A meandering fluvial-distributary was initiated into the interdistributary bay of a Carboniferous (Yoredale) delta lobe by avulsion. Initiation immediately preceded abandonment of the lobe, and lateral migration of the channel produced a meander belt sandstone in the short period of channel activity. The channel fill comprises an 8 m fining upwards sequence with lateral accretion surfaces in the coarse member which permit calculation of palaeochannel parameters. The coarse member also exhibits inclined, erosive discontinuities which reflect temporal variations in flow. Paleochannel regime was dominated by frequently recurring normal floods which produced the lateral accretion surfaces, and less frequent exceptional floods which were primarily effective in scouring the bar surface, producing the discontinuities.