Calcite precipitation at Skateraw Harbour, exposed after recent erosion of till by the sea.
Calcite precipitation at Catcraig
Subglacial calcite precipitation
Definition: the precipitation of CaCO3 from subglacial meltwater on to the glacier bed
Modern glaciers moving over a bed of limestone often display a range of subglacial karst landforms (Ford, 1987). Solution forms include sinkholes and karren, the group of limestone surface features created by differential solution of limestone surfaces. Precipitation features include a range of surface crusts of carbonate minerals.
The meltwater film beneath a glacier crossing limestone may be saturated with CaCO3. The induced melting of ice on the up glacier side of bedrock bumps, both large and small, allows CaCO3 to go into solution. Refreezing leads to precipitation in lee-side cavities. The precipitated calcite typically has a fluted surface texture which runs parallel to the former direction of ice flow (Felix and Hallet, 2002).
Possible examples of subglacial calcite precipitation occur at two sites on the East Lothian coast where recent marine erosion has stripped away till. South of Torness Power Station, the Carboniferous Skateraw Limestone shows calcite precipitation on the down ice side of small rock steps, with ribs of calcite oriented to 80°. At Catcraig, similar features occur. At both sites calcite precipitation extends into fractures below the limestone surface. These patterns have been described as striae at each site, but the surface textures are generally of ridges rather than scratches.