Beachrock

Beachrock is a friable to well-cemented sedimentary rock that consists of a variable mixture of gravel-, sand-, and silt-sized sediment that is cemented with carbonate minerals and has formed along a shoreline.

[1][2] Beachrock units form under a thin cover of sediment and generally overlie unconsolidated sand.

The main processes involved in the cementation are : supersaturation with CaCO3 through direct evaporation of seawater,[3] groundwater CO2 degassing in the vadose zone,[4] mixing of marine and meteoric water fluxes[5] and precipitation of micritic calcium carbonate as a byproduct of microbiological activity.

Because beachrock is lithified within the intertidal zone and because it commonly forms in a few years, its potential as an indicator of past sea level is important.

Thus, the older zones are located in the outer part of the formation when the younger ones are on the side of the beach, possibly under the unconsolidated sand.