Improving Agricultural Productivity of Podzolic Soils in Schefferville using Local Amendments and Fertilizers

Mineral resources have been important to the Alaskan economy for hundreds of years. The Indians, Eskimos, and Aleuts used gold, copper, and other metals for jewelry, utensils, and weapons and as items of trade. The Russians, who arrived in 1728, showed only minor interest in minerals, focusing instead on furs. Nonetheless, records show that they mined iron ore on the Kenai Peninsula in 1793 and located gold there in 1834. In addition, the Russians were aware of copper-rich occurrences in the Copper River basin.The mining industry grew rapidly in Alaska after the United States purchased the region from Russia in 1867. By 1870, gold was being mined near Windham Bay and near Sitka, in southeastern Alaska. The first major hard-rock gold mining began at the Alaska-Juneau, Perseverance, and Treadwell mines near present-day Juneau following the discovery of placer gold near tidewater in 1880. Significant placer mining operations for gold soon spread northward into districts such as Fairban ks, Nome, Iditarod, and Circle.The exploitation of mineral resources, particularly gold, influenced the settlement and development of much of the state. Major cities such as Nome, Fairbanks, and Juneau, the capital, were originally built around early mining camps. By1996, more than 33 million oz of gold, as well as significant amounts of copper, lead, zinc, silver, and platinum-group elements, had been produced. In addition, there has been minor production of nickel. tin, mercury, and uraniumAlaska is presently experiencing a renaissance in mining on federal, state, private, and native lands. From 1990 to 1996, the minerals industly had an annual value of approximately $600 million, with a record 1 billion in 1996. Nearly 3,500 year-round jobs were directly attributed to the minerals industq. Looking forward into the twenty-fi rst centu1y, the outlook is even better. Major mines such as Heel Dog are in production. Recently completed exploration at the Red Dog sedimenta1y exhalative deposit has significantly expanded the reserve base and major mine expansion is contemplated. The Nixon Fork gold skarn deposit was put into production in 1995, with the first ore poured in November. The Greens Creek mine resumed production in late 1996, following renewed exploration and development of the volcanogenic massive sulfide deposit. The Fort Knox gold mine, near Fairbanks, is under construction and is scheduled to yield ore by late 1996. In southwest Alaska exploration success has yielded a significant gold resource at Donlin Creek. In addition, the Kensington-Jualin project is

Tertiary ore deposits and prospects in Trans-Pecos Texas and adjacent Mexico have Pb isotope ratios that indicate probable sources of metals. Sulfides from these deposits have a wide range of Pb isotope ratios: 206 Pb/ 204 Pb, 17.74 to 20.04; 207 Pb/ 204 Pb, 15.46 to 15.69; 208 Pb/ 204 Pb, 37.52 to 40.37. In part, this variability reflects derivation of Pb from contrasting basement and Tertiary igneous rocks across a major lithospheric boundary between the North American craton on the northwest and terranes accreted during the late Paleozoic Ouachita orogeny to the southeast. Precambrian basement and Tertiary igneous rocks northwest of a northeast-trending zone through Trans-Pecos Texas and Chihuahua, Mexico, are less radiogenic than Phanerozoic and Precambrian basement and Tertiary igneous rocks to the southeast.Although isotopic ratios from ore deposits and prospects in the region generally reflect basement type, steep arrays on 206 Pb/ 204 Pb versus 207 Pb/ 204 Pb diagrams from some deposits in the northwest basement province indicate mixing with additional, more radiogenic, sources of Pb. We infer that these sources are local sedimentary rocks or basinal fluids. Vein- and porphyry-type prospects hosted by igneous rocks show the least influence from these radiogenic sources. They have Pb isotope ratios that fall within the range of Pb isotope ratios of local Tertiary igneous rocks. In contrast, red-bed-hosted Ag-Cu-Pb deposits in the northwest, with no apparent igneous source of fluids, generally have relatively high 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios, which are apparently inherited from their host sediments. Veins hosted by sedimentary rocks and high-temperature carbonate-hosted Ag-Pb-Zn deposits (manto, chimney, and skarn) have intermediate Pb isotope ratios that range between the lower 207 Pb/ 204 Pb igneous-hosted deposits and the higher 207 Pb/ 204 Pb sedimentary-hosted deposits. They appear to contain variable mixtures of Pb from mid-Tertiary igneous sources and sedimentary rocks. In the northwest basement province Ag-Pb-Zn deposits at Shafter, Texas, have low Pb isotope ratios derived from associated igneous rocks and indicative of underlying Precambrian crust with low 206 Pb/ 204 Pb and 207 Pb/ 204 Pb. Similar, but larger, deposits at Santa Eulalia, Chihuahua, contain a mixture of Pb from at least two sources. It appears that a low 207 Pb/ 204 Pb component associated with Tertiary igneous rocks and ultimately derived from Precambrian basement has mixed with a higher 207 Pb/ 204 Pb component derived from the sedimentary wall rock. Published fluid inclusion and S isotope studies also suggest that mixing of magmatic and sedimentary components is common in the genesis of high-temperature carbonate-hosted Ag-Pb-Zn deposits.

