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Schopf et al.—Berkuta and Chulaktau microbiotas


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Figure 3. Quartz- and apatite-permineralized organic-walled microfossils from the Chulaktau Formation shown in optical photomicrographs (1, 6, 11, 16, 21); confocal laser scanning micrographs (2, 7, 12, 17); two-dimensional Raman images documenting the spatial distribution of kerogen (3, 8, 13, 18, 22; blue, acquired at its ~1605cm−1 major Raman band); and apatite (4, 9, 14, 19, 23; red, acquired at its ~965cm−1 major Raman band); and two-dimensional spectroscopic fluorescence images showing the spatial distribution of fossil-permineralizing apatite (5, 10, 15, 20; orange, acquired in the spectral range centered at ~603nm that includes its major fluorescence bands)—fluorescent because of the presence of Sm+3 replacing both Ca I and Ca II sites—and of later-emplaced fossil-encrusting apatite in which Sm+3-replaced Ca I sites (24; orange, acquired at ~597 nm) and Ca II sites (24; green, acquired at ~605 nm) are spatially distinct. The red rectangle in (1) denotes the part of the specimen shown in (3–5); that in (6), in (8–10); that in (11), in (13–15); and that (21), in (22–24); (16) shows the same area as that in (17–20); the arrows in (16) and (17) indicate sites of apatite nucleation. (1-5) Obruchevella parva Reitlinger, 1959, 4681-391 (102) specimen location point (p.) 11, England Finder Slide (EFS) G32[1], GINPC 202. (6–10) O. cf. meishucunensis Song, 1984, 4681-391 (102), p. 17, EFS K41[4], GINPC 197. (11–20) Tetraphycus acutus Sergeev, 1989: (11-15) 4681-391 (102), p. 29, EFS R29[0], GINPC 210; (16–20) 4681-399 (103), p. 26b, EFS P31[0], GINPC 1269. (21–24) Siphonophycus solidum Golub, 1979, 4681-1026 (273), p. 81, EFS W23[1], GINPC 1270.


cyanobacterium Tetraphycus acutus (Fig. 3.14 and 3.19) in which sites of apatite-nucleation are discernible both in optical (Fig. 3.16) and CLSM images (Fig. 3.17). Raman spectra (Fig. 5.1) document the kerogenous


composition of the cell walls and associated organic matter of the Berkuta and Chulaktau fossils. Analyses of these spectra to determine their Raman Index of Preservation (RIP) value—an easily calculated metric that ranges from 1 to 10 used to compare the molecular-structural composition and fidelity of preserva- tion of kerogenous permineralized fossils in permineralized


fossil assemblages (Schopf et al., 2005)—shows them to have an RIP of ~7.5. This value indicates that the kerogen comprising the Berkuta and Chulaktau fossils is appreciably less geochemi- cally altered (“better preserved”) than that of the carbonaceous components of numerous Proterozoic and Archean microbiotas but is more altered than that of the especially well-preserved ~800-Ma-old Bitter Springs Formation (RIP = 9.0), the ~1900-Ma Gunflint Formation (RIP = 8.8), and the ~750-Ma- old Berkuta- and Chulaktau-underlying Chichkan Formation (RIP = 8.6; Schopf et al., 2005, 2010a).


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