Existing stratigraphic nomenclature, lithologic descriptions, and geological interpretations for an economically important Mesoproterozoic dolostone in the Milne Inlet Graben, Borden Basin, Nunavut, do not adequately portray its unusual facies or their spatio-temporal configuration. Four new stratigraphic units are introduced to replace this dolostone, formerly known as the Society Cliffs Formation. In the southeastern half of the graben, the Iqqittuq Formation represents a distally steepened ramp that grades northwestward into deep-water mudstone that is indistinguishable from that of the underlying Arctic Bay Formation. The overlying Angmaat Formation represents a rimmed, restricted peritidal platform that grades northwestward across a tepee – cortoid shoal barrier into the unusual, deep-water dolo-laminite of the Nanisivik Formation. Deep-water carbonate mounds up to hundreds of metres thick and kilometres in areal dimensions belong to the Ikpiarjuk Formation; these mounds are geometrically equivalent to upper Arctic Bay Formation mudstone, Iqqittuq Formation outermost ramp, and part of the Nanisivik Formation dolostone. The Iqqittuq, Nanisivik, and Ikpiarjuk formations conformably overlie mudstone of the Arctic Bay Formation. The Angmaat and Nanisivik formations are unconformably overlain by mudstone of the lower Victor Bay Formation. These new, formal, mappable stratigraphic entities were deposited in two time stages, and their three-dimensional configuration depicts an unusual, tectonically influenced basin that was also affected by high-amplitude eustatic cyclicity in shallow water.

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