Lithostratigraphy of the uppermost Fossil Bluff Group(Early Cretaceous) of Alexander Island, Antarctica: history of Albian regression

The Fossil Bluff Group of south-east Alexander Island contains strata ranging from Kimmeridgian to Albian in age and represents the infill of a fore-arc basin to the west of the Antarctic Peninsula volcanic arc. Recent field work has identified approximately 2800 m of younger rock above the 4000 m already defined, including the top of the previously described Pluto Glacier Formation. A new unit, the Rhea Corner Member is defined, near the top of the Pluto Glacier Formation. The sequence above this is named as the Neptune Glacier Formation, comprising three members, the Deimos Ridge, Triton Point and Mars Glacier members. They represent the youngest part of the Fossil Bluff Group. Both the Deimos Ridge and Mars Glacier members are fully marine, but the Triton Point Member, which is late Albian in age, contains the only record of emergent conditions in 6.8 km of strata. It is a fluvial unit and contains extensive fossil forest horizons, with standing trees up to 5 m tall preserved by widespread flood deposits. The Neptune Glacier Formation therefore records a significant regression-transgression cycle of Albian age.