Sedimentology and fossil-fuel potential of the Upper Carboniferous Barchois group, western Newfoundland

The coal-bearing Upper Carboniferous Barachois Group of western Newfoundland consists of the youngest known rocks in the St. George's Bay Lowlands. These lowlands are part of the Bay St. George Subbasin, which, in turn, is part of a network of Carboniferous depositional areas in eastern Canada. A detailed sedimentological study of the Barachois Group was undertaken as part of a more general study (involving geology and geophysics) to assess the fossil-fuel potential of the western Newfoundland Carboniferous subbasins. -- Cores and exposures of the Barachois Group in the St. George's Bay Lowlands define a lower coarse unit and an upper fine unit. The coarse unit consists of alternating red-brown mudstone-dominated units and grey sandstone and conglomerate-dominated units. The fine unit consists of thick grey or red-brown mudstone-dominated units with interspersed sandstone units. Eleven facies (A to K) are recognized in the two units. The facies are organized into three facies associations and eight subassociations. Facies association I includes fluvial channel sandstones and conglomerates found in outcrops and the BSG£1 core (subassociation IA) and channel and minor sheetflood deposits found in the FB2-76 core (subassociation IB). Facies association II comprises sandstones and mudstones deposited in proximal crevasse channel and levee environments (subassociation IIA), in undifferentiated crevasse splay, levee, and floodplain environments (subassociation IIB), and by progradation of crevasse splay, levee, and delta environments (subassociation IIC). Facies association III includes mudstone-dominated subassociations which represent the deposits of floodplain lakes (subassociation IIIA), poorly-drained swamps (subassociation IIIB), and well-drained swamps (subassociation IIIC). -- Sandstones of the Barachois Group are classified predominantly as arkose and subarkose, with up to 65% feldspar. The sandstones include a variety of authigenic minerals such as kaolinitie, chlorite, illite, calcite, and silica. Sandstone mineralogy does not identify any distinctive provenance. Potential sources of the arkoses could have included several of the presently exposed igneous intrusive complexes in the Long Range Mountains located southeast, east, and north of the study area. -- X-ray diffraction of the