Till Cover Research Articles

Till Geochemistry as a Vector to Metasomatic Iron and Alkali-Calcic Systems and Associated Deposits in the Great Bear Magmatic Zone, Northwest Territories, Canada

Recent advances in the characterization of metasomatic iron and alkali-calcic (MIAC) systems with associated iron-oxide apatite (IOA) prospects and iron-oxide–copper–gold (IOCG) and metasomatic cobalt deposits of the Great Bear magmatic zone were used to determine if the geochemistry of glacial sediments can unveil pathfinder elements indicative of mineralization and associated alteration. Analysis of variance within bedrock lithogeochemical (n = 707 samples) and till geochemical datasets (n = 92 samples) are compared. Results show that Fe, Co, Ni, Cu, As, Mo, Bi, La, Th, U, and W were identified as potential vectoring elements in different fractions of till due to their anomalous concentrations down-ice of various mineralized outcrops within the study area. For instance, Fe, Co, Cu, and Mo were established as the most useful vectoring elements in the locally derived till (<2 km down-ice) near the Sue Dianne IOCG deposit, and Fe, Co, Ni, Cu, Mo, W, Bi, and U near the Fab IOCG prospect. At the Sue Dianne deposit, the ratios of near-total (4-acid digestion) versus partial (modified aqua regia digestion) concentrations in the silt + clay-sized till fraction (<0.063 mm) for both La and Th reflect the mineralization alteration signature and define a more consistent dispersal train from mineralization compared to element concentrations mapped alone. Additional testing in an area of continuous till cover near an isolated point source is recommended to further develop the elemental ratio method for exploration of MIAC systems.

Net evolution of subglacial sediment transport in the Quebec–Labrador sector of the Laurentide Ice Sheet

The Laurentide Ice Sheet's (LIS) interior had a dynamic polythermal base, but the spatiotemporal variations of subglacial processes related to ice divide migration and other transient changes remain largely unknown, limiting our understanding of regional glacial dynamics. Previous studies focused on the regional glacial landform record, while ice sheet models lacked detailed parameterization within these regions, leading to an overestimation of cold-based subglacial conditions' extent and duration. In this study, glacial sediment dispersal patterns as identified by heavy minerals, clasts, and multivariate statistics of till matrix geochemistry were used to assess ice sheet dynamics within the Quebec–Labrador sector of the LIS. The earliest ice-flow phase produced and transported till across the study area (>175 km). However, major oxide data from till matrix geochemistry show a correlation with underlying bedrock, and this relationship is relatively common in areas of thin till cover and resistant bedrock lithologies. These results suggest a switch from an early phase of widespread erosion and long, sustained sediment transport to one of more limited erosion, perhaps abrasion dominant and shorter transport. Till compositional data and related dispersal patterns add supporting evidence to earlier ice sheet reconstructions based on ice-flow indicators and 10Be data together suggesting a transition from widespread uniform warm-based conditions during the earliest ice flow, followed by the development of an ice divide, its migration, and more sporadic warm-based conditions. Consequently, a thorough understanding of ice-flow history is essential for ice sheet modelling and future mineral exploration programs in inner ice sheet regions of the LIS.

The threatened karst of the Great Western Lakes, Ireland

Limestone is a notoriously leaky rock. In many areas that are underlain by limestone, surface rivers are few and disjointed. They disappear into sinks only to reappear, sometimes many kilometres away, at springs. It is not an environment in which lakes are typically found. Some 40 percent of Ireland is underlain by limestone, yet the Irish lowlands are scattered with countless lakes, large and small. In many the limestone beneath is effectively sealed by a cover of glacial till; others have formed where hollows descend below a shallow water table. Around the shores of many, exposed limestone bedrock and boulders support a range of peculiar etched features that are virtually confined to this lakeshore environment.

