Burial diagenesis model for the Macumber Formation on Cape Breton Island - implications for the tectonic evolution of the Windsor Group
DOI :
https://doi.org/10.4138/2078Résumé
The Macumber Formation, a finely laminated limestone consisting of two thin units, represents a key stratigraphic marker at the base of the Visean Windsor Group. On Cape Breton Island the formation hosts numerous Pb-Zn occurrences, and its upper boundary is in contact with rocks ranging in age from Visean (early Carboniferous) to Westphalian (middle Carboniferous), the origin of the stratigraphic omissions being debatable. This first inorganic diagenesis study identifies nine post-depositionat processes, including the stabilization of marine components, and evaporite and anhedral calcite precipitation. The δ18OPDB (-13.0 to 2.0%o), 87Sr/86Sr (0.7076 to 0.7079) and [Sr] (50 to 10000 ppm) of samples, including upper and basal whole-rock units and anhedral calcite cements, show two trends enveloping the entire field of data. The trends suggest that an evaporite-derived, non-radiogenic fluid and a clastic-derived radiogenic fluid mixed and interacted with the limestone sediments, in a progressively deeper burial environment. The evaporite-derived fluid mostly imprinted the top unit of the formation. The field investigations, microscope observations and geochemical results do not indicate a meteoric overprint as would be expected if an unconformity existed along the top of the formation. The burial history documented here, and the presence of fibrous calcite indicating bedding parallel shearing, support a detachment model to explain the stratigraphic omissions within the Windsor Group. RÉSUMÉ La Formation de Macumber, composeé de calcaires fins en deux minces unités, représente un marqueur stratigraphique crucial à la base du Groupe de Windsor. À l’ile du Cap Breton, la formation encaisse plusieurs indices Pb-Zn et constitue la limite inférieure d'une série d'omissions stratigraphiques à l'intérieur du Groupe de Windsor, l'origine-desquelles est fortement débattue. Cette première investigation de la diagenèse inorganique place neuf processus en une succession post-dépositionnelle incluant la stabilisation des éléments marins, et la précipitation d'évaporites et de ciments calcitiques anédriques. Les δ18OPDB (-13.0 to 2.0%o), 87Sr/86Sr (0.7076 to 0.7079) et [Sr] (50 to 10000 ppm) de microéchantillons des unites inférieures et supérieures, et de ciments anédriques montrent deux tendences envcloppant l’ensemble des résultats. Ces tendences suggèrent qu'un fluide non-radiogéltest;nique, eévaporitique et un fluide radiogénique dérivé de roches clastiques, auraicnt affecté les sédiments calcaires au cours de leur enfouissement progressif plus profond. Le fluide évaporitique aurait principalement affecté l'unité supérieure de la formation. Les données de terrain, les observation microscopiqucs et les résultats géochimiques n'indiquent pas l'empreinte météorique attendue si une discordance existait au sommet de la formation. L'histoirc diagénétique ici documentée, ainsi que l'existence de calcite fibreuse développée le long de plans de cisaitlement parallèles au litage supportent le modele de détachement pour expliquer les omissions stratigraphiques du Groupe de Windsor.Téléchargements
Publié-e
1996-04-01
Comment citer
Savard, M. M., Lynch, G., & Fallara, F. (1996). Burial diagenesis model for the Macumber Formation on Cape Breton Island - implications for the tectonic evolution of the Windsor Group. Atlantic Geoscience, 32(1). https://doi.org/10.4138/2078
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