Stratigraphy of the Pliocene Sorsdal Formation, Marine Plain, Vestfold Hills, East Antarctica

The Sorsdal Formation and one member, Graveyard Sandstone Member constitute a sedimentary sequence covering approximately 10 km(2) of Marine Plain, Ve stfold Hills, East Antarctica. The new Formation consists dominantly of fri able diatomaceous siltstone and sandstone with dark limestone lenses. It is in situ, essentially horizontal, 7.2 m thick in its type section and lies less than 25 m a.s.l. Graveyard Sandstone Member occurs near the top of the formation, is highly lithified sandy diamictite, 30-50 cm thick and widesp read through the Marine Plain region. Using diatoms, the Formation is Early Pliocene in age (Fragilariopsis barronii; 4.5-4.1 Ma). The Graveyard Sands tone Member probably was deposited during the Gilbert Chron interval (lower Chron 2Ar or C3n.1r) of reversed magnetic polarity. The Sorsdal Formation contains fossil cetaceans and a diverse and well-preserved invertebrate fau na. Foraminifera are rare partly because of diagenesis, but include Ammoelp hidiella antarctica. No evidence of coeval terrestrial vegetation has been recovered. The deposit accumulated in a series of small bays probably in an environment warmer than exists in the region today. There is no lithologic al evidence of glacial influence except in Graveyard Sandstone Member that may represent local glacial influence in a shallow marine to intertidal env ironment.