Plate 143

Microstructure of stromatolites

The two pictures illustrate the microscopical aspect of bacterial mats. The organic matter of the filaments is usually decomposed and does not fossilize. It may happen that the filaments are coated by a sheath of carbonate, which allows their preservation. With the addition of carbonatic or gypsum cement in the pores, the fabric, or microstructure of the mat can also be maintained. One can thus observe it in the most minute details either on a polished section (A: the bar is 1 mm long) or in a thin section (B). The difference between the two images derives from the fact that light is reflected and transmitted, respectively (the thin section is a slice of rock, so thin as to be transparent; the picture is a negative print). The microstructure of the mat resembles that of spaghetti, with some organic matter and iron sulfide in the "sauce."

Same formation and provenance as plate 142.

Photo: P. Ferrieri 1976.