Silt particle shapes in Saharan dust intrusions across Europe: implications for formative processes and sedimentary...

We present the application of particle-shape parameters for silt grains in the 4-8 µm, 8-15 µm, and 15-31 µm fractions obtained using automatic particle-shape image analysis (Morphologi G3SE). Four shape parameters (HS Circularity, Convexity, Solidity, and Aspect Ratio), supported by scanning electron microscopy (SEM) investigations and multivariate statistical analyses, were used to aid interpretation of processes and formulation of hypotheses regarding possible sedimentary environments responsible for grain shape. The analysis examined dust particles collected during four Saharan dust intrusions into Europe: Greece (2016, 2018) and Poland (2021, 2024). The results suggest that the Convexity parameter is the most useful for distinguishing individual dust events (2016, 2018, 2021, and 2024), identifying similarities between them (particularly between 2021 and 2024), and demonstrating internal variability within a single dust plume between different deposition sites during the 2021 event. In contrast, HS Circularity and Solidity exhibited lower discriminatory and interpretative potential. Grain-size fractions below 10 µm showed the strongest ability to differentiate between dust events and deposition sites. This analysis may provide a basis for linking particle shapes with environments that may have contributed to the formation of the final shape of dust particles and may reflect a long, multi-stage pathway (MSteP). More than 75% of the analyzed dust particles were classified as subrounded, rounded or well rounded, and exhibited more isometric shapes with shallow or absent microdepressions. The predominance/presence of subrounded and rounded grains may suggest processes characteristic of subaqueous (fluvial or beach) environments.