g, h Optical

images of two specimens of modern Oscillatoria sp. showing the rounded terminal cells (left), disk-shaped medial cells, and partial septations (arrows) characteristic see more of oscillatoriacean cyanobacteria. i Optical image of the fossil oscillatoriacean, Oscillatoriopsis media, descending into a thin section at a low angle from left to right, shown in a photomontage in which the red rectangles denote the areas of the trichome shown in CLSM images (j through n) and 3-D Raman images (o through q). j The trichome terminus, showing its rounded end-cell and subtending disk-shaped medial cells. k A part of the trichome situated ~14 μm deeper in the section than the trichome terminus (and ~28 μm below the upper surface of the section) that exhibits partial septations (arrows) like those shown in g and h. l–n A deeper part of the trichome (~39 μm below the upper surface of the section) that similarly exhibits partial

septations (arrows), in l and m showing the specimen as viewed from above its upper surface (the same perspective as shown in i, but in m with the trichome tilted slightly to the right to show its interior) and in n showing the trichome as viewed from its side. o–q 3-D Raman images (acquired in a spectral window centered in the kerogen “G” band at ~1605 cm−1) showing the kerogenous composition of the trichome and its partial septations: o, the part of specimen denoted by the red rectangle in l, as viewed from above the trichome; p, the part denoted in m, selleck products titled slightly to the left; q, the part denoted in n, showing the specimen from its side. r A low-magnification optical image of stromatolitic laminae formed by find more laterally interlinked colonies (at arrows) of the entophysalidacean Sirolimus mouse cyanobacterium Eoentophysalis The trichomes of the great majority of members of the Oscillatoriaceae are characterized by rounded terminal cells, disk-shaped medial cells, and partial septations, incipient cell walls that grow inward to produce daughter cells (Fig. 4g and h). Although

in fossil specimens such structures are not always evident by optical microscopy, CLSM and Raman imagery can establish their presence. For example, compare the photomicrographs of modern Oscillatoria sp. (Fig. 4g and h) with that of its fossil equivalent, Oscillatoriopsis media, shown in Fig. 4i in a thin section of chert from the ~775-Ma-old Chichkan Formation of southern Kazakhstan. Owing to the CLSM laser-induced fluorescence of the coaly kerogen (primarily, interlinked polycyclic aromatic hydrocarbons), which comprises the cell walls of the fossil, its detailed morphology is appreciably better defined in the CLSM images (Fig. 4j though n) than in the corresponding optical image (Fig. 4i), whereas 3-D Raman imagery documents the carbonaceous composition of its permineralized cells (Fig. 4o–q).