The Ust Pinega Formation is an Upper Ediacaran geological formation in northwestern Russia. It spans from around to and contains fossils of the Ediacaran biota throughout its sequence.
Geology
The formation was first established and described from the core of the Ust-Pinega borehole drilled in the settlement of Ust-Pinega, Arkhangelsk Region of Russia, where its thickness is 284 m. Its natural outcrops within the same region are known from the Onega Peninsula and the Winter Coast of the White Sea, as well as from small, isolated outcrops in the basin of the Onega River and on the northern slope of the Vetreny Poyas (Windy Belt) Ridge.
The formation rests with erosion on Proterozoic terrigenous deposits or Archean crystalline rocks. It is subdivided, from bottom to top, into the following Subformations (initially defined as "Beds" by A.F. Stankovsky, 1985): Tamitsa, Lyamtsa, Arkhangelsk, Verkhovka, Syuzma, Vaizitsa, and Zimnegory. It is unconformably overlain by deposits of the Ediacaran Mezen Formation, as well as by Paleozoic or Quaternary sediments.
In 2003, D.V. Grazhdankin proposed an alternative subdivision scheme for these deposits, based on the original scheme by A.F. Stankovskiy. This scheme includes the Lyamtsa (= Lyamtsa + Arkhangelsk Beds), the Verkhovka (= Verkhovka + Syuzma Beds), and the Zimnegory (= Vaizitsa + Zimnegory Beds) Formations. In this revision, the use of the Ust' Pinega Formation was abandoned in favor of these three formations.
Currently, the Ust' Pinega Formation and its subformations remain the official stratigraphic scheme used on state geological maps of Russia.
Dating The Lyamtsa, Verkhovka and Vaizitsa Subformations contain volcanic ashes. Zircon U-Pb dating of volcanic tuffs from the Verkhovka and Vaizitsa beds has yielded ages of and , respectively. Furthermore, an Rb–Sr age of was obtained for clays of the Arkhangelsk Subformation. The formation is unconformably overlain by the deposits of the Mezen Formation, from the lower part of which a U-Pb age of has been obtained for tuffites.
Paleobiota The Ustʹ Pinega Formation is home to many rare and common Ediacaran fauna, from the well known motile forms such as Dickinsonia and Kimberella, to the rarer, more elusive forms like Ventogyrus and Zolotytsia. All forms within this formation are preserved in layers of ash beds, which are not only good at preserving the fine exterior details of organisms, but also their internals, like Burykhia.
Proarticulata
GenusSpeciesNotesImagesAndivaA. ivantsoviElongated oval motile organism.ArchaeaspinusA. fedonkiniOval motile organism.ArmilliferaA. parvaElongated oval motile organism.CephalonegaC. stepanoviOval motile organism.CyanorusC. singularisElongated motile organism.DickinsoniaDickinsonia sp.Oval to elongated motile organism.KarakhtiaK. nessoviOval motile organism.KeretsaK. brutoniElongated motile organism.LossiniaL. lissetskiiElongated motile organism.OvatoscutumO. concentricumRounded motile organism.PalaeoplatodaP. segmentataElongated motile organism.ParavendiaP. janaeElongated motile organism.VendiaV. sokolovi V. rachiataElongated motile organism.YorgiaY. waggoneriOval motile organism.
Petalonamae
GenusSpeciesNotesImagesBomakelliaB. kelleriSessile frondose organism.CharniaCharnia sp.Sessile frondose organism.CharniodiscusCharniodiscus sp.Sessile frondose organism.PteridiniumPteridinium sp.Sessile frondose organism.RamellinaR. pennataSessile frondose organism.
Trilobozoan
GenusSpeciesNotesImagesAlbumaresA. brunsaeTri-radial organism.AnfestaA. stankovskiiTri-radial organism.TribrachidiumT. heraldicumTri-radial organism.
Cnidarian
GenusSpeciesNotesImagesBonataB. septataDiscoid organism.BrachinaBrachina sp.Discoid organism.EdiacariaEdiacaria sp.Discoid organism.EoporpitaE. medusa.Discoid organism.InariaI. karliSac-like organism.MedusinitesMedusinites sp.Discoid organism.StaurinidiaS. cruciculaDiscoid organism.TirasianaTirasiana sp.Discoid organism.ZolotytsiaZ. biserialisDeformed mass of ovals along a mid-line groove.
Chordata
GenusSpeciesNotesImagesBurykhiaB. huntiSac-like organism, possible tunicate.
Annelida
GenusSpeciesNotesImagesCalyptrinaC. striataTubular organism.
incertae sedis
GenusSpeciesNotesImagesCyclomedusaCyclomedusa sp.Discoid organism.HiemaloraHiemalora sp.Discoid organism, possibly holdfasts of petalonamids.KimberellaKimberella sp.Egg-shaped organism, possible mollusc.MawsonitesM. spriggiDiscoid organism.NimbiaN. occlusaDiscoid organism.OrbisianaOrbisiana sp.Palaeopascichnid organism.PalaeopascichnusPalaeopascichnus sp.Palaeopascichnid organism.ParvancorinaP. sagittaAnchor-shaped organism, possible mollusc or arthropod.SolzaS. margaritaEgg-shaped organism. HarlaniellaHarlaniella sp.Ribbon-like organism.VendotaenidVendotaenidRibbon-like organisms.
Flora
GenusSpeciesNotesImagesArchyfasmaA. dimera A. lamellataBranching macroalgae.BeltanelliformisBeltaneillformis sp.Cyanobacterial colony.EoholyniaE. fruticulosaBranching macroalgae.FavosiphycusF. wukiiFlattened thallus crust-like, consisting of densely packed cells.GandvikiaG. caudataRibbon-shaped macroalgae.MezeniaM. kossovoyiSausage shaped macroalgae.SerebrinaS. crustaceaEncrusting macroalgae.
Ichnogenera
GenusSpeciesNotesImagesEpibaionEpibaion sp.Feeding traces of proarticulates.KimberichnusKimberichnus sp.Feeding traces of Kimberella.NenoxitesNenoxites sp.Movement traces.NeonereitesNeonereites sp.Burrows.PlanolitesPlanolites sp.Burrows.
See also
List of fossiliferous stratigraphic units in Russia
References