Fixed grain size ratios - useful proxies for past loess sedimentation dynamics or just a function of pedogenesis?

Abstract

Loess-paleosol sequences are sensitive terrestrial archives of past aeolian dynamics and paleoclimatic change.Numerous paleoenvironmental reconstructions from loess records have traditionally depended on the analysisof grain size (GS) distributions. A number of GS based statistical approaches are widely used. However, theGS distribution of a loess sample is not solely a function of aeolian dynamics; rather, complex polygeneticdepositional and post-depositional processes must also be taken into account.This study assesses the reliability of fixed GS ratios as proxies for past sedimentation dynamics, using sev-eral case studies from different regions in the Eurasian loess belt. Highly resolved GS data derived by laserdiffraction are visualized using heatmap signatures (Schulte in press). Based on this, meaningful proxies forgrain-size shifts due to post-depositional pedogenic processes are identified. Our proposed approach facilitates theidentification of variability within loess-paleosol sequences without horizontal or vertical data loss.We conclude that fixed grain size ratios are unreliable proxies for past aeolian dynamics on their own andlead to the loss of important data. Soil formation processes cause “true” variations within sensitive GS classes(e.g. clay and fine silt formed by pedogenesis), but these variations may be masked by relative changes in the morefrequently occurring size fractions when single value parameters are used.

Resources

• https://publications.rwth-aachen.de/record/751881

Bibliography

Schulte, P., Sprafke, T., Rodrigues, L., Fitzsimmons, K., Lehmkuhl, F. (2018): Fixed grain size ratios - useful proxies for past loess sedimentation dynamics or just a function of pedogenesis?. EGU General Assembly 2018, 08.-13.04.2018, Vienna, Austria