Origin and paleoenvironmental significance of Fe-Mn nodules in the Holocene perialpine sediments of Geneva Basin, western Switzerland

Article Article scientifique Article Origin and paleoenvironmental significance of Fe-Mn nodules in the Holocene perialpine sediments of Geneva Basin, western Switzerland eng 2018 author Segvic Branimir 812937 author Girardclos Stéphanie 40596 author Zanoni Giovanni 726565 author Arbiol Carlos 805898 author Steimer Tara 0000-0002-8665-7278 811497 author Besse Marie 0000-0002-4752-9070 28306 22-39 10.1016/j.clay.2018.01.027 0169-1317 http://linkinghub.elsevier.com/retrieve/pii/S0169131718300334 Perialpine areas of central Europe have undergone significant changes following the last Alpine glaciation and especially through the Holocene time. This study relies on geochronological, mineralogical and geochemical clues to explain the formation and paleoenvironmental significance of FeMn nodules reported from the young soils (~4.5 ka BCE) of Geneva Basin in western Switzerland. Having on average 2 mm in diameter, the nodules usually possess an onion-like and quasi-layered internal architecture defined by selective enrichments in Fe and Mn. Fe-rich mica is largely present in soil matrix and has served as a main source of Fe and Mn. Susceptible to favourable Eh-pH conditions several steps in mica weathering were recognised leading to the formation of nodules – vermiculitization, microcracking, FeMn segregation and re-precipitation. Mineral alterations were boosted by long periods of summer warm climate during Boreal and Atlantic times as suggested by the increasing illite-smectite content and a disappearance of hydroxyl-interlayered clays from analysed colluvium. Moreover, archaeological ages and radiocarbon dating of charcoal yielded coherent FeMn encrustation ages (4.8–4.3 ka BCE and 4.5–4.4 ka BCE, respectively) that coincide with the Holocene temperature maximum (~4 ka BCE) in Central Europe. Terrain morphology that led to better water retention formed earlier than ~8 ka BCE ago, during undefined Late Glacial time, promoting seasonal changes in redox conditions, thus facilitating the mobilization, distribution and re-precipitation of Fe and Mn. Established conditions lasted until Late Neolithic (3.4–2.2 ka BCE) when different agricultural practices changed favourable hydromorphic environment effectively putting an end to further nodule formation. FeMn nodules Clay minerals Surficial geology Mid-Holocene Paleoclimatology Alps Switzerland Geneva Soil Dewey 333.7-333.9 Dewey 550 18 Institut des sciences de l'environnement 0DB 41 Département F.-A. Forel des sciences de l'environnement et de l'eau 153 42 Département des sciences de la Terre 154 false 943 ISE Climat 944 ISE Eau 945 ISE Energie 938 ISE Pôle Sciences 946 ISE Villes et territoires 754 Laboratory of Prehistoric Archeology and Anthropology 753 Limnology and Environmental Geology 664 Limnology and Geomicrobiology Applied Clay Science 160 c95d6989-8393-4033-925b-74e21681dc10 Article (Published version) Public 1-s2.0-S0169131718300334-main.pdf 3440357 application/pdf CC BY-NC-ND openAccess Centres et instituts / Institut des sciences de l'environnement Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département F.-A. Forel des sciences de l'environnement et de l'eau Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre

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Origin and paleoenvironmental significance of Fe-Mn nodules in the Holocene perialpine sediments of Geneva Basin, western Switzerland	Applied Clay Science			2018	657	313

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Arbiol, Carlos