First Record of Beachrock in High-Altitude Soda Lakes, Lake Van, Eastern Türkiye

This study presents, for the first time, evidence of beachrock formation along the shores of a highly alkaline soda lake. The carbonate cement binding the grains consists of radially grown aragonite, scalenohedral Mg-calcites, and spar calcites filling cavities. Dogtooth cement extending into cavities and meniscus cement textures are also present. These data indicate that the Lake Van beachrock formed through cementation with carbonate polymorphs precipitated from highly saturated lake waters under intense evaporation in extremely arid conditions. There are similarities in the conditions that support the formation of both beachrock and microbialites in the same shoreline zone. The role of high lake alkalinity, bacterial activity, and groundwater supplying Ca to the lake waters is crucial in the precipitation of binding carbonates. The formation of the beachrocks likely occurred between 3.5 ka BP, when the lake began experiencing a pronounced arid trend, and 2 ka BP, when the lake's climate reached a stabilized state. Thus, it can be inferred that the beachrocks predate the microbialites observed on the shelf of the studied shoreline.