Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena Radiocarbon age discrepancies between the carbonate cement and the root relicsofrhizolithsfromtheBadainJaranandtheTengerideserts,Northwest China Qingfeng Sun a, ⁎ , Hong Wang b,c , Kazem Zamanian d a Department of Geography, Northwest Normal University, Lanzhou, Gansu 730070, PR China b Interdisciplinary Research Center of Earth Science Frontier, Beijing Normal University, Beijing 100875, PR China c Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA d Department of Soil Science of Temperate Ecosystems, Georg August University of Goettingen, Buesgenweg 2, 37077 Goettingen, Germany ARTICLEINFO Keywords: Rhizoliths 14 C dating Age discrepancies Carbonate cement Root relics Dune soil ABSTRACT Carbonaterhizolithisoneofmineralencrustationsofplantroots.Theradiocarbon( 14 C)datesandstablecarbon isotopesofrhizolithsarewidelyusedtostudygeochronology,paleoclimate,paleoecologyandpaleoenvironment changes. However, due to a few available comparisons of 14 C dates of the carbonate cement and the plant root relics within the same rhizoliths, the carbon sources that form rhizolith cements are largely unknown. Here, we present accelerator mass spectrometry (AMS) 14 Cdatesofcarbonatecementandtheplantrootrelicswithinthe same rhizoliths from dune surface soils in the Badain Jaran and the Tengeri deserts, Northwestern China. The modern dead plant roots and bulk soil carbonates nearby were also dated. It is found that the root relics range from 1825 CE to 1983, while the carbonate cements of the rhizoliths have ages from ~6,900 to ~4,700 cali- brated years before present (calBP). The ages of the bulk soil carbonates vary from 18,700 to 35,300 and 39,300calBP,revealingcomplicatedsoilcarbonatematrix.Theresultssuggestedthatthecarbonsourcesforthe carbonate cements of the rhizoliths were derived mainly from ancient soil carbonates with a small contribution from dead plant roots and a minor contribution from lithogenic carbonates. Mass balance of stable carbon isotopeswasusedtocalculatetheproportionalcontributionofthecarbonfromancientsoilcarbonatesandplant roots relics. After subtracting the modern carbon contribution from the decomposed plant roots in fraction of modern carbon (F 14 C), the mass balance estimated that the ancient soil carbonates were formed within 7,750–5,000calBP, about 850–300years older than obtained rhizolith cement ages. It is proposed that dead roots decay triggered the rhizoliths formation by releasing CO 2 to form acid media with free HCO 3 1− /CO 3 2– ions,whichcauseddissolutionoftheoldsoilandlithogeniccarbonatesinsoilmatrix.Carbonaterecrystallization took place to form rhizoliths tubes around the dead roots. Detailed age discrepancies between rhizolith cements and dead root relics provide new insight for better understanding the dynamics of the rhizolith formation and associated implications for paleoenvironment reconstructions. 1. Introduction Rhizoliths,knownascarbonateroottubes,arecylindricalortubular forms of secondary calcium carbonate that encrusts plant roots, and belong to the soil (pedogenic) carbonates (e.g. Wang et al., 2004a; Monger et al., 2015; Zhao et al., 2016; Zamanian et al., 2016a; Golubtsov et al., 2019). Rhizoliths occur commonly in arid and semi- aridregionsindunefelds,lakesandlittoralphaseofwatershed,aswell as loess deposits. Rhizoliths have been widely used to study landscape evolution and paleo-habitat in response to the changing climate (e.g. Kosir, 2004; Wang et al., 2004a; Gocke et al., 2010a, 2010b, 2011, 2014; Li et al., 2015a, 2015b) and for geochronology and stratigraphic studies by applying 14 C dating on their carbonate cements (Chen et al., 2004; Joseph and Thrivikramaji, 2005; Cramer and Hawkins, 2009; Gockeetal.,2011; Lietal.,2015a,2015b).However,carbonatecement and root relics in the same rhizolith - except one case in a loess record (Gocke et al., 2011) - have not been dated simultaneously. Due to lack of well-preserved root fabric relics, the dynamics of the rhizolith for- mation and consequently implications of their 14 C dates remain poorly understood. https://doi.org/10.1016/j.catena.2019.04.011 Received 20 July 2018; Received in revised form 26 March 2019; Accepted 9 April 2019 ⁎ Corresponding author. E-mail address: sqf@nwnu.edu.cn (Q. Sun). Catena 180 (2019) 263–270 0341-8162/ © 2019 Elsevier B.V. All rights reserved. T