Archaean–Proterozoic transition: geochemistry, provenance and tectonic setting of metasedimentary rocks in central Fennoscandian Shield, Finland

The Stumsnäs 1 core, drilled in 2011 in the southern part of the Siljan Ring, represents a structurally complex section and provides new insights into the impact-induced local structure in central Sweden. The Siljan Ring was formed around the central uplift of a Late Devonian meteorite crater, the largest known impact structure in Europe. The Stumsnäs 1 core section reveals that about 90 m of Palaeozoic (Lower to Upper Ordovician) sedimentary rocks are sandwiched between Proterozoic igneous basement rocks. The sedimentary contact to the underlying ∼260 m of Proterozoic basement is a prominent unconformity. The contact to the overlying ∼190-m-thick slab of Proterozoic basement is a few metres wide complex fault zone, comprising alternating thin slices of sedimentary and granitic rocks together with fault breccia and gouge. The tectonic emplacement of basement rocks over the Palaeozoic sedimentary succession is apparently impact-related and caused folding and faulting of the underlying sediments, some of which were overturned and cut out. Minor fault zones occur throughout the Stumsnäs 1 core section and have large damage zones with intense fracture networks along which alteration and mineralisation took place, likely also impact-related. Small-scale faults and fractures are common and are critical for fluid migration and hence for ongoing exploration for natural gas and geothermal energy reservoirs in the Siljan impact structure.

Previous Cu isotope work has documented a clear disparity between δ65Cu values of sheet-style (–0.5 to 0.5‰) and conduit-style (0.5–2.0‰) intrusions associated with the Midcontinent rift system. The application of metal isotopes to the study of magmatic Ni-Cu-platinum group element (PGE) deposits is in an early stage, and very little is known regarding isotope distributions and mechanisms of fractionation at high temperatures. In order to resolve the previously mentioned Cu isotope disparity, to determine metal sources for the intrusions, and to assess sources of high-temperature metal isotope fractionation, we have measured Cu and Ni isotope ratios from a suite of exceptionally well characterized Ni-Cu-PGE massive sulfides that occur in sedimentary country rocks near intrusions within the Midcontinent rift system in Michigan and Minnesota. Previous mineralogic and S, Pb, and Os isotope measurements indicate that the massive sulfides are of magmatic origin and provide a framework for the interpretation of the Cu and Ni isotope data in terms of magmatic processes, including assimilation of Proterozoic country rocks. Copper and Ni isotope ratios were determined for massive sulfides as well as local sedimentary sulfides, and these results were compared with available Cu and Ni isotope results of magmatic and sedimentary sulfides in the Midcontinent Rift and elsewhere. Nickel isotope ratios of the sulfides have been modeled in terms of the effects of variable silicate/sulfide ratios, or R-factors (the mass ratio of silicate magma to sulfide magma), crustal contamination, and olivine fractional crystallization. The near-zero and slightly negative δ60Ni values of country rock-hosted magmatic sulfides (–0.45 to 0.17‰) near Tamarack and Eagle can be explained by minor degrees of crustal contamination of a mantle-derived melt at variable R-factors. Igneous-sourced, Cu-poor sulfides from below the Partridge River intrusion generally have lower δ60Ni values (−0.77 to –0.52‰) that require substantially more contamination from a low δ60Ni source, similar to some of the local sedimentary rocks. Copper isotope ratios of country rock-hosted massive sulfides near Eagle and Tamarack are lower than those reported by previous workers and are mostly about 0‰, similar to those expected for unaltered mantle. Tamarack samples require very little crustal contamination to explain their isotope ratios, whereas Eagle samples require no contamination from local sedimentary rocks to explain their Cu isotope compositions. Copper isotope ratios of samples beneath the Partridge River intrusion are similar to those from previous analyses of igneous-hosted sulfides, supporting their origin from a magmatic sulfide liquid. The low δ65Cu values (–1.14 to 0.25‰) from samples below the Partridge River intrusion cannot be explained by contamination from the Virginia and Thomson Formations, which are characterized by mostly positive δ65Cu values (–0.33 to 3.12‰), unless a lighter reservoir remains to be discovered in the local Proterozoic rocks. We suggest these values may have been produced by a combination of incomplete sulfide melting during partial melt generation and fractionation related to sulfide segregation at variable R-factors.

