Proglacial Environments Research Articles

The hydrochemistry of Bayelva, a high Arctic proglacial stream in Svalbard

Major ion, silica and pH data from a high Arctic proglacial stream network are examined. Factor analysis shows that the major controls upon hydrochemistry in the basin include snowpack solute elution, rapid alteration of minerals via surface reactions and slow, incongruent silicate dissolution. The importance of chemical weathering is found to increase downstream at the expense of solute acquisition from the transient snowpack. Data from a series of snow pits show that snowpack solute elution is characterised by the preferential elution of SO42−. Evidence for the preferential elution of NO3− is equivocal. However, NO3− levels in proglacial runoff may be enhanced by the leaching of cryotic soils later in the ablation season.Chemical weathering is dominated by calcite dissolution at high elevations and a combination of calcite and dolomite dissolution in the downstream proglacial environment. Silicate weathering at high elevations is characterised by the enrichment of K+ relative to Si. Concentrated active layer soil waters show less enrichment of K+ and constitute a potentially important source of dissolved silica to the river system. Na+ is also produced by silicate weathering, but its mobility is believed to be largely governed by ion exchange with Ca2+ early in the ablation season.All chemical weathering environments are characterised by high p(CO2) due to either respiration within the soil or, at higher elevations within the catchment, H+ provision from acid aerosol and sulphide oxidation. However, rates of sulphide oxidation are limited because the cold-based thermal regime of the glaciers effectively prevents access of meltwaters to freshly comminuted sub-glacial sulphide minerals. The restricted sub-glacial weathering therefore means that ice marginal and proglacial environments are the most important zones of solute acquisition by meltwaters, causing significant enrichment of major ions, silica and dissolved CO2 within only a short distance of the contemporary ice margin.

Late Weichselian glacimarine depositional processes in the southern Skagerrak revealed by high-resolution seismic facies analysis

Thirty kilometres of high-resolution, seismic-reflection (boomer) data were collected in the Skagerrak area, between Norway, Sweden and Denmark, to reconstruct the seismic stratigraphy in an area of late Weichselian shelf–margin progradation. By the use of lap-out style, five depositional units, A–E, were recognised in the boomer profiles. No stratigraphic control was available, but tentative correlation has been made on the basis of previous studies in the region. Unit A is interpreted as till. In unit B, the seismic facies association includes shingled, mounded, oblique channel fill, and parallel-bedded reflection configurations, which are interpreted to have formed in a channelled, proximal, pro-glacial environment. In unit C, discrete mounds and semi-continuous lensoid bodies with divergent channelled flow style constitute the facies association, and are interpreted predominantly as debris-flow deposits that accumulated in a distal pro-glacial environment. In unit D, the facies association constitutes mounds and oblique in-fill between mounds; positive relief and the distribution of facies shows that the deposits were laid down under the influence of a unidirectional current. Units B–D are interpreted as late Weichselian in age. Unit E is interpreted as the Holocene marine cover of laminated clay to fine sand. This seismic–stratigraphic succession reveals a high-resolution record of late Weichselian deglaciation in this area.

The burial of ice in the proglacial environment on Bylot Island, Arctic Canada

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Solute generation and transfer from a chemically reactive alpine glacial-proglacial system

