Lithostratigraphic revisions of the Upper Carboniferous to Lower Permian strata in the Cumberland Basin, Nova Scotia and the regional implications for the Maritimes Basin in Atlantic Canada

The Late Paleozoic strata exposed in the Cumberland Basin, part of the larger regional Maritimes Basin of Atlantic Canada, have been considered as classic Carboniferous sections since their original description in the mid-1800s (Joggins Section). Stratigraphic nomenclature applied to the Upper Carboniferous strata, which locally exceed a thickness of 7 km, is problematic due to numerous poorly defined or informal units and a confusing mixture of litho-, bio-, and chrono- stratigraphic terminology. The Cumberland Basin is a key area in the regional nomenclature because it contains the type sections of the Cumberland and Pictou groups, and well exposed sections of strata traditionally assigned to the Riversdale group (abandoned) and Canso group (abandoned and replaced by the Mabou Group). Mapping and definition of lithostratigraphic units at the formation level has necessitated examination of the criteria for group nomenclature. The constituent formations of the Cumberland and Pictou groups examined by this study include in ascending order: Cumberland Group, 1. Claremont and 2. Boss Point, (both formerly assigned to the Riversdale group, now abandoned); 3. Polly Brook (new); 4. Joggins (redefined); 5. Springhill Mines (new); 6. Ragged Reef (new); 7. Malagash (new); and Pictou Group, 8. Balfron (new); 9. Tatamagouche (new); and 10. Cape John (redefined). The resulting revision of the groups is based upon formal formation subdivisions and utilizes lithostratigraphic criteria such as composition, occurrence of coal and related strata, predominant colour and grain size, vertical and lateral variation, and stratigraphic relationships. This eliminates or minimizes the historical bio- and chrono-stratigraphic bias. The revised Cumberland Group conformably and unconformably overlies strata of the Mabou Group and includes all of the grey (dominated) coal-bearing strata in the basin. It also includes greybeds that were previously assigned to the base of the Pictou Group in the type section. The revised Pictou Group includes all of the redbed dominated, non coal-bearing strata above the Cumberland Group. The proposed lithostratigraphic subdivisions (new and revised) and group assignment criteria will facilitate regional correlation and basin analysis within the Maritimes Basin.