Michel Parent

Palimpsest glacial dispersal trains and their significance for drift prospecting

Abstract Palimpsest glacial dispersal trains are residual trains that are produced when the lithic components of an earlier dispersal trains are incompletely re-entrained by a subsequent glacial movement in a different direction. As evidence for multiple ice-flow directions comes from an ever growing number of regions, palimpsest trains increasingly appear as common features of glacial dispersal patterns produced by Quaternary ice sheets. The major characteristics of these trains, particularly their trend and outline, are predominantly related to an earlier glacial movement and only partly related to the glacial movement that produced the till sheet in which they occur. Palimpsest dispersal trains owe their characteristics to the cumulative effects of two or more succeeding ice-flow directions. The concept of palimpsest trains leads not only to a better understanding of the factors which control glacial dispersal patterns but also to an integrated classification of dispersal trains. The three main types of glacial dispersal trains, ribbon-shaped, fan-shaped and amoeboid, owe their characteristics features to the direction, number and succession of former glacial movements. The concept of palimpsest dispersal trains is supported by an empirical glacial dispersal model which do not only constrains the conditions under which these trains may form but also identifies two key factors of subglacial clastic dispersal: (1) the travel distance of basal ice and (2) the rate of subglacial erosion. The basis of this glacial dispersal model is a corollary of Krumbeins exponential decay model: the concentration of lithic components of a rock type in subglacial debris increases exponentially until its distal contact is crossed, at which point the exponential increase of lithic components of rock types lying downglacier will cause the concentration of lithic components of the first rock type to decrease exponentially. The proposed model carries out multiple iterations during each of which compositional data obtained by the previous iteration are redistributed through an exponential decay function. Our work shows that not only is it important to know the sequences of ice-flow directions which occurred in glaciated terrains but also to recognize that older glacial movements are most likely to have residual effects on dispersal patterns produced during subsequent glacial movements. The recognition of palimpsest dispersal trains provides a new tool to better assess these residual effects on regional geochemical patterns in glacial sediments and thus to adjust drift prospecting strategies.

Dendrogeochemical distinction between geogenic and anthropogenic emissions of metals and gases near a copper smelter

For countries where metal resources represent an important economic sector, one of the main challenges of environmental research is to distinguish between natural and anthropogenic accumulations of potentially toxic metals in mining districts. The present work aims to evaluate a new environmental monitoring tool combining dendrochronology with natural (Ca, Ca/Mn, δ13C) and anthropogenic (Cd, Pb, 206Pb/207Pb, 208Pb/206Pb) geochemical tracers in tree rings in such a region. We compare spruce trees sampled at a control site near Hudson Bay, with those sampled near the Horne smelter active since 1928 in Rouyn-Noranda. The first effect of smelter emissions is detected by the tree-ring carbon isotope records. The δ13C values obtained on trees near the smelter show major changes immediately after 1928. This is due to the presence of atmospheric SO2 which generates a rapid response of the foliar system. The Ca/Mn ratios in tree-ring pairs of 1936–1937 and younger suggest a SO2-related soil acidification. The concentrations in Cd and Pb show a major increase starting in 1944 which coincides with a decrease of the 206Pb/207Pb ratios. The smelter activities likely generated this increase and the apparent delay of 14 years may have been generated mainly by the residence time of metals in airborne particulates, the buffering effect of the soils and, to a lesser extent, perhaps by mobility of heavy metals in tree stems. The 206Pb/207Pb and 208Pb/206Pb ratios indicate that the growth rings contain at least three types of Pb: natural, derived from the mineral soil horizons; industrial, from coal burning urban pollution; and mining, typical of the volcanogenic massive sulphides treated at the Horne smelter. This new combination of natural and anthropogenic tracers allows recognition of the succession of atmospheric and pedogeochemical changes related to industrial activities in the Rouyn-Noranda mining area.

Lead concentrations and isotope ratios in the exchangeable fraction: tracing soil contamination near a copper smelter

A total of 75 soil samples were collected from podzolic soils at eight sites in northwestern Quebec in order to compare results in contaminated locations near the Horne Copper smelter in Rouyn-Noranda with those near Hudson Bay, 800 km further north, and a priori devoid of pollution. Lead concentrations and Pb isotopic compositions were determined on soil samples leached by 0.25 M HCl. Lead is enriched in the surface organic horizons at all sites in Rouyn-Noranda. Its concentration decreases abruptly from the surface organic horizons to the underlying mineral horizons. The 206Pb/207Pb ratios are low in surface organic horizons, and they increase sharply in the mineral horizons. Along a NE–SW transect, the highest average Pb concentration (869 ppm) in organic horizons is found at the test site, 9 km from the smelter. The lowest average of 39 ppm Pb in surface organic layers is accompanied by the highest average 206Pb/207Pb ratio (1.15) at site 5, 116 km NE of the Horne smelter. At the test site, the highest Pb concentration of 1414 ppm is also accompanied by the lowest 206Pb/207Pb ratio (0.98), which is close to the isotopic composition of Noranda galena (206Pb/207Pb=0.92). Both Pb concentration and isotopic composition indicate that the Horne smelter is the main source of Pb contamination of soils in the Rouyn-Noranda region. The two soil profiles from near Hudson Bay display much lower Pb concentration and different trends of isotope ratios with depth.

