Synthesis

Veevers, J. J.; Powell, C. McA.; Collinson, Joseph; López-Gamundí, Oscar R.

doi:10.1130/mem184-p331

Cited by 45 publications

(17 citation statements)

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“…Of the 26 concordant Triassic ages in the Ecca Group, 18 were obtained from tuffs just below the presumed tuff gap (12ZA07, CVX12, 12ZA23, 12ZA61). These four samples all yield~250-251 Ma weighted mean ages, which coincides with the basal age of the tuff gap (~251 Ma) elsewhere in Gondwana (Veevers et al 1994b). Since the base of the tuff gap is approximately the boundary between the Permian and Triassic, ages just below this interval would be expected to straddle the boundary, with a range of~249-254 Ma ages, which is observed in Ecca tuffs and is compatible with our age interpretation.…”

Section: Maximum Depositional Ages From U-pb Zircon Analysessupporting

confidence: 68%

“…In contrast, above the gap, tuffs are distinctly either white and chalky or light brown and gritty/sandy with thicknesses varying from 5 cm up to 40 cm. We speculate here that this 'tuff gap' is similar to the 'tuff gaps' reported throughout southern Gondwana (New Zealand, Australia, and Antarctica), where volcanic tuffs are rare to absent within otherwise ash-rich strata (Veevers et al 1994b). It remains unclear whether those tuff gaps are related to a hiatus in volcanic activity or dilution and lack of preservation in a terrestrial depositional environment (Retallack and Krull 1999;Veevers 2004); these gaps, however, are thought to be synchronous across Gondwana (Veevers 2004).…”

Section: Tuff Distribution and Composition-gondwanan Tuff Gapmentioning

confidence: 72%

“…Choiyoi and Puesto Viejo magmatism dates from~276 to~234 Ma and is responsible for air-fall ash deposits in the Paraná (Rocha-Campos et al (Spalletti et al 2008) in South America, in addition to the Karoo Basin in South Africa ( Figure 1B), based on palaeogeography and geochemistry (López-Gamundi et al 2006). The Choiyoi and Puesto Viejo magmatic suites, which are separated by a~251-240 Ma tuff gap (Veevers et al 1994b;Veevers 2004;Spalletti et al 2008;Kleiman and Japas 2009), contain distinct zircon populations. The Permian Choiyoi Group contains an abundant Permian zircon population (Domeier et al 2011;RochaCampos et al 2011) with some mixing of mid-Permian (>260 Ma) and late Permian (250-260 Ma) zircon in late Permian tuffs (Rocha-Campos et al 2006).…”

Section: Geologic Backgroundmentioning

confidence: 99%

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U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls

McKay

Weislogel

Fildani³

et al. 2015

International Geology Review

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Along the >650 km long southern margin of the Karoo Basin in South Africa, we traversed four evenly spaced stratigraphic transects and collected 22 samples of volcanic, air-fall tuffs thought to be distal deposits derived from the Permian-Triassic Southern Gondwanan volcanic arc. We present 469 new U-Pb zircon ages determined by sensitive high-resolution ion microprobe reverse geometry (SHRIMP-RG) at the Stanford-USGS Microanalytical Center in order to constrain the maximum depositional ages for the southern Karoo Basin strata. Weighted means of these youngest coherent zircon populations were selected to maximize the number of analyses while minimizing the mean square weighted deviation (MSWD) to increase the robustness and decrease the influence of Pb-loss and inheritance in determining the maximum depositional age. Maximum depositional ages for the marine Ecca Group range from 250 to 274 Ma, whereas in the conformably overlying terrestrial Beaufort Group maximum depositional ages ranged from 257 to 452 Ma. Across the southern Karoo Basin, the Ecca Group tuffs produce maximum depositional ages that young upward; however, the Beaufort Group tuffs yield maximum depositional ages that are geochronologically out of sequence. Furthermore, maximum depositional ages of the Beaufort Group tuffs are consistently older than ash ages within the underlying marine strata. Our results are supported by previously published U-Pb tuff zircon geochronology in the Karoo Basin and demonstrate that the presence of out-of-sequence, older tuff ages are repeatable in Beaufort Group tuffs along the southern margin of the basin. We propose that tuffs in the Karoo Basin are correlative with tuffs in southern South America, and that the age spectra of these tuffs were influenced by magmatic crustal recycling. We use these data to highlight the complexity of U-Pb zircon datasets from tuffs, address the use of U-Pb zircon ages to provide absolute age controls, and discuss the implications of these new age controls on the Permian-Triassic Karoo strata.

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Section: Maximum Depositional Ages From U-pb Zircon Analysessupporting

confidence: 68%

Section: Tuff Distribution and Composition-gondwanan Tuff Gapmentioning

confidence: 72%

Section: Geologic Backgroundmentioning

confidence: 99%

See 1 more Smart Citation

U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls

McKay

Weislogel

Fildani³

et al. 2015

International Geology Review

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show abstract

“…F35106-10). Recent high-precision dating of the D. odontopteroides zone indicates that it began at 243 Ma (Retallack et al 1993) and ended at about 230 Ma (Veevers 1989;Veevers et al 1994).…”

Section: Geological Settingmentioning

confidence: 99%

“…Some of these riddles were solved by the theory of plate tectonics, but others have remained as evidence of global climate very different in the past than now. During the Middle Triassic (240 Ma), for example, Antarctica was at high latitudes (73-69Њ: Barrett 1991;Scotese 1994;Veevers et al 1994), yet fossil wood and leaves of forests are found in the continent now shrouded in ice (E.L. ; E.L. Taylor et al 1992;Creber 1990). Fossil plants of such geological antiquity have only distant relatives in modern vegetation (T.N. )…”

Section: Introductionmentioning

confidence: 99%