Importance of biological loess crusts for loess formation in semi-arid environments

The essential abiotic components for loess formation are: material (dust), atmospheric circulation (wind), suitable surface conditions for the trapping of aeolian material, and for the subsequent development of typical loess sedimentary structures. In spite of the world-wide distribution of loess deposits, knowledge of the processes of dust accumulation and its transformation to mature loess sediment is still inadequate. Loess accumulation appears greatest during the most arid periods and in semi-arid regions. Biological crusted surfaces (BCS) are of potentially great importance in loess formation, especially in semi-arid regions. BCS are highly specialized extremophile communities and apparently play an important role in atmospheric dust trapping and erosion prevention. Results indicate that cyanobacterial strains isolated from current Carpathian Basin loess exhibit specific morphological and eco-physiological characteristics that play a key role in loess formation, warranting adoption of the new term biological loess crusts (BLC). A model of the influence of cyanobacterial BLC life strategies on loess formation explains trapping, accumulation and preservation, as well as loess texture and structure. This potential significance of BLC in the accumulation and preservation of loess sediments may be considered as a model suitable model database for recognition of bioorganic modification of geological strata. Mycosporine and scytonemin pigments can serve as BLC biomarkers, elucidating their role in soil evolution and in aiding paleoclimatic, paleoenvironmental and paleovegetation reconstructions.