Diversity of inland playas and aspects of marginal calcium carbonate landform formation

This work firstly presents a newly compiled literature-based database of global playas (Part 1) and later reviews geomorphological aspects of lake margin calcium carbonate (CaCO3) landforms (CCLs) and recommends research priorities (Part 2). In Part 1 literature data reveal that playa occurrence is not limited by topography per se but is mainly constrained by climatic factors and the excess of evaporation over total inflow. Playa evaporation rates vary between ∼4200 mm/yr and ∼760 mm/yr. Evapo-concentration effects take place along with increasing salinity or Total Dissolved Solids (TDS). pH values vary between pH 2 to pH 10, although globally most playas comprise carbonate and soda lakes. Part 2 compiles CCL data from large bioherms to crusts, marginal calcretes, tufa pinnacles and mounds. The literature shows that, for example, while playa marginal calcretes occur most dominantly in southern Africa and Australia, further research is required to establish the role of groundwater incursions in relation to the land-palustrine-playa interface. In contrast, work on mostly biogenic carbonate precipitation resulting in bioherm and crust formation is more advanced. Nonetheless the review highlights the need for more research to establish direct links between (micro) textural fabrics and mound or crust building processes as similar carbonate fabrics may result from different pathways of precipitation and diagenetic replacement.