The Palaeogene Slieve Gullion Igneous Centre in southern Armagh, Northern Ireland, consists of a layered central intrusive complex surrounded by a prominent and slightly older ring-dyke that intrudes both Lower Palaeozoic sedimentary rocks and the Caledonian Newry Granodiorite pluton (452 Ma). The ring-dyke comprises two major rock types: porphyritic felsite and porphyritic granophyre. We analysed both ring-dyke lithologies, both types of country rock, and a local Palaeogene basalt dyke sample for Sr and Nd isotopes. Trace element and whole rock data for this suite suggest that there are two distinct groups of both felsite and granophyre: one Si-rich and one Si-poor, most likely representing two magmas from a zoned chamber and their mushy chamber wall equivalents (McDonnell et al. 2004). Isotope data show the low-Si rocks to be higher in radiogenic Sr than the high-Si rocks, which is inconsistent with a simple AFC-scenario of increasing sediment assimilation with higher degrees of differentiation. However, using MORB-type basalt as a starting composition, the low-Si ring-dyke rocks can be modelled through AFC with Lower Palaeozoic sedimentary rock as the contaminant. The decreasing 87Sr/86Sr trend from low-Si to high-Si dyke rocks, in turn, represents a second stage of contamination. Selective assimilation of the most fusible portions of Newry Granodiorite, which is lower in radiogenic Sr than the local sedimentary rocks, appears to be the most plausible solution. The Sr and Nd data are consistent with (a) at least a two-stage contamination history during upper crustal residence and storage, whereby fractionating magmas of basaltic and intermediate composition are contaminated by local sedimentary rocks, giving rise to rhyolite magmas that experience additional shallow contamination by Newry Granodiorite, and (b) a zoned rhyolite magma chamber where high-Si magma is stored in the upper part of the chamber where crystallization and crustal contamination are most extensive.

This study was undertaken to determine the source of iron in Comus Formation sedimentary rocks that were sulfidized during deposition of gold in the Megapit area of the Twin Creeks Carlin-type deposit. Sedimentary rocks in and near the Megapit contain ferroan dolomite, largely as overgrowths on iron-poor dolomite. Iron to form these overgrowths appears to have been released from mafic volcanic rocks that are interlayered with the sedimentary rocks. These igneous rocks have undergone two stages of hydrothermal alteration. The first stage involved formation of albite and iron-rich chlorite, possibly caused by interaction with seawater. The second stage involved destruction of the iron-rich chlorite by illite or sericite, which released iron to form ferroan dolomite in the sedimentary rocks. Comparisons show that transfer of iron from the igneous rocks to the sedimentary rocks can account for the present distributions of iron in these rocks. Relative to basalts, Comus Formation igneous rocks are enriched in iron and potassium. These results suggest that ferroan dolomite in sedimentary rocks is not solely a product of diagenetic processes and can form when iron is released from adjacent iron-bearing igneous rocks. Recognition of this additional mechanism for formation of ferroan dolomite expands the range of geologic settings that can be favorable for formation of gold deposits formed by sulfidation.

