A Deep Alteration and Oxidation Profile in a Shallow Clay Aquitard: Example of the Tégulines Clay, East Paris Basin, France

Figure 3

(a) Proportions of the major clay minerals reported in a triangular kaolinite (illite-smectite) mixed layers (noted IS) illite/micas/glauconite. (b) Glauconite content estimated as a function of depth. (c) Chlorite-smectite and biotite flakes (AUB1010-6.63 m) (transmitted light). (d) Chlorite flake with numerous iron hydroxides between the sheets (AUB1010-4.80 m) (BSE image). (e) Electron microprobe analyses of clay minerals of the <2 μm fraction that are reported in a 4Si-M⁺-R²⁺ diagram modified from Meunier and Velde [19]. Gray lines indicate the fields of compositions of chlorite, low- (0.33) to high-charge (0.66) beidellites, and of low- (0.33) to high-charge (0.66) montmorillonites. (f) Well-preserved green and brownish oxidized rounded aggregates of glauconite (noted Gl) in sample AUB1010-16.1 m (transmitted light). (g) Electron microprobe analyses of glauconite at different depths of the AUB1010 borehole reported in the M⁺·(Si/4)⁻¹ versus cations diagram indicating compositional domains of glauconite-smectite and illite-smectite according to [20, 21].

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