STRATIGRAPHY AND REGIONAL SIGNIFICANCE OF THE UPPER-JURASSIC LOWER-CRETACEOUS BYERS GROUP, LIVINGSTON ISLAND, ANTARCTICA

The Byers Group, exposed on Byers Peninsula, western Livingston Island , Antarctica, comprises a mudstone dominated sequence at least 1 km th ick which accumulated in a marginal fore-are environment. The basal, 1 05 m thick Anchorage Formation consists of radiolarian mudstones and t uff-rich interbeds of Kimmeridgian-Tithonian age; it correlates with U pper Jurassic organic-rich mudstone units throughout the proto-South A tlantic region. The succeeding 244 m thick Devils Point Formation mark s the first major pulse of coarse volcaniclastic material into the bas in. It is in turn followed by the extensive President Beaches Formatio n, comprising several hundred metres of finely laminated mudstones wit h at least two major sandstone intercalations. Molluscan and dinoflage llate cyst taxa indicate a Berriasian age and comparatively nearshore depositional environment for this unit. An unconformity of late Berria sian or early Valanginian age separates the three lowest formations fr om the Chester Cone Formation. The fine-grained Sealer Hill Member at the base of the latter is dated as Valanginian, and grades up into sev eral hundred metres of pebbly sandstones and pebble-granule conglomera tes. These mark the second major volcaniclastic pulse and may be of Ha uterivian or even younger age. Definition of this major new group will facilitate more precise Upper Jurassic-Lower Cretaceous stratigraphic al correlations within the southern South America-Scotia arc-Antarctic Peninsula region. It will also aid our understanding of the critical palaeogeographical transition in the northern Antarctic Peninsula from anoxic basin to active magmatic are.