Muara area, 'Brooketon Colliery' Outcrops

Outcrops in the Brunei Muara area show fining upward cycles of variable thickness, in each case with carbonaceous shale/coal seams at the top of each cycle. Each cycle begins with an erosive based sandstone with an overlying pebble lag. The sandstones have large scale cross-bedding and are interpreted as distributary channels. Rapid lateral facies transitions are indicative of an upper delta plain environment in which the vertical stacking of channel bodies would imply a rapid rate of relative subsidence. The presence of ferruginous concretions is, however, better reconciled with somewhat slower subsidence and therefore a transitional lower delta-plain environment is preferred.

Picture below: Brooketon; massive channelised sandstones (right) overlain by coaly shales and coal (left)

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