The Upper Carboniferous Clifton Formation of northern New Brunswick: coal-bearing deposits of a semi-arid alluvial plain

Two contiguous successions within Member B of the Westphalian Clifton Formation are exposed on the coast of Chaleur Bay east of Bathurst, New Brunswick. The upper succession is dominated by sandstone, and the lower by shale, which encloses isolated channel and lenticular sandstone bodies. Distinctive features of the shale are thin coals, casts of tree trunks, calcareous paleosols, and deep desiccation cracks with calcareous coatings. Markov chain analysis of the shale-dominated succession defines a repetitive sequence of shale, rippled fine-grained sandstone, paleosol, and coal. This sequence is attributed to filling of flood basins followed by emergence and pedogenesis under semi-arid conditions, which prevented thick coal accumulation. The major sandstone bodies are interpreted as channels, associated with lenticular levee, crevasse-splay, or mouth-bar deposits of a semi-arid alluvial plain on which anastomosing channels dominated. The Okavango River of south-central Africa and Cooper's Creek in central Australia are proposed as modern analogues.The upper succession of Member B is characterized by sheet sandstones made up of top-truncated trough and planar cross-stratified units, with abundant plant litter and calcareous intraclasts. The rocks are interpreted as braided-fluvial sand sheet deposits that blanketed the lower succession floodplain. Petrographic and paleocurrent data suggest a common source for both successions. The progradation of the braided sand sheet may reflect a sedimentary response to climate change, tectonic rejuvenation, or a combination of both.