Search

We report on a 4.1 (±0.2) km diameter and 185 m deep circular submarine structure exposed on the seabed in >40 m water depths in the northwestern Gulf of St. Lawrence (Eastern Canada) from the analysis of high-resolution multibeam bathymetric and seismic data. The presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures. Also, other origins, such as kimberlites, intrusions, karsts, or diapirs, can be eliminated on geological criteria. A single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition, assumed to be impact melts, and a single quartz grain with planar intersection features thought to be shock-induced planar deformation features ( PDFs). The absolute age of this possible impact structure is unknown, but its geological setting indicates that it was formed long after the Mid-Ordovician and before regional pre-Quaternary sea-level lowstands. Present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure. [ABSTRACT FROM AUTHOR]

The method of soil stabilization is well known and has been used throughout the world for many decades to improve some soil properties. Although many researchers have studied the effect of adding a cementing agent to a soil, not many of these researchers have explored the effect of treatment on the resulting properties of high water content soils like dredged material. Also, there has been little work concerning the prediction of the mechanical changes to the soil. Therefore, this paper summarizes the results of a research project conducted to define the general mechanical behavior of high water content clayey soils from eastern Canada treated with lime or cement, in terms of compressibility. In the light of this research, the general compressibility behavior has been obtained, defined by relationships between initial void ratio, additive content, and vertical yield stress for a given inorganic or organic soil. These relationships have been normalized on the basis of the one-dimensional compression curve of the remolded and reconstituted untreated soil to give a simple method for predicting the vertical yield stress of a treated soil for any initial void ratio and its resistance to compression.Key words: stabilization, compressibility, yield stress, clayey soils, lime, cement.La méthode de stabilisation des sols est bien connue et a été utilisée depuis plusieurs décades à travers le monde pour améliorer certaines propriétés des sols. Quoique plusieurs chercheurs aient étudié l'effet de l'addition d'un agent de cimentation au sol, peu d'entre eux ont exploré l'effet du traitement sur les propriétés résultantes des sols à teneur en eau élevée tels que les matériaux dragués. Également, il y a eu peu d'études portant sur la prédiction des changements mécaniques apportés au sol. En conséquence, cet article résume les résultats d'un projet de recherche réalisé pour définir un comportement mécanique général en terme de compressibilité de sols argileux à hautes teneurs en eau de l'est du Canada avec de la chaux ou du ciment. À la lumière de cette recherche, on a obtenu le comportement général en compressibilité défini par la relation entre l'indice des vides initial, la teneur en additif, et la contrainte de préconsolidation apparente verticale pour un sol donné organique ou inorganique. Finalement, ces relations ont été normalisées sur la base de la courbe de compression unidimensionnelle du sol non traité remanié et reconstitué pour donner un méthode simple pour prédire la contrainte de préconsolidation apparente verticale d'un sol traité pour n'importe quel indice de vide initial, et sa résistance à la compression.Mots clés : stabilisation, compressibilité, contrainte de préconsolidation apparente, sols argileux, chaux, ciment.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Disturbed lacustrine deposits of eastern Canada have been associated with past seismic events in the intraplate Western Québec Seismic Zone (WQZ) and the Charlevoix–Kamouraska Seismic Zone (CKSZ). With five major earthquakes that occurred during historical times and hundreds of minor earthquakes, the CKSZ is the most active seismic zone in eastern Canada. Here we present new high-resolution multibeam bathymetric, subbottom profiler and sediment core data collected in Lake Témiscouata, southeastern Québec, the largest lake located within the influence of the CKSZ. The occurrence of mass-movements in the highly cohesive glaciolacustrine deposits of the lake produced a peculiar lacustrine landscape consisting of steep slide scars and residual mounds and very narrow residual crests. Our data indicate that postglacial times were marked by recurrent seismically-induced mass-movement events that cannot be individually identified in the sedimentary record due to the highly disturbed stratigraphy of the lake and to the absence of significant postglacial background sediments between events. The most recent recorded mass-movement is a distinct debris flow sediment layer on the lake floor that was deposited at ~ 1300 cal BP, very shortly after a distinct large-scale mass-movement event observed across the entire lake basin. The presence of silt layers in gyttja overlying these disturbed units suggests that the region was affected by other seismic events following this event, although no MMDs could be directly related to these layers. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution seismic profiles along with physical and sedimentological properties of sediment cores from the Saguenay (Eastern Canada) and Reloncavi (Chile) Fjords allowed the identification of several decimeter to meter-thick turbidites. In both fjords, the turbidites were associated with large magnitude historic and pre-historic earthquakes including the 1663AD (M>7) earthquake in the Saguenay Fjord, and the 1960 (M 9.5), 1837 (M~8) and 1575AD major Chilean subduction earthquakes in the Reloncavi Fjord. In addition, a sand layer with exoscopic characteristics typical of a tsunami deposit was observed immediately above the turbidite associated with the 1575AD earthquake in the Reloncavi Fjord and supports both the chronology and the large magnitude of that historic earthquake. In the Saguenay Fjord, the earthquake-triggered turbidites are sometimes underlying a hyperpycnite associated with the rapid breaching and draining of a natural dam formed by earthquake-triggered landslides. Similar hyperpycnal floods were also recorded in historical and continental geological archives for the 1960 and 1575AD Chilean subduction earthquakes, highlighting the risk of such flood events several weeks or months after main earthquake. In both fjords, as well as in other recently recognized earthquake-triggered turbidites, the decimeter-to meter-thick normally-graded turbidites are characterized by a homogeneous, but slightly fining upward tail. Finally, this paper also emphasizes the sensitivity of fjords to record historic and pre-historic seismicity. [Copyright &y& Elsevier]