The environs of the Glacier de Tsanfleuron, Switzerland, was used as a study site to investigate the controls on the relative efficiency of solute generation and removal from glacial and proglacial environments. Here, a 1500 m wide glacier forefield consists of a karstic limestone plateau flanked to the north by a till-floored valley. Bedrocks and glacial debris are composed of chemically reactive pure and impure Mesozoic and Tertiary limestones with accessory pyrite. Spot sampling of ice, snow and meltwaters in the late melt season was supplemented by systematic measurements of the main meltstream, including during periods of rainfall, and simple laboratory leaching and weathering experiments. Isotopic parameters were used to investigate water sources. Most meltwater and glacier ice samples lay close to a meteoric water line (δ D= 8·3 δ18O + 14) defined by waters from small tributary streams. Heavy isotopic excursions of bulk meltwater chemistry were caused by rainfall events, recovering within days to a δ18O baseline around −12 permil. No regular diurnal variations in δ18 O were apparent. The atmosphere is the source of Cl− and most Na+, but the bulk of other solutes are generated in the environment. Ion loads of up to 1 meq l−1 are rapidly attained by calcite dissolution. Over periods of weeks to months pyrite oxidation generates sulphate and acidity that drives further calcite dissolution. Low water–rock ratio weathering environments have characteristically high SO42−, Mg2+, Sr2+, and ratios of these species to calcium. The characteristic cation ratios are influenced by non-congruent calcite dissolution. The ratio of sulphate to other species is highest where water–rock contact times are highest, although this relationship is complicated by spatial variations in pyrite abundance. Meltstream time series illustrate that 90 per cent of daily ion yields in fine weather are concentrated in the 12 h time period of higher discharge. Ion yields increase downstream mainly by a combination of dissolution of calcareous suspended sediment and input from tributaries and seepage from the till banks. Rainstorms lead to increased solute concentrations and resulting hourly fluxes can match daily fine weather ion fluxes. Excess nitrate appears to be largely sourced from the proglacial surface. The capacity of the proglacial environment for yielding significant subsurface water as a result of the storm seems low, unlike non-glacial environments. This implies that most of the excess solutes mobilized by storms comes from subglacial sources. Increased efficiency of yield of solutes from low water/rock ratio subglacial weathering environments persists after the isotopic signature of the rainfall event has died away. A simple conceptual model of the sources of water and solutes agrees with conclusions from attempts at hydrograph separation, that mixing of water reservoirs of fixed solute composition cannot be used for quantitative descriptions of the system. Estimated annual solute yields (17 ton per km2 per m precipitation) are high, but cannot be readily expressed in purely areal terms because of likely significant losses to the underlying karstic system. A tentative conclusion is that the proglacial environment is overall less efficient at producing solutes than the glacial environment, but more information is required on processes in the early melt season to substantiate this statement. Copyright © 1999 John Wiley & Sons, Ltd.

Late Pleistocene and early Holocene ecological response of Lake El Trébol (Patagonia, Argentina) to environmental changes

Stratigraphy of Lake El Trebol (41°S 71°W, 758 m a.s.l.) described from an 11 m long sediment core provided a continuous record of patecenvironmental changes occurred during the last 14,000 years in southern South America east of the Andes. Located in an ecotonal area within a strong humidity gradient, this lake offers a unique opportunity to develop paleolimnological studies. Using a geochemical approach that includes elemental analysis, bulk organic matter, major nutrients and pigments combined with chironomids and pollen analysis, three zones were identified in the sedimentary record of this take. The oldest one (between 680 and 1,100 cm) corresponds to the late Glacial period. During that time, clayish laminated sediments were formed in a proglacial environment. Low organic matter, biogenic silica and nitrogen contents and the absence of pigments, pollen and chironomids characterise this period. At the end of this period, ca. 14,000 yr BP, a sharp increase in phosphorus concentrations predates major changes in limnological parameters. The transition zone (between 560 and 680 cm) is related to major changes in the drainage system that started soon after ca. 14,000 yr BP and continued to ca. 10,500 yr BP. The chemical composition of the sediments was affected by an increase in physical weathering mechanisms almost coincident with the increase in the regional volcanic activity that produced suspended volcanic detritus. The increase of mainly coarser detritical components may indicate a reorganisation of the fluvial system by that time. Simultaneously, an increase in the productivity of the lake accompanied by a gradual replacement of open vegetation with Nothofagus, Poaceae and Ericaceae, by Nothofagusforest, was observed. In the last zone (between 0 and 560 cm) the productivity of Lake El Trebol achieves maximum values. The trends in geochemical and biological indicators observed at Lake El Trebol can be up to some extent, correlated to those registered in Lake Mascardi. The results support earlier paleoctimatic scenarios from southern South America.

