Alteration of fossil-bearing shale (Autun, France; Permian), part II: Monitoring artificial and natural ageing by combined use of S and Ca K-edge XANES analysis, Rock-Eval pyrolysis and FTIR analysis

Abstract

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Alterations of fossil-bearing shale (Autun, France; Permian), part III: Framboidal pyrite and sulfur as the main cause of efflorescence

“…As reported by others authors (Tuttle et al, 2014), these rust deposits occurred laterally, depending on the shale bedding plans. This is in-line with previous work (Odin et al, 2015a(Odin et al, , 2015b showing that (i) the shale was transversally poorly permeable to water and impermeable to air and (ii) sulfur was mostly present as organic and inorganic sulfide. Also black shale samples were selected for artificial ageing, as they were believed to have been relatively spared from weathering.…”

“…In order to reproduce damage in laboratory conditions, it was chosen to sample new shale material in the outcrop of Muse (Dracy Saint Loup, Saône-et-Loire, France) that comprises several layers, the most famous of which being commonly called the "Muse fish layer" and hereafter referred to as Muse FL. The motivation of this choice are fully explained elsewhere (Odin et al, 2015b). This layer (Late Carboniferous -Lower Permian of the Autun Basin) is located at the base of the bedding of Muse above a pebble layer (sandstones of Lally).…”

“…The shale fraction of this specimen was analyzed (Odin et al, 2015a(Odin et al, , 2015b, showing that matrix-sulfur is almost entirely oxidized as sulfate (gypsum and belonging to jarosite group). In contrast, vitrinite is not much affected by oxidation.…”

“…This work is organized in three parts. The first two are dedicated to the characterization of sulfur-and iron-bearing compounds present in the shale matrix (Odin et al, 2015a(Odin et al, , 2015b and led to the conclusion that these compounds could not account for the large efflorescence noticed nearby the fossil line.…”

Alteration of fossil-bearing shale (Autun Basin, France; Permian), part I: Characterizing iron speciation and its vulnerability to weathering by combined use of Mössbauer spectroscopy, X-ray diffraction, porosimetry and permeability measurements

“…On the contrary, the presence of sulfates in Muse, Muse FL, and Surmoulin shale samples appears relatively unlikely for two reasons: firstly, these samples were kept apart from oxygen between their collection and their analysis; secondly S K-Edge XANES analysis (Odin et al, 2015) performed on similar samples confirmed that sulfur speciation was almost exclusively corresponding to sulfides.…”