| Popis: |
The origins of intertidal indentations and undercuts (nips and notches) in calcareous shores has long been disputed. In recent years this dispute has centered on the efficacy of solution by seawater vs the erosional effects of marine organisms. Little attention has been given to solution by fresh groundwater even though it is a proven solvent of calcareous rocks whereas seawater is not. The solutional effects of groundwater—either floating as a surface layer on seawater or seeping through porous rocks at the shoreline—would be strictly confined to the intertidal zone and most intense at midtide level. Just such a distribution of erosional effect is required for the formation of nips and notches, yet such a distribution of effect has yet to be demonstrated either for seawater or for most erosional marine organisms. On purely theoretical grounds, then, solution by groundwater deserves consideration as a major factor in the origin of coastal undercuts. In Greece, notches in calcareous rocks occur only in proximity to coastalsprings, where surface seawaters are locally diluted by freshwater. Per cent saturation of these waters with respect to calcium carbonate is not known, but the one-to-one correspondence of notches with springs is by itself persuasive circumstantial evidence that solution by groundwater is the chief factor in the origin of the notches. |