The Pliocene Silver Creek porphyry Mo deposit at Rico, southwest Colorado, is the youngest known porphyry Mo deposit in the Colorado mineral belt. Associated sulfate replacement deposits, epithermal Pb-Zn-Ag vein and replacement deposits, and Recent hot springs also occur. We investigated the S, C, Sr, and Pb sources at the various levels of this well-preserved hydrothermal system by isotopic studies of the mineralization, and of sedimentary and igneous rocks in the area.Hydrothermal sulfide delta 34 S values are tightly grouped at ca. 0 per mil (x = 0.3 + or - 2.0ppm, 1Sigma ; n = 107) and are substantially lower than those of the hydrothermal sulfates (x = 15.2 + or - 1.6ppm, 1Sigma ; n = 14). Pliocene hydrothermal carbonate delta 13 C values (-7.9 to +1.1; x = -4.9 + or - 2.7ppm, 1Sigma ; n = 16) are similar to those for the Pennsylvanian Hermosa Formation carbonate (delta 13 C = -6.7 to +2.6ppm; x = -3.0 + or - 3.2, 1Sigma ; n = 5), which hosts most of the base and precious metal mineralization, whereas Recent hot spring tufas have somewhat higher values (delta 13 C = 1.8-5.5ppm; x = 3.7 + or - 1.3ppm, 1Sigma ; n = 5). Pliocene hydrothermal carbonates have delta 18 O values between -5.1 and 12.3 per mil (x = 5.0 + or - 6.3ppm, 1Sigma ; n = 16). The tufas have higher delta 18 O values (x = 15.4 + or - 2.6ppm, 1Sigma ; n = 5).Hydrothermal carbonates (including tufa) and sulfate have initial 87 Sr/ 86 Sr (sub (i)) values between 0.70700 and 0.71168. Pennsylvanian sedimentary rocks in the Rico district had 87 Sr/ 86 Sr ratios between 0.70877 and 0.71694 at the time of mineralization. Fresh and altered Pliocene monzonite intrusions at Rico have initial 87 Sr/ 86 Sr (sub (4)) values of 0.70581 and 0.70563, respectively, whereas variably altered rholite dikes have initial 87 Sr/ 86 Sr (sub (4)) values of 0.70987, 0.71574, and 0.71716. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 206 Pb/ 204 Pb ratios of molybdenite, pyrite, and galena taken together are 18.27 to 19.65, 15.55 to 15.70, and 37.75 to 38.62. Pliocene lamprophyre and rhyolite dikes at Rico have equivalent Pb isotope ratios of 18.26, 15.48, and 37.81 and 18.79, 15.65, and 38.02, respectively. These Pb isotope data are typical of Tertiary volcanic rocks and associated sulfides in southwest Colorado.Our delta 34 S data indicate a magmatic S source for the porphyry Mo and epithermal base metal sulfide mineralization. Most of the sulfide Pb is also of magmatic origin. In contrast, hydrothermal sulfate replacement deposits peripheral to the porphyry Mo deposit, carbonate gangue from the base metal deposits, and the Recent hot spring tufa derived their respective S, C, and Sr from local sedimentary rocks. Our delta 18 O data indicate that the hydrothermal carbonates were deposited from 18 O-shifted meteoric waters. Our comprehensive isotopic data set presents a similar genetic picture to that of other molybdenite deposits in the mineral belt, in that the porphyry Mo mineralization was dominated by magmatic components, whereas the peripheral base metal mineralization contains both magmatic and upper crustal components. These important genetic similarities are independent of fundamental differences in tectonic setting.

Sourlie, near Irvine (Fig. 1), is certainly one of the few and probably the only site in the whole of Scotland where, to date, irrefutable stratigraphical evidence demonstrates that during the Quaternary period the country was subjected to glaciation in both Late Devensian and pre-Late Devensian times (cf. [Mitchell et al. 1973][1]; [Lowe 1984][2]; [Bowen et al. 1986][3], pp. 320–3; [Bowen and Sykes 1988][4]). The relevant field evidence, preliminary results of laboratory analysis and some conclusions concerning the significance of the site at Sourlie are presented below. Temporary, open-cast coal excavations at Sourlie in 1986 exposed thin (to 0.6 m) lenses of organic-rich sediments (unit D1, Table 1 and Fig. 2) contained within local pockets on the upper surface of a layer of glacio-fluvial deposits (C). The latter sediments overlie an ablation deposit (B), which rests on a basal grey lodgement till (A) that contains clasts of (mainly) local sedimentary rocks. Units D1 and D2 are overlain by two distinctly different deposits. The lower of these, a thinly developed pink-brown diamicton (E), contains a mixture of clasts of local and far-travelled sedimentary, igneous and metamorphic rocks, together with occasional fragments and rare complete valves of marine molluscs. The overlying, thicker, upper grey lodgement till (F) is devoid of shell fragments. In grain-size characteristics, clay mineralogy and geochemistry its matrix closely resembles that of unit A, but, in addition to containing clasts of local sedimentary rocks, unit F contains basic igneous rock fragments that have been transported at least a . . . [1]: #ref-16 [2]: #ref-12 [3]: #ref-1 [4]: #ref-2