An Early Pleistocene interglacial deposit at Pingorsuit, North‐West Greenland

At the Pingorsuit Glacier in North‐West Greenland, an organic‐rich deposit that had recently emerged from the retreating ice cap was discovered at an elevation of 480 m above sea level. This paper reports on macrofossil analyses of a coarse detritus gyttja and peaty soil, which occurred beneath a thin cover of till and glacifluvial deposits. The sediments contained remains of vascular plants, mosses, beetles, caddisflies, midges, bryozoans, sponges and other invertebrates. The flora includes black spruce, tree birch, boreal shrubs and wetland and aquatic taxa, which shows that mires, lakes and ponds were present in the area. We describe a new extinct waterwort species Elatine odgaardii. The fossils were deposited in a boreal environment with a mean July air temperature that was at least 9 °C higher than at present. The fossil assemblages show strong similarities with others from Greenland that have been assigned an Early Pleistocene age, and we suggest a similar age for the sediments found at the margin of the Pingorsuit Glacier.At the Pingorsuit Glacier in North‐West Greenland, an organic‐rich deposit was discovered at an elevation of 480 m above sea level. The sediments contained remains of vascular plants, mosses, beetles, caddisflies, midges, bryozoans, sponges and other invertebrates. The fossils were deposited in a boreal environment with a mean July air temperature that was at least 9 °C higher than at present.

Amending mine tailing cover with compost and biochar: effects on vegetation establishment and metal bioaccumulation in the Finnish subarctic

In the northern boreal zone, revegetation and landscaping of closed mine tailings are challenging due to the high concentrations of potentially toxic elements; the use of nutrient-poor, glacigenic cover material (till); cool temperatures; and short growing period. Recycled waste materials such as biochar (BC) and composted sewage sludge (CSS) have been suggested to improve soil forming process and revegetation success as well as decrease metal bioavailability in closed mine tailing areas. We conducted two field experiments in old iron mine tailings at Rautuvaara, northern Finland, where the native mine soil or transported cover till soil had not supported plant growth since the mining ended in 1989. The impacts of CSS and spruce (Picea abies)–derived BC application to till soil on the survival and growth of selected plant species (Pinus sylvestris, Salix myrsinifolia, and grass mixture containing Festuca rubra, Lolium perenne, and Trifolium repens) were investigated during two growing seasons. In addition, the potential of BC to reduce bioaccumulation of metals in plants was studied. We found that (1) organic amendment like CSS markedly enhanced the plant growth and is therefore needed for vegetation establishment in tailing sites that contained only transported till cover, and (2) BC application to till soil-CSS mixture further facilitated the success of grass mixtures resulting in 71–250% higher plant biomass. On the other hand, (3) no effects on P. sylvestris or S. myrsinifolia were recorded during the first growing seasons, and (4) accumulation of metals in cover plants was negligible and BC application to till further decreased the accumulation of Al, Cr, and Fe in the plant tissues.Graphical abstract

Metal anomalies in till in the Sarvlaxviken area, Lovisa, southern Finland

Geochemical investigations of till is a widely used method in metal exploration as the till commonly inherits the geochemical signature (including the metal contents) of the parent bedrock. In this investigation, over 2000 till samples were collected in the Sarvlaxviken area, southern Finland, where several polymetallic (Cu, Zn, Pb, As, Sn, W and In) veins recently have been discovered in Proterozoic crust along the border between Late Svecofennian granites and the Wiborg Batholith. The bedrock is commonly covered by compact and poorly sorted basal till, formed during the Late Weichselian glaciation event. Several glacial-transported boulders, with high contents of Cu, Zn, As, Sn, Mo and Bi and derived from the local bedrock, have also been discovered on top of the till and provide evidence for concealed mineralisation in the local bedrock under the till cover. The frequent distribution of till in the Sarvlaxviken area provides excellent conditions for the search of such hidden mineralisation by means of systematic till sampling, even if large farm field areas, composed of clay-rich sediments, and seawater-covered areas (Sarvlaxviken bay), had to be avoided in the sampling program. The till samples were collected during university courses and training programs led by the authors and were analysed in a cost-efficient and certified laboratory. Obtained geochemical data were statistically processed by using K-means clustering algorithms which can be used to treat large sets of geochemical data. The results provided anomalies that mainly occur in till with a thickness of <1 m and are considered to be derived from a local bedrock source. The discovered anomalies provide strong evidence for numerous undiscovered veins beneath the till cover.

