The internal architecture and external form of fluvial channel bodies is governed by both intrinsic and extrinsic controls. Extrinsic controls such as climate, eustasy, and tectonism are believed to have modest effects on channel-body types and geometries in high-subsidence settings. The effects of climate are particularly cryptic in high-accommodation settings and have proven extremely difficult to separate from other extrinsic controls such as tectonics and eustasy. The thick successions preserved in such basins have the potential to be relatively stratigraphically complete and are, therefore, valuable for interpreting basin evolution. This study documents the external geometry and internal architectural styles of fluvial channel bodies in a spectacularly exposed, 7-km-thick, Mississippian–Permian section from the Cumberland Basin, Atlantic Canada. Four fluvial styles are recognized: perennial, strongly seasonal, ephemeral, and fixed. Fluvial styles are not randomly distributed throughout the stratigraphic succession; instead discrete stratigraphic intervals consist of predominantly one type of fluvial style. Four stratigraphic intervals (E1–E4) in which strongly seasonal fluvial styles are predominant are recognized and alternate with intervals that are characterized by either perennial or ephemeral deposits. This suggests that a coherent record of climate change as manifested by changes in precipitation and runoff regime is recorded in the internal architecture of sandbodies.