Large-scale channel fill structures in Late Ordovician glacial deposits in Mauritania, western Sahara

Late Ordovician siliciclastic glacial and related deposits on the North Gondwana continental shelf comprise striking incised features referred to as large-scale channel-fill structures. These are described from exposures and aerial photographs in two areas (Adrar and Hodh) in Mauritania. The channel-fill structures are up to several kilometres in length and several hundred metres wide. They are slightly sinuous narrow sandstone bodies deeply incised into the Late Ordovician glacial drift and the Cambro–Ordovician bedrock. Palaeogeographical reconstructions indicate that these structures were located in the ice-marginal zone. They are preferentially oriented parallel to palaeo-ice-flow directions. Sedimentary facies analysis reveals three vertically stacked architectural units infilling a U-shaped erosional basal unconformity. Unit 1 is thin and made up of conglomeratic sandstones of various origins comprising debris-flows, deltaic-like progradational foresets and trough cross-stratified sands. In Adrar, architectural unit 2 shows sheet-like, evenly laminated, fine- to medium-grained, well sorted sandstones characteristic of a high-energy marine environment. In contrast, in the Hodh area, unit 2 displays vertically stacked successions of coarse-grained sandstones that indicate high-discharge sediment-laden flows; these are interpreted as meltwater sediments. In both Adrar and Hodh, architectural unit 3 is made up of gravelly coarse-grained, trough cross-stratified sandstone emplaced in a braided, low sinuosity fluvial environment. The three-stage infilling history and the palaeogeographic location combined with size and shape criteria make it possible to compare the channel-fill structures with Pleistocene tunnel-valleys found in areas of low-relief in cool temperate and low Arctic zones. Such features are incised by high-pressure subglacial meltwater and later infilled by proglacial to postglacial deposits. Based on this comparison, architectural unit 1 represents subglacial or proglacial outwash, high sediment discharge in unit 2 took place in a proglacial environment in the Hodh area while an isostatically downwarped shelf was responsible for a marine incursion in the Adrar channels, and deposits in unit 3 are fluvial postglacial sediments. Identification of preserved channel-fill structures may be useful in reconstructing Late Ordovician ice-sheet dynamics.

Sedimentary facies and depositional environments related to Gondwana glaciation in Batovi and Suspiro regions, Rio Grande Do Sul, Brazil

Sedimentary facies were produced by Late Paleozoic Gondwana ice sheets in the Batovi and Suspiro regions, Rio Grande do Sul State, southern Brazil. The glaciogenic sediments, assigned to the Itararé Group of Paraná Basin, are the result of processes related to the subglacial, supraglacial and proglacial (ice-contact, glaciofluvial and glaciolacustrine) environments of the glacial depositional system. Several features developed by the action of glaciers were identified in the studied outcrops: striated and grooved pavements; striated, polished and faceted stones; finely laminated rhythmites bearing dropstones (varvites); erratic clasts and deposits exhibiting deformational structures such as folds, normal and reverse faults, and beds with abnormal dips. The available evidence suggests that the glacial episodes took place in a terrestrial (continental) context, far from direct marine influence.

