Earth's earliest global glaciation? Carbonate geochemistry and geochronology of the Polisarka Sedimentary Formation, Kola Peninsula, Russia

Brasier, A.T., Martin, A.P., Melezhik, V.A., Prave, A.R., Condon, D.J. and Fallick, A.E. (2013) Earth's earliest global glaciation? Carbonate geochemistry and geochronology of the Polisarka Sedimentary Formation, Kola Peninsula, Russia. Precambrian Research, 235, pp. 278-294. (doi: 10.1016/j.precamres.2013.06.007)

Abstract

As part of the International Continental Scientific Drilling Program’s Fennoscandian Arctic Russia–DrillingEarly Earth Project (ICDP FAR–DEEP), Palaeoproterozoic diamictic and associated rocks were targeted andrecovered in Hole 3A on the Kola Peninsula of NW Russia. In addition to the diamictites, carbonate sed-imentary rocks and volcanic ash layers (all metamorphosed to greenschist grade) were encountered.Sedimentology and geochemistry suggest deposition of the diamictites in an open-marine aragonite-precipitating environment. Sampling of the core and of outcrops from the same geographical area yieldeda number of zircons for analyses, the majority of which were inherited. However a tuff at 20.01 m coredepth yielded zircons dated at 2434 ± 1.2 Ma (±6.6 Myr including decay constant uncertainties) that weinterpret as a magmatic age. These data, combined with dates from underlying intrusions, indicate depo-sition of the Polisarka Sedimentary Formation diamictites and underlying carbonates during an intervalof time from ca. 2430 to 2440 Ma. The carbonate rocks, which likely originally included aragonitic lime-stones, were deposited mostly in a deep-water setting (i.e. at least below storm wave base) and occurbelow the diamictite. They record two inorganic carbon �13C excursions, from values of ca. 0‰ to min-ima of ca. −5.4‰, as the contact with the overlying diamictite is approached. The older (stratigraphicallylower) excursion occurs about 9 m below the base of the diamictic units and the younger one at 1 m below.Throughout that interval, Mg/Ca ratios correlate strongly with �13C (n = 38, r = 0.85), and combined withpetrographic observations, this indicates that the first (stratigraphically lower) excursion was modified bysecondary alteration and the second is recorded in resedimented dolostone clasts. It is tempting to spec-ulate that these dolostone clasts were deposited in penecontemporaneous shallow-marine waters, andthat their low �13C values might reflect input of oxidised atmospheric methane to the ocean surface (andtherefore the cause of the glaciation); the dolostones were subsequently resedimented into the deepermarine settings. However this must be left as a hypothesis to be tested when further age-constrainedcontemporaneous pre-glacial carbonate sections are found.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Fallick, Professor Anthony
• Authors: Brasier, A.T., Martin, A.P., Melezhik, V.A., Prave, A.R., Condon, D.J., and Fallick, A.E.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Precambrian Research
• ISSN: 0301-9268
• ISSN (Online): 1872-7433
• Copyright Holders: Copyright © 2013 Elsevier B.V.
• First Published: First published in Precambrian Research 235:278-294
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher