The lower carboniferous stratigraphy of the Musquodoboit valley, Central Nova Scotia

The Windsor Group in the Musquodoboit Valley consists of 460 meters (1,500 ft.) of marine carbonate, anhydrite and siltstone which lie with angular unconformity upon the folded slates and metagreywackes of the Meguma Group (Ordovician) and are unconformably overlain by unconsolidated Cretaceous fire clays and Pleistocene till. The study was undertaken to revise and compile a geologic map of the Musquodoboit Valley area; to describe, measure and interpret the units encountered, with emphasis placed on the base of the section; and to correlate the succession with the Windsor Group type section at Windsor, Nova Scotia. Detailed examination of drill cores and available outcrops was augmented by thin section petrography. Intensive base metal exploration has provided abundant subsurface data previously unavailable in areas of limited outcrop. A fossiliferous dolomitized carbonate, the Gays River Formation (new name), is found at the base of the succession and may be correlative with the Macumber Limestone. The Gays River Formation displays two principal facies: a "Bank Facies", up to 60 meters thick, associated with positive basement features and laterally continuous with an "Interbank Facies" generally less than two meters thick. The basal Windsor Carbonate, which is elsewhere only sparsely fossiliferous is found in the Musquodoboit Valley to possess an abundant fauna and flora. The Gays River Formation is overlain by a 300 meter succession of anhydrite and mixed clastic-carbonate sediments belonging to the Gleason Brook and Meaghers Grant Formations (new names) respectively. The Meaghers Grant Formation is interpreted to be the nearshore equivalent of the Gleason Brook Formation with which it interfingers, indicating a paleoshoreline to the south of the Musquodoboit Valley. The units described above are designated the Lower Beds and are disconformably overlain by 150 meters of interbedded marine carbonates and siltstones which are informally termed the Upper Beds. A mound shaped carbonate member occurs at the base of the Upper Beds and is composed of abundant brachiopod shells and batostomellid bryozoa. This member is seen to interfinger with a thin dark argillaceous crinoidal carbonate and is faunally and lithologically similar to the Miller or Maxner Limestone (B Subzone) of the type area. These mound shaped 'bodies display broad simi- larity to the Waulsortian Banks of Fire and the bryozoan mounds in the Mississippian of the U.S.A. A limestone unit bearing the Gigantoproductus faunal assemblage is well represented and is informally named the Musquodoboit Limestone. Previous works have placed it in the E and F subzones of the Upper Windsor, but this study favours a possible equivalence to the limestones of the C subzone (Herbert River Limestone). The study area contains lithologies interpreted to be deposited in an area marginal to the main Windsor basin but not totally isolated from it.