Stratigraphie du Quaternaire et phoque fossile, région de la Durantaye, Québec

Le squelette presque complet d'un phoque fossile a été découvert près de La Durantaye, Québec, dans des sédiments marins associés à la submersion de la mer de Goldthwait. Une identification préliminaire a révélé qu'il s'agit d'un phoque gris ou d'un phoque à capuchon. Le cadre stratigraphique de la région a été précisé. De la base au sommet les unités suivantes se succèdent: 1) des sables et graviers grossiers (5 m) ; 2) des rythmites de type distal (2 m) ; 3) un till rougeâtre argileux très compact (1 à 2 m) ; 4) des sables et graviers fins biens lités (2 m) ; 5) des rythmites de type proximal (2 m) ; 6) un diamicton glacio-marin à Balanus hameh (2 m) ; 7) une argile silteuse parfois très noire (où fut trouvé le phoque fossile) (3 m) ; 8) des silts sableux très fossilifères contenant parfois des blocs (5 m) ; 9) une argile grise massive (jusqu'à 50 m) ; 10) des sables et graviers littoraux (1 m) ; 11) des sédiments fluviatiles récents (1 m). Les rythmites préglaciaires et postglaciaires sont associées respectivement aux varves de Beaupré et aux sédiments varvés de la rivière Chaudière. L'extension vers l'est de la moraine de Breakeyville est également proposée. Enfin, les silts sableux marqueraient un abaissement du niveau marin caractérisé par une activité glacielle pendant l'épisode marin.The almost complete squeleton of a fossil seal has been found near La Durantaye, Québec, in marine sediments associated with the submersion of the Goldthwait Sea. A preliminary identification has revealed it to be a grey or a hooded seal. The stratigraphie setting of the region has been defined. The following units are, from bottom to top : 1 ) coarse sand and gravel (5m); 2) distal-type rythmites (2m); 3) a reddish, very compact clay till (1 to 2 m); 4) well-bedded fine sands and gravels (2) ; 5) proximal-type rythmites (2m) ; 6) a glacial marine diamicton with Balanus hameri (2m); 7) a silty, sometimes very black, clay (the fossil seal was found here) (3m); 8) very fossiliferous sandy silts occasionally containing blocks (5m); 9) a massive grey clay (up to 50m); 10) littoral sands and gravels (1m); 11) recent fluvial sediments (1m). The pre-glacial and post-glacial rythmites are associated with the Beaupré varves and the varved sediments of the Rivière Chaudière respectively. The extension of the Breakeyville moraine towards the east is suggested. Finally, the sandy silts would mark a lowering of the sea level characterized by floating ice activity during the marine episode.Das fast vollstàndige Skelett eines Seehund-Fossils wurde in der Nâhe von La Durantaye, Québec, in Meeres-Sedimenten entdeckt, die mit der Ùberschwemmung durch das Goldwaith-Meer in Verbindung gebracht werden. Eine vorlàufige Identifizierung zeigte, daB es sich um einen grauen Seehund oder einen Kapuzenseehund handelt. Der Schichtungsrahmen des Gebiets wurde prâzisiert. Von der Basis bis zur obersten Schicht findet man nacheinander die folgenden Einheiten: I) grober Sand und Kies (5 m); 2) Rythmite vom Distal-Typus (2 m); 3) ein rôtliches, sehr kompaktes Ton-Till (1-2 m); 4) feiner, gut geschichteter Sand und Kies (2 m); 5) Rythmite des Proximal-Typus (2 m); 6) ein glazial-marines Diamikton mit Balanus hameri (2 m); 7) schlammiger, manchmal sehr schwarzer Ton (hier wurde das Seehund-Fossil gefunden) (3 m); 8) sandhaltiger, sehr fossilisierter Schlamm, der manchmal Blôcke enthâlt (5 m); 9) grauer, massiver Ton (bis zu 50 m); 10) Kustensand undkiesel (1m); II) neuere Flup-Sedimente (1 m). Die voreiszeitlichen und nacheiszeitlichen Rythmite werden jeweils mit den Warwen von Beaupré und den Bander-Sedimenten des Chaudière-Flusses in Verbindung gebracht. Die Ausdehnung der Moràne von Breakeyville nach Osten wird unterbreitet. Endlich sollen die sandhaltigen Silte eine Senkung des Meeres-Niveaus deutlich machen, charakterisiert durch eine Treibeis-Aktivitàt wâhrend der marinen Episode

