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A composite reference section for terminal Proterozoic strata of southern Namibia

Beverly Z. Saylor, Alan J. Kaufman, John P. Grotzinger and Frank Urban
A composite reference section for terminal Proterozoic strata of southern Namibia
Journal of Sedimentary Research (November 1998) 68 (6): 1223-1235


Integrated sequence stratigraphic and chemostratigraphic data yield a framework for correlations of stratigraphic units in the terminal Proterozoic to Cambrian Witvlei and Nama Groups of Namibia. Coupled with precise U-Pb zircon age constraints, these correlations make it possible to construct a composite reference section for use in calibrating terminal Proterozoic chronostratigraphy. The Namibian reference section starts with two distinct glacial horizons and extends up to within 1 million years of the Proterozoic-Cambrian boundary. The two glacial horizons may represent each of two distinct Varanger-age glaciations better known from the North Atlantic region. From the higher of the two glacial horizons up, the composite stratigraphy preserves one of the thickest and most complete available records of carbon-isotope variability in post-Varanger terminal Proterozoic seawater. Four carbon-isotope chemostratigraphic intervals are recognized: (1) a postglacial negative delta (super 13) C excursion (Npg interval); (2) a rising interval (Pr interval) of increasing positive delta (super 13) C values; (3) a falling interval (Pf interval) characterized by decreasing positive delta (super 13) C and culminating in near zero or negative values; and (4) an interval of moderately positive, relatively invariant delta (super 13) C values (I interval) that extends up to the unconformity that contains the Proterozoic-Cambrian boundary. Each of these chemostratigraphic intervals can be recognized in widely separated correlative sections around the world. By comparing sediment accumulation rate in the radiometrically calibrated Namibian stratigraphy with sediment accumulation rates in correlative sections in Arctic Canada and Oman, a maximum age of 564 Ma is estimated for the end of the younger Varanger glaciation, 25 m.y. younger than previous estimates.

ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 68
Serial Issue: 6
Title: A composite reference section for terminal Proterozoic strata of southern Namibia
Affiliation: Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge, MA, United States
Pages: 1223-1235
Published: 199811
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 60
Accession Number: 1999-038109
Categories: StratigraphyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. cols., sketch map
S27°00'00" - S25°00'00", E15°00'00" - E16°00'00"
Secondary Affiliation: Harvard University, USA, United StatesHobart College, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 199913
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