Microbial fossils from the lower Yudoma Suite, earliest Phanerozoic, eastern Siberia
1980; Elsevier BV; Volume: 13; Issue: 2-3 Linguagem: Inglês
10.1016/0301-9268(80)90002-9
ISSN1872-7433
Autores Tópico(s)Hydrocarbon exploration and reservoir analysis
ResumoWell-preserved nannofossils are here described from black chert lenses in dolomitic and carbonaceous limestones of the lower Yudoma Suite from the Khanda (or Belaya) and Aldan Rivers in eastern Siberia. In this area, Yudoma rocks conformably underlie Lower Cambrian and unconformably overlie Upper Proterozoic strata. Radiometric ages based mainly on glauconite from weakly metamorphosed strata date the Yudoma as 675 ± 25 Ma to 570 ± 10 Ma ago. A K-Ar date for one of the localities here studied is 650 Ma. The Yudoma nannofossils are preserved in the chert as light amber to dark organic residues. The mode of preservation is similar to microbial assemblages in cherts from the older and now classic Gunflint and Bitter Springs formations. Sixteen categories of nannofossils are identified, including 12 species and 4 morphogroups of filamentous and coccoid microorganisms assigned to 11 genera. Of these, three genera and eight species are new. Six of 16 categories are identical to or closely comparable with forms in the roughly 850 Ma old Bitter Springs microbiota. Seven of the 16 categories are identical to or closely comparable with forms in the roughly, 1,900 Ma old Belcher Islands microbiota. Most of the elements of this well-preserved microbiota appear to be cyanophytic, with coccoid forms dominant over filamentous. One form, Micrhystridium, may be planktonic; the others are probably benthic. Age, stratigraphic relations, and microflora all are most consistent with an Ediacarian and Early Phanerozoic age (i.e., pre-Cambrian or sub-Cambrian, but not Precambrian in the sense of conventional usage).
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