The edge of a carbonate platform may be marked by an abrupt change in slope or there may be a lower angle transition to deeper water facies.
The front of a reef can form a vertical ‘wall’ and along with other slopes too steep for sediment accumulation are by-pass margins.
Sediment accumulates at the base of the slope, brought in by processes ranging from large blocks fallen from the reef front to submarine talus slopes, slumps, debris flows and turbidites.
The most proximal material forms rudstone deposits, which are sometimes called mega breccias if they contain very large blocks, passing distally to redeposited packstones, to turbiditic wackestones and mudstones.
Depositional margins form on more gentle slopes with a continuous spectrum of sediments from the reef boundstones or shoal grainstones of the shelf margin to packstones, wackestones and mudstones further down the slope.
Finer grained sediments tend to be unstable on slopes and slumping of the mudstones and wackestones may occur, resulting in contorted, redeposited beds.