Beach cement: incipient CaCO3-cemented beachrock development in the upper intertidal zone, North Uist, Scotland

Beachrock has only rarely been observed previously along high latitude coas ts. On several beaches on North Uist, NW Scotland at over 57 degrees N ther e is evidence of small-scale beach cementation. An area of beach cement at the back of Traigh Ear, as well as unconsolidated sands from the beach and the adjacent Traigh Hornais, have been studied using SEM, XRD and petrograp hical thin sections to throw light on the nature and causes of cementation. Unconsolidated sands from both beaches are similar in grain sizes, shape a nd mineralogy, but Traigh Ear grains commonly possess abundant cover of hig h Mg calcite. The beach cement on Traigh Ear exhibits low porosity, with ab undant micritic and aragonitic cements, showing no evidence of vadose cemen tation along with traces of microorganisms. These findings contrast with th e vadose, low Mg calcite cements commonly reported from temperate zone beac hrocks. (C) 2000 Elsevier Science B.V. All rights reserved.