Panel (A): a photomicrograph of the sampled thin section, CM in the form of biofilms and clots are distributed throughout a silica matrix. For more detailed description of layers (a)–(e), see text. The white rectangles indicate the locations of the areas shown in more detail in panels (D) through (K). Panel (B): Raman spectral map of the thin section highlighting the ubiquitous presence of silica (yellow/orange = area of the 465 cm⁻¹ quartz band). Panel (C): Raman spectral map of the thin section highlighting the CM (yellow/orange = area of the 1350 cm⁻¹ CM D1 band), showing the close association of CM with the pseudomorphed volcanic ash and dust. Panel (D): a close-up view of the stratigraphy of the sedimentary layers of the bottom part of the thin section. For a more detailed description of layers (a)–(e), see text. Panels (E) and (F): volcanic particles (clear, light gray appearance) coated with CM (black), occurring in the upper part of the thin section. (G) and (H): clots coated in CM, occurring in the upper part of the thin section. (I) and (J): finely laminated and wavy laminae of carbonaceous nature intermixed with trapped carbonaceous clots, occurring in the lower part of the thin section. Both laminae and clots may be of biogenic origin (see F. Westall et al. 2015a; K. Hickman-Lewis et al. 2020). (K) and (L): a photomicrograph and Raman spectral map of a carbonaceous clot from the lower part of the thin section, demonstrating the distribution of CM around a rectangular particle, probably a pseudomorphed plagioclase crystal.