SEQUENCE STRATIGRAPHY OF THE LATE CARBONIFEROUS CLIFTON FORMATION, NEW BRUNSWICK

The Maritimes Basin of Atlantic Canada contains a rich record of coal-bearing, Pennsylvanian cyclothems. Previous studies focused on rapidly subsiding depocenters in the central part of the Maritimes Basin where cycles are composed of alternations between terrestrial and marginal marine strata. In contrast, the Pennsylvanian Clifton Formation was deposited on the more stable New Brunswick platform and contains almost entirely terrestrial strata. Early studies noted a cyclic architecture, particularly within the middle part of the formation (Member B). However, no modern sedimentological or sequence stratigraphic framework has been applied to the formation.

In this study we provide a modern sedimentological framework for the lower 75 meters of Member B, develop a sequence stratigraphic interpretation of cyclicity, and place the Clifton Formation within a broader regional and temporal context. Near the base of the section, the highstand systems tract is composed of red floodplain mudrocks; the overlying sequence boundaries are composed of calcretes and/or incised paleovalleys. The transgressive systems tract and maximum flooding surfaces are represented by coals or aquatic bivalve-bearing mudrocks. In the upper part of the section, the highstand systems tract remains largely unchanged, however sequence bounding paleosols are less well developed and are composed of discontinuous calcic horizons rather than amalgamated calcretes. The transgressive systems tract is not preserved and the maximum flooding surface is composed only of discontinuous organic-rich horizons. These changes in cyclic architecture could be attributed to a decreased subsidence rate, increased sediment supply, decreased amplitude of glacioeustatic changes, or climate change. The progressive decrease in marginal marine influence in Clifton Formation cyclothems improves our understanding of cyclicity in the terrestrial realm.