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The influence of paleogeomorphology on the stable isotope signals of paleosols

Barta, G., Bradák, B., Novothny, Á., Markó, A., Szeberényi, J., Kiss, K., Kovács, J.
Geoderma 2018 v.330 pp. 221-231
carbon, evapotranspiration, loess deposition, oxygen, paleoecology, paleosolic soil types, runoff, soil formation, stable isotopes, topography, vegetation cover, Hungary
The stable carbon and oxygen isotope composition of three different local variations of the same MIS5e paleosol horizon were studied in the Verőce loess-paleosol sequence (Hungary). These variations developed in local top, paleoslope and paleovalley topographic positions with characteristic secondary carbonate features, such as hypocoatings (HCs).Based on the ¹³C/¹⁸O enrichment or depletion of the secondary carbonate samples, the so-called ‘stable isotope matrix’ (SIM) was established, and this was used to characterize stable isotope signals as potential paleoenvironmental indicators. To complete the SIM, box-and-whiskers plot analysis of δ¹³C and δ¹⁸O values were elaborated on the pedogenic horizons of the paleosol variations.The joint application of the SIM and the box-and-whiskers plot analysis revealed the way in which the climatic stable isotope signal of HCs can be overwritten by the various topographic positions of the hosting paleosols. The local top paleosol variation will necessarily have developed under climatic influence: the expected transition from cold to warm phases (as loess deposition characterized by upbuilding pedogenesis was followed by more effective soil development due to the takeover of topdown pedogenesis) was characterized by increasingly negative stable isotope values in the upward succession of genetic horizons in the sequence. The same transition was identified by different stable isotope patterns in the case of the other two paleosol variations. The paleovalley position implies hydromorphic effects and significant evapotranspiration under denser vegetation cover. The paleoslope position was affected by abrupt environmental changes, such as run-off processes triggered by higher precipitation, leading to continuous disturbance in the course of the development of the sequence.