Neoproterozoic microfossils from the northeastern margin of the East European Platform

Abstract

The Kel'tminskaya-1 borehole, drilled along the northeastern margin of the East European Platform (EEP), reveals some 3,600 m of Neoproterozoic sedimentary rocks, mostly confined to the subsurface. The upper 1,000 m of the drilled section correlates with late Ediacaran Redkino and Kotlin successions on the EEP, whereas the lowermost 2,000 m can be related to pre-Sturtian (Upper Riphean) deposits in the Ural Mountains. In between lies the Vychegda Formation, a 600 m siliciclastic succession that has no counterpart in classic EEP stratigraphy.Vychegda microfossils can be separated into three assemblages. The upper part of the formation contains large, profusely ornamented acritarchs broadly comparable to those of the Ediacaran Complex Acanthomorph Palynoflora, including species of the generaAlicesphaeridium, Asterocapsoides, CavaspinaandTanariumconfined to Ediacaran-aged assemblages elsewhere. Diverse large acanthomorphs are known from Ediacaran strata around the world, but have not previously been recognized from the EEP, an absence attributed to a hiatus between the glacial Laplandian (>635 Ma) and Redkino (mostly <555 Ma) successions. The large acanthomorphic acritarchs record eukaryotic organisms with resting stages in their life cycles and likely include egg or diapause cysts of early animals. In contrast, the lower Vychegda assemblage, found in the basal 10 m of the succession, contains taxa typical of earlier Neoproterozoic successions. The middle assemblage contains only simple filaments and spheroidal acritarchs.The most parsimonious interpretation of Vychegda biostratigraphy is that pre-Marinoan rocks in the basal part of the formation are separated by a cryptic unconformity from early and middle Ediacaran deposits above. This interpretation is consistent with data from China and Australia, which indicate that the major paleontological transition to diverse ECAP assemblages took place within the Ediacaran Period and not in association with the preceding ice age. Vychegda acritarch assemblages thus contribute to a biostratigraphic model for the initial Ediacaran boundary.

Neoproterozoic microfossils from the margin of the East European Platform and the search for a biostratigraphic model of lower Ediacaran rocks

“…4 a-c,e), as well as forms not previously reported (Fig. 4d, f-j; see Vorob'eva et al, 2009). The Kel'tma microbiota also contains morphologically simple filamentous and coccoidal microfossils of broad stratigraphic range, including Chuaria circularis, Polytrichoides oligofilum, Polysphaeroides filiformis, Elatera binata, Glomovertella eniseica, Leiosphaeridia spp., Siphonophycus spp., and some unusual morphotypes, such as large multilayered stalks made up of carbonaceous cones nested inside one another (Fig.…”

“…Even when these factors have been taken into account, it is clear that the uppermost Vychegda assemblage contains forms not previously described from other localities. Nonetheless, it shares at least four morphospecies (Alicesphaeridium medusodieum, Cavaspina acuminata, Tanarium conoideum, and T. tuberosum) with ECAP assemblages in Australia, Siberia or both (Vorob'eva et al, 2009). The chief caveat in this interpretation is our limited understanding of microfossil assemblages in uppermost Cryogenian (post-Sturtian/preMarinoan) rocks.…”

Ediacaran Microfossils from the Ura Formation, Baikal-Patom Uplift, Siberia: Taxonomy and Biostratigraphic Significance

“…These pair-wise comparisons indicate that Ediacaran acanthomorph assemblages are less similar to one another than are widely distributed Cambrian acritarch assemblages from a common biostratigraphic zone (Vorob'eva et al, 2009a). The relatively low similarity of Ediacaran acanthomorph assemblages across the present day Russian land mass could reflect age, environment or biogeographic provinciality.…”

“…Relying on the best documented assemblage from central Siberia, that of the Khamaka Formation (Moczydłowska et al, 1993;Moczydłowska, 2005), we can quantify similarities across Russia using Sorensen's Quotient of Similarity (Q/S=100 x 2j/(a + b), where a and b are the number of taxa found in each assemblage and j equals the number of taxa in both assemblages; Vorob'eva et al, 2009a). In their discussion of the Ediacaran acanthomorph assemblage from the Vychegda Formation, northeastern Russia, Vorob'eva and coauthors found its composition to be more similar to that of the Khamaka assemblage than it was to contemporaneous assemblages from Australia or China.…”

Large spinose microfossils in Ediacaran rocks as resting stages of early animals

“…Most also bear one to many spinose or branched processes distributed across vesicle surfaces. LOEMs are minor components of lower Ediacaran successions, but increase dramatically in both abundance and diversity at higher stratigraphic levels (2,13). Where microfossils and carbon isotopic data are available for the same succession, LOEMs disappear within or just below an interval marked by a pronounced negative C-isotopic excursion tightly constrained by a 551 Ϯ 0.7 Ma U-Pb date near its top but only loosely bracketed from below by ca.…”