Abstract
AbstractPaleoenvironmental reconstructions are commonly based on isotopic signatures of a variety of carbonate types, including rhizoliths and land-snail shells, present in paleosol-loess sequences. However, various carbonate types are formed through distinct biotic and abiotic processes over various periods, and therefore may record diverging environmental information in the same sedimentological layer. Here, we investigate the effects of carbonate type on δ13C, δ18O, and clumped isotope-derived paleotemperature [T(Δ47)] from the Quaternary Nussloch paleosol-loess sequence (Rhine Valley, SW Germany). δ13C, δ18O, and T(Δ47) values of co-occurring rhizoliths (-8.2‰ to -5.8‰, -6.1‰ to -5.9‰, 12–32°C, respectively), loess dolls (-7.0‰, -5.6‰, 23°C), land-snail shells (-8.1‰ to -3.2‰, -4.0‰ to -2.2‰, 12–38°C), earthworm biospheroliths (-11‰, -4.7‰, 8°C), and “bulk” carbonates (-1.9‰ to -0.5‰, -5.6‰ to -5.3‰, 78–120°C) from three sediment layers depend systematically on the carbonate type, admixture from geogenic carbonate, and the duration of formation periods. Based on these findings, we provide a comprehensive summary for the application of the three isotopic proxies of δ13C, δ18O, and Δ47in biogenic and pedogenic carbonates present in the same sediment layer to reconstruct paleoenvironments (e.g., local vegetation, evaporative conditions, and temperature). We conclude that bulk carbonates in Nussloch loess should be excluded from paleoenvironmental reconstructions. Instead, pedogenic and biogenic carbonates should be used to provide context for interpreting the isotopic signature for detailed site- and time-specific paleoenvironmental information.
Highlights
Paleosol-loess sequences have a long history of use in paleoenvironmental reconstructions for a broad range of paleoclimate, geology, biology, and anthropology investigations (e.g., Riecken, 1950; Fisk, 1951; Kyuma et al, 1985; Wu et al, 2007; Zech et al, 2012; Lechler et al, 2018)
We examine paleoenvironmental information recorded by carbonate types from a well-known paleosol-loess sequence, the Upper Pleistocene Nussloch paleosol-loess in the Rhine Valley of southwestern Germany (Zoller et al, 1988; Hatté et al, 1999; Rousseau et al, 2002, 2017a, b; Antoine et al, 2009; Prud’homme et al, 2018)
Isotopic results for Upper loess, Paleosol, and Lower loess samples are summarized in Table 1, and full data for samples and standards is provided in Supplementary Table A1
Summary
Paleosol-loess sequences have a long history of use in paleoenvironmental reconstructions for a broad range of paleoclimate, geology, biology, and anthropology investigations (e.g., Riecken, 1950; Fisk, 1951; Kyuma et al, 1985; Wu et al, 2007; Zech et al, 2012; Lechler et al, 2018). To this end, investigating isotopic compositions of carbon (δ13Ccarb) and oxygen (δ18Ocarb) of loess materials, and in particular carbonates formed in these sequences, has been a staple of paleoenvironmental reconstructions for decades. Carbonate δ13C values provide information about paleovegetation (Quade and Cerling, 1995; Liu et al, 1996; Bayat et al, 2016), and δ18O values are related to the temperature and the isotopic composition of oxygen in the soil water (δ18Owater) from which the carbonates precipitated (Cerling, 1984; Bayat et al, 2016; Lechler et al, 2018)
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