Zircon geochronology of the Mashak volcanic rocks and the problem of the age of the lower-middle Riphean boundary (Southern Urals)

Краснобаев, А. А.; Козлов, В. В.; Пучков, В. Н.; Busharina, S. V.; Сергеева, Н. Д.; Paderin, I. P.

doi:10.1134/s0869593813050055

Cited by 23 publications

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“…B). The age of Burzyan deposition is constrained by the approximately 1380 Ma Mashak volcanics in the overlying Middle Riphean Yurmata Group (Krasnobaev et al ., ; Puchkov et al ., ) and approximately 1750 Ma basalts 200 m above the base of the Ai Formation (Puchkov et al ., ; Krasnobaev et al ., ; Fig. B).…”

Section: Geologic Backgroundmentioning

confidence: 98%

“…Other abbreviations: PP , Paleoproterozoic; LP , Lower Proterozoic; MR , Middle Riphean; Y ur, Yurmanta Group; ISC , International Stratigraphic Chart. Asterisks mark geochronological constraints for the L ower R iphean (Puchkov et al ., , ; Krasnobaev et al ., ,b). Symbols denoting rock types are (1) limestone; (2) dolomite; (3) shale; (4) siltstone; (5) sandstone; (6) conglomerate; (7) tillite, tilloid; (8) bioherms with columnar stromatolites; (9) tuff, tuffaceous sandstone, and diabase; (10) dolomite with chert lenses; (11) marl; (12) clay dolomites; (13) hiatus, unconformity; (14) azimuthal discordance; and (15) basement gneiss.…”

Section: Introductionmentioning

confidence: 99%

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Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean

et al. 2014

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2 INTRODUCTIONHow the Earth's atmosphere and ocean transitioned from their early, essentially anoxic state to our familiar oxygen-rich world remains controversial. It is well documented that an oxygenation event at ~2400 Ma (Ma: million years) established a persistently oxic atmosphere and surface ocean, but deep ocean chemistry remains uncertain through the remainder of the Proterozoic Eon (Kah and Bartley, 2011).Geologists long posited that the widespread disappearance of banded iron formation at ~1800 Ma reflects oxygenation of the deep ocean (Holland, 1984); however, Canfield (1998) proposed that under relatively low atmospheric O 2 , the deep ocean would remain anoxic and indeed become euxinic, reflecting increased rates of bacterial sulfate reduction at depth. The nature of subsurface ocean chemistry is critical to our understanding of Earth surface history and biological evolution. noting that oscillations between ferruginous and euxinic conditions in basinal strata track sedimentary total organic carbon contents, which suggests that euxinia is most likely to develop when organic carbon delivery exceeds the delivery of electron acceptors that outcompete sulfate (e.g. nitrate, ferric iron; see also Planavsky et al., 2011;Sperling et al., 2013). Adding to this emerging heterogeneity, data from mineral assemblages suggest that despite widespread anoxia in oxygen minimum zones, dysoxia (oxygen present but at low levels) apparently persisted in the deepest parts of at least some mid-Proterozoic oceans (Slack et al., 2007; Chandler, 1992), we also document the composition of microfossils preserved in basinal Arlan shales. These data are then placed in the context of information from other basins to examine redox heterogeneity in Mesoproterozoic oceans. GEOLOGIC BACKGROUND Geology of the Ural Mountains and Volgo-Ural regionFor many years, Russian geologists discussed Meso-and early Neoproterozoic stratigraphy in terms of a Riphean stratotype located in the Bashkirian meganticlinorium, a large structure on the western slope of the southern Ural Mountains (Chumakov and Semikhatov, 1981; Keller and Chumakov, 1983). In the southern Urals, the lower (Fig. 1B).In the Volgo-Ural region to the west, sub-surface Riphean stratigraphy is known from core and geophysical data. According to new geological and geophysical data the correlative stratigraphy to the Burzyan Group in this region, the Kyrpy Group, is subdivided into the Sarapul, Prikamskii and Or'ebash subgroups, and its base has not been penetrated by drilling (Kozlov et al., 2009. The A perennial question in pre-Mesozoic paleoceanography concerns the water-depth of sediments deposited beneath storm wave-base --these basinal strata are almost 7 certainly not 'deep' in the oceanographic sense of an average ocean depth of four kilometers. While the only hard constraint on these strata is that they were deposited in water depths persistently greater than ~150 meters (as indicated by the lack of wavegenerated sedimentary structures), such strata are generally con...

