Mesozoic radiolarian faunas from the Antarctic Peninsula: age, tectonic and palaeoceanographic significance

Abstract

New assemblages of Radiolaria, including some of the few occurrences of high southern latitude Jurassic and Cretaceous radiolarian faunas, show that several localities in the LeMay Group of Alexander Island range in age from latest Jurassic–earliest Cretaceous to at least Albian. By demonstrating that sedimentation and deformation in the LeMay Group was diachronous, younging oceanwards to the northwest, these new age assessments support the model of the LeMay Group as an accretionary complex. The polarity of subduction beneath Alexander Island was not affected by arc collisions from at least the Lower Jurassic to the Oligocene, and such a long period of continuous accretion appears to be unusual. Deposition of the LeMay Group spans the Kimmeridgian to Albian sedimentation in the Fossil Bluff Group fore-arc basin, thus making the earlier concept of the LeMay Group as pre-Jurassic ‘basement’ untenable. Allochthonous latest Jurassic–earliest Cretaceous radiolarian assemblages with some supposed Tethyan affinities are present in the LeMay Group. In contrast, an in situ latest Jurassic assemblage from the Nordenskjöld Formation of the back-arc basin and a further Jurassic assemblage from a probable trench-slope basin have characteristics believed diagnostic of high latitudes. The biogeographic affinities of radiolarians from cherts in the LeMay Group accretionary complex suggest that both these cherts, and associated basalts, are far-travelled slices of the Phoenix plate. Rocks from the probable trench-slope basin, formerly assigned to the younger Fossil Bluff Group fore-arc basin sequence, now appear to be part of a new, previously unrecognized formation.

Autochthonous v. accreted terrane development of continental margins: a revised in situ tectonic history of the Antarctic Peninsula

“…Similarly, on the Peninsula this magmatism records a period of lithospheric extension and consequent upwelling of fertile nonmetasomatized mantle during the resumption of subduction after a Late Jurassic pause (Macdonald et al 1999). This is supported stratigraphically by the presence of contemporaneous OxfordianKimmeridgian radiolarian cherts associated with pillow basalts and volcanic tuffs within the oldest LeMay Group outcrops (Burn 1984;Holdsworth & Nell 1992), a typical feature of suprasubduction-zone ophiolite sequences (Metcalf & Shervais 2008), and the appearance of volcanolithic material higher up the LeMay Group stratigraphy indicating a proximal mafic arc source (Willan 2003). A similar association of Late Jurassic to Early Cretaceous OIB, E-MORB and arc-like mafic dykes are recorded in the Central Domain in NW Palmer Land (Scarrow et al 1998) and the Eastern Domain in NE Palmer Land (Wever & Storey 1992), further supporting a shared tectonic history of the three terranes.…”

“…1; Thomson & Tranter 1986;Holdsworth & Nell 1992). This sequence is interpreted as representing an accretionary trench-fill assemblage (Suárez 1976;Doubleday et al 1993).…”

“…Units for the Western Domain are as follows. Sed: LeMay Group, Sinnemurian-Albian (Thomson & Tranter 1986;Holdsworth & Nell 1992); Fossil Bluff Group, KimmeridgianAlbian (Butterworth et al 1988);Adelaide Is., c. 150-113.9 Ma (Thomson 1972;Riley et al 2012a). Vol: Alexander Is., 157-152 Ma (Macdonald et al 1999), 80-46 Ma (McCarron 1997 and 2.5-0.5 Ma (Hole 1988); Adelaide Is., 76-39.2 Ma (Griffiths & Oglethorpe 1998;Riley et al 2012a);South Shetland Is., 135-22.6 Ma (Smellie et al 1998;Haase et al 2012) and 2.4-0.1 Ma (Pankhurst & Smellie 1983).…”

Structural geology of the Mesozoic Miers Bluff Formation and crosscutting Paleogene dikes (Livingston Island, South Shetland Islands, Antarctica) – Insights into the geodynamic history of the northern Antarctic Peninsula

“…The Hathway and Lomas (1998), Holdsworth and Nell (1992), Rees and Cleal (2004) and Fleming and Thomson (1979).…”

Sedimentary provenance study of the post-Early Permian to pre-Early Cretaceous metasedimentary Duque de York Complex, Chile

“…13). The oldest LMG outcrops contain radiolarian cherts of Late Triassic age (Holdsworth and Nell, 1992). Early Jurassic shelly fauna are also present at two localities in the Lully Foothills accreted volcanic-island succession (Thompson and Tranter, 1986;cited in Willan, 2003).…”