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Toward a Neoproterozoic composite carbon-isotope record
Galen P. Halverson
Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138-2902, USA and Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Building 54-1126, Cambridge, Massachusetts 02139, USA
Paul F. Hoffman Daniel P. Schrag Adam C. Maloof
Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138-2902, USA
A. Hugh N. Rice
Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
ABSTRACT Glacial deposits of Sturtian and Marinoan age occur in the well-studied Neoproterozoic successions of northern Namibia, South Australia, and northwestern Canada. In all three regions, the Marinoan glaciation is presaged by a large negative δ13C anomaly, and the cap carbonates to both glacial units share a suite of unique sedimentological, stratigraphic, and geochemical features. These global chronostratigraphic markers are the bases of a new correlation scheme for the Neoproterozoic that corroborates radiometric data that indicate that there were three glacial epochs between ca. 750 and 580 Ma. Intraregional correlation of Neoproterozoic successions in the present-day North Atlantic region suggests that glacial diamictite pairs in the Polarisbreen Group in northeastern Svalbard and the Tillite Group in eastern Greenland were deposited during the Marinoan glaciation, whereas the younger of a pair of glacials (Mortensnes Formation) in the Vestertana Group of northern Norway was deposited during the third (Gaskiers) Neoproterozoic glaciation. Gaskiers-aged glacial deposits are neither globally distributed nor overlain by a widespread cap carbonate but are associated with an extremely negative δ13C anomaly. The chronology developed here provides the
E-mail: Present address: Laboratoire des Mécanismes de Transferts en Géologie, Université PaulSabatier, 14 avenue Edouard Belin, 31400 Toulouse, France; e-mail: galen.halverson@lmtg.obs-mip.fr. Present address: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Building 54, Cambridge, Massachusetts 02139, USA.

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