FIG. 18.

Geochemistry of sedimentary fragments (see Fig. 17) in lagoonal deposits, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) Vertical section through a typical fragment in petrographic thin section. Boxed area enlarged in (B). (B) Higher magnification view of fragment with the area analyzed using Raman indicated by the box. (C) Raman maps showing the mineralogical composition of the fragment. The goethite map was produced using the ∼400 cm⁻¹ goethite Raman peak, the quartz map using the ∼465 cm⁻¹ Raman quartz peak, and the carbon map using the ∼1600 cm⁻¹ Raman carbon peak. (D) A typical Raman spectrum from a carbonaceous area within the fragment. This image shows background quartz (Q) and goethite (G) peaks, together with the ∼1350 and ∼1600 cm⁻¹ carbon peaks (C) that are characteristic of thermally mature but disordered organic carbon.