Shards of glass: incorporation of trash in modern beachrock on Eleuthera Island, Bahamas, and its implications for in situ studies of fast carbonate cementation

Beachrocks are bodies of beach sediment cemented with carbonate minerals. They are not only useful archives of coastal evolution, but are also investigated as means of protection from coastal erosion. Beachrock formation is known to permanently alter the morphodynamics of a coastline and lock sediment in place, while reflecting wave energy. The cementation occurs on a scale of years rather than millennia, but observations of very young beachrocks with well constrained ages are still rare. Furthermore, our understanding of the cementation process is limited, although crucial to the creation of artificial beachrocks for engineering purposes.

On the Bahamian island Eleuthera modern beachrocks have incorporated high amounts of trash such as glass, rubber and microplastics. While the inclusion of anthropogenic materials into the rock record raises questions on limestone nomenclature, it also provides chances for the study of beachrocks. The glass is of particular interest as it shows no signs of rounding, indicating very recent cementation. This facilitates an in situ observation of the cementation process over an extended period of time, uncovering possible links to environmental parameters like temperature, availability of freshwater, inundation and weather phenomena like storms. To unravel the structure of the microbial communities involved in cementation a combination of petrography, SEM and environmental DNA can be used on the cements.