Mid-Jurassic age for the Botany Bay Group: implications for Weddell Sea Basin creation and southern hemisphere biostratigraphy

Abstract

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.

Permo-Carboniferous conglomerates in the Trinity Peninsula Group at View Point, Antarctic Peninsula: sedimentology, geochronology and isotope evidence for provenance and tectonic setting in Gondwana

“…10) with sedimentation of the Middle Jurassic Botany Bay Group (Hunter et al 2005), Powell Island Conglomerate (Cantrill, 2000) and Miers Bluff Formation (Hervé et al 2006). Jurassic relaxation may also be the key to the intrusion of the subcordillaran granites in Early Jurassic times (Rapela et al 2005).…”

“…The formation of the Rocas Verdes Basin and Sarmiento Ophiolite in Late Jurassic times (Stern & de Wit, 2003) may be a further effect of this episode. A northward opening or 'unzipping' of a wedge-shaped basin is recognized by both Stern & de Wit (2003) and Hunter et al (2005).…”

“…The only palaeontological age constraint comes from the South Orkney Islands where Triassic microfossils are reported (Dalziel et al 1981) and where the upper age limit is constrained by subduction-related deformation and metamorphism of Early Jurassic age (Flowerdew, Daly & Riley, 2007). Similarly, Lower Jurassic alluvial fan deposits of the Botany Bay Group (Hunter et al 2005) rest unconformably on the turbidites at Hope Bay, and Triassic fossils occur within an allochthonous sedimentary olistolith at Cape Legoupil (Thompson, 1975) (Fig. 1).…”

The Jurassic flora of Western Australia

“…Harris, 1979 Type species. -Elatocladus heterophylla Halle, 1913; Now dated as Middle Jurassic (Hunter et al 2005); Hope Bay, Graham Land, Antarctica.…”

Spesia antarctica gen. et sp. nov. - a new fertile fern spike from the Jurassic of Antarctica

“…Two recently published papers (Ociepa 2007;Birkenmajer and Ociepa 2008) have presented a survey on new material collected from Hope Bay by Prof. K. Birkenmajer in 1988 during the 3 rd Polish Geodynamic Expedition to West Antarctica and from Prof. A. Gaździcki during the following 4 th Polish Geodynamic Expedition. The age of the Hope Bay flora is considered to be Early or Middle Jurassic (Birkenmajer 1993) or Middle Jurassic based on new radiometric data (Hunter et al 2005).…”