RESERVOIR POTENTIAL OF GLACIO-FLUVIAL SANDSTONES: MERRIMELIA FORMATION, COOPER BASIN, SOUTH AUSTRALIA

Sedimentological analysis of cored sections within the Merrimelia Formation (basal Gidgealpa Group, Cooper Basin, S.A.) reveals a complex glacigenic environment, including glacio-lacustrine, deltaic, shorezone, fluvial, aeolian and other terrestrial facies. These facies are observed within terminoglacial and proglacial environments, and interfinger constantly throughout the Merrimelia Formation, exhibiting rapid environment change related to position of the ice sheet. Detailed sedimentological and petrological analysis, suggests that Tirrawarra sandstone-type facies belongs within the Merrimelia depositional realm. Provenance data indicates that the lithic component of the Tirrawarra Sandstone, is sourced from reworked Merrimelia coeval depositional facies. A high proportion of labile grains, which are commonly observed in the Merrimelia Formation, are only observed rarely in the Tirrawarra Sandstone (sensu stricto). It is proposed that the fluvial sandstones of the Merrimelia Formation are part of the same fluvial deposystem as the Tirrawarra Sandstone (sensu stricto) and the two sandstone sequences are the natural progression of coarsening sediment as more detritus was released from melting glaciers. It is suggested that there no longer remains any sedimentological, stratigraphical or petrographical reasons why the Tirrawarra Sandstone should not be included within the Merrimelia Formation. It is further proposed that all the braided glacio- fluvial sandstones within the Merrimelia Formation and Tirrawarra Sandstone (sensu stricto) be grouped together as 'Tirrawarra-type' facies within the Merrimelia glacigenic domain.The concept that the glacio-fluvial sandstones within the Merrimelia Formation are of the same genetic origin as the Tirrawarra Sandstone (sensu stricto), must point to the economic potential of similar sandstones found throughout the Merrimelia Formation. The thickness, sediment style and lateral extent of the proglacial braidplains is controlled by the duration of glacial melting. The Merrimelia Formation reveals a sequence of major freezing and thawing episodes with the overlying Patchawarra Formation representing the cessation of glacial influence in the Cooper Basin. Therefore, the youngest 'Tirrawarra-type' sandstone facies found at the top of the Merrimelia Formation is likely to contain the least amount of labile grains, a highly rigid siliceous framework and will be well sorted. The risk of lower reservoir quality increases down section where, with time, freezing dominated over thawing and the sediments were less rinsed, and where the resultant sandstones are more likely to be thin, more poorly sorted and chemically immature with a high proportion of labile framework grains. Thus compositional variation, controlling the diagenetic overprint, together with sandstone facies and bedform style exert profound control on the reservoir quality in the Tirrawarra-Moorari Field area, on potential gas reservoirs in the Merrimelia Formation.

Jökulhlaup deposits in proglacial areas

This paper discusses the main causes and characteristics of jökulhlaup (‘glacier burst’) floods, and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of ‘normal’, braided river outwash (‘Type I’ outwash). Two main jökulhlaup outwash environments are identified: Type II outwash, produced by sudden drainage of ice-dammed lakes; and Type III, associated with drainage during subglacial geothermal activity, and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows. In fluid flows, especially ones yielding Type II outwash, the most common deposits are large-scale expansion bars (and locally, eddy and pendant bars), and ‘mega-ripples’ or dunes, both forms normally composed of large-scale gravel-cobble cross-bedding, often capped by an imbricated boulder lag (a ‘Type B2’ lithofacies sequence). The armour is absent only where runoff decreased too rapidly to allow surface winnowing. Other jökulhlaup facies include extensive boulder beds (Type C), inverse-normally graded cobble beds (Type DS), ice-proximal debris flow deposits and deformed bedding containing diamicton clasts (Types G and H), and slack-water sediments (Type A). Type III outwash is dominated by massive, homogeneous, flood surge granules, underlain by pre-surge gravels, and capped by post-surge fluid bedforms, reflecting deposition during both the rising and falling limbs of the flood hydrograph (Type E4). The paper demonstrates that jökulhlaups do generate distinctive assemblages of depositional landforms and sediments, and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jökulhlaup drainage.

The sedimentary record of Moose Lake: implications for glacier activity in the Mount Robson area, British Columbia

The postglacial sedimentary environment of Moose Lake was investigated using 3.5 kHz subbottom profiles and cores from the sediment surface. A late phase in the deglaciation of the upper Fraser River valley involved a valley glacier that flowed east to west and that terminated near the present-day outlet of Moose Lake. The overdeepened Fraser valley was infilled with ice-contact sediments, including terminal and recessional moraines, thereby damming westward drainage and forming Moose Lake. Eastward glacier retreat resulted in the deposition of ice blocks in the shallow west zone of the lake, where subsequent melting disturbed conformable glaciolacustrine deposits. The main Moose Lake basin records a transition from proximal to distal proglacial environments. However, late glacial and postglacial sediments are dominated by settling from suspension. Coarse, but localized, sediment inputs are derived from the Thunder Creek fan-delta and avalanche activity on the north-facing slope of the south shore. Depths to major acoustic reflectors and known modern accumulation rates of 2.7 mm a−1 indicate that the upper 15.5 m of sediment fill represents deposition during the Holocene and accounts for less than one third of the total late glacial and postglacial sediment yield. Sedimentary structures visible in cores and 14C dating confirm the varved nature of the upper 3 m of sediment. Extreme positive departures in varve thickness are related to above-average discharge to Moose Lake following persistent, glacier-melt-augmented summer flows. The Moose Lake varve chronology confirms the general pattern inferred from other regional evidence of climate deterioration after 1600 AD, which led to glacier advance and moraine emplacement in the Canadian Rocky Mountains.

