Comparison of recent sediments from different geomorphological environments using automated static image analysis with insight into its applicability to paleo archives

The relationship between depositional environments and transportation processes associated with the general properties of formed siliciclastic sediments has greatly interested researchers. The grain shape properties of the sediments reflect the transport mechanisms of different geomorphological and sedimentary environments. The spread of new, high-resolution analytical methods has made it possible to quickly examine the grain shape properties of a large number of individual mineral grains. We investigated three sediment types from different environments (aeolian, fluvial, glacial, [n=27]) using automated image analysis (Malvern Morphologi G3-ID). During the analysis and data processing (e.g. Kruskal-Wallis, MANOVA, PCA) we examined four variables related to grain shape, which were the following: HS circularity (form, roundness), convexity (surface texture), solidity (roundness) and elongation (form). Our vital aim was to determine the key variables that can help to distinguish certain geomorphological environments and define the possible limits and boundaries of each granulometric feature of the medium sand fraction (250-500 µm). Five groups were distinguished according to the three types of environment (p<0.001; α=0.05). The grains from the aeolian and glacial sediments each formed a separate group, while the grains from the fluvial environments were classified into three groups. HS circularity was the most effective attribute, and the elongation variable proved to be the least influential parameter in differentiating sedimentary environments. However, the high values (mean: 0.24-0.3) of the elongation variable indicate a very fresh state of grains from glacial and certain fluvial samples. The HS circularity value changes slowly over time, and a large amount of energy is needed to increase the roundness value, but relatively less time and presumably shorter distance are required to decrease the surface roughness. We tried to interpret the results by comparing the granulometric properties of recent sediment grains with paleo sediments (aeolian and fluvial, n=15). One additional group was formed containing the highest granulometric values of the investigated samples, and the other sediments were classified into the recent fluvial and aeolian groups. Although according to their stratigraphic position, they should have been classified into the opposite sediment groups, indicating that the paleo-aeolian sediments bear the transport features of the fluvial medium and vice versa. By increasing the number of samples and documentation of grains in various geomorphological environments makes it possible to delineate preliminary grain shape boundaries (e.g. for solidity glacial-fluvial: 0.95; fluvial-aeolian: 0.97). However, this may also have a hindering effect, as the grouping methods hide the differences in some parameters within the classified sediments. Presumably, for example, the aeolian environments may be as diverse as the fluvial ones and need to be studied separately. It is important to note that the presented granulometric fingerprinting method can only provide comprehensive and detailed insights into the depositional environment of the mineral particles when applied together with other proxies.

Support of the National Research, Development and Innovation Office (Hungary) under contract NKFIH FK138692 is gratefully acknowledged.