| Abstract: | The Brownstones form the highest Lower Old Red Sandstone in South Wales and the Welsh Borderlands. Sections from the Brecon Beacons of Central South Wales consist of laterally extensive sheets of interbedded sandstone and siltstone. Facies sequence A consists of parallel laminated sheet sandstones and siltstones and is interpreted as a sandy sheetflood and distal muddy floodflat association. Facies sequence B comprises sheet sandstones composed of multistorey channel fills, small calcrete-clast filled channels and massive siltstones with thin interbedded sandstones. This sequence is interpreted as low sinuosity channel deposits merging laterally and downslope into a muddy flood-basin, with calcrete clasts infilling intrabasinal channel systems. Facies sequence C consists of multistorey sandstones and is interpreted as a proximal low sinuosity channel system. The Brownstones of the Brecon Beacons formed on an extensive alluvial plain with low sinuosity sand-bed channels merging downslope into sheetfloods and muddy floodflats, in a system broadly analogous to that of the Eyre Basin of South Australia. |
