Marine Deposits

Sub-tidal beds
Nearshore subtidal deposits are those which accumulate in relatively shallow water below low tide. They are characterized by ripples in the sand surface, which are a product of multi-directional water currents associated with wave and tidal action. In the Pleistocene sub-tidal limestones of Bermuda, these ripples are recorded as somewhat chaotic small scale cross-bedding.

Sub-tidal deposits commonly include particle sizes which are larger than typical beach sand. This is expected, as sub-tidal deposits are closer to the source of limestone debris and have consequently undergone less sorting than beach sand.

Where a Pleistocene sub-tidal limestone is found above present sea level, it is a sure indication of previous higher sea level - assuming, as we do for Bermuda, that the land has not shifted upwards.