Earth:Starorusskaya Formation

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Starorusskaya Formation
Stratigraphic range: late Ediacaran
~559–557 Ma[1]
↓
TypeFormation
Unit ofValdai Group
Sub-unitsLower, middle, and upper members
UnderliesVasilevskyostrov Formation
Overlies(Unconformably) Priozerskaya Formation
Thickness44–52 m (144–171 ft)
Lithology
PrimaryArgillite, Sandstone, Siltstone
OtherConglomerates, Clay
Location
CountryNorthwest Russia
Type section
Named forStaraya Russa
Named byGeisler
Year defined1967[2]

The Starorusskaya Formation, also known as the Staraya Russa Formation, is a fossiliferous Ediacaran geologic formation found on the northwestern side of the East European Platform in Northwestern Russia.

Geology

The Starorusskaya Formation is primarily composed of grayish green siltstones, and consists of three members, all of which are fossiliferous in nature. The formation unconformably overlies the quartz-sandstone of the Priozerskaya Formation.[3] The Starorusskaya Formation is overlain by the lower sandy layers of the Vasilevskyostrov Formation,[4]

Members

The three members are as follows, in ascending stratigraphic order (lowest to highest):

  • Lower Member: This member is characterised by clays with sandstone interbeds. There are also greenish-gray to blueish thin-bedded sandy and silty clays, which is replaced in the upper sections of the member by dense greenish-gray clays. There are also light gray quartz sandstones, ranging from fine-medium-grained to coarse-grained, and contain a mixture of gravels. It is up to 16.3 m thick, and contains the microfossils of the formation.[5]
  • Middle Member: This member is composed primarily of clays. This includes dark red clays with thin interbeds of light gray siltstones. Other areas contain gray, thin-bedded silty clays, containing interbeds of fine-gravel and sandstones. It is up to 22 m thick, and contains the least amount of fossils in the formation[5]
  • Upper Member: This member is composed of thin interbedded sandstones, siltstones and clays. The clays are predominately blueish to greenish-gray, which are finely laminated and leafy, containing dark red spots through-out. The sandstones and siltstones are greenish-gray also, with the sandstones being coarse-grained. It is up to 13.4 m thick, and contains the macrofossils of the formation.[5]

Dating

U-Pb dating had been performed on zircon crystals collected throughout the Starorusskaya Formation in 2017, although it was discovered that all yielded dates were older than 1.5 Ga, being dominated by crystals from the Paleoproterozoic and Mesoproterozoic, including some samples being Archean in age, whilst samples from the overlying Vasilevskyostrov Formation yielded dates expected for the region.[2] In 2019, the Starorusskaya Formation was dated based on sequence stratigraphy, with it corresponding to the Lyamsta Formation in the Southeastern White Sea area, as well as the Staropechny and Perevalok formations, which dates the Starorusskaya Formation to between 559 Ma and 557 Ma, some 9 to 7 million years older than the Kotlin Crisis.[1]

Paleoenvironment

From the information gathered from the lithology of the Starorusskaya Formation, its paleoenvironment was most likely a sloped environment either below the wave base or even storm wave base, and was within the photic zone, inferred from the presence of Doushantuophyton lineare, overall suggesting a prodelta environment where organisms could be buried in situ.[5]

Paleobiota

The Starorusskaya Formation contains a number of organisms from the Ediacaran, from a small collection of aritarchs such as Leiosphaeridia, classic Ediacaran algae such as Doushantuophyton, and some unique forms such as the rod-like Redkinia.[5][3]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

incertae sedis

Genus Species Notes Images
Orbisiana[3][5]
  • Orbisiana sp.
  • O. simplex
 Palaeopascichnid organism.
Redkinia[3]
  • R. spinosa
 Rod-like fossils, possible jaw fragments of stem-arthropods.
Cucullus[3]
  • Cucullus sp.
 Tubular organism.
Sinospongia[5]
  • S. typica
 Sponge-like fossil, may also be an algae similar to the Huainan biota.[6]

Flora

Genus Species Notes Images
Siphonophycus[3]
  • Siphonophycus sp.
 Filamentous cyanobacteria.
Oscillatoriopsis[5]
  • Oscillatoriopsis sp.
 Filamentous cyanobacteria.
Zinkovioides[5]
  • Zinkovioides sp.
 Filamentous cyanobacteria.
Obruchevella[5]
  • O. parva
 Filamentous cyanobacteria.
Doushantuophyton[3][5]
  • D. lineare
 Branching macroalgae.
Specimen from China
Morania[3]
  • M. zinkovi
 Filamentous cyanobacteria.
Specimen from Utah
Chuaria[3]
  • C. circularis
 Enigmatic fossil, possibly synonymous with Tawuia.
Specimen from China
Polytrichoides (?)[3]
  • Polytrichoides (?) sp.
 Filamentous algae.
Mezenia-like fragments[5]
  • Mezenia (?) sp.
 Ribbon-like fragments, which bare similarities to the macroalgae Mezenia.

