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Nussloch revised: high-resolution multi-proxy analyses of syn- and postsedimentary features in a new loess profile at Nussloch (SW Germany)

Martina Gocke1, Eileen Eckmeier2, Ulrich Hambach3, Manfred Löscher4, Lorenz Schwark5, Ludwig Zöller3, Guido Wiesenberg1
1 Agrarökosystemforschung, Universität Bayreuth
2 INRES-Bodenwissenschaften, Universität Bonn
3 Geomorphologie, Universität Bayreuth
4 Max-Reger-Weg 3, 69181 Leimen, Germany
5 Geowissenschaften, Universität Kiel

V 2.4 in Löss und terrestrische Archive

17.09.2012, 17:10-17:30, H8

 

 

The loess-paleosol sequence at Nussloch (SW Germany) has been investigated for several decades, mainly in the four standard profiles P1 – P4, established between 1995 and 2002. In this Weichselian sequence, which comprises mainly the Middle and Upper Pleniglacial, paleovegetation and -climate were studied by various approaches, including e.g. bulk organic carbon (Corg), alkane molecular proxies, partially combined with stable carbon isotope composition (δ13C).

While high resolution sampling is commonly applied for some proxies like e.g. grain size and magnetic susceptibility, other proxies are often measured in lower resolution over loess sequences, especially bulk Corg or molecular proxies. This means that either each loess unit and each paleosol is sampled solely in their middlepart, or samples collected from various depths of the respective unit are pooled prior to analyses. However, this can lead to misinterpretations, as pedogenic features are not necessarily restricted to the (partially very thin) paleosols and can strongly vary within stratigraphic units.

High-resolution investigation of such loess-paleosol sequences with respect to organic proxies and related features is important for the following reason: The general presumption of paleoenvironmental studies using organic remains in loess (e.g. bulk Corg, sugars, lipids), is that these originate solely from aboveground biomass of the vegetation prevailing during loess deposition. Recent studies show that a considerable portion of loess organic matter can be attributed to postsedimentary incorporated, root- and rhizomicrobial-derived organic matter.

Therefore, a new profile was prepared ca. 100 m distant from P4 to assess the paleoenvironmental record with a high-resolution multi-proxy approach including the following proxies:

-          magnetic susceptibility

-          VIS spectra and color indices

-          carbonate contents

-          organic carbon contents

-          contents of free extractable lipids and fractions thereof (n-alkanes and fatty acids)

All of these proxies were determined in 10 – 20 cm intervals from top to bottom of the 13.5 m thick loess profile, except for in situ color measurements which were performed with even higher resolution of 1 – 2 cm.

Further, to assess and differentiate root-related features from the original loess organic matter, for the first time abundances of recent and ancient calcified roots (rhizoliths) per square meter were determined to assess their correlation with recent and ancient phases of pedogenesis.

The results clearly show several phases of root development documented in the profile, whereas the root features of the individual phases were not restricted to individual paleosols, but crossed borders between loess and paleosols. This argues for a general recognition of root features in sedimentary context and a proper adjustment of sampling strategies to avoid misinterpretations.

 



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Letzte Änderung 31.07.2012