FN Archimer Export Format
PT J
TI Rare earth element and neodymium isotope tracing of sedimentary rock weathering
BT 
AF Bayon, Germain
   Lambert, Thibault
   Vigier, Nathalie
   De Deckker, Patrick
   Freslon, Nicolas
   Jang, Kwangchul
   Larkin, Christina S.
   Piotrowski, Alexander M.
   Tachikawa, Kazuyo
   Thollon, Maude
   Tipper, Edward T.
AS 1:1;2:2;3:3;4:4;5:1,5;6:6;7:7;8:7;9:8;10:1;11:7;
FF 1:PDG-REM-GM-LGS;2:;3:;4:;5:PDG-REM-GM-LCG;6:;7:;8:;9:;10:PDG-REM-GM-LGS;11:;
C1 IFREMER, Marine Geosciences Unit, Brest, France
   Institute of Earth Surface Dynamics, University of Lausanne, Switzerland
   Laboratoire Océanographique de Villefranche sur Mer (LOV, OOV), CNRS, UPMC University of Paris VI, Villefranche-sur-Mer, France
   Research School of Earth Sciences, The Australian National University, Canberra, Australia
   Université de Bourgogne, UMR CNRS 6282 Biogéosciences, Dijon, France
   Division of Polar Paleoenvironment, Korea Polar Research Institute, Incheon, South Korea
   Department of Earth Sciences, University of Cambridge, UK
   Aix Marseille University, CNRS, IRD, INRAE, Collège de France, CEREGE, Aix-en-Provence, France
C2 IFREMER, FRANCE
   UNIV LAUSANNE, SWITZERLAND
   UNIV PARIS 06, FRANCE
   UNIV AUSTRALIAN NATL, AUSTRALIA
   UNIV BOURGOGNE, FRANCE
   KOPRI, SOUTH KOREA
   UNIV CAMBRIDGE, UK
   UNIV AIX MARSEILLE, FRANCE
SI BREST
SE PDG-REM-GM-LGS
   PDG-REM-GM-LCG
IN WOS Ifremer UPR
   copubli-france
   copubli-europe
   copubli-univ-france
   copubli-int-hors-europe
IF 4.015
TC 17
UR https://archimer.ifremer.fr/doc/00641/75351/76084.pdf
LA English
DT Article
DE ;World rivers;Iron oxides;Neodymium isotopes;Mid-REE enrichment;Concavity index;Silicate weathering;Carbonate weathering;Sulphide weathering
AB Chemical weathering plays an important role in sequestering atmospheric CO2, but its potential influence on global climate over geological timescales remains debated. To some extent, this uncertainty arises from the difficulty in separating the respective contribution of sedimentary and crystalline silicate rocks to past weathering rates in the geological record; two types of rocks having presumably different impact on the long-term carbon cycle. In this study, we investigate the use of rare earth element (REE) and neodymium isotopes (εNd) in leached iron oxide fractions of river sediments for tracing the origin of weathered rocks on continents. A new index, called ‘concavity index’ (CI), is defined for measuring the degree of mid-REE enrichment in geological samples, which enables the determination of the source of iron oxides in sediments, such as seawater-derived Fe-oxyhydroxide phases, ancient marine Fe oxides derived from the erosion of sedimentary rocks, and recent secondary oxides formed in soils via alteration of crystalline silicate rocks or pyrite oxidation. Using this index, we demonstrate that the εNd difference between paired Fe-oxide and detrital fractions in river sediments (defined here as ∆εNd Feox-Det) directly reflects the relative contribution of sedimentary versus crystalline silicate rocks during weathering. While rivers draining old cratons and volcanic provinces display near-zero ∆εNd Feox-Det values indicative of dominant silicate weathering (0.5 ± 1.1; n = 30), multi-lithological catchments hosting sedimentary formations yield systematically higher values (2.7 ± 1.2; n = 44), showing that sedimentary rock weathering can be traced by the occurrence of riverine Fe oxides having more radiogenic Nd isotope signatures compared to detrital fractions. This assumption is reinforced by the evidence that calculated ∆εNd Feox-Det values agree well with previous estimates for carbonate and silicate weathering rates in large river basins. Examining the influence of climate and tectonics on measured Nd isotopic compositions, we find that ∆εNd Feox-Det is strongly dependent on temperature in lowlands, following an Arrhenius-like relationship that reflects enhanced alteration of silicate rocks and formation of secondary Fe oxides in warmer climates. In contrast, in high-elevation catchments, ∆εNd Feox-Det defines striking correlation with maximum basin elevation, which we also interpret as reflecting the intensification of silicate weathering and associated Fe oxide formation as elevation decreases, due to the combined effects of thicker soils and warmer temperature. Overall, our new findings are consistent with previous assertions that the alteration of sedimentary rocks prevails in high-elevation environments, while silicate weathering dominates in floodplains. This novel approach combining REE and Nd isotopes opens new perspectives for disentangling the weathering signals of sedimentary and crystalline silicate rocks in the geologic record, which could be used in future studies to reassess the causal relationships between mountain uplift, erosion and climate throughout Earth's history 
PY 2020
PD OCT
SO Chemical Geology
SN 0009-2541
PU Elsevier BV
VL 553
UT 000575085100007
DI 10.1016/j.chemgeo.2020.119794
ID 75351
ER

EF