Late Winconsinan glacial dynamics, deglaciation, and marine invasion in southern Quebec

Deglaciation patterns of the Laurentide ice sheet in southern Québec were related to climatic and nonclimatic factors. Thinning of the ice sheet and thermolatitudinal ice retreat are directly linked to the global warming at the end of late Wisconsinan time, between 17 ka and 11 ka. However, correlations between regional deglacial events and global climatic oscillations during that period have yet to be established, except for the St. Narcisse Moraine event, which has been assigned to the Dryas III, and perhaps for the reactivation of Laurentide ice in the middle Chaudiere Valley area during an older cold event. Nonclimatic factors also played a major role on the deglaciation of the region. After the last glacial maximum, the Laurentide ice sheet began to decrease, and the St. Lawrence corridor channelized a major ice stream, the St. Lawrence ice stream, which became a major feature of the southeast sector of the ice sheet. The St. Lawrence ice stream is a flow convergence zone caused by a combination of ice dynamics and topographic factors and rapid ablation at its terminus. The head of the flow convergence migrated deeply into the Laurentide ice sheet and caused thinning of adjacent ice masses. As a consequence of this accelerated ablation, an Appalachian sector became differentiated from the main ice sheet. Regionally, the terminus of the ice stream was a calving bay that retreated along the Laurentian channel to the mouth of the Saguenay fjord. The ice stream and the deglaciated estuary generated the well-known flow reversal along much of the northern margin of the Appalachian sector. In addition to these generalized deglaciation processes, local and regional topographic features influenced the ice dynamics and the final deglaciation patterns. Occhietti, S., Parent, M., Shilts, W.W., Dionne, J.-C., Govare, É., and Harmand, D., 2001, Late Wisconsinan glacial dynamics, deglaciation, and marine invasion in southern Québec, in Weddle, T.K., and Retelle, M.J., eds., Deglacial History and Relative Sea-Level Changes, Northern New England and Adjacent Canada: Boulder, Colorado, Geological Society of America Special Paper 351, p. 243–270. E-mails: Occhietti, ochietti.serge@uqam.ca; Parent, parent@gsc.nrcan.gc.ca; Shilts, shilts@geoserv.isgs.uiuc.edu; Dionne, ggr@ggr.ulaval.ca; Govare, e.govare@sympatico.ca; Harmand, harmand@clsh.univ-nancy2.fr on February 28, 2015 specialpapers.gsapubs.org Downloaded from

Are industrial SO2 emissions reducing CO2 uptake by the boreal forest

Although the boreal forest has been proposed to accommodate increasing amounts of CO2, the large-scale response of photosynthesis to widespread noxious gases is largely unknown. Here we present carbon isotope ratios for ring series from trees subjected to different levels of SO2 emitted from a copper smelter. Our results indicate that noxious gases drastically lower the ability of trees to capture CO2 in the region of the smelter, and that this ability may also be reduced in an extensive region of the Canadian boreal forest undergoing effects from diffuse pollution. This raises concerns about the proposed increased capacity of boreal forests to sequester excess anthropogenic CO2.

Late Wisconsinan—Early holocene deglaciation of Québec-Labrador

Abstract During the Wisconsinan, the area of Quebec-Labrador was completely covered by the Laurentide Ice Sheet (LIS), except for nunataks in the Torngat Mountains. For this reason, pre-Upper Pleistocene events are only documented in scattered stratigraphic sections, and by erosional glacial marks. After the Last Glacial Maximum (LGM), the Labradorean Sector of the LIS evolved from a single, predominant dispersal centre with subsidiary ice divides, into peripheral ice domes and masses which remained connected or not to the central dome. The central dome was not a simple and stable dome-shaped ice mass, but an evolving ice mass. Thinning of the LIS through ablation, and mechanical drawdown along its margins as the result of diachronic ice streams in the St. Lawrence Corridor and Hudson Strait are the main features of Late-Glacial ice flow dynamics. In the areas south of the St. Lawrence Corridor, ice masses over the Appalachian uplands evolved from a glacier complex confluent with the LIS into separate local ice caps. During a part of the warm Bolling-Allerod phase, a series of ice front positions mark a fast retreat of the ice front in the Appalachians of southern Quebec, between about 11,900 (or as recent as 11,600) and 11,600 (or 11,300) conventional 14 C years B.P. (equivalent of ages of terrestrial fossils). The ice mass over the Canadian Shield, north of the St. Lawrence Corridor, dissipated slowly, between about 11,000 (or several centuries later) and 6,500 B.P. The deglaciation pattern includes the differentiation of an ice mass over the Hudson Bay, early deglaciation of the Labrador Highlands, a major change of ice flow in the Ungava Bay, and a very roughly concentric ice retreat pattern in the south-west, south and south-east margins of the remnant main ice mass. In the northern Ungava and Labrador peninsulas, major glacial lakes in low-lying areas were dammed between the ice front and the tilted deglaciated land. Lowlands depressed by glacioisostasy were momentarily invaded by marine waters, mostly between 13 ka and 7 ka. The last glacial ice masses were located in the Labrador Trough and Nunavik and finally disappeared c. 6.5 ka.

