Tectonic versus climatic control on the evolution of a loess–paleosol sequence at Beremend, Hungary: an integrated approach based on paleoecological, clay mineralogical, and geochemical data

Abstract

The role of two major factors, climate and tectonism, in controlling loess–paleosol evolution has been evaluated in the present study based on a multi-proxy dataset comprising mollusc, bulk and clay mineralogical, and geochemical data. A recent trend has been to use chemical indices such as the chemical index of alteration (CIA) for paleoclimate reconstructions in loess–paleosol sequences spanning several hundreds of thousands of years, but without any tectonic interpretation. Possible effects of geodynamic factors on physical erosion, chemical weathering and consequently weathering proxies are discussed. Clearly, the relative rates of physical erosion and chemical weathering in a sedimentary environment could be significantly influenced by geodynamic factors and governed not just by climate. Intensifying tectonic uplift gives rise to enhanced physical erosion, leading to increased supply of fresh mineral surfaces having less time to react with weathering agents. In theory, this process may point towards decreasing chemical weathering in a sequence without any real changes of climate. In the studied loess–paleosol sequence at Beremend (Hungary) a trend of decreasing chemical weathering has been observed, which can be explained by a global climate deterioration and accelerating uplift in and around the sedimentary basin. Increasing dust sedimentation could theoretically also contribute to this process as a result of increasing aridification and wind strength reflecting climate change in weathering records following a non-linear amplification. The findings refer to the fact that the impact of tectonism should also be taken into consideration in tracing past chemical weathering trends on timescales of hundreds of thousands (or millions) of years. This is because tectonic effects may impose on the CIA signal and distort it suggesting a potential bias in reconstructing paleoclimate change based only on this proxy from certain loess sequences associated with young orogenic belts.