Oxic and post-oxic chemical changes related to eogenesis and mesogenesis in a Miocene paleolake
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ORIGINAL PAPER
Oxic and post-oxic chemical changes related to eogenesis and mesogenesis in a Miocene paleolake Christophe Renac . Aure´lie Barats . Andre´ Mexias . Je´roˆme Barriere . Martina Rozmaric . Marie-Christine Gerbe
Received: 16 February 2019 / Accepted: 19 May 2020 Ó Springer Nature B.V. 2020
Abstract In the Forez Basin of the French Massif Central, clay-rich alluvial deposits include a series of red- and green-colored sediments and carbonate cement that record evaporation and oxidizing/reducing conditions related to intra-continental climate during the Early to Middle Miocene. The mineralogy, chemistry and relative chronology of authigenic calcite-ankerite, ferroan dolomite, pyrite, and analcite-clinoptilolite in clay-rich sediment enabled reconstruction of a series of processes related to deposition, eogenesis, and mesogenesis. The low-Mg calcite, ankerite, and ferroan-dolomite cement, systematically associated with zeolites (analcite and clinoptilolite),
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10933-020-00131-3) contains supplementary material, which is available to authorized users. C. Renac (&) A. Barats Universite´ Coˆte d’Azur, CNRS, Observatoire de la Coˆte D’Azur, IRD, Ge´oazur UMR 7329, Sophia Antipolis, 250 rue Albert Einstein, 06560 Valbonne, France e-mail: [email protected] A. Mexias Instituto de Geocieˆncias, Universidade Federal do Rio Grande do Sul, Av. Bento Gonc¸alves 9500 Campus Do Vale, Porto Alegre, RS, Brazil
represent eogenetic precipitation associated with oxic to post-oxic water with Ca–Fe–Mg carbonic, then Na– Al–Si(OH)4-rich water. Occurrence of framboidal and cubic pyrites with low-Mg calcite and analcite is related to post-oxic conditions associated with deposition, eogenesis and times of early mesogenesis. Changes in the morphology, size, and chemistry of framboidal and cubic pyrite grains were related to reducing-oxidizing cycles and to the growth of grains. Sulfur isotope measures on framboidal and cubic pyrite suggest that both morphologies are related to bacterial reduction of SO42- to H2S and HS-1. With the exception of some sample depths (0–40 m below surface), similar chemical contents (trace elements [TE], rare earth elements [REE] and platinoids) suggest a similar, constant reservoir of metal and metalloids associated with the clayey sediment and M. Rozmaric IAEA Environment Laboratories, 4a Quai Antoine 1er, 98000 Monaco, Principality of Monaco M.-C. Gerbe Universite´ de n, UJM-Saint-Etienne, CNRS Laboratoire Magmas Et Volcans, UMR 6524, 42023 Saint-Etienne, France
J. Barriere HYDRO INVEST 514 Route D’Agris, 16430 Champniers, France
123
J Paleolimnol
volcanic fragments. Moreover, the TE and REE chemistry of cubic pyrite, in contrast to carbonates, indicates growth of pyrite during eogenesis to mesogenesis stages. The mineralogical and chemical changes are interpreted as reflecting dissolution of iron oxyhydroxides, rather than ankerite and ferroa
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