Long-lived stable shelf deposition along Gondwana's southern margin during the Ordovician-Silurian: Inferences from U Pb detrital zircon ages of the Table Mountain Group (South Africa) and correlatives in Argentina and the Falklands/Malvinas Islands

Vorster, Clarisa; Kramers, Jan D.; Beukes, Nicolas J.; Penn-Clarke, Cameron R.

doi:10.1016/j.chemgeo.2021.120274

Cited by 7 publications

(1 citation statement)

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“…Detritus within the cover successions of southern Africa has been shown to consist largely of recycled sedimentary rocks (Figure 12; Andersen, Kristoffersen, et al., 2016; Andersen, Elburg, et al., 2016; Vorster, 2014), and this feature is strongly echoed by the Clarens Formation as evidenced by high ZTR abundance in the heavy minerals assemblages, a lack of variation in the heavy mineral suite, a high degree of rounding of zircon grains and zircon age fractions similar to those in older successions of the Karoo Supergroup and Pan‐African (Cambrian to Early Neoproterozoic) aged successions (Andersen, Kristoffersen, et al., 2016; Andersen, Elburg, et al., 2016; Bordy, Abrahams, et al., 2020; Viglietti et al., 2018). When comparing the zircon populations from the Clarens Formation to that in the Beaufort Group (Viglietti et al., 2018), a strong similarity is evident, although the proportions of each zircon age population are different.…”

Section: Discussionmentioning

confidence: 99%

Sedimentation tempo in an Early Jurassic erg system: Refined chronostratigraphy and provenance of the Clarens Formation of southern Africa

Head,

Bordy,

Bolhar

2024

Basin Research

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The Clarens Formation is a widespread aeolianite deposited over southern Gondwana and represents the final phase of erg evolution in the main Karoo Basin during the Early Jurassic. Previous age assessments of the formation hinge on limited detrital zircon data, supplemented by relative ages from the biostratigraphy and geochronology of the adjacent Karoo units. This study refines the depositional history of the Clarens Formation, including its sediment source dynamics as well as basin‐wide geochronological framework, based on U–Pb dating of detrital zircon grains, together with petrographic and sedimentological characterization. The abundant presence of heavy minerals like zircon, tourmaline and rutile suggests large‐scale detritus recycling, while the uniform sandstone composition on a regional scale is an indication of sediment homogenisation across the basin. Based on the prominent detrital zircon age fractions, the sediments are interpreted as having been reworked from pre‐existing rocks of the Karoo Supergroup (Permian), the Damara and Saldania Orogenic belts (650–490 Ma), whereas minor sources can be assigned to the Namaqua‐Natal Mobile Belt (1.35–1.1 Ga) and the western Sierras Pampeanas (1.30–1.33 Ga). Unstable minerals (hornblende, garnet, titanite, feldspar) provide evidence for a nearby granitic source east and southeast of the basin, related to likely Grenvillian rocks (1.0–1.3 Ga). An Early Jurassic zircon age fraction is linked to volcanic activity in the Chon Aike Magmatic Province that, at the time, was situated south and southwest of the study area. Maximum depositional ages derived from these detrital zircon dates suggest that the sedimentation of the Clarens Formation spanned an interval of ~10 Ma during the Pliensbachian and early Toarcian. More specifically, the lower part of the formation is of early Pliensbachian age or younger (~191–192), while the upper part is of early Toarcian age or younger (~181–183 Ma). These age patterns are particularly prominent in the south of the basin that was situated closer to the volcanic source.

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