Germinated seeds from 11 populations of green alder [Alnus crispa (Ait.) Pursh] sampled in four Canadian provinces were analysed for electrophoretically demonstrable diversity of 10 enzymes encoded by 15 structural loci. Of these, nine were polymorphic, and on average, 52% of the loci per population were polymorphic. Assuming a diploid model of expression, average level of expected heterozygosity was 0.11 with nearly all populations in Hardy‐Weinberg equilibrium for the set of polymorphic loci analysed. No significant inbreeding and associated subpopulation structuring were noted. Rates of gene flow appeared high within and among populations. Although little divergence was observed among populations, genetic and geographical distances between populations were related. Discriminant and cluster analyses revealed a pattern of genetic variation associated with geography. Populations from northern Quebec were poorly differentiated, whereas western populations from Alberta exhibited a larger degree of genetic differentiation. Introgresive hybridization with the sympatric species Alnus sinuata (Regel) Rydberg and partial isolation in the West are suggested as an explanation for this larger differentiation. The occurrence and significance of rare alleles is discussed in relation to the importance of geographical distance in the process of population differentiation in this species.

Nicholson. S. W., Cannon, W.F. and Schulz,'K.J ., 1992. Metallogeny of the Midcontinent rift system of North America. In: G. Gaal and K. Schulz (Editors). Precambrian Metallogeny Related to Plate Tectonics. Precambrian Res., 58: 000-000. The 1.1 Ga Mtidcontinent rift system of North America is one of the world's major continental rifts and hosts a variety of mineral deposits. The rocks and mineral deposits of this 2000 km long rift are exposed only in the Lake Superior region. In the Lake Superior region, the rift cuts across Precambrian basement terranes ranging in age from ~1850 Ma to more than 3500 Ma. Where exposed, the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks. Beneath the center of Lake Superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection proflles. This region hosts two major classes of mineral deposits, magmatic and hydrothermal. All important mineral production in this region has come from hydrothermal deposits. Rift-related hydrothermal deposits include four main types: (1) native copper deposits in basalts and interflow sediments: (2) sediment-hosted copper sulfide and native copper: (3) copper sulfide veins and lode.s hosted by rift-related volcanic and sedimentary rocks: and (4) polymetallic (five-element) veins in the surrounding Archean country rocks. The scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals. Where hydrothermal sulfides occur (i.e., shale-hosted copper sulfides), the source of sulfur was local sedimentary rocks. Mtagmatic deposits have locally supported exploration and minor production, but most are subeconomic presently. These deposits occur in intrusions exposed near the margins of the rift and include Cu-Ni-PGE and Ti-Fe (V) in the Duluth Complex. U-REE-Nb in small carbonatites, and breccia pipes resulting from local hydrothermal activity around small felsic intrusions. Mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization. Most of the sulfide deposits in intrusions, however, contain sulfur derived from country rocks: the interaction between magma and country rocks was important in generation of the magmatic Cu-Ni sulfide deposits. A mantle plume origin has been proposed for the formation of the Midcontinent rift. Mtore than 1 million km3 of mafic magma was erupted in the rift and a comparable volume of mafic intrusions are inferred beneath the rift. providing a ready and structurally confined supply of mafic source rocks that were available for leaching of metals by basinal brines. These brines were heated by a steep geothermal gradient that resulted from the melting and underplating of magma derived from the plume. Hydrothermal deposits were emplaced for at least 30-40 m.y. after rift magmatism and extension ceased. This time lag may reflect either the time required to heat deeply buried rocks and fluids within the rift. or may be due to the timing of post-rift compression that may have provided the driving mechanism for expulsion of hydrothermal fluids from deep ponions of the rift.

