Peat accumulation on a drowned coastal braidplain: the Mullins Coal (Upper Carboniferous), Sydney Basin, Nova Scotia

Abstract

The Mullins Coal lies within the braided-fluvial South Bar Formation. The lateral extent (15 km) and thickness (2 m) of the coal suggest that controls for peat accumulation were allogenic. Marine inundation of the distal braidplain, as indicated by the high-sulphur content of the coal and the occurrence of agglutinated foraminifera in associated shales, caused ponding of freshwater near maximum marine transgression, with accumulation of thick paralic peat across a stable platform of sandy fluvial sediments. Highstand parasequences with thin capping coals were subsequently incised beneath a sequence boundary as the braidplain readvanced. The Mullins Coal thins and splits in association with muddy bayfill deposits eastward towards the Glace Bay Syncline, a long-lived palaeotopographic element related to fault-bounded basement blocks. Although relative sea-level change controlled the stratigraphic position of the precursor peats, differential tectonic subsidence and/or compaction modified their extent, thickness and quality.