Soil Organic Carbon Dating of Paleosoils of Alluvial Fans in a Blown Sand Area (Nyírség, Hungary)

Abstract

The most widely used dating techniques in quaternary research are the radiocarbon (14C) and optically stimulated luminescence (OSL) dating methods. In some environments, the investigated sediments do not contain enough material for 14C dating. In these cases, 14C dating of bulk sediment may be used as a last resort. The major aim of the present study was to determine the reliability and limitations of the different fractions of the soil organic carbon (SOC) 14C ages in the Nyírség blown-sand study area, in Hungary. Therefore, the low- and high-temperature combustions of SOC (LT-SOC and HT-SOC) 14C age of fossil soils were compared with the charcoal ages from the same fossil soil layer, and their (LT-SOC, HT-SOC, and charcoal) age reliability was verified independently by applying OSL to the quartz fraction of the sediment samples. The 14C data show variable agreement with OSL ages. Charcoal fragments were collected from some of the best material for 14C dating and their ages are in agreement with the LT and HT-SOC 14C ages and OSL data. The 14C age LT-SOC gives a reliable, credible ages, which were confirmed by independent OSL measurements. If buried soils do not contain any other macroscopic remnants for 14C dating, the LT-SOC 14C ages can be used, in the case of the Nyírség study area. The LT-SOC, which is the younger fraction of the soil organic carbon, may be considered to represent the burial time of the fossil soil layer. The HT-SOC 14C ages are sometimes unrealistically older than expected and cannot be considered to be reliable.

Accumulation of radiocarbon in ancient landscapes: A small but significant input of unknown origin

“…All samples for total organic carbon determination and radiocarbon dating were acid-washed to remove inorganic carbon. To test the hypothesis that paleosols contain organic C that is radiocarbon-dead, we chose acid washing 15 rather than acid fumigation 32 of samples for removal of inorganic C. Acid-washing samples presumably leads to the removal of some or all of the soluble organic C from bulk samples 33 , which may have removed both modern and ancient soluble C materials. If some amount of radiocarbon is detected after acid washing, this would imply that any radiocarbon may have been composed of insoluble C compounds that were, for example, associated with clay minerals or amorphous/nanocrystalline phases 34 .…”

“…For example, carbon from microbial biomass and/or plant root exudates from the modern weathering zone can leach downwards and accumulate in paleosols (e.g., 14 ). Eolian and groundwater-driven deposition of allochthonous C are additional possibilities 15 , though groundwater found in bedrock can be depleted in modern C 16 . Therefore, a method to constrain the sources and approximate ages of organic carbon in bulk paleosol samples would provide a valuable technique to understand if and how modern carbon tends to accumulate in ancient exhumed landscapes.…”

New Radiocarbon Dates From Polish Inland Dunes Point to Prevalence of Human Impact on Dune Mobility

“…Radiocarbon ( 14 C) dating of paleosols buried in aeolian sandy deposits remains the centerpiece of such studies in Poland and adjacent countries for more than 40 years (Sokołowski et al 2022 and references therein). However, as new outcrops become available, the need for conducting further 14 C age measurements persists (Tolksdorf and Kaiser 2012; Buró et al 2019, 2022; Kappler et al 2019; Moska et al 2020, 2022; Sokołowski et al 2022). New 14 C dates can help corroborate or reevaluate existing knowledge on the chronology of dune activity and stabilization.…”