I am currently studying the deposition process in coastal environments and I came across a point which I do not understand concerning grading of grain size.
According to "Petroleum Geology by North F.K."
- 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.