Late Jurassic foraminifera, Wallaby Plateau, Offshore Western Australia

Foraminifera are recorded from one sample dredged by RV Sonne from 4438–4049 m water depths on the southwestern margin of Wallaby Plateau, eastern Indian Ocean (25.5 S, 108.5 E). An Oxfordian/Kimmeridgian age is estimated based on the foraminiferal fauna, but it conflicts with Early Cretaceous zircon dates that suggest some recycling or mixing during dredging. The Jurassic age is significantly older than any previously known age in the region and predates age estimates for the initiation of seafloor spreading along the Western Australian margin as India departed from Australia/Antarctica during the break-up of Gondwana. The fauna is of low diversity possibly due in part to dissolution at depth and thus probably does not accurately reflect the original diversity. It is dominated by Conicospirillina wallabyensis n. sp. (Spirillinacea), Conorboides falveyi n. sp. and Lenticulina muensteri (Roemer, 1839). Diversity is greatest among nodosariacean species; agglutinated forms are very rare and planktonic and miliolid species are absent. The foraminifera are accompanied by diverse fragmentary invertebrates. The sediment accumulated in shallow, fully marine, (warm-?) temperate conditions and the locality has subsided some 4000 m since deposition. Descriptions of taxa similar in form to Conicospirillina should be studied under crossed polars to determine whether or not the skeleton has grown in crystallographic continuity. Marginulina suprajurassica Gordon is shown to be pre-occupied.