Fe-rich microspheres pseudomorphs after pyrite framboids in Holocene fluvial deposits from NE Spain: Relationship with environmental conditions and bacterial activity

Mayayo, M.J. (Universidad de Zaragoza) ; Yuste, A. (Universidad de Zaragoza) ; Luzón, A. (Universidad de Zaragoza) ; Corzo, A. ; Muñoz, A. (Universidad de Zaragoza) ; Pérez, A. (Universidad de Zaragoza) ; Soriano, A. (Universidad de Zaragoza)

Resumen: Three iron oxides-rich microsphere types (Type I to III) were detected in an Holocene 17 m-thick stratigraphic succession located in the Iberian Range (NE Spain). Lithofacies features indicate that the studied materials were generated in an alluvial-dominated setting, with a channeled area fringed by floodplain zones. During high water levels and high-energy floods, gravels and sands deposited in the active area and in lateral overbank areas. In these lateral areas, mud settling took place when flood decreased and then anoxic conditions could be reached due to microbial oxidation of organic matter and the low permeability of the marly sediment. X-ray diffraction (XRD) analysis of 32 samples and microtextural observation of 10 samples by Field Emission Scanning Electron Microscopy (FESEM) revealed the occurrence of Fe oxi-hydroxides microspheres showing different surficial structure. These microspheres are pseudomorphs after pyrite framboids although the formation of some primary Fe oxy-hydroxides aggregates cannot be rejected. Pyrite framboids genesis in sediments underlying oxic-dysoxic water column would have been favored by anoxic conditions reached in lateral overbank areas after main flooding, involving the activity of Fe reducing bacteria and sulfate-reducing bacteria (SRB), given the high SO 4 = availability provided by the highly mineralized groundwater from the upstream Baños de Ariño spring. Subsequent change to oxic conditions during the exposition of the floodplain enhanced the transformation of pyrite into Fe oxy-hydroxides, as well as in microenvironments around cracks and roots. Pyrite oxidation likely took place with the implication of neutrophilic iron oxidizing Bacteria and Archaea living in microaerophilic conditions, as well as cyanobacteria, given the close association of Fe oxides framboids with microbial features. In addition, pyrite and/or Fe oxi-hydroxides framboids from marl levels could have been incorporated to sand sediments during further overbank flooding episodes. Under these new oxic conditions pyrite oxidation would have been favored and even the formation of primary Fe oxy-hydroxides.

Idioma: Inglés

DOI: 10.1016/j.sedgeo.2019.04.003

Año: 2019

Publicado en: Sedimentary Geology 386 (2019), 103-117
ISSN: 0037-0738

Factor impacto JCR: 2.728 (2019)

Categ. JCR: GEOLOGY rank: 8 / 47 = 0.17 (2019) - Q1 - T1

Factor impacto SCIMAGO: 1.468 - Stratigraphy (Q1) - Geology (Q1)

Financiación: info:eu-repo/grantAgreement/ES/UZ/UZ2014-CIE-04
Financiación: info:eu-repo/grantAgreement/ES/UZ/UZ2015-CIE-08

Tipo y forma: Article (PostPrint)

Área (Departamento): Área Geodinámica Externa (Dpto. Ciencias de la Tierra)
Área (Departamento): Área Estratigrafía (Dpto. Ciencias de la Tierra)
Área (Departamento): Área Cristalografía Mineralog. (Dpto. Ciencias de la Tierra)