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New U–Pb zircon ion-microprobe ages from the alluvial conglomerates and flood plain sediments of the Botany Bay Group demonstrate that sedimentation occurred at c. 167 Ma, coeval with rift-related silicic volcanism in the northern Antarctic Peninsula. In contrast, rift-related volcanism and sedimentation in the southern Antarctic Peninsula (Latady Basin) occurred at c. 183 Ma. The new data indicate that syn-rift sedimentation and volcanism was diachronous from south to north, consistent with early opening of the Weddell Sea embayment by anti-clockwise rotation of the Antarctic Peninsula in the Mid-Jurassic. A definitive date for the Botany Bay Group floras has important implications for Southern Hemisphere biostratigraphic correlations.

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Recent detailed mapping, section logging and an improved understanding of

Silurian and lower Devonian sedimentary successions are uncommon within the remnants of Gondwana. The Port Stephens Formation, the basal unit of the middle Palaeozoic West Falkland Group, presents a rare opportunity to study Gondwanan material of Siluro-Devonian age. The formation on West Falkland is c . 2560 m thick and consists of five members: Plantation, Albemarle, Mount Alice, South Harbour and Fish Creek. Thirty-five lithofacies are defined using variations in grain size and bedding characteristics. The distribution of these lithofacies and their associated ichnofacies between the various members lead us to suggest terrestrial and shallow marine deposition on an extensive, gently shelving alluvial to coastal plain. Vertical facies trends through the Port Stephens Formation, and into the base of the overlying Fox Bay Formation, record a complex superposition of subenvironments within a distinct overall transgressive–regressive–transgressive pattern, with the bulk of sediment accumulating during the regressive phase. Palaeocurrents indicate a basin to the present-day NE throughout. These results, together with lithostratigraphic correlations between the Port Stephens Formation and the Nardouw Subgroup in South Africa, are consistent with a reconstructed position off eastern South Africa and on the palaeo-Pacific margin of Gondwana, requiring a near-180° rotation of the Falkland Island microplate during break-up, in agreement with previous models. We suggest that global changes in sea level during the mid–late Silurian and early Devonian strongly influenced changes in the depositional environment. Enhanced erosion of the continental margin and extensive sediment bypass during the regressive phase of this cycle could help to explain the low abundance of preserved Gondwanan material of this age.