Fig. 4

Pleistocene stromatolite (specimen LBA-9a). a Polished section of a portion of the specimen, with laminae identification beside the sampled points (A and B refer to the types of laminae described in the text); b Composite photomicrograph in optical microscope showing the two types of laminae. Note: in type B laminae the presence of bush-shaped filament arrangement, and the gradual passage from 14B to 14A, and the sharp contact at the top of the type A laminae. At the base of 15B, an erosional surface is arrowed; c Detail of a bush-shaped body consisting of calcite filamentous bodies, likely from cyanobacteria