A GIS‐based multi‐proxy analysis of the evolution of subglacial dynamics of the Quebec–Labrador ice dome, northeastern Quebec, Canada

AbstractThe glacial records of the inner‐core regions of the Laurentide Ice Sheet (LIS) document complex yet coherent patterns reflecting ice‐sheet change (e.g. ice‐divide migration), providing unique insights into past glacial conditions. This study develops a conceptual model of subglacial dynamics evolution within a major ice‐dispersal centre of the LIS in northeastern Quebec, Canada using a GIS‐based analysis of the surficial geologic record. Multiple proxies of subglacial conditions (subglacial streamlined landforms, lake density and lake area over thin drift/bedrock) were analysed through grid‐overlay techniques and then classified based on different proxy variables ranging from highly mobile warm‐based to immobile cold‐based conditions. An additional proxy (till blanket) was used to identify areas of thick till deposition, but with few proxies (few lake or landform metrics). Based on local ice‐flow reconstructions, the most ‘relict’ glacial terrain zone (GTZ1) has warm‐based conditions over 66% of its area and is remarkably well preserved, suggesting laterally extensive warm‐based conditions during the oldest identified ice‐flow phase. This relict glacial terrain is partially overprinted by two subsequent ice‐flow phases in spatially restricted zones in the northeast (73% warm‐based), east‐central (41% warm‐based), and northwest (33% warm‐based) of the study area. A zone of more sluggish conditions (only 3% warm‐based) was identified in the highlands at the centre of the study area, characterized by thin till cover, few landforms, yet with large patches of relatively abundant small lakes, indicative of areal scouring. No clear evidence of sustained cold‐based conditions (i.e. high chemical index of alteration values or high 10Be abundances) was found in the study area. These results suggest that warm‐based conditions (active erosion and/or deposition) were uniformly widespread during the earliest ice‐flow phase, later becoming more spatially restricted with broader sluggish ice conditions. These spatially restricted regions of warm‐based subglacial regimes were likely controlled by surrounding and down‐flow ice streaming. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd

Effect of shifting ice flow and basal topography in shaping three-dimensional dispersal patterns, Lac de Gras region, Northwest Territories, Canada

Tracing indicator minerals and geochemical pathfinders in glacial sediments back to their up-ice source is a common mineral exploration approach in prospective, formerly glaciated regions. In this study, we utilize surface and subsurface data from the Lac de Gras area of the Northwest Territories to develop a three-dimensional understanding of till compositional anomalies emanating from two known kimberlite pipes, DO-18 and DO-27. Specifically, this study examines the three-dimensional shape of dispersal trains as defined by geochemical pathfinder elements and kimberlite indicator minerals shed from a pair of kimberlite pipes within a till cover of variable thickness. From our ninety-four reverse circulation boreholes (n = 251 till samples), and other publicly-available geologic datasets, we have reconstructed bedrock topography, till thickness, and the subsurface geometry of two dispersal trains. Utilizing our three-dimensional dataset, we have documented the role of basal topography in creating dispersal patterns with contrasting geometries from two adjacent kimberlites, as well as in the preferential preservation of older till units. The combination of field observations of ice-flow indicators and till compositional data demonstrates that features produced by multiple ice flows are preserved in both the erosional and depositional records in this region. Three-dimensional dispersion patterns of kimberlite indicators reflect the effect of shifting ice-flow direction with respect to slope aspect of bedrock topography in governing compositional variability within glacial drift. Our findings suggest that surficial data do not capture the full extent of dispersion patterns even in areas of relatively thin and discontinuous till cover.

