Context of the Falkland Islands in the pre-breakup fabric of Gondwana: Evidence from detrital and ash fall zircon

The Falkland Islands, within the South Atlantic Ocean, display expansive Paleozoic sedimentary successions for which affinities with coeval depositional systems in southern Gondwana have been debated. New U-Pb zircon age spectra for ash and sandstone samples from the Falklands successions assist in elucidating relationships. Dating of ash samples shows the Port Sussex Formation (Falklands Islands) is younger than the lower Ecca Group of the Karoo Basin, not contemporaneous, as previously proposed. The Falklands and South African Paleozoic sequences differ only modestly, suggesting their accumulation and subsequent inversions were similar, but they represent discrete, basinal entities. Detrital zircon age spectra for samples from the Falklands successions show remarkable age-related comparability. Those from Silurian−earliest Permian samples are dominated by late Neoproterozoic to Cambrian (650−490 Ma) and mid-Mesoproterzoic−earliest Neoproterzoic (1235−940 Ma) age clusters. Populations from younger, post-glacial, Permian strata are dominated by arc-derived Permian clusters, consistent with the occurrence of ashfall horizons in the Port Sussex Formation, as well as subordinate older zircon grains matching the populations from the older successions. Age spectra from the Falkland successions match those of rock assemblages of the Terra Australis Orogen, which developed across southern Gondwana during the late Neoproterozoic and Paleozoic, indicating enduring, large scale, provenance linkages. Two overlapping Paleozoic superbasinal systems, distributed as linear belts extending for 6000 km are recognized as parts of southern Gondwana, stratigraphically separated by a disconformity embracing much of the Carboniferous. A remarkably similar upper-plate subsidence response to subduction along this margin is evident from the Silurian to Permian.