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

Beitrag in einer Fachzeitschrift
(Originalarbeit)


Details zur Publikation

Autorinnen und Autoren: Stollhofen H, Bangert B, Lorenz V, Armstrong RA
Zeitschrift: Journal of African Earth Sciences
Jahr der Veröffentlichung: 1999
Heftnummer: 1
Seitenbereich: 33-49
ISSN: 0899-5362
Sprache: Englisch


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.



FAU-Autorinnen und Autoren / FAU-Herausgeberinnen und Herausgeber

Stollhofen, Harald Prof. Dr.
Lehrstuhl für Geologie (Exogene Dynamik)


Einrichtungen weiterer Autorinnen und Autoren

Australian National University (ANU)
Julius-Maximilians-Universität Würzburg


Zitierweisen

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://dx.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.

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