The geochronology and significance of ash-fall tuffs in the glaciogenic Carboniferous-Permian Dwyka Group of Namibia and South Africa

Stollhofen H, Bangert B, Lorenz V, Armstrong RA (1999)

Publication Language: English

Publication Type: Journal article, Original article

Publication year: 1999

Journal

Journal of African Earth Sciences

Pages Range: 33-49

Journal Issue: 1

DOI: 10.1016/S0899-5362(99)00078-0

Abstract

Centimetre thick, laterally extensive tuff horizons occur within dark, marine mudstones of the Carboniferous-Permian Dwyka Group (Karoo Supergroup) in southern Namibia and South Africa. These pyroclastic deposits preserve the earliest evidence of volcanism in Karoo-equivalent strata of southern Africa.
Four deglaciation sequences (DS I-IV) recorded in the Dwyka Group of Namibia and South
Africa are capped by mudstone units such as the 45 m thick marine fossil-bearing Ganigobis
Shale Member in Namibia in which 24 thin ash-fall horizons are preserved. Ion microprobe
analyses (SHRIMP) of juvenile, magmatic zircons from the tuff horizons were used to determine
their age. They permit a new radiometric age calibration of the top of deglaciation sequence II
and of the Dwyka/Ecca Group boundary in southern Africa. Juvenile zircons of two tuff
horizons near Ganigobis (southern Namibia) give *06’Pb/238U ages of 302.Ok3.0 Ma and
299.2 f 3.2 Ma (latest Kasimovian) for the top of DS II. Juvenile zircons from two tuff horizons
of the basal Prince Albert Formation, sampled north of Klaarstroom and south of Laingsburg in
the Western Cape (South Africa), were dated at 288.O~t3.0 and 289.6k3.8 Ma (earliest
Asselian). According to these age determinations, the deposition of Dwyka Group sediments
in southern Africa started by the latest at about 302 Ma and ended at about the Carboniferousl
Permian boundary, 290 Ma before present.

Authors with CRIS profile

Harald Stollhofen Lehrstuhl für Geologie (Exogene Dynamik)

Involved external institutions

Julius-Maximilians-Universität Würzburg DE Germany (DE) Australian National University (ANU) AU Australia (AU)

How to cite

APA:

Stollhofen, H., Bangert, B., Lorenz, V., & Armstrong, R.A. (1999). The geochronology and significance of ash-fall tuffs in the glaciogenic Carboniferous-Permian Dwyka Group of Namibia and South Africa. Journal of African Earth Sciences, 1, 33-49. https://doi.org/10.1016/S0899-5362(99)00078-0

MLA:

Stollhofen, Harald, et al. "The geochronology and significance of ash-fall tuffs in the glaciogenic Carboniferous-Permian Dwyka Group of Namibia and South Africa." Journal of African Earth Sciences 1 (1999): 33-49.

BibTeX: Download