional geological features may have been caused by a pre-existing, W-trending subsurface basement structure. Reverse faults bounding the E-striking triangle zone may have acted as low permeability aquitards that directed mineralizing fluids up-dip into reactive carbonate stratigraphy in the eastern Nadaleen trend. Gold-rich mineral deposits in the eastern Nadaleen trend occur preferentially in SSW-plunging anticlines and near faults, both of which probably influenced the migration of mineralizing fluid.     

Temperatures of the past 2000 years inferred from lake sediments,southwest Yukon Territory,Canada

Lake sediments from four sites in the southwest Yukon Territory, Canada, provided paleotemperature records for the past 2000 yr. An alpine and a forest site from the southeastern portion of the study area, near Kluane Lake, and another alpine-forest pair of lakes from the Donjek River area located to the northwest yielded chironomid records that were used to provide quantitative estimates of mean July air temperature. Prior to AD 800, the southwest Yukon was relatively cool whereas after AD 800 temperatures were more variable, with warmer conditions between ~ AD 1100 and 1400, cooler conditions during the Little Ice Age (~ AD 1400 to 1850), and warming thereafter. These records compare well with other paleoclimate evidence from the region.