02868naa a2200361 a 450000100080000000500110000800800410001902200140006002400540007410000160012824501650014426000090030952017910031865000130210965000150212265000160213765000190215365000190217265000150219165000230220665000190222965000160224865300220226465300250228665300250231165300290233670000160236570000160238170000170239770000170241470000190243177300560245021756412025-05-15       2025    bl uuuu     u00u1 u    #d  a1040-61827 ahttps://doi.org/10.1016/j.quaint.2025.1097792DOI1 aRAMALHO, B.  aA novel sequential chemical extractions protocol to access mineral phases stabilizing organic matter in Amazonian Dark Earths (Holocene).h[electronic resource]  c2025  aThe association of organic matter with pedogenic minerals plays a crucial role in the stabilization of soil organic matter (SOM). To evaluate the contribution of different mineral phases to mineral-organic associations, the clay fractions of both small (&lt500 μm) and large (&gt500 μm) soil aggregates from Amazonian Dark Earths (ADEs) and reference soils (Ref) across five sites in the Brazilian Amazon were subjected to of sequential chemical extraction: hydroxylamine (HL), sodium dithionite (DT), sodium pyrophosphate (PYR), and NaOH. The extraction residues were analyzed by X-ray diffraction, thermogravimetry, and dry combustion for carbon (C) concentration. On average, PYR extracted 58 % of the C in both ADE and Ref soils, indicating that this extracted C predominantly corresponds to fractions associated with individual or poorly polymerized Fe and Al octahedral groups. The sequential extraction protocol, incorporating dithionite before PYR, facilitated an enhanced separation of mineral-organic association compartments. Among the minerals analyzed, kaolinite and hematite of low crystallinity were found to be more significant in mineral-organic associations compared to their high crystalline counterparts. Despite the presence of abundant small crystal-sizeof goethite in the samples, hematite was more effective in organo-mineral interactions. In the Amazonian environment, mineral-organic associations in the clay fraction occur indistinctly in ADE and adjacent Refs soils lacking an anthropic A horizon. These specific organic-mineral associations are likely responsible for the reduced decomposition rates and the sustained high levels of SOM in ADEs for over thousands of years since their anthropic formation (Holocene), even under the humid tropical climate.  aAmazonia  aExtraction  aIron oxides  aOrganic matter  aPyrophosphates  aExtração  aMatéria Orgânica  aOxido de Ferro  aPirofosfato  aDithionite method  aHorizonte antrópico  aMétodo de ditionito  aTerra preta da Amazônia1 aMELO, V. F.1 aDIECKOW, J.1 aBROWN, G. G.1 aSIMON, P. L.1 aCORRÊA, R. S.  tQuaternary Internationalgv. 730-731, 109779, 2025.