Tidal notches are known to undercut limestone rock formations in the mid-littoral zone, especially in microtidal marine areas. Fossil tidal notches in uplifted or submerged positions have often been used to deduce former sealevel stands and tectonic movements. In particular, the good preservation of a tidal notch profile after emergence or submergence may be used as excellent evidence that the relative sea-level change was rapid, possibly coseismic. Tidal notches are believed to result mainly from marine bioerosion processes during periods of stable relative sea level. While in tropical environments their development may often include bioconstruction layers near the notch base, in temperate environment they tend to be purely erosional features, mainly caused by the boring capacity of endolithic and epilithic algae and by the grazing gastropods that rasp away the microflora together with rock particles in the intertidal range.

Micro-erosion measurements have shown that the rate of deepening of a tidal-notch profile may be very variable (from less than 0.1 mm/yr to about 1 mm/yr, with averages of the order of 0.2 to 0.3.mm/yr in some sites of the Mediterranean). This high variability may depend from seasonal changes in the environment (temperature, salinity, air pressure) that have an influence not only on intertidal vegetation and grazing organism, but also on sea-level changes over seasonal or inter-annual scales. In spite of this variability, the inward depth of fossil notches may be used as an approximate method to roughly estimate the duration of a period of relative sea-level stability. All carbonate rocks are not equally sensitive to tidal-notch development: the slope of the rock layers and irregularities on the rock structure or surface may locally prevent the development of a tidal notch. This means that tidal notches may be present in some locations but not at some nearby sites. Therefore the absence of tidal

notches can hardly be used as a reliable criterion to interpret the lack of a sea-level stillstand. During the last two centuries tide gauges have shown that the global sea level was rising at a rate faster than the possibilities of bioerosion. As a consequence, new tidal notches have not been forming in most places during the last couple of centuries. This is causing a general lacuna in geologic marks.

In conclusion fossil tidal notches can be useful to interpret relative sea-level change in places where they are preserved. However, the lack of tidal notches does not provide evidence of the absence of a sea-level stillstand and coastal geomorphic archives are most often incomplete.