Shore platform downwearing rates and processes in the upper and lower intertidal zones in eastern Canada

This study examines weathering processes in the upper and lower intertidal zones of shore platforms in eastern Canada. Over 90 transverse micro-erosion meter stations were installed in six areas. Basalts, argillites, and sandstones from three areas were immersed or exposed in artificial sea water and de-ionized water to replicate tidal conditions at different elevations within the upper and lower intertidal zones. The results suggest that surface downwearing by salt weathering is important on some types of rock in the upper intertidal zone, but that wetting and drying is ineffective. Downwearing is very slow in the lower intertidal zone. A comparison of field and laboratory data indicates that weathering can account for much of the downwearing occurring in the upper intertidal zones of the study areas. Weathering-generated downwearing may have reduced the upper portions of shore platforms by one to several meters since sea level reached its present elevation.