Glacial geomorphology of Teesdale, northern Pennines, England: Implications for upland styles of ice stream operation and deglaciation in the British-Irish Ice Sheet

The glacial geomorphology of Teesdale and the North Pennines uplands is analysed in order to decipher: a) the operation of easterly flowing palaeo-ice streams in the British-Irish Ice Sheet; and b) the style of regional deglaciation. Six landform categories are: i) bedrock controlled features, including glacitectonic bedrock megablocks or ‘rubble moraine’; ii) discrete mounds and hills, often of unknown composition, interpreted as weakly streamlined moraines and potential ‘rubble moraine’; iii) non-streamlined drift mounds and ridges, representing lateral, frontal and inter-ice stream/interlobate moraines; iv) streamlined landforms, including drumlins of various elongation ratios and bedrock controlled lineations; v) glacifluvial outwash and depositional ridges; and vi) relict channels and valleys, related to glacial meltwater incision or meltwater re-occupation of preglacial fluvial features. Multiple tills in valley-floor drumlin exposures indicate that the subglacial bedform record is a blend of flow directions typical of areas of discontinuous till cover and extensive bedrock erosional landforms. Arcuate assemblages of partially streamlined drift mounds are likely to be glacially overridden latero-frontal moraines related to phases of “average glacial conditions” (palimpsests). Deglacial oscillations of a glacier lobe in mid-Teesdale are marked by five inset assemblages of moraines and associated drift and meltwater channels, named the Glacial Lake Eggleshope, Mill Hill, Gueswick, Hayberries and Lonton stages. The Lonton stage moraines are thought to be coeval with bedrock-cored moraines in the central Stainmore Gap and likely record the temporary development of cold-based or polythermal ice conditions around the margins of a plateau-based icefield during the Scottish Readvance.

Geometry of indicator mineral and till geochemistry dispersal fans from the Pine Point Mississippi Valley-type Pb-Zn district, Northwest Territories, Canada

An indicator mineral and till geochemical dispersal case study was conducted at the Pine Point Mississippi Valley-type (MVT) Pb-Zn district in northern Canada to document glacial dispersal down ice from a known orebody. Indicator minerals in the non-ferromagnetic heavy mineral (specific gravity >3.2) concentrate of till down ice of the mined-out O-28 Pb-Zn deposit in the east end of the district include sphalerite, galena, and pyrite, as well as secondary Pb-Zn minerals anglesite (as coatings on galena), smithsonite, and cerussite. These minerals are sufficiently physically and chemically robust to survive glacial transport as well as post-glacial weathering in the carbonate-rich till of the region. Pathfinder elements in the <0.063 mm fraction of till, determined using a modified aqua regia digestion, include Zn, Pb, Cd, Tl, and S.Evidence for multiple ice flow phases, each with an erosional and depositional record across the district, includes cross-striated bedrock surfaces, streamlined landforms, and till clast fabrics. At the O-28 pit, two main phases of ice flow eroded and dispersed Pb- and Zn-rich debris first to the southwest and then to northwest, producing a fan-shaped palimpsest dispersal train defined best by indicator minerals, but also by till geochemistry. The last ice-flow phase during deglaciation had a minimal effect on the dispersal train geometry. This case study presents another example of complex glacial transport and dispersal by multiple ice flows that have been defined by both glacial ice flow indicators and glacial transport data. Complex ice flow and transport are to be expected over large parts of the glaciated terrain of Canada.The key implications of this study to mineral exploration are that: 1) till sampling is a viable exploration method in the district; 2) in the eastern part of the district where the till is generally thin (<5 m), surface till sampling will be cost effective; further west where till cover exceeds 30 m overburden drilling methods will be needed to collect till samples at depth; 3) indicator minerals and till geochemistry (transport data) combined with the reconstructed phases of ice flow define a palimpsest pattern of glacial transport in the region.

