Abstracts
Abstract
Displaced glacial striae were examined at outcrops within the central area of Saint John, New Brunswick. Displacements are mostly confined to north-facing slopes of small bedrock hills left after the glacial erosion of Cambrian-Early Ordovician rocks in the southeast limb of a syncline. The striae are generally offset by high-angle reverse faults a few metres in length and with throws up to 60 mm. The faults trend parallel to bedding and dip southward at angles similar to the dip of individual beds.
The displacements have long been considered as evidence of postglacial tectonic stresses in the area. However, from a detailed analysis of the extent and orientation of the small faults, we propose that the displacements represent the response of multilayered sedimentary rocks with anisotropic strengths, to differential rates of glacitec tonic loading and unloading. Therefore, the last major displacements likely occurred very soon after deglaciation of the area.
RESUME
On a examine' les deplacements affectant des striures glaciaires sur des affleurements situes en plein centre de Saint-Jean, au Nouveau-Brunswick. Ces deplacements sont surtout confines aux versants nord de petits moles modeles par l'erosion gladairedesnxhescambriennesaeo-ordovkiennesd^msleflancsud-estd'unsynclinal. Les striures sont generalementaffectees par des failles inverses a fort pendage, d'une longueur de quelques metres et dont le re jet atteint 60 mm. Les failles sont paralleles au litage et penchent vers le sud avec des inclinaisons semblables aux pendages des lits individuels.
On a longtemps vu dans ces deplacements le signe Evident de contraintes tectoniques postglaciaires dans cette region. Cependant, une analyse detaillee de 1 'etendue et de l'orientation des petites failles nous permet d' avancer que les deplacements reprdsentent la r£ponse de roches sedimentaires, disposers en couches multiples et do tees de resistances anisotropes, a divers taux de chargement et de d£lestage glaciotectoniques. Les demiers deplacements majeure se manifesterent vraisemblablement tres tot apres la deglaciation de la region.
Download the article in PDF to read it.
Download