Lower Cretaceous inoceramid bivalves from the Antarctic Peninsula region
The occurrence of rich faunas of Lower Cretaceous inoceramid bivalves in the Antarctic Peninsula region further emphasizes their widespread distribution, and enhances their potential for regional biostrati-graphic correlations. The Antarctic material is contained in approximately seven of twelve species groups that are recognized on a worldwide scale. Six of these are assigned to the genus Inoceramus and one to Birostrina. The comparatively rare genus, Anopaea, is left undivided.In the Fossil Bluff Formation of Alexander Island, Berriasian representatives of the I. ovatus group (I. cf. ovatus Stanton and I. sp. aff. ellioti Gabb) are succeeded by A. trapezoidalis (Thomson and Willey) which has undifferentiated Berriasian-Aptian affinities. This is in turn followed by an Aptian member of the I. neocomiensis group (I. deltoides sp. nov.) and in the Albian there are occurrences of Anopaea sp. nov. aff. mandibula (Mordvilko), B.? cf. concentrica (Parkinson) (B. concentrica gp.), I. cf. anglicus elongatus Pergament, I. sp. aff. bellvuensis Reeside, I. sp. aff. comancheanus Cragin (all I. anglicus gp.), and I.flemingi sp. nov. (I. liwerowskyae gp.). Aptian-Albian strata on James Ross Island have yielded both I. stoneleyi sp. nov. (I. liwerowskyae gp.) and Anopaea sp. nov. beta. These are followed by the Albian species I. cf. sutherlandi M'Coy and I. carsoni M'Coy (both I. carsoni gp.) and the highest Lower Cretaceous specimens within this sequence have been referred to B. concentrica (Parkinson).Although specimens of I. cf. heteropterus Pokhialainen (I. heteropterus gp.) and I. annenhovensis sp. nov. (unclassified) from Annenkov Island are of probable Hauterivian-Barremian age, it is noticeable that there is a marked lack of Valanginian-Barremian inoceramids in the Antarctic Peninsula region. This gap probably reflects a period of regional uplift and non-deposition.Representatives of the I. ovatus and I. heteropterus groups provide a means of correlation between the Berriasian-Barremian of the Antarctic Peninsula and the North Pacific region. I. deltoides sp. nov. can be closely matched with Northern Hemisphere Aptian members of the I. neocomiensis group and I. stoneleyi sp. nov. and I.flemingi sp. nov. have possible counterparts within the Aptian-Albian of Spitzbergen, south-east USSR and far eastern USSR. Of the various Albian species groups, that based on I. carsoni provides a direct link between Antarctica and Australia and those based on I. anglicus and B. concentrica facilitate a range of long-distance correlations. The latter category, in particular, may be one of the first truly cosmopolitan inoceramid groups.