L’influence de la granulométrie sur la mesure des carbonates par la méthode du Chittick

Des études récentes sur la composition minéralogique de sédiments argileux de la vallée du Saint-Laurent incluaient l'utilisation de la méthode du Chittick pour la détermination des quantités respectives de calcite et de dolomite. Lors d'essais préliminaires de calibration, il est apparu que la granulométrie de ces phases minérales pouvait grandement influencer les résultats. Afin de quantifier ce problème, plusieurs échantillons de granulométrie variée et contrôlée ont été dosés. La méthode du Chittick s'avéra alors très bonne pour le dosage de la teneur totale en carbonates mais faible pour le dosage individualisé de la calcite et de la dolomite en raison de sa forte sensibilité à la granulométrie des carbonates et à leur surface spécifique. Ainsi, les échantillons de dolomite pure ont montré une teneur apparente en calcite de 15 à 66%, selon leur granulométrie. L'addition d'une analyse chimique de la solution résiduelle obtenue au terme de l'essai permet toutefois d'obtenir les concentrations réelles de ces deux carbonates.Recent work on the mineralogical composition of clayey sediments included the use of the Chittick method for determining the various amounts of calcite and dolomite in sediments. At the stage of preliminary calibration on pure minerals, it appeared clear that the grain size distribution of the particles tested was largely influencing the results. To evaluate this problem, numerous samples of the two minerals were prepared with various and controlled grain size distributions. The Chittick method was found adequate to obtain the total carbonate content but poor for evaluating individual phases, being very sensitive to the grain size distribution and to the specific surface area of the carbonate particles. However, the addition of a chemical analysis of the solution obtained after the test enables an exact determination of both phases