Waste Rock Biogeochemistry in a Permafrost Environment: Examination of a Cover Design for a Low-Sulfide, Granitic Waste Rock

ABSTRACTAt the Diavik Waste Rock Project's mine-research site, the microbial colonization and oxidation of waste rock sulfide minerals are attenuated by the extreme freeze-thaw cycle of a permafrost environment. The closure design for the waste rock stockpile consists of a low-sulfide waste rock and low-permeability till, covering a relatively higher sulfide waste rock. This design was examined at the mine site through construction of experimental waste rock piles and active zone lysimeters with and without the till cover. Leachate from these experiments indicates variable pH and SO4 concentrations that correlate with sulfide content and the thermal moderating influence of the till cover. The till initially provided a moderated environment for the production of acid, growth of acidophilic Fe- and S-oxidizing bacteria, and enhanced weathering until wet up and freezing of the till and underlying waste rock as a permafrost. Greater sulfide oxidation was observed above the till cover because of greater exposure to the annual freeze-thaw cycle. An examination of the bacterial communities at the genus level indicates the prevalence of Pseudomonas, Rhodanobacter, Sideroxydans, and Thiobacillus in the waste rock. Pseudomonas spp. were dominant in the drier and more extreme temperature environment above the till cover, while Thiobacillus spp. were dominant in the more sulfide-rich, wetter/frozen environment below the till. A decreasing trend in Thiobacillus spp. from the exterior to the interior and an opposing trend in Acidithiobacillus spp. suggest greater acid generation deeper in the waste rock further from the extreme temperature variation of the tundra climate. The presence of the till cover moderated temperature variations, enhanced the initial rate of sulfide oxidation, and allowed for greater microbial diversity, but the freezing of the till cover and underlying waste rock drastically reduced sulfide oxidation and the generation of acid rock drainage. These results highlight the importance of temperature on microbially catalyzed acid production and our ability to use the extreme temperatures of the tundra climate to minimize potential environmental effects from mining through formation of waste rock permafrost.

Ecological, topographic and successional patterns across wetlands in a rugged land uplift coast in Nyby, northern Finland

We studied 45 mid-boreal wetlands in a rugged land uplift coast with a thin cover of till. Wetlands ranged from 1 to 53 m a.s.l. and were of highly various sizes. Our aims were to examine, if vegetation types are valid in comparing wetlands, what kind of ecological major pattern the vegetation type composition of wetlands shows and how vegetation types distribute across altitudes. On those ground we discuss the wetland succession of the study area. We used the Finnish mire site types as vegetation types. Mire site types could be used for an ecological classification and ordination of the wetlands. As was expected, the major gradient consisted of the transition from mire margin (swamp) to expanse. The distribution of the Major Vegetational Wetland Groups (MVWG) responded to a general water-flow pattern in the landscape. Partly different peatland succession sequences occur in areas with small mire basins and in areas with larger mire basins with evolving mire complexes. Sequences of small wetlands and those of mire complexes follow the same trajectory only as far as the major gradient is considered while they differ with regard to the vegetation type composition of locally rare vegetation types and with regard to peatland morphology. Trajectories of mire complexes at catchment divides differ from those at catchment centers where the waters in the landscape tend to gather. Peatland forms of aapa mires experience a change reaching altitudes of 30–50 m a.s.l. Small bog complexes at catchment divides reach a stage of an unpatterned Sphagnum fuscum bog in the study area. Mature mixed complexes with aapa-mire parts and patterned sloping-bog parts only occur at altitudes higher than 60 m a.s.l. Peculiarities in the succession of the wetlands of Nyby, which include the presence of separate incomplete successional sequences in the same area, are mainly caused by the peculiar topography with various sub-areas and with an abundance of rock outcrops.