Field characterization and data integration to define the hydraulic heterogeneity of a shallow granular aquifer at a sub-watershed scale

Providing a sound basis for aquifer management or remediation requires that hydrogeological investigations carried out to understand groundwater flow and contaminant transport be based on representative data that capture the heterogeneous spatial distribution of aquifer hydraulic properties. This paper describes a general workflow allowing the characterization of the heterogeneity of the hydraulic properties of granular aquifers at an intermediate scale of a few km2. The workflow involves characterization and data integration steps that were applied on a 12-km2 study area encompassing a decommissioned landfill emitting a leachate plume and its main surface water receptors. The sediments composing the aquifer were deposited in a littoral–sublittoral environment and show evidence of small-scale transitional heterogeneities. Cone penetrometer tests (CPT) combined with soil moisture and electrical resistivity (SMR) measurements were thus used to identify and characterize spatial heterogeneities in hydraulic properties over the study area. Site-specific statistical relationships were needed to infer hydrofacies units and to estimate hydraulic properties from high-resolution CPT/SMR soundings distributed all over the study area. A learning machine approach was used due to the complex statistical relationships between colocated hydraulic and CPT/SMR data covering the full range of aquifer materials. Application of this workflow allowed the identification of hydrofacies units and the estimation of horizontal hydraulic conductivity, vertical hydraulic conductivity and porosity over the study area. The paper describes and discusses data acquisition and integration methodologies that can be adapted to different field situations, while making the aquifer characterization process more time-efficient and less labor-intensive.

Methods and Tools for Natural Hazard Risk Analysis in Eastern Canada: Using Knowledge to Understand Vulnerability and Implement Mitigation Measures

AbstractWhile Canada is exposed to a variety of natural hazards, most risk and emergency managers currently lack the necessary tools and guidance to adequately undertake rigorous risk assessments. Unlike the complex computer models for natural hazard risk assessment intended for use by a small number of technical experts, user-friendly rapid risk-assessment tools are being developed to allow nonexpert users from the public-safety community to run otherwise complex risk scenarios at a so-called press-of-a-button. This paper reports on the roles and responsibilities of different levels of government in Canada. Part of the ongoing activities carried out jointly by the government and academia in eastern Canada on the development of inventory and seismic and flood risk-analysis tools is discussed, and examples at urban scales for Ottawa, Gatineau, Quebec City, and Fredericton are given.

Three-dimensional hydrostratigraphical modelling of the regional aquifer system of the St. Maurice Delta Complex (St. Lawrence Lowlands, Canada)

In the central part of the St. Lawrence Lowlands (Mauricie, Québec), Late Quaternary deglacial events led to the formation of a series of complex granular aquifers, such as those in the (1) Saint-Narcisse morainic complex, (2) paleodelta formed by the Saint-Maurice River, and (3) sandy littoral terraces left during marine regression. The aquifers are an important supply of potable water for most municipalities in the region, including the City of Trois-Rivières, which is a mid-size city where groundwater accounts for 46% of the water supply. The main objectives of this study were to build a three-dimensional (3D) model of the Quaternary deposits to define the main hydrogeological contexts of the Mauricie region and to characterize the regional aquifers. The compilation of existing hydrogeological data led to the selection of 5386 well logs that contained stratigraphic information of variable quality, ranging from only surficial sediment thickness to descriptions of fully cored boreholes. To supplement the existing data, fieldwork was undertaken in areas where few data were available, including 63 km of high-resolution seismic reflection surveys and 34 new boreholes. The final 3D model consists of six layers, from the bedrock surface to the upper littoral and deltaic sands. The total thickness of the deposits ranges from zero, on bedrock outcrops, to 150 m beneath central Trois-Rivières. Taking into account the thickness of the saturated layer and the porosity of the sand and gravel, the upper unconfined aquifer contains an estimated 364 million m3 of water. The 3D model helped refine the understanding of regional aquifers and was used to identify unexploited aquifers, notably around the Saint-Narcisse morainic complex and along the St. Cuthbert Fault. The model clarified the regional stratigraphic architecture, especially topography of the bedrock surface, the lateral extent of Late Quaternary sands and development of Holocene post-glacial sediment sequences.

Regional VS30 model for the St. Lawrence Lowlands, Eastern Canada

ABSTRACT Shear-wave velocity of the top 30 m, VS30, is commonly used for prediction of the seismic site response. This paper presents development, validation and uncertainty assessment of a regional VS30 model based on a combination of simplified 3D geology and statistically representative velocity values. Results identify soft marine sediments in deep sedimentary basins as zones most susceptible to seismic shaking. Compared to the available urban-scale seismic zonation studies, the regional model showed a success rate of roughly 64% in predicting local site category. The standard deviation was in average 30% of the expected VS30 value.