The Kamouraska Formation is an uppermost Cambrian -lowermost Ordovician quartz-arenite-dominated unit of controversial origin deposited on the southeastern slope of Laurentia bordering the Iapetus Ocean. It is exposed in the Quebec Appalachians on the south shore of the St. Lawrence Estuary. The formation consists of basal polymictic conglomerate and overlying massive sheet-like quartz arenite. The conglomerate beds are reversely and reversely to normally graded. The quartz arenite beds are generally massive, although they may show coarse-tail grading. Beds containing full or partial Bouma sequences are rare. Paleoflow directions from ripple-cross lamination, ripple marks on bed surfaces, and sole marks point towards southeast, south, and southwest. The clastic sediments of the Kamouraska were transported into the deep sea by sediment gravity flows that evolved from hyperconcentrated to concentrated density flows, and then to turbidity currents. The depositional environment is interpreted to have been a southwest-trending meandering submarine canyon. The exposed part of the canyon deposits is slightly oblique to the strike of slope. If correct, our interpretation establishes the preservation of continental-slope deposits in more distal deep-water siliciclastic sedimentary rocks of the Taconian orogen in Quebec, which traditionally have been interpreted as submarine-fan and (or) basin-plain deposits. The orientation of a canyon near parallel-to strike of the slope may have been controlled by syn-depositional growth faults. The coarsest hyperconcentrated flows, which deposited the conglomerate, were restricted to the deepest parts of the canyon during its early stages of development, whereas the concentrated density flows that deposited the massive quartz-arenite beds covered a wider area.Résumé : La Formation de Kamouraska est une unité du Cambrien supérieur -Ordovicien inférieur dominée par une aré-nite quartzique d'origine controversée déposée sur la pente sud-est de la Laurentie bordant l'Océan Iapetus. Elle affleure dans les Appalaches du Québec sur la rive sud de l'estuaire du Saint-Laurent. La formation comprend un conglomérat de base polymictique sous une arénite quartzique en forme de feuillet massif. Les lits de conglomérat sont à gradation inverse et inverse à normale. Les lits d'arénite quartzique sont généralement massifs bien qu'ils puissent avoir un granoclassement frustre à la base. Les lits contenant des séquences entières ou partielles de Bouma sont rares. Les directions des paléo-écou-lements à partir de laminations obliques de rides, de rides de plage à la surface des lits et de marques de structure basale pointent vers le sud-est, le sud et le sud-ouest. Les sédiments clastiques de la Formation de Kamouraska ont été transportés en profondeur dans la mer par des écoulements gravitaires de sédiments qui ont évolué à partir de courants de densité hyperconcentrés à concentrés puis à des courants de turbidité. L'environnement de déposition est interprété comme ayant été un canyon à méandres à tendan...
The Kamouraska Formation is a quartz-arenitic unit of latest Cambrian -earliest Ordovician age in the Quebec Appalachians that was deposited by hyperconcentrated to concentrated density flows in a meandering submarine canyon on the continental slope bordering the Iapetus Ocean, as outlined in a companion paper. Detailed petrographic study of the quartz arenites of the Kamouraska Formation combined with scanning electron microscopy of grain surface textures suggests that the quartz sands are of eolian origin having been derived from an inland desert or, less likely, a barrier beach dune system. Transport of the mature quartz-arenitic sand onto the shelf and deposition into the deep sea was not accompanied by substantial mixing with material from other sources thus preserving the inherited eolian characteristics. A modern analogue for the eolian interpretation of the deep-sea quartz-arenite beds is as follows: thick, Late Pleistocene eolian sand beds on a modern abyssal plain in the East Atlantic referred to as eolian-sand turbidites that were deposited in the deep sea during glacial sea level lowstands when eolian sand transport to canyon heads was enabled by an exposed and shortened shelf. Similarly, an established sea level lowstand at the Cambro-Ordovician boundary would have facilitated the introduction of eolian sand of the Kamouraska Foundation into canyon heads on the upper slope from where turbidity currents and related density flows were triggered. Correlation of the Kamouraska Formation with the quartz arenites of the Cairnside Formation of Quebec (Keeseville Formation in northern New York State, Nepean Formation in southern Ontario) links the deep-sea deposits with remnants of an inland dune system. Résumé : La Formation de Kamouraska est constituée d'une unité d'arénite quartzique (Cambrien supérieur -Ordovicien inférieur) dans les Appalaches du Québec; elle a été déposée par des courants de densité hyperconcentrés à concentrés dans un canyon sous-marin à méandres sur la pente continentale à la bordure de l'Océan Iapetus, tel que souligné dans un article complémentaire. Une étude pétrographique détaillée des arénites quartziques de la Formation de Kamouraska jumelée à une microscopie électronique à balayage des textures de surface des grains suggèrent que les sables quartzeux sont d'origine éolienne et qu'ils proviennent d'un désert d'arrière-pays ou, ce qui est moins probable, d'un système de dunes de cordon littoral. Le transport du sable arénite-quartz mature sur la plateforme continentale et sa déposition en mer profonde n'ont pas été accompagnés d'un malaxage important avec du matériel d'autres sources, préservant ainsi les caractéristiques éoliennes héri-tées. Un analogue moderne pour l'interprétation éolienne des lits d'arénite quartzique de mer profonde est le suivant : d'épais lits de sables éoliens (Pléistocène tardif) sur une plaine abyssale moderne dans l'Atlantique Est, connus en tant que turbidites de sables éoliens, qui ont été déposés en mer profonde durant les périodes de bas niveau de...
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