Shi et al.—Silicified Paleoproterozoic microbiota from China
small fusiform microfossil Leioarachnitum sp. (Fig. 11.1–11.5), which is abundant in the Dahongyu microbiota, is a unique microfossil in the Yanshan Basin. It occurs in the upper part of the Changcheng Group along with the carbonate-dominated strata and is distributed in several strata of the Jixian Group (Cao, 2005; Shi et al., 2014). It is worth mentioning that a well-preserved eukaryote-bearing microbiota reported from the 1500 Ma Kotuikan Formation in Siberia is not comparable with the Roper Group and the Ruyang Group. Based on these dif- ferences, it is obvious that large regional disparities of micro- biotas existed between continents. These could be caused by regional disparity of depositional environment, habitat, or other conditions. Causal factors behind these disparities need further study.
Conclusions
The new Dahongyu microbiota is dominated by cyanobacteria filaments and coccoids, including endobenthic, epibenthic, and allochthonous forms, which illustrated well a vertical distribu- tional profile of an intertidal microbiota from the transitional Paleoproterozoic and Mesoproterozoic time. High content and large size of allochthonous forms are the
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According to the statistics of width, three morphological species from the Dahongyu Formation are present: O. obtusa (>3.0–8.0 μm in width), O. amadeus (>8.0–14.0 μm in width), and O. longa (>14.0–25.0 μm in width). In addition to this, some Oscillatoriopsis trichomes, which are more than 25 μmin width, are placed under O. princeps formally (>25–50 μm).
Oscillatoriopsis princeps Zhang and Yan, 1984, emend. Shi and Feng, herein Figure 3.5, 3.6
1984 Oscillatoriopsis princeps Zhang and Yan, p. 198, pl. 1, fig. 6.
Holotype.—Specimen illustrated by Zhang and Yan (1984, pl. 1, fig. 6.).
Description.—Multicellular, unbranched trichome without sheath. Trichomes are 25–35.8μm in diameter (mean = 29.5μm; N = 30). Single cells are 5.1–10.5μm in length and their ratio of length to width is 0.2–0.3. Septa are not constricted.
defining characteristics that make the Dahongyu microbiota extraordinarily different from other microbial mat biotas recovered from cherts of this contemporary time. Most micro- fossils of the new Dahongyu microbiota are smooth-surfaced and morphologically simple, yet a few possess ornaments or odd morphologies that suggest their potential eukaryotic nature. During deposition of the Dahongyu Formation, significant
regional disparity of microbiotas existed within the Yanshan Basin. The newly studied Dahongyu microbiota has certain distinctions, but is mostly similar to the microbiota from the underlying Changcheng Group. Absence of typical eukaryotes from the coeval time and the presence of unique elements (especially small fusiform microfossils) make the Dahongyu microbiota and subsequent microbiotas in the Jixian Group distinct from coeval eukaryote-bearing microbiotas.
Systematic paleontology
Kingdom Eubacteria Woese and Fox, 1977 Phylum Cyanobacteria Stanier et al., 1978 Class Hormogoneae Thuret, 1875 Order Oscillatoriales Elenkin, 1949
Family Oscillatoriaceae (Gray) Kirchner, 1900
Genus Oscillatoriopsis Schopf, 1968, emend. Mendelson and Schopf, 1982, emend. Butterfield et al., 1994
Type species.—Oscillatoriopsis obtusa Schopf, 1968.
Remarks.—More than 100 “species” of Oscillatoriopsis have been reported, but it is problematic to distinguish or compare them. Having undergone several amendments, width was chosen as the species-level principal criterion (Butterfield et al., 1994). Although morphological species based on width have limited information regarding their biological nature, it is effi- cient to distinguish Oscillatoriopsis species using this diagnosis.
Remarks.—Oscillatoriopsis princeps was first named for its extremely large diameter (19–37.5 μm in diameter) (Zhang and Yan, 1984). It used to be assigned to O. longa (Butterfield et al., 1994). Considering that the holotype of O. princeps is 37.5 μm in diameter, here it is formally emended in the range of 25–50 μm in diameter and all large Oscillatoriopsis filaments from the Dahongyu Formation (25–35.8 μm in diameter) were assigned into O. princeps.
Class Coccogoneae Thuret, 1875
Order Chroococcales Wettstein, 1924 Family Chroococcaceae Nägeli, 1849
Genus Gloeodiniopsis Schopf, 1968, emend. Knoll and Golubic, 1979
Type species.—Gloeodiniopsis lamellosa Schopf, 1968, Bitter Spring Formation, Australia.
Gloeodiniopsis sp. indet. Figure 8.1–8.12
Description.—Colonially preserved spherical microfossils with thin, transparent, smooth-surfaced flexible wall. Single cells are 19–68 μm in diameter (N = 100). Cell walls are occasionally multi-layered. Figure 8.3 displays their reproduction procedure of straight splitting. Envelope containing two cells (Fig. 8.4, 8.5) and broken envelope with a small cell (Fig. 8.6) shows the subsequent procedures of splitting, during which the daughter cells slipped out of the common envelope. Tens to hundreds of cells are loosely distributed into colonies.
Discussion.—These microfossils differ from Leptoteichos golubicii and Myxococcoides grandis because some have multi- layered walls. They differ from G. lamellosa because their outer sheaths are thin and ghost-like.
Incertae sedis Genus Clonophycus Oehler,1977, emend. Oehler,1978
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