Drumlin sedimentology in a hard‐bed, lowland setting, Connemara, western Ireland: implications for subglacial bedform generation in areas of sparse till cover

ABSTRACTCores of coastal drumlins in Connemara contain stratified diamictons that interdigitate with gravelly clinoforms and finer grained rhythmites. The diamictons are interpreted as subaqueous mud apron deposits delivered by subglacial till advection to continuously failing subaqueous ice‐contact fans, whose strata were being syn‐depositionally over‐steepened by glacitectonic deformation. The localized nature of the stratified sediments reflects the emergence of subglacial deforming tills and meltwater deposits in a glacilacustrine environment to produce interdigitated mass flow diamictons and grounding line fans/wedges. These depo‐centres became glacitectonized and subglacially streamlined during glacier overriding and hence regional drumlin sedimentology reflects the varying degrees of inheritance of pre‐existing glacigenic deposits and suggests that drumlin production relates more to the position of localized sediment accumulations at the glacier bed than full‐depth till deformation processes (e.g. instability mechanisms) within the same drumlin field. Till cored drumlins give way down ice to stratified cored drumlins with till caps and then to stratified drumlins. This zonation is compatible with the increased lateral variability in drumlin composition that would arise from the occurrence of linear assemblages of glacifluvial (esker) and subaqueous (grounding line) sediments in an otherwise marginal‐thickening till sheet.

Receiver operating characteristics (ROC) as validation tool for prospectivity models — A magmatic Ni–Cu case study from the Central Lapland Greenstone Belt, Northern Finland

A prospectivity model for magmatic Ni–Cu deposits was created by integrating spatially referenced geophysical and geochemical datasets based on a simple and practical exploration model. The study area is the Central Lapland Greenstone Belt, Northern Fennoscandian Shield, Finland. Magmatic nickel deposits are related to rock types that are typically characterized by local magnetic and gravity anomalies. These deposit types can also be a source of nickel, copper and cobalt anomalies in the overlying glacial till cover. This straightforward exploration criterion was translated into a fuzzy logic prospectivity model. The model validation is an essential step in justifying the validity of the prospectivity model. This was accomplished by using receiver operating characteristics (ROC) technique. We used the known Ni–Cu occurrences and deposits as true positive cases and other deposit type locations or random points as true negative cases in the validation process. It appears that the ROC technique provides a robust model validation and optimization technique, providing that suitable validation data exists.

One million cubic kilometers of fossil ice in Valles Marineris: Relicts of a 3.5 Gy old glacial landsystem along the Martian equator

Self-consistent landform assemblages suggest that Valles Marineris, the giant valley system that stretches along the Martian equator, was entirely glaciated during Late Noachian to Early Hesperian times and still contains huge volumes of fossil ice. Some of these glacial landform assemblages are illustrated here, with representative examples selected in three regions: Ius Chasma, Central Candor Chasma and the junction between Coprates Chasma and Capri Chasma. A morphological boundary separating an upper spur-and-gully morphology from a smooth basal escarpment has been spectacularly preserved along valley walls throughout Valles Marineris. The boundary winds around topographic obstacles and displays long-wavelength variations in elevation. It is associated with lateral benches, hanging valleys and truncated spurs. Comparisons with terrestrial analogs indicate that it is most reasonably interpreted as a glacial trimline. Chasma floors are covered by various kinds of terrains, including hummocky terrains, platy terrains, lateral banks, layered benches and a draping mantle. Landforms in these terrains and their spatial relationship with the interpreted trimline suggest that they correspond to various disintegration stages of an ancient glacial fill, currently protected by a superficial cover of ablation till. Altogether, these landforms and terrains compose a full glacial landsystem with wet-based glaciers that were able to flow and slide over their beds. It was most probably fed by ice accumulating at low elevations directly from the atmosphere onto valley floors and walls, with only minor contributions from tributary glaciers flowing down from higher elevations. Similar fossil glacial landsystems dating back from the early Martian history are to be expected in many other low-latitude troughs such as chasmata, chaos, valleys, impact craters and other basins.

