Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Geological Magazine

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by GAUCHER, C. Articles by GERMS, G. J. B. Search for Related Content GeoRef GeoRef Citation

Organic-walled microfossils and biostratigraphy of the upper Port Nolloth Group (Namibia): implications for latest Neoproterozoic glaciations

CLAUDIO GAUCHER^*,*, HARTWIG E. FRIMMEL and GERARD J. B. GERMS

^* Departamento de Geología, Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay
Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa
Department of Geology, Rand Afrikaans University, Auckland Park 2092, South Africa

^* Author for correspondence: gaucher{at}chasque.apc.org

The occurrence of organic-walled microfossils is reported for the first time from the Neoproterozoic Port Nolloth Group, Gariep Belt (southern Namibia). Acritarchs assigned to Bavlinella faveolata occur in the Hilda Subgroup below the younger of two glaciogenic diamictite units (Numees Formation) within the Port Nolloth Group. The microfossil assemblage in the overlying upper Holgat Formation, above the Numees Formation, is characterized by low diversity (six species), dominance of Soldadophycus bossii, and absence of acanthomorphic or large sphaeromorphic acritarchs. The agglutinated foraminifer Titanotheca also occurs in the Holgat Formation. Combined with available chemostratigraphic data and Pb–Pb ages, this microfossil assemblage indicates an upper Ediacaran age of around 555 Ma for the Holgat Formation. Virtually identical microfossil assemblages, negative-to-positive ¹³C trends, ⁸⁷Sr/⁸⁶Sr values between 0.7080 and 0.7085, as well as Pb–Pb carbonate ages, make it possible to correlate the Holgat Formation with the Buschmannsklippe Formation (Witvlei Group, central Namibia), the Kombuis Member (Cango Caves Group, southern South Africa) and the uppermost Polanco to lowermost Cerro Espuelitas Formation (Arroyo del Soldado Group, Uruguay). Based on these data, the underlying Numees Formation, the age of which has been only loosely constrained so far and subject to considerable debate, can now be assigned to the c. 580 Ma Gaskiers or the possibly younger (< 570 Ma) Moelv glacial event. The Numees glacial event may be represented in the uppermost Nooitgedagt Member (Cango Caves Group, South Africa) and the lower Barriga Negra formations (Arroyo del Soldado Group, Uruguay), characterized by a negative ¹³C excursion and a strong sea-level drop. If this correlation is confirmed, lack of glacial deposits there might have implications for the palaeogeographic extent of upper Ediacaran glaciations. Our preliminary studies show that acritarch biostratigraphy can make a significant contribution to unravelling the stratigraphy of Neoproterozoic glacial deposits, especially when combined with C and Sr isotopic data.

Key Words: Neoproterozoic • Ediacaran • glaciation • acritarchs • Namibia

This article has been cited by other articles:

				P. J. Pazos, L. S. Bettucci, and J. Loureiro The Neoproterozoic glacial record in the Rio de la Plata Craton: a critical reappraisal Geological Society, London, Special Publications, January 1, 2008; 294(1): 343 - 364. [Abstract] [Full Text] [PDF]

				C. Gaucher and G. J.B. Germs Recent advances in South African Neoproterozoic-Early Palaeozoic biostratigraphy: correlation of the Cango Caves and Gamtoos Groups and acritarchs of the Sardinia Bay Formation, Saldania Belt South African Journal of Geology, June 1, 2006; 109(1-2): 193 - 214. [Abstract] [Full Text] [PDF]

				A. van Staden, T. Naidoo, U. Zimmermann, and G. J.B. Germs Provenance analysis of selected clastic rocks in Neoproterozoic to lower Paleozoic successions of southern Africa from the Gariep Belt and the Kango Inlier South African Journal of Geology, June 1, 2006; 109(1-2): 215 - 232. [Abstract] [Full Text] [PDF]