Le fjord du Saguenay : une physiographie et un registre exceptionnels

Le fjord du Saguenay est un laboratoire géoscientifique naturel exceptionnel. Sa physiographie et ses caractéristiques géomorphologiques, révélées par les levés multifaisceaux et de sismique-réflexion ainsi qu’une série de carottages, nous fournissent un éclairage nouveau sur l’évolution du fjord du Saguenay à partir du début de la déglaciation du fjord, il y a environ 11 000 ans, ainsi que sur l’enregistrement des différentes catastrophes naturelles majeures qui se sont produites dans la région. De plus, à cause de sa morphologie, le fjord du Saguenay est aussi un endroit de prédilection pour l’analyse des changements climatiques dans cette région du continent nord-américain. À partir de l’analyse morpho-sédimentologique du fjord du Saguenay, nous proposons de le subdiviser en trois parties : le supérieur, le moyen et l’inférieur. Le Saguenay inférieur correspond à la zone comprise entre Tadoussac (kilomètre zéro), à une profondeur d’environ 20 m, et jusqu’à environ 42 km en amont. Ce secteur est dominé par une morphologie glaciaire avec très peu d’accumulations postglaciaires. Le Saguenay moyen comprend la partie profonde du Saguenay comprise entre l’île St-Louis et la confluence de la baie des-Ha! Ha! et du Bras‑Nord. On y retrouve surtout des accumulations hémipélagiques, turbiditiques et des coulées de débris. Finalement, il y a le Saguenay supérieur qui correspond à la zone amont qui inclut le Bras‑Nord et la baie des‑Ha! Ha!. Ce secteur représente une zone d’accumulation et de comblement, surtout dans le Bras‑Nord où on retrouve le delta de la rivière Saguenay. Le fjord, en apparence tranquille, nous a révélé plusieurs traits géologiques intéressants, dont la présence de plusieurs glissements sous-marins, la présence importante de gaz dans la partie profonde et des évidences d’activités sismiques reliées aux séismes de 1663, 1870, et possiblement 1988.The Saguenay Fjord is a natural geoscientific laboratory. Its physiography and geomorphological characteristics, as revealed by multibeam sonar and seismic reflection surveys, and sampling shed a new light on the fjord evolution since the onset of deglaciation in the area, i.e. about 11,000 years ago. It also provides a record of the major natural disasters which have occurred in the area. In addition to its morphology, the Saguenay Fjord is unique for the analysis of climate change for this part of North America. From the morpho-sedimentological analysis of the Saguenay Fjord, we propose to subdivide it into three parts: Lower, Middle and Upper Saguenay Fjord. The Lower Saguenay Fjord corresponds to the sector between Tadoussac (at kilometer 0), at a depth of about 20 m, up to kilometer 42. This part of the fjord consists mostly of glacial sediments with little postglacial accumulations. The Middle Saguenay Fjord encompasses the deeper part of the fjord between Île St. Louis, and the confluence between the Bras-Nord and Baie-des-Ha! Ha!. The seafloor of the fjord, in this sector, consists mostly of hemipelagic, turbiditic and debris flow sediments. Finally, the Upper Saguenay Fjord includes the Bras-Nord and the Baie-des-Ha! Ha!. The seafloor of this part of the fjord is largely made of infilling deltaic sediments. Although apparently quiet, the fjord has revealed interesting geological information including the signature of many submarine mass movements, the presence of gas in the deeper part and evidences of seismic activities linked to the 1663, 1870 and likely the 1988 earthquakes

Notes sur la minéralogie des sédiments fins du lac Ojibway, en particulier ceux de la région de Matagami, Québec

La minéralogie des sédiments fins glacio-lacustres du lac Ojibway est revue et commentée à partir d'un certain nombre d'analyses récentes. On constate que la minéralogie de la fraction argileuse est dominée par les minéraux felsiques tels que le feldspath et le quartz. L'illite et la chlorite prédominent parmi les phyllosilicates qui comprennent aussi des minéraux interstratifiés et des traces de vermiculite. La prédominance des minéraux felsiques dans la fraction argileuse traduit le caractère détritique de ces sédiments d'origine glaciaire. En outre, des données tirées des analyses chimiques totales et des amorphes sont aussi compilées. Deux minéraux peuvent être utilisés comme traceurs minéralogiques: la kaolinite et les carbonates. La teneur en carbonates des sédiments est mis en corrélation avec les épisodes glaciaires du Nouveau-Québec et les récurrences de Cochrane I et II. L'étude en microscopie électronique a révélé l'existence d'une structure floculée dans la fraction fine. Les carbonates et le calcium, en particulier, seraient responsables du type de microstructure observée dans les sédiments : le calcium comme agent de floculation et les carbonates comme ciment entre les particules.The mineralogy of Lake Ojibway fine-grained sediments is reviewed and discussed from recent analyses. The mineralogy of the clay fraction is dominated by felsic minerals such as feldspath and quartz. Illite and chlorite are the most abundant clay minerals which are also represented by traces of mixed-layer clay minerals and vermiculite. The dominance of felsic minerals even in the clay fraction reflects the detritic nature of these glacial sediments. Data on total chemical analysis and amorphous material are also compiled. Two minerals can be used as tracers: kaolinite and carbonates. The amount of carbonates has been correlated to glacial episodes of Nouveau-Québec and the Cochrane I and Il readvances. Electron microscopic studies have confirmed the existence of a flocculated structure in the fine fraction of the varves. Carbonates and calcium in particular have affected the microstructure of the sediment. Calcium has acted as a flocculating ion and the carbonates as cementing agent between the particles.Ausgehend von einer gewissen Anzahl neuer Analysen wird die Minéralogie der feinen glazialen Seesedimente des Ojibway Sees neu interpretiert und kommentiert. Es wird festgestellt, dap die Minéralogie der Lehmschicht von den felsitischen Mineralien dominiert wird wie Feldspat und Quarz. Illit und Chlorit sind vor allem unter den phillosilikatischen Mineralien zu finden, die auch zwischengeschichtete Mineralien und Spuren von Vermikulit enthalten. Das Vorherrschen felsitischer Mineralien in der Lehmschicht bezeugt den TrCimmer-Charakter dieser Sedimente eiszeitlichen Ursprungs. Auperdem wurden die Ergebnisse totaler chemischer Analysen und des amorphen Materials kompiliert. Zwei Minérale kônnen benutzt werden zum Aufspuren von Mineralen: Kaolinit und die Karbonate. Der Karbonatgehalt der Sedimente wird in Beziehung zu den Eiszeitperioden von Neu-Québec gebracht und zu den Rùcklàufigkeiten von Cochrane I und II. Die Untersuchung mit dem Elektronenmikroskop hat eine ausgeflockte Struktur inder Feinstruktur der Warwen auf-gezeigt. Die Karbonate und insbesondere das Kalzium kônnten verantwortlich fur den Mikrostrukturentypus, der in den Sedimenten beobachtet wurde: das Kalzium wirkt als Flockungs-lon und die Karbonate wirken als Bindemittel zwischen den Teilchen

