Reviews and syntheses: Tufa microbialites on rocky coasts towards an integrated terminology

Microbialites are known from a range of terrestrial, freshwater, marine, and marginal settings. The descriptive terminology used in each instance depends largely on the historical legacy derived from previous studies in similar environments. This has led to a diversity of nomenclature and a lack of conformity in the terms used to describe and categorise microbialites. As the role of microbial mats and biofilms is increasingly recognised in the formation of tufa and terrestrial carbonates, deposits such as tufa microbialites bridge the spectrum of microbialites and terrestrial carbonate deposits. Groundwater spring-fed tufa microbialites in supratidal rock coast environments that occur at the interface of terrestrial and marine domains demonstrate the need for an integrative and systematic nomenclature approach. To date, their global distribution and complex relationships with pre-defined deposits have resulted in the application of a variety of descriptive terminologies, most frequently at the macro- and mesoscale. Here we review and consolidate the multi-scale library of terminologies for microbialites and present a new geomorphological scheme for their description and classification. This scheme has greater alignment with terrestrial carbonate nomenclature at the macroscale and with marine and lacustrine microbialites at the mesoscale. The proposed terminology can primarily be applied to tufa microbialites in spring-fed supratidal environments but may also be applicable in other relevant depositional environments including terrestrial carbonates, microbial mats, and other microbialites.