LOESSFEST'09 | Aug. 31st – Sept. 3rd, 2009 |Novi Sad-Serbia
Stable Isotopic Evidence for Middle Pleistocene Environmental Change From a Loess Palaeosol Sequence: Kärlich, Germany
Gallant, C.E.1, Candy, I.1, Rose, J.1, Silva, B.N.1, Turner, E.2
1Department of Geography, Royal Holloway, University of London, Egham, Surrey, TW20 0EX
2Forschungsbereich Altsteinseit des Römisch-Germanisch Zentralmuseum, Mainz, Schloss, Monrepos, Neuwied, Germany
Isotopic studies of carbonates within loess-palaeosol sequences have employed both carbon and oxygen isotopes as potential proxies of climate change. It has been demonstrated that the carbon isotopic record of such carbonates is responsive to vegetational changes. The oxygen isotope composition of soil carbonates has been shown to be directly related to temperature at the time of formation and thereby has the potential to reconstruct past temperatures. Although there is only a small analytical error associated with isotopic analysis, there can be local factors that can result in subtle isotopic shifts. However, large scale isotopic variations can be understood in terms of major climatic shifts on Milankovitch timescales. Isotopic studies have great potential for understanding palaeoclimates; allowing for a quantitative assessment of climatic shifts and a tool for relative comparison.
Isotopic studies of carbonates in loess are gaining attention; however, they are rarely carried out in connection with micromorphology. The employment of micromorphology allows; 1) a detailed understanding of the carbonate material being analysed and, therefore, any potential diagenetic issues to be identified, and 2) a second proxy for environmental change, namely pedological processes, that can be combined with the isotopic information. The environmental shifts indicated by both micromorphology and more importantly isotopic analysis can, therefore, be used to indicate major climatic shifts in terrestrial environments. Where a robust stratigraphy, supported by geochronology, exists it is possible to compare these shifts with those recorded within marine and ice core sequences.
This paper presents the sedimentological, micromorphological and isotopic analysis of a middle Pleistocene loess-palaeosol section located within Kärlich, Germany. The section at Kärlich has been placed within the Middle Pleistocene period; through biostratigraphy and geochronology (K-Ar dating of tephras) the study profile has been correlated with MIS12 through to MIS11.
Micromorphology was carried out through the entirety of the MIS 12/11 loesspalaeosol sequence. The results show that MIS12 is represented by small scale accretionary development of calcitic pedofeatures during loess accumulation. MIS11 is characterised by a well-developed palaeosol, with much greater concentration of carbonate features, characterised by the formation of a calcic hardpan overlain by iron rich sediments with increased clay content. Isotopic analysis of the MIS11 sediments show little variation, within both 13C and 18O signals.
The isotopic values of the calcic horizon are characteristic of interglacial carbonates from elsewhere in Europe. The carbon isotope record of carbonate pedofeatures within the MIS12 loess shows little variation, whereas the oxygen isotope signal records progressive enrichment in 18O up profile by 2.95‰. Such a variation is too large to be consistent with internal processes operating within a soil profile and must reflect significant climatic amelioration during loess accumulation.
Evidence presented by sedimentology, micromorphology and isotopic analysis indicate two different styles of pedogenesis operating on the section; a characteristic interglacial unit showing extensive post-depositional pedogenesis and cold climate accretionary pedogenesis containing a large oxygen isotopic shift. The chronology and stratigraphy of this site does not support the climatic amelioration as being the onset of MIS11. Instead they indicate that the warming occurred during MIS12 and as such must reflect a major warming event (interstadial) within the glacial period. Such an event is visible in both marine and ice core isotopic sequences.
The identification of this climatic amelioration has only been possible through stable isotope analysis as the micromorphology and sedimentology of the section suggests only a minimal change in pedogenesis. This study highlights the potential of carbon and oxygen isotope studies in loess-palaeosol sequences. With robust geochronology, employment of this technique can improve and further the palaeoclimatic information which may be derived from loess-palaeosol sequences.