The Late Cryogenian Warm Interval, NE Svalbard: chemostratigraphy and genesis

Research output: Contribution to journalArticle

Authors

  • Edward Fleming
  • Nathalie Grassineau
  • Pierre Bonnand
  • Ian Parkinson
  • Galen Halverson
  • Michael Hambrey

Colleges, School and Institutes

External organisations

  • Royal Holloway Univ London
  • Department of Earth Sciences; University of Oxford; Oxford; UK
  • BRISTOL UNIVERSITY
  • McGill University, Department of Earth and Planetary Sciences
  • Aberystwyth University

Abstract

The Late Cryogenian Warm Interval (LCWI) refers to a non-glacial interval that separates presumed representatives of the Sturtian and Marinoan panglaciations. Its duration is poorly constrained radiometrically and its deposits are relatively poorly known in most geographic regions. This paper aims to constrain the duration, palaeoenvironments and petrogenesis of such deposits in the classic region of NE Spitsbergen, Svalbard. The succession comprises a 200-205 m dolomitic shale (Macdonaldryggen Member, known as E3, of the Elbobreen Formation) overlain by oolitic dolomite Slangen Member (E4), 15-25 m thick, with limestone developed at top and base of E3 in the south of the area. The assumed age context of the succession has been confirmed by the presence of a typical Sturtian cap carbonate profile of negative to positive 13C, and primary Sr isotope compositions of basal E3 limestones <0.7072 and of upper E3 limestones of 0.7076. At the base of E3, interstratification of cap carbonate with ice-rafted and redeposited glacial sediments occurs. Early diagenetic stabilization of carbonate mineralogy from a precursor, possibly ikaite, to calcite or dolomite is inferred. E3 is predominantly dolomitic silt-shale, with sub-millimetre lamination, lacking sand or current-related sedimentary structures. Thin fine laminae are partly pyritized and interpreted as microbial mats. Dolomite content is 25-50%, with 13C values consistently around +4‰, a value attributed to buffering by dissolution of a precursor metastable carbonate phase. Local calcite cement associates with low 13C values. The carbonates form silt-sized, chemically zoned rhombic crystals from an environment with dynamically changing Fe and Mn. Three-dimensional reconstructions of cm-scale disturbance structures indicate that they represent horizontally directed sock-like folds, developed by release of overpressure into thin surficial sediment overlying an early-cemented layer. A shoaling upwards unit near the top of E3 displays calcium sulphate pseudomorphs in dolomite in the north, but storm-dominated limestones in the south, both being overlain by peritidal oolitic dolomites, exposed under the succeeding Wilsonbreen glacial deposits. There is no Trezona 13C anomaly, possibly implying top-truncation of the succession. Regular 0.5 m-scale sedimentary rhythms, reflecting subtle variations in sediment texture or composition occur throughout E3 and are interpreted as allocyclic. They are thought to be mainly primary in origin, locally modified slightly during early diagenetic cementation. Rhythms are proposed to represent ca. 18 kyr precession cycles, implying 6-8 Myr deposition between glaciations.

Bibliographic note

Fairchild, I.J., Bonnand, P., Davies, T., Fleming, E.J., Grassineau, N., Halverson, G.P., Hambrey, M.J., McMillan, E.A., McKay, E., Parkinson, I.J. and Stevenson, C.T.E. 2016 The Late Cryogenian Warm Interval, NE Svalbard: chemostratigraphy and genesis of dolomitic shales. Precambrian Research

Details

Original languageEnglish
Pages (from-to)128-154
JournalPrecambrian Research
Volume281
Early online date28 May 2016
Publication statusPublished - Aug 2016

Keywords

  • Cryogenian, Shale, Rhythmic sedimentation , Chemostratigraphy , Orbital forcing , Dolomite

ASJC Scopus subject areas