Microorganisms

Genus Species Notes Images
Leiosphaeridia[3][5]
  • Leiosphaeridia sp.
  • L. jacutica
  • L. crassa
  • L. minutissima
  • L. tenuissima
 Acritarch.
Tynnia[5]
  • T. precambrica
 Acritarch.
Tuberculum[5]
  • T. mamillatum
 Acritarch.
Pterospermopsimorpha[5]
  • P. insolita
 Two-layed acritarch.
Ceratosphaeridium[4]
  • Ceratosphaeridium sp.
 Acritarch.
Ostiana[4]
  • Ostiana sp.
 Acritarch.
Ceratophyton (?)[4]
  • Ceratophyton (?) sp.
 Cone-shaped acritarch, material has been compared to similar looking structures seen in protoconodonts.[7]

Ichnogenera

Genus Species Notes Images
Chondrites[5]
  • Chondrites sp.
 Branching burrows.

See also


References

  1. ↑ 1.0 1.1 Maslov, A. V.; Grazhdankin, D. V.; Podkovyrov, V. N. (January 2019). "Late Vendian Kotlinian Crisis on the East European Platform: Lithogeochemical Indicators of Depositional Environment". Lithology and Mineral Resources 54 (1): 1–26. doi:10.1134/S0024490219010048. 
  2. ↑ 2.0 2.1 Podkovyrov, V. N.; Maslov, A. V.; Kuznetsov, A. B.; Ershova, V. B. (January 2017). "Lithostratigraphy and geochemistry of Upper Vendian‒Lower Cambrian deposits in the northeastern Baltic monocline". Stratigraphy and Geological Correlation 25 (1): 1–20. doi:10.1134/S086959381606006X. 
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Golubkova, E. Yu.; Kushim, E. A.; Kuznetsov, A. B.; Yanovskii, A. S.; Maslov, A. V.; Shvedov, S. D.; Plotkina, Yu. V. (March 2018). "Redkinian Biota of Macroscopic Fossils from the Northwestern East European Platform (South Ladoga Region)". Doklady Earth Sciences 479 (1): 300–304. doi:10.1134/S1028334X18030169. 
  4. ↑ 4.0 4.1 4.2 4.3 Golubkova, E. Yu.; Kushim, E. A.; Kuzmenkova, O. F.; Laptsevich, A. G.; Plotkina, Yu. V.; Silivanov, M. O. (December 2023). "Stratigraphic Distribution of Fossil Organisms in the Upper Vendian Deposits of the Central and Southwestern Regions of the East European Platform". Paleontological Journal 57 (S3): S211–S236. doi:10.1134/S0031030124600124. 
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 5.16 Golubkova, E. Yu.; Bobrovskiy, I. M.; Kushim, E. A.; Plotkina, Yu. V. (September 2021). "Fossil Organisms of the Redkino Regional Stage of the Upper Vendian of the Northwestern Russian Platform (Leningrad Region)". Paleontological Journal 55 (5): 579–587. doi:10.1134/S0031030121050051. 
  6. ↑ Xiao, Shuhai; Yuan, Xunlai; Steiner, Michael; Knoll, Andrew H. (2002). "Macroscopic Carbonaceous Compressions in a Terminal Proterozoic Shale: A Systematic Reassessment of the Miaohe Biota, South China". Journal of Paleontology 76 (2): 347–376. ISSN 0022-3360. https://www.jstor.org/stable/pdf/1307146.pdf. 
  7. ↑ Slater, Ben J. (February 2025). "Cambrian carbonaceous protoconodonts and the early fossil record of the Chaetognatha". Proceedings of the Royal Society B: Biological Sciences 292 (2041). doi:10.1098/rspb.2024.2386. PMID 39968616. 



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