Slope Failure Hazard in the Atlantic Provinces: A Review

Slope failures present a common hazard throughout the world and have considerable impact on transportation, forestry, coastal and urban development, and other human activities. Although little recognized in much of Atlantic Canada, mass movements have resulted in as many as 71 fatalities in Newfoundland. Due to the high relief of Newfoundland, rockfalls have caused several fatalities and damage to property is frequent. In the Ferryland disaster of ca. 1823, 42 fishermen were reportedly killed when a cave roof collapsed onto them. Debris torrents and flows are widespread particularly in areas of higher relief in Newfoundland and Cape Breton Island, and tend to be most hazardous for highway engineering and community development. Typically, a thin cover of till or colluvium overlies a steeply sloping and polished bedrock substrate. Failure is generally triggered by rainfall events. Rotational slumps of glaciomarine clays are particularly evident along the major river valleys of Labrador and are an important consideration for hydroelectric development such as along the lower Churchill River. Numerous sackungs have been identified, notably in the ultramafic rocks of western Newfoundland. In other areas of Atlantic Canada, earthflows frequently affect transportation routes and commonly involve movement of saturated sediment during spring thaw. Along the Gulf of St. Lawrence and Northumberland Strait and the Bay of Fundy coastlines, the combination of friable Carboniferous and Permian sediments, glaciotectonic activity, frost wedging, and coastal erosion has resulted in numerous small failures, along with incremental retreat of coastal cliffs. Ongoing climate change will have an impact on slope failure activity. The pattern of increasing summer frequency and intensity of thunderstorms and hurricane events, increased winter precipitation in some locations, and more erratic freeze-thaw events during late winter and spring, will result in an increase in debris torrents triggered by precipitation, and rockfalls triggered by freeze-thaw. Human utilization of coastal areas for recreation and residential construction is also increasing both the frequency and hazard of slope failures across Atlantic Canada.

Lead isotope ratios in till and vegetation over a VMS occurrence under significant allochthonous cover

Two size fractions of till, &lt;250 μm and &lt;2 μm, humus, moss and black spruce bark, as well as sulphides, host rocks and Palaeozoic cover dolostone from drill cores were sampled at the Talbot Lake volcanogenic massive sulphide (VMS) prospect in the Flin Flon-Snow Lake terrane, Manitoba, Canada. Lead isotope-ratios in organic surface media indicate significant input of anthropogenic Pb from the Flin Flon smelter at 160 km distance to the northwest, with 206 Pb/ 204 Pb between 16.5 and 18.2, whereas background till and upper dolostone range between 21.6 and 23.1. At deeper levels, the influx of Pb from Proterozoic mineralization from greater than 100 m depth is recognized. Strontium isotope ratios in these media indicate enhanced vertical fluid flow in the till cover at a fault zone, coincident with the Pb isotope anomaly, as well as relative contributions of Sr from carbonates, silicates and vegetation to the till profile. In humus, sphagnum moss and black spruce bark, the Pb isotope ratios are progressively more similar to that of the feed of the Flin Flon smelter. Measurements of Pb and Sr isotope ratios reveal that Pb from Proterozoic mineralization situated beneath 100 m of Palaeozoic dolostone can be distinguished from Pb contributed by anthropogenic and other geogenic sources.