RATES OF ORGANIC CARBON ACCUMULATION IN YOUNG MINERAL SOILS NEAR BURROUGHS GLACIER, GLACIER BAY, ALASKA

The functional relationship between organic carbon in surface mineral horizons of fine-grained soils and time of soil development is examined in a chronosequence of soils deglaciated within 40 years of sampling. Rates of carbon accumulation increased through time in the first 4 decades of pedogenesis. Little carbon accumulated in the first 10 years, but rapid accumulation occurred over the next 22 years as alders (Alnus crispa) began to colonize. Several chronofunctions of carbon accumulation are derived for the Burroughs data. A second-order polynomial function provides a good model of carbon accumulation in the first four decades of pedogenesis that is stronger and more significant than conventional exponential and power function models. A data set extended to 1000 years based on earlier studies in the region, indicates that carbon accumulation rates in this proglacial environment can be expressed by a sigmoidal curve. Several conventional chronofunctions derived from the extended data are appropriate f...

Depositional environments during a glaciolacustrine to marine transition in the Richardson and Rae River basin, N.W.T.

This paper describes the principal glaciolacustrine deposits of a sequence of overlapping ice-marginal lakes known as glacial Lake Richardson and its transition to a postglacial sea following the retreat of a lobe of the Laurentide ice sheet from the Richardson and Rae River basin. The glaciolacustrine to marine transition is characterized by an upward-fining sequence of facies deposited in proglacial lacustrine environments, succeeded by an upward-coarsening trend corresponding to a regressive marine sequence. A composite stratigraphic section includes (a) basal diamicton, (b) stratified subaqueous sand and gravel, (c) glaciolacustrine silty clay rhythmites, (d) massive marine silty clay, and (e) littoral marine sands. The sudden passage from lacustrine to marine environments is reflected in the abrupt change in depositional mechanisms. Turbidity currents prevailed in the proglacial lake as inferred from thick sequences of varve-like couplets, whereas the salinity of marine waters, impeding the sedimentation of fines by density underflows, led to the deposition of massive structureless marine silty clays by flocculation.

Evidence for a Till Layer Beneath Storglaciären, Sweden, Based on Electrical Resistivity Measurements

AbstractElectrical resistivity measurements were made in a series of closely spaced holes drilled to the base of Storglaciären. Electrodes were lowered to the bottoms of the holes where they made contact with the substrate beneath the glacier. The measurements show that a layer of till, ~0.4–0.7 m thick, is present at the base of the glacier. The low resistivity of the layer indicates that it has a high water content, compared with tills of similar composition in the pro-glacial environment. A marked reduction in resistivity after a heavy rain storm demonstrates that the water content is sensitive to variations in water input at the surface.

Evidence for a Till Layer Beneath Storglaciären, Sweden, Based on Electrical Resistivity Measurements

AbstractElectrical resistivity measurements were made in a series of closely spaced holes drilled to the base of Storglaciären. Electrodes were lowered to the bottoms of the holes where they made contact with the substrate beneath the glacier. The measurements show that a layer of till, ~0.4–0.7 m thick, is present at the base of the glacier. The low resistivity of the layer indicates that it has a high water content, compared with tills of similar composition in the pro-glacial environment. A marked reduction in resistivity after a heavy rain storm demonstrates that the water content is sensitive to variations in water input at the surface.

Ground Data Inputs To Image Processing for Estimating Terrain Characteristics for Glacio-Hydrological Analysis

Remote-sensing research in glacial and pro-glacial environments raises several methodological problems relating to the handling of ground and satellite radiometric data. An evaluation is undertaken of the use of ground radiometry to elucidate properties of relevant surface types in order to interpret satellite imagery. It identifies the influence that geometric correction and re-sampling have on the radiometric purity of the resulting data set. Methodological problems inherent in deriving catchment terrain characteristics are discussed with reference to currently glacierized and pro-glacial zones of south-western Switzerland.

