Antarctic Science

Earth Sciences

Reworked late Neogene Austrochlamys anderssoni (Mollusca: Bivalvia) from northern James Ross Island, Antarctica

D. Pirriea1 c1, H.A. Jonkersa2, J.L. Smelliea3, J.A. Cramea4 and J.M. McArthura5

a1 Helford Geoscience LLP, Menallack Farm, Treverva, Penryn, Cornwall TR10 9BP, UK

a2 Dommerswijk 10, 7782 PA De Krim, The Netherlands

a3 Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK

a4 British Antarctic Survey, NERC, High Cross, Madingley Road, Cambridge CB3 OET, UK

a5 Department of Geological Sciences, University College London, Gower Street, London WC1E 6BT, UK

Abstract

We report on the discovery of a new outcrop of fossiliferous Neogene sediments on northern James Ross Island, northern Antarctic Peninsula. Approximately 100 specimens of the pectinid bivalve Austrochlamys anderssoni (Hennig, 1911) were collected from the permafrost active layer. This bivalve species has a late Miocene to late Pliocene range and has previously been reported from both the glaciomarine Hobbs Glacier Formation and the interglacial Cockburn Island Formation in the James Ross Island area. The localized presence of abundant A. anderssoni within the permafrost suggests that the fossils have been frost heaved from an outcrop of either the Cockburn Island or the Hobbs Glacier formations, originally deposited on northern James Ross Island. The overall shell form, general absence of associated Antarctic Peninsula-derived clasts in the host sediment, and the measured 87Sr/86Sr isotope ratio of the shells (0.709050) which is indistinguishable from that for pectinid bivalves from the Cockburn Island Formation on Cockburn Island (0.709047) suggest that the shells were derived from a unit similar in age to the Cockburn Island Formation. This suggests that the Cockburn Island Formation was originally more laterally extensive than was previously known.

(Received January 26 2004)

(Accepted September 08 2010)

(Online publication January 26 2011)

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