Development of a long term monitoring network of sensitive clay slopes in Québec in the context of climate change

The Government of Québec recently initiated the deployment of a vast groundwater pressures monitoring network in postglacial marine clays to document their variations in time and improve our understanding of the relationship between failure initiation and climate in clay slopes. This project aims at evaluating the impacts of climate change on clay-slope stability and how it can be integrated in landslide risk management to improve public safety. Hydrogeological data will be acquired at sites located throughout the Québec Province’s post-glacial clay deposits to create a public georeferenced index of typical hydrogeological conditions. The project goes beyond the characterization of groundwater pressures and their variations in clay slopes. Indeed, slope deformation will be measured at several sites. Also, two sites in flat terrain will be instrumented in order to evaluate mechanical properties of clay layers in simple 1-D conditions and groundwater recharge. The unsaturated clay crust in slopes susceptible to superficial landslides will be characterized and instrumented. The current lifetime of the monitoring project has been set to a period of 25 years.

Field performance of four vibrating-wire piezometer installation methods

Vibrating wire piezometers provide a number of advantages over the traditional hydraulic piezometer design. There are many methods and configurations for installing vibrating-wire piezometers, with the most common being: single piezometers in sand packs (SP), multilevel piezometers in sand packs (MLSP), and fully-grouted multilevel piezometers using either bentonite (FGB) or cement-bentonite grout (FGCB). This study assesses the performance of these four different installation methods for vibrating wire piezometers at a field site possessing complex stratigraphy, including glacial and marine sediments. Pore pressure data recorded between December 2017 and July 2019 were analyzed to accomplish this objective. Data indicate that SP, MLSP, and FGB piezometers performed well. This determination is based on the fact that piezometers installed at the same depth with these arrangements recorded similar pressure variations that were coherent with the hydrogeological setting. Of the two fully-grouted installations using cement-bentonite grout, one installation failed completely due to a hydraulic short circuit, caused either by shrinkage of the grout or flow occurring along the wires of the embedded instruments. While the FGB-type piezometers used in this study worked correctly, the lack of standard methods concerning both the construction of fully-grouted piezometers is concerning. Furthermore, the lack of a standard method for mixing cement-bentonite grout likely contributed to the failure of the FGCB installations. Thus, due to the lack of guidance for both construction and grout preparation, the use of a bentonite grout removes a degree of uncertainty when fully-grouted installation techniques are used

