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A formal transfer of the fossil to a new genus of fossil …
Biology Articles » Paleobiology » Micropaleobiology » Decastronema kotori gen. nov., comb. nov.: a mat-forming cyanobacterium on Cretaceous carbonate platforms » Figures
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Figure 1: Area of study, the frame of the map sheet Orahovac and the outlines of the countries superimposed on NASA World Wind satellite image.
Figure 2: A simplified presentation of the geological setting of the Decastronema sampling site above the bauxite palaeokarst horizon of the Metohia, Mirdita zone, internal Dinarides. 1. Karstified Lower Cenomanian limestone: Pseudorhapydionina dubia (De Castro), Rotalia mesogeensis Tronchetti, Nummoloculina sp. and other miliolids; 2. Three types of Santonian or Lowermost Campanian limestones were recognized: a) limestone with numerous Fe ooids and Rotorbinella scarsellai Torre, discorbids, and rare Clypeina dusanbrstinai Radoičić; b) limestone with dispersed fertile ampullae of Neomeris and c) Limestone with foraminifera Accordiella conica Farinacci, Pseudocyclammina sphaeroidea Gendrot, Dicyclina and Nezzazatinella sp.; red - bauxite; black - lentiform level, in the lower part with layers of densely packed and well sorted fragments of Decastronema kotori.
Figure 3: Petrographic thin section of Decastronema kotori (De Castro) combinatio nova: (A) A filament in longitudinal section; note the thinning and bending of diverging outer layers of the wall; (B) Fragmented filaments of varied orientation in transverse and oblique sections; note the conspicuously clear lumina; (C-E) Filaments in nearly longitudinal section, becoming tangential at the lower end where the filaments curve out of the plane of the section; (F) Filament with "terminal chamber", representing a combination of longitudinal and transversal section at the position of a false branch (modified from De Castro, 1975). Scale bar in C is 50 µm long for all pictures.
Figure 4: SEM images of Decastronema kotori on polished slightly etched rock surfaces: (A) View of a filament almost 1 mm long with upward diverging wall layers; (B-C) Oblique, transverse and longitudinal sections through filaments showing a concentric, upward divergent layering of the wall; the wall is comprised of micritic grains, whereas the lumen is filled with microsparite similar to that occupying pore spaces in the surrounding sediment; (D) Two fossil filaments etched from the matrix by prolonged application of acid. The wall appears spongy for it consists of a Fe-enriched non-crystalline material; (E-F) A similar etching of filaments in longitudinal and oblique sections; (G) Enlargement of a negative print of B, as negative, showing grain relationships in the micritically preserved sheath; (H) Detail of E, showing the spongy Fe-enriched texture of the wall; note the fine submicron-size porosity; (I) Detail of D: The upper filament, a nearly transverse section viewed from below, shows the core and two layers of the wall (comp. with Fig. 5B ). The scale bar in A is 50 µm long; the scale bar in F is 50 µm long valid for B-F; the scale bars in G-I are 10 µm long.
Figure 5: SEM of critical-point-dried specimens of Recent (modern) Scytonema sp. from the mats covering intertidal carbonate mud flats on the west coast of Andros Island, Bahamas. (A) Intact, upward curving filaments; the surface shows no appreciable carbonate precipitation. (B) View down a fractured filament of Scytonema showing the concentric arrangement of layered sheath enveloping a trichome cf. Fig. 4I . (C) Oblique view of another fractured filament with a still turgescent cell in the center of concentric sheath layers. Note the reticulate texture of the polysaccharide in the upper part of the picture. Scale bars are 10 µm long; the bar in C is valid for B.
Figure 10: Aerial view of tidal creeks on the NW coast of Andros Island, Bahamas, rimmed by Scytonema cover (reddish brown) around bright carbonate mud in shallow ponds.
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