The δ¹³C, δ¹⁸O and Δ₄₇records in biogenic, pedogenic and geogenic carbonate types from paleosol-loess sequence and their paleoenvironmental meaning

Abstract

Paleoenvironmental 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 Δ47 in 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.

Late Pleistocene Climate and Dust Source From the Mobarakabad Loess–Paleosol Sequence, Northern Foothills of the Alborz Mountains, Northern Iran

“…Soil carbonate isotope studies of modern soils and paleosols have typically focused on samples collected from temperate or warm environments (e.g., Quade et al, 2007;Hough et al, 2014;Diaz et al, 2016;Gallagher and Sheldon, 2016;Ringham et al, 2016;Bayat et al, 2017;Dietrich et al, 2017). The carbon and oxygen isotope composition of pedogenic carbonate (δ 13 C pc and δ 18 O pc ) and land snail shell carbonate within successions of rapidly buried Quaternary soils exhibit stratigraphic trends that are interpreted to record a history of significant climate variation and provide an additional technique for investigating Quaternary climate and ecologic changes (McDonald and McFadden, 1994;Monger et al, 1998;Lechler et al, 2018;Huth et al, 2019;Újvári et al, 2019Zamanian et al, 2021). Recent studies suggest a strong summer seasonal bias in some (Breecker et al, 2009;Passey et al, 2010;Quade et al, 2013;Huth et al, 2019) but not all pedogenic carbonates (Peters et al, 2013).…”

“…Some authors suggested that δ 13 C bc in loess represents a mixed signal derived from both detrital carbonate and authigenic pedogenic carbonate (Ning et al, 2007;Liu et al, 2011;Koeniger et al, 2014), and the effects of multiple formation times on bulk soil carbonate isotope composition should also be considered (Burgener et al, 2016). Also, Zamanian et al (2021) studied isotopic signatures of different types of carbonates in the Nussloch paleosol-loess sequence in Germany, and they excluded the stable isotope composition of bulk carbonate for reconstructing the local paleoenvironment because the bulk carbonates in the section were detrital materials from the diagenetic conditions of carbonates in the deflation area.…”

Palaeo-environmental evolution of Central Asia during the Cenozoic: new insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)

“…8), compared with the surrounding regions, indicate that less precipitation and long-term, sustained arid climatic conditions prevailed in the late Eocene until the early Miocene (Cerling and Quade, 1993;Kent-Corson et al, 2009;Takeuchi et al, 2010;Caves et al, 2015;Li et al, 2016;Caves Rugenstein and Chamberlain, 2018). An influence of the height and extension of the Tibetan Plateau or the retreat of the Paratethys on the hydroclimate in Central Asia at this time (An et al, 2001;Zhang et al, 2009) is barely documented in the sedimentary record of the Valley of Lakes, although it cannot be excluded, which would be expressed in monsoon-dominant environmental pattern and varying amounts of precipitation (Zhang et al, 2013).…”

Palaeo-environmental evolution of Central Asia during the Cenozoic: New insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)

“…An influence of the height and extension of the Tibetan Plateau or the retreat of the Paratethys on the hydroclimate in Central Asia at this time (An et al, 2001;Zhang et al, 2007) is barely documented in the sedimentary record of the Valley of Lakes, but cannot be excluded, which would express in monsoon-dominant environmental pattern and varying amounts of precipitation (Zhongshi et al, 2007). (Hendrix et al, 1994;Macaulay et al, 2016;Hellwig et al, 2017;Wang et al, 2020). The resultant effects on the fractionation of δ 18 O and δ 13 C isotopes in soil carbonates are detailed in Caves Rugenstein and Chamberlain ( 2018), but are directly related to the development and the establishment of the Altai rain shadow front.…”

“…towards lighter δ 13 C and δ O values and drier conditions favor an excursion towards heavier δ 13 C and δ 18 O values (Richoz et al, 2017). Hence, variations in chemical weathering indicators (CIA, PIA and CIW) and in the δ 13 C and δ 18 O profiles of soil carbonates across a sedimentary succession can be used to trace and assess fluctuations in the climatic conditions that prevailed in the source areas and in the sedimentary basin at the time of sediment deposition, and during pedogenesis (Nesbitt and Young, 1982;Bahlburg and Dobrzinski, 2011;Fischer-Femal and Bowen, 2020;Kelson et al, 2020;Zamanian et al, 2021). The formation of soil carbonates is a highly complex process that can complicate the interpretation of their δ 13 C and δ 18 O isotopic values (Richoz et al, 2017), as global climatic trends may be overprinted by regional factors, such as contamination with detrital carbonates, dolomitization, meteoric diagenesis, maturation or oxidation of organic matter, dis-equilibrium conditions between atmospheric (or biogenic) CO2 and soil solution, evaporation, basalt hydrothermalism, etc.…”