Detrital zircon provenance ages of the “Dwyka Tillite” in South Africa and the Falkland Islands

• Main Authors: Craddock, John, Thomas, Robert
• Format: Text
• Language: English
• Published: 2011
• Subjects: Earth Sciences; Fitzroy; Isbell; Ice Sheet
• Online Access: http://nora.nerc.ac.uk/id/eprint/15127/; https://nora.nerc.ac.uk/id/eprint/15127/1/Geosynthesis_abs.pdf; http://www.geosynthesis.org.za/

Reconstructions of Gondwana show that the Falkland Islands lie on a rotated microplate that originally lay off the Eastern Cape-Kwa-Zulu Natal (KZN) provinces of South Africa (e.g. Marshall, 1994). This implies that the Permo-Carboniferous tillites (diamictites) of South Africa and the Falklands were once contiguous. In the Western Cape, South Africa, thin tuff layers within the Dwyka Group have been precisely dated at ca 290 Ma, close to the Permian-Carboniferous boundary (Bangert et al., 1999). In our study, U-Pb dates from detrital zircons, extracted from five samples of the tillite, have been dated by ICP-MS laser ablation at the University of Arizona (approximately 100 zircons per sample). The samples were taken from the Western Cape Province (near Laingsberg), the Eastern Cape (east of Oudtshoorn) , northern and central KZN (near Vryheid and Pietermaritzburg respectively), and from East Falkland (west of Port Stanley). In South Africa, the samples were taken from the “southern facies” of the Dwyka Group, known as the Elandsvlei Formation (Johnson et al., 2006), whereas in the Falklands, the equivalent unit is known as the Fitzroy Tillite Formation of the Lafonia Group. All the samples analysed were composed of massive tillite (diamictite). Published models of ice sheet flow directions in South Africa, show ice movements generally from NE to SW across the area (e.g. Isbell et al., 2008)