Figure 5.

Subfossil microstromatolite from the quasi-marine Satonda Crater Lake (Central Indonesia) interpreted as the product of a multilayered coccoid cyanobacterial mat analogous to the studied artificial cyanobacterial mat. (a) Optical micrograph of vertical petrographic thin section of the Satonda stromatolite showing well-expressed alternation of micritic and sparitic layers. (b) Magnification of a series of alternating micrite and sparite layers with indicated stable carbon isotope (δ¹³C vs. PDB) signatures. (c) and (d) SEM images of vertical sections of polished and with 5% formic acid etched micritic (c) and sparitic (d) layers; note the well-preserved, due to in vivo mineralization, pattern of the common mucilage sheaths (glycocalyx) in the micritic layer, and the almost totally degraded remains of mucilage sheaths in the sparitic layer. Scale bars: (a) 500 μm, (b) 200 μm, (c) 2 μm, (d) 5 μm.