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Section: Geologic Backgroundmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean

et al. 2014

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“…The age of Kaltasy correlatives in the southern Ural Mountains is constrained by the ~1380 Ma Mashak volcanics in the overlying Middle Riphean (Mesoproterozoic) Yurmata Group Krasnobaev et al, 2013a) and by ~1750 Ma basalts 200 meters above the base of the Ai Formation (Puchkov et al, 2012, Krasnobaev et al, 2013b (Keller and Chumakov, 1983; all age estimates have an uncertainty of approximately 3%; Gorozhanin, personal communication, 2015). Illite from mudstone of the underlying Norkino Formation penetrated by Borehole 20005 in the Karachevo area, is dated at 1400±42Ma by K-Ar (Gorozhanin, 1995), and K-Ar dates of 1368, 1377 and 1310 Ma were obtained for whole-rock samples of gabbroids that intruded the overlying Nadezhdino Formation (Keller and Chumakov, 1983).…”

Section: Age Of the Kaltasy Formationmentioning

confidence: 99%

Microfossils from the lower Mesoproterozoic Kaltasy Formation, East European Platform

Сергеев

Knoll

Воробьева

et al. 2016

Precambrian Research

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Basinal shales of the lower Mesoproterozoic Kaltasy Formation, sampled from three boreholes drilled into the southeastern East European Platform, Russia, contain abundant and moderately well preserved microfossils. 34 distinct entities have been identified, most assigned to simple sphaeromorphic or small filamentous taxa found widely and characterized by long stratigraphic ranges. Ornamented microfossils found in coastal successions of other lower Mesoproterozoic basins are absent, but large filamentous microfossils interpreted as possible benthic photosynthetic eukaryotes are recorded, drawing comparisons to relatively deep water shales in Siberia. In overall aspect, the Kaltasy microfossils are consistent with other broadly coeval assemblages, but they highlight the importance of environment, as well as age, in determining the distributions of remains that record the early diversification of marine eukaryotes. Rectia magna is described as a new species.

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“…We suggested changing the rank of the unit and regarding it as a series (Kozlov et al, 2011a). The study of zircons extracted from the volcanic rocks of Igonino Formation of this series led us to conclude a polychronous character of the Arshinian volcanism, with two main stages of activity at levels of 707.0 ± 2.3 and 732.1 ± 1.7 Ma (Krasnobaev et al, 2012). Taking into account that the accepted age of the base of the Vendian is now at 600±10 Ma and that of the Vendian/Riphean boundary is not older than 635-650 Ma, we suggest a new unit at the top of the Riphean -as the Terminal, Uppermost Riphean.…”

Section: Precambrianmentioning

confidence: 99%

“…A new series of U-Pb zircon analyses was carried out in VSEGEI (SHRIMP). An average weighted date of rhyolites for four samples was 1383 ± 3 Ma; a presence of rare ancient crystals was also registered (1597 ± 27 Ma) (Krasnobaev et al, 2013a). At the same time, two samples of zircons were sent to SHRIMP in Australia (one new and one for a control).…”

Section: Precambrianmentioning

confidence: 99%

New data on geology of the Southern Urals: a concise summary of research after the period of EUROPROBE activity

Пучков

2016

Solid Earth

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Abstract. The period of official activity of the EUROPROBE commission was conducted in the Urals with implementation of the URALIDES program, which stimulated many qualified geologists from western research institutes and universities to come to the region and work with local geologists on topical problems of Uralian geology. The author aims to answer questions as to what interesting results have been obtained in the Southern Urals in the last decade, after most foreign researchers left the Urals, and how these results correspond to the scientific conclusions that had been reached before.

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Zircon geochronology of the Mashak volcanic rocks and the problem of the age of the lower-middle Riphean boundary (Southern Urals)

Cited by 23 publications

References 5 publications

Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean

Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean

Microfossils from the lower Mesoproterozoic Kaltasy Formation, East European Platform

New data on geology of the Southern Urals: a concise summary of research after the period of EUROPROBE activity

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