A new Middle Jurassic fauna from Antarctica

THOMSON, M.R.A.; DAMBORENEA, S.E.

Londres, Gran Bretaña

Simposio; Arkell International Symposium on Jurassic Geology; 1993

Birbeck College

In Antarctica, exposures of marine Mesozoic strata are confined to the 2000 km long Antarctic Peninsula region. Despite the widespread occurrence and thickness (locally several thousand metres) of relevant successions, fossil faunas almost invariably indicate ages of Late Jurassic to Cretaceous. Proving the existence of older strata is a somewhat serendipitous and time-consuming process. Thus, during the last 25 years, only two faunas of Triassic age, one of Early Jurassic and one of Middle Bajocian and Callovian age have been reported, all from isolated localities. Marine mudstones at Cape Wallace, Low Island, in the South Shetland islands, contain poorly preserved inoceramid bivalves, Retroceramus sp. ex gr. haasti (Hochstetter), Epimayaites aff. transiens (Waagen) and Hibolithes (?) sp. and referred to the Late Jurassic (possibly Oxfordian). However, the description and illustration of inoceramid faunas from Argentina by SED suggested that the Antarctic material was actually much closer to Retroceramus stehni Damborenea from the latest Bathonian-earliest Callovian of Chacay Melehue, Neuquén. New collections from Low Island include further specimens of R. stehni, and the external mould of an ammonite body chamber probably from a species of Stehnocephalites or Xenocephalites. Although a more precise identification of the ammonite is not possible, both genera and the inoceramid species all indicate a latest Bathonian-Early Callovian age. The recognition of the Low Island fauna as being Middle Jurassic in age provides an important new insight into the Mesozoic stratigraphy of Antarctica and strengthens palaeobiogeographical relations with southern South America, and possibly New Zealand.