Use of axial tomography to follow temporal changes of benthic communities in an unstable sedimentary environment (Baie des Ha! Ha!, Saguenay Fjord)

In the upper layer of the sediment column, organic matter recycling is greatly influenced by bioturbation. However, there are many physical changes in the nature of the sediment that may disturb benthic communities and create a biogeochemical imbalance. Following a very heavy rainfall between 26 and 29 July 1996, an intense flash flood in the Saguenay Fjord caused discharges of 6 million cubic metres of sediments into Baie des Ha! Ha!. Unstable sediment deposits located at the top of the delta of the Rivie`re des Ha! Ha! were sporadically exported to the deep basin. After this physical disturbance, meiobenthic and macrobenthic organisms progressively re-colonised the sediment column. To determine the impacts of such sedimentary depositions on benthic fauna, two stations, one at the head and one at the mouth of the Baie des Ha! Ha!, have been monitored since 1996. During this survey, we developed a new method for the quantification of biogenic structures using computer axial tomography (CAT-Scan). Benthic fauna analysis showed that the two stations were characterised by different temporal changes in the benthic dynamics according to their geographic location. Using CAT-Scan analysis of sediment cores, we were able to characterise the stability of the sediment column for the two stations in 1999 and 2000. Scan results suggest that colonisation processes were closely linked with the stability of the sediment column. Erosion and redeposition of surficial sediments caused a succession in the formation of biogenic structures. These variations were characterised for the first time using CAT-Scan, which is a nondestructive, rapid, and precise method. Tomographic analysis showed the importance of the production and destruction rates of biogenic structures and the sedimentation rate for the preservation of burrows and potentially reactive components. This study finally demonstrated that each erosional event could be followed by a rapid formation of biogenic structures, allowing the re-oxidation of old deposits

Assessment of the influence of the slope stability conditions of an inactive open-pit mine on the design of a nearby highway

This paper presents a review of the literature on the design of public roads in the vicinity of open-pit mines, focusing on the latter's impact on slope stability. It then presents a case study on the design of a major new regional highway along the crest of an abandoned mine in the city of Thetford Mines, Québec, Canada. The first step involved a back analysis of a recent slope failure close to the location of the planned highway in order to derive rock mass properties at the slope scale. Analyses were conducted using the Shear Strength Reduction (SSR) method coupled with finite element (FE) modeling as well as the limit equilibrium analysis (LE) method. Airborne LiDAR surveying results were used in order to calibrate and validate the models. Forward modelling was then performed to assess future slope stability

Analysis of a large rock slope failure on the east wall of the LAB chrysotile mine in Canada : LiDAR monitoring and displacement analysis

A major mining slope failure occurred in July 2012 on the East wall of the LAB Chrysotile mine in Canada. The major consequence of this failure was the loss of the local highway (Road 112), the main economic link between the region and the Northeast USA. This paper is part of a proposed integrated remote sensing–numerical modelling methodology to analyze mining rock slope stability. This paper presents the Light Detection and Ranging (LiDAR) monitoring of this slope failure. The main focus is the investigation of that rock slide using both terrestrial (TLS) and airborne (ALS) LiDAR scanning. Since 2010, four ALS and 14 TLS were performed to characterize and monitor the slide. First, laser scanning was used to investigate the geometry of the slide. The failure zone was 1100 m by 250 m in size with a mobilized volume of 25 hm3. Laser scanning was then used to investigate the rock slide’s 3D displacement, thereby enabling a better understanding of the sliding kinematics. The results clearly demonstrate the ability of the proposed approach to monitor and quantify large-scale rock mass failure. The slope was monitored for a period of 5 years, and the total displacement was measured at every survey. The maximum cumulative total displacement reached was 145 m. This paper clearly shows the ability of LiDAR scanning to provide valuable quantitative information on large rock mass failures involving very large displacements