Ground Data Inputs To Image Processing for Estimating Terrain Characteristics for Glacio-Hydrological Analysis

Remote-sensing research in glacial and pro-glacial environments raises several methodological problems relating to the handling of ground and satellite radiometric data. An evaluation is undertaken of the use of ground radiometry to elucidate properties of relevant surface types in order to interpret satellite imagery. It identifies the influence that geometric correction and re-sampling have on the radiometric purity of the resulting data set. Methodological problems inherent in deriving catchment terrain characteristics are discussed with reference to currently glacierized and pro-glacial zones of south-western Switzerland.

Ground Data Inputs To Image Processing for Estimating Terrain Characteristics for Glacio-Hydrological Analysis

Remote-sensing research in glacial and pro-glacial environments raises several methodological problems relating to the handling of ground and satellite radiometric data. An evaluation is undertaken of the use of ground radiometry to elucidate properties of relevant surface types in order to interpret satellite imagery. It identifies the influence that geometric correction and re-sampling have on the radiometric purity of the resulting data set. Methodological problems inherent in deriving catchment terrain characteristics are discussed with reference to currently glacierized and pro-glacial zones of south-western Switzerland.

Some observations on suspended sediment dynamics in Storbregrova, Jotunheimen

AbstractObservations are reported of the dynamics of suspended sediment transport in the meltstream of Storbreen in the Jotunheimen. Fine sediment is transferred from the subglacial to the proglacial environment during low flow (meltdominated) periods, and then removed from the catchment during high flow (rainfall‐controlled) events. Both diurnal and storm period sediment load‐discharge relationships involve clockwise hysteresis, but separate multivariate rating curves define variations of load with streamflow according to (1) the relative importance of meltwater and rainfall runoff, and (2) changes in the sediment source areas contributing to the stream at different times. Particle size variations in the suspended sediment also reflect varying source area influences.

Kansan proglacial environment, East-central Nebraska

Kansan proglacial environment, East-central Nebraska

Petrology of glacial sand: implications for the origin and mechanical durability of lithic fragments

ABSTRACTThe petrology of first cycle (unmodified) and second cycle (reworked) sand at the termini of eleven valley glaciers eroding coarse‐ to fine‐grained bedrock types is determined in order to evaluate the origin and mechanical durability of lithic sands. First cycle sands are coarse‐ to medium‐grained, poorly sorted, fine‐skewed, non‐modal lithic sands with an average composition of Q21F6L73. Grain‐size distributions do not vary with composition or source rock types, although sands derived from finer grained source rocks contain more lithic fragments than sands from coarser grained sources. By contrast, second cycle sands are medium‐grained, poorly sorted, fine‐ to coarse‐skewed arkosic to lithic sands with an average composition of Q19F40L41, and contain fewer lithic fragments than do first cycle sands.We propose that the origin, mechanical durability and survival potential of lithic fragments are related to the types and abundances of their internal planes of weakness, and the particular stress field of the transporting medium. As a result of abrasion, glacial clasts and lithic fragments are subjected to shear stress so that fractures propagate along intracrystal and intercrystal planes of weakness resulting in a continuous grain‐size spectrum of lithic fragments and monomineralic grains irrespective of the type of source rock. Upon subsequent aqueous transport in the proglacial environment lithic fragments are subjected to point‐loading during saltation in addition to shear stress. Point‐loading produces extensional fractures which preferentially propagate along intercrystal planes of weakness, so the lithic fragments break into smaller monomineralic grains and/or lithic fragments.Lithic fragments of very coarse sand‐size are abundant in first cycle sands, thus refuting, at least for glacial sands, the widely held view that grains of this size are deficient in nature. The presence of fewer grains of this size in second cycle sands indicates that very coarse sand‐size lithic fragments can survive recycling, but in greatly reduced proportions due to breakage.