| Summary: | 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 ...
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