• If deposition exceeds subsidence, high-energy deposits prograde over lower-energy deposits;hence grain size coarsens upwards.
• If deposition and subsidence are in general equilibrium, stacked or multistorey sand bodies result.
• If subsidence exceeds deposition, a series of isolated narrow, linear bars of sand become separated by wide strips having less sand. The sand bodies may still coarsen in grain upwards.

I actually don't understand why this happens, I tried to Google it but still no clue.