Simulating the formation of overdeepenings with coupled ice, water, and sediment models

Eyles identified Kvı́árjökull, an outlet of the icecap Öræfajökull, southeast Iceland, as an exemplar of the glaciated valley landsystem, emphasising rockfall debris supply, passive transport and reworking of a thick cover of supraglacial morainic till. In this paper, we take a fresh look at the sediments and landforms of Kvı́árjökull, focusing on clast form analysis to reconstruct primary transport pathways. New data demonstrate the importance of active transport of debris derived from the glacier bed. Substantial portions of the supraglacial debris cover can be traced back to englacial channel fill deposits or anomalously thick exposures of basal ice. These two types of sediments also make up much of Kvı́árjökull's large Neoglacial moraine rampart. We attribute the abundance of these non-rockfall sediments to the presence of a terminal overdeepening, and the switch from predominantly subglacial to predominantly englacial drainage that this induces. This hydrological switch enhances retention of debris within ice transport, preventing it from being washed away and making it available to feed ice-marginal moraine formation. The complexity of sediment transport processes observed at Kvı́árjökull and the contrast between it and alpine glaciers undermines any single concept of the glaciated valley landsystem; accordingly, we propose Kvı́árjökull as the type example of a distinct subclass, defined by its moderate relief, high-debris turnover, and drainage behaviour characteristic of an overdeepened basin.

Can using a strip-tilled cover cropping system followed by surface mulch practice enhance organisms higher up in the soil food web hierarchy?

Field trials were conducted in 2008 and 2009 to evaluate the potential of using sunn hemp (SH), Crotalaria juncea, and marigold (MG), Tagetes patula, in a strip till cover cropping system (STCC) followed by clipping SH and MG to provide surface mulch (SM). The overall objective was to examine if the STCC + SM could improve the structure of the soil food web compared to bare ground (BG) system where weeds were maintained at minimum level prior to planting. Cucumber ( Cucumis sativus) and winter gourd ( Benincasa hispida) were planted as cash crops in 2008 and 2009, respectively. Both the SH and MG in STCC + SM system suppressed herbivorous nematodes through the end of 2008 and up to mid-term crop cycle in 2009. The abundance of bacterivorous and fungivorous nematodes were consistently greater in SH plots during both trials. The structure index was significantly greater in SH treatment plots in 2009, indicating a more structured soil food web than BG treatment. SH and MG plots resulted in higher ( P < 0.05) abundances of collembolans and predatory mites, respectively. Although crop yields were similar among treatments in 2008, winter gourd yield was significantly higher in SH during 2009. Possible mechanisms of why using the SH STCC + SM system resulted in improved soil food web structure in a relatively short time frame is discussed.

Groundwater hydrology of boreal peatlands above a bedrock tunnel – Drainage impacts and surface water groundwater interactions

Summary Little attention has been given to the pattern of hydrological connectivity between peatlands and water bearing fracture zones in crystalline bedrock. The construction of the railway tunnel Romeriksporten provided an opportunity for studying impacts of bedrock tunnelling on peatland hydrology and the hydraulic connectivity between peat deposits and deeper layers in an area with fractured Precambrian gneisses, exposed bedrock, and surficial covers of thin till deposits and peatsoils. Above the tunnel the water level in peat wells fluctuated with maximum depths up to 3 m, and water that otherwise would have generated surface runoff infiltrated in the peat. Drawdowns of the groundwater table in peatlands were observed as far as 340 m away from the tunnel trace. The deep drainage base provided prolonged water table drawdowns in peatlands in dry periods, and differential settlements in drained peatsoils resulted in secondary changes in patterns of surface water storage and flow. The groundwater drawdowns were influenced by the balance between tunnel leakage and water supplies from catchments and the wetland position within the groundwater flow system. Deep and simultaneous lowering and fluctuations of hydraulic heads in wells in the peat, the subpeat sediments and the bedrock above the tunnel demonstrated hydraulic connectivity between the peat layers and the bedrock, and revealed vertical flow even through highly humified peat layers in the catotelm. This shows that in peatlands with a subsurface of a relatively thin till cover above fractured crystalline bedrock, favourable conditions for groundwater flow from peatsoils to rock are not always restricted to a few specific sites, and indicates that attention should be given to the influence of peat water–bedrock water connectivity on impacts of groundwater exploitation, droughts and climate changes in such areas.