Beachrock ispresent in deep, stablesectionsof a mixed sand and gravel beach at Whitepark Bay (55o14′N) on theparaglacial coast of Northern Ireland. The beachrock was revealed following progressive and extreme beacherosion during two particularly stormy winters (2013/14 and 2014/15). It occurs as large (up to 1 m diameter,0.2 m thick), rounded, disc-shaped concretions in which original beach bedding structures are preserved. Bothsand and gravel beach facies are cemented. The cements are similar to those of tropical beachrocks and comprisean initial thin micrite rim, and subsequent grain rims of aragonitic needles. The cementation is attributed tosaturation of beach groundwater with calcium carbonate sourced from adjacent Cretaceous chalk outcrop in cliffsbehind the beach and dunes. The micrite rims suggest microbial activity in the initial cementation, possibly byscavenging from chalk and skeletal carbonate grains. Subsequent aragonite rims were formed through degassingof CO2aided by tidal water level ﬂuctuations. Despite similar cementation processes to low latitude beachrocks,only isolated concreti ons occur rather than extensive shore-parallel outcrops. Conditions necessary forcementation (and ultimat ely preservation) in this cold temperate and paraglacial setting include long-termbeach stability, a carbonate source (in this case, adjacent chalk cliffs and stream sapping) and tidal water levelﬂuctuations. Bacterial activity may initiate calcite precipitation. Following extreme storms and with progressiveshoreline retreat prompted by rising sea levels, increased reporting of cold-water beachrocks is to be expected asformerly stable sections of beaches are exposed to wave action.
|Early online date||24 Aug 2017|
|Publication status||Published (in print/issue) - Oct 2017|
- Carbonate cement
- beach facies
- Preservation potential