Metallogeny of the midcontinent rift system of North America

Nicholson. S. W., Cannon, W.F. and Schulz,'K.J., 1992. Metallogeny of the Midcontinent rift system of North America. In: G. Gaal and K. Schulz (Editors). Precambrian Metallogeny Related to Plate Tectonics. Precambrian Res., 58: 000-000. The 1.1 Ga Mtidcontinent rift system of North America is one of the world's major continental rifts and hosts a variety of mineral deposits. The rocks and mineral deposits of this 2000 km long rift are exposed only in the Lake Superior region. In the Lake Superior region, the rift cuts across Precambrian basement terranes ranging in age from ~1850 Ma to more than 3500 Ma. Where exposed, the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks. Beneath the center of Lake Superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection proflles. This region hosts two major classes of mineral deposits, magmatic and hydrothermal. All important mineral production in this region has come from hydrothermal deposits. Rift-related hydrothermal deposits include four main types: (1) native copper deposits in basalts and interflow sediments: (2) sediment-hosted copper sulfide and native copper: (3) copper sulfide veins and lode.s hosted by rift-related volcanic and sedimentary rocks: and (4) polymetallic (five-element) veins in the surrounding Archean country rocks. The scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals. Where hydrothermal sulfides occur (i.e., shale-hosted copper sulfides), the source of sulfur was local sedimentary rocks. Mtagmatic deposits have locally supported exploration and minor production, but most are subeconomic presently. These deposits occur in intrusions exposed near the margins of the rift and include Cu-Ni-PGE and Ti-Fe (V) in the Duluth Complex. U-REE-Nb in small carbonatites, and breccia pipes resulting from local hydrothermal activity around small felsic intrusions. Mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization. Most of the sulfide deposits in intrusions, however, contain sulfur derived from country rocks: the interaction between magma and country rocks was important in generation of the magmatic Cu-Ni sulfide deposits. A mantle plume origin has been proposed for the formation of the Midcontinent rift. Mtore than 1 million km3 of mafic magma was erupted in the rift and a comparable volume of mafic intrusions are inferred beneath the rift. providing a ready and structurally confined supply of mafic source rocks that were available for leaching of metals by basinal brines.

Spodosols characterized by the presence of spodic and albic horizons, are problem soils due to low productivity, coarse texture and low nutrient status. This soil was generally covered by alang-alang or shrub and bush. The soils were generally distributed in cold climate or wet tropical areas with high rainfall. The objectives of this paper were to discuss the characteristics of Spodosols in Kalimantan and Sumatra and the possibility of their utilization. In Indonesia, this soil is found in Kalimantan, Sulawesi, Sumatra, and Papua Islands. Parent materials of the soils were originated from quartz sand, sediment or acid sedimentary rocks (quartz sandstone) with low nutrients status. Physiographically, the soils were distributed in alluvial plain, colluvial, sand beach, sand dune, tectonic plain and sandstone plateau on elevation of 5 to >1,500 m asl, with flat to nearly undulating relieves. The soil physical properties were characterized by coarse texture and the presence of root limiting layer such as fragipan, duripan, or placic horizon (organo-metal complex) with various depth. The soil chemical properties were characterized by acid soil reaction, very low exchangeable bases, P and K nutrient, and mineral reserve. Cation exchange capacity of the soils depends on their soil organic matter content. Based on the soil characteristics, most Spodosols were not suitable for agricultural land development. Therefore the Spodosols usages should be directed not only for production increases but also for environmental healthiness and soil care. The Spodosols land that have been opened needs to be optimally used in order to increase soil quality through appropriate soil and plant management. The new land cleared for agriculture and production forest needs carefully actions with localizing the Spodosols distribution in order to maintain the natural vegetations as conservation forest or recreation areas.

This paper reports on the paludification of kettle holes formed in a proglacial esker complex at Lake Bienville in northern Quebec. Deep hollows on the central islands of this large subarctic lake (c. 900 kin2), are highly exposed to northeasterly and southwesterly winds over long fetches, and accumulate large amounts of drifting snow (c. 4 m). Modifications in local snow distribution associated with Holocene vegetation and climate changes contributed to an increased water supply in kettle holes. Podzolic soils with light patches in the B horizon are attributed to differential water circulation during thawing in coarse-textured soils with high moisture supply associated with thicker snow. Peat started to form over well-drained podzolic soils after 600 BP, especially c. 200 BP, when suitable conditions for Sphagnum growth established at the front of snowbeds. The recent development of patchy podzolic soils and paludification of kettle holes are interpreted as the result of a combination of bioclimatic events including: (l) the development of a postfire, open-vegetation cover after c. 1500 BP associated with cooler conditions exacerbated by the presence of a large water body; and (2) the shift from a boreal-to a subarctic-like (wind-controlled) snow regime permitting the accumulation of large amounts of snow and late melting.