Comparative¹⁴C and OSL dating of loess-paleosol sequences to evaluate post-depositional contamination ofn-alkane biomarkers

Abstract

There is an ongoing controversial discussion as to whethern-alkane lipid biomarkers—and organic matter of loess in general—reflect a synsedimentary paleoenvironmental/climate signal or whether they are significantly affected by postdepositional “contamination,” for example related to root and rhizomicrobial activity. In order to address this issue at our study site (the Middle to Late Weichselian loess-paleosol sequence Gleina in Saxony, Germany), we determined and compared radiocarbon ages of bulkn-alkanes and sedimentation ages, as assessed by optically stimulated luminescence (OSL) dating. The bulkn-alkanes of the four dated samples yielded calibrated14C ages ranging from 24.1 to 49.7 cal ka BP (95.4% probability ranges). While the three uppermostn-alkane samples are well within the range or even slightly older than the OSL-inferred sedimentation ages, the lowermostn-alkane sample is slightly younger than the OSL ages. There is hence little or no evidence at our study site forn-alkanes in loess-paleosol sequences being significantly “contaminated” by deep subsoil rooting or microbial processes. We propose a14C isotope mass balance calculation for estimating such contaminations quantitatively. Radiocarbon dating of bulkn-alkanes might have great potential for Quaternary research, and we encourage further comparative14C and OSL studies.

Radiometric dating of late Quaternary loess in the northern piedmont of South Tianshan Mountains: Implications for reliable dating

“…Radiocarbon dating is the most commonly used method to establish chronologies of late Quaternary sediments. The datable materials in loess are usually organic macrofossils (e.g., plant remains, charcoals), gastropod shells, rhizoliths, carbonates, and soil organic matter (SOM) or total organic carbon of bulk sediments, new datable materials such as bulk n ‐alkanes (Zech et al, ) and earthworm calcite granules (Moine et al, ; Prud'homme et al, ). These might have great potential for Last Glacial loess dating.…”

“…Modern carbon contamination is likely to be the main cause of underestimation of radiocarbon, consistent with previous discussions (Song et al, ). In further radiocarbon dating of Central Asian loess, we should pay more attentions to find charcoal and explore new datable materials such as bulk n ‐alkanes (Zech et al, ) and earthworm calcite granules (Moine et al, ; Prud'homme et al, ).…”

Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications

“…In soils or sediments, n-alkanes can be preserved due to their chemical inertness, resistance against degradation and low water solubility (Eglinton and Eglinton 2008). If the catchment area does not yield old carbon pools and the residence times for biomarkers are short, bulk nalkane dating that was previously undertaken by (Bliedtner et al 2020;Häggi et al 2014;Haas et al 2017;Zech et al 2017) is hence corroborated as a valuable tool for dating lacustrine sediments in addition to compound-specific n-alkane 14 C dating (Gierga et al 2016).…”

Chemotaxonomic patterns of vegetation and soils along altitudinal transects of the Bale Mountains, Ethiopia, and implications for paleovegetation reconstructions – Part II: lignin-derived phenols and leaf-wax-derived <i>n</i>-alkanes

“…Unlike with lignin phenols, a noteworthy influence from root-derived n-alkanes on O layers and A h horizons can be excluded. This is based on the notion that roots contain lower n-alkane concentrations by several magnitudes than above-ground plant material and results from studies using 14 C dating of n-alkanes in loess-paleosol sequences (Häggi et al, 2014;Zech et al, 2017).…”