If I recall correctly, indications of a very large impact crater partially on antarctica (subglacial today) have been found, the rest would be on the australian plate. Read this a few years ago here.
Two Catastrophe ScenariosAbout 2.2 million years ago, a chunk of space debris about a kilometer in diameter splashed down in the Bellingshausen Sea between Antarctica and South America. It was some splash! The splash zone was about 20 kilometers across, waves 4 kilometers high raced away from Ground Zero, and a column of salt water ascended miles high into the upper atmosphere. The TNT equivalent is estimated at 12 billion tons. Ice clouds formed and shaded the planet, causing severe climate changes. On the floor of the Bellingshausen Sea, 5 kilometers deep, lies the Eltanin Impact Structure.
by William CorlissOcean splashdownAn asteroid between one and four km in diameter that splashed into the Southern Ocean, 1500 km SW of Chile, just over two million years ago, may have worsened a period of global cooling that saw the emergence of modern humans... The impact in question was first discovered during a cruise of the Eltanin in the 1960s: betrayed by anomalously high amounts of iridium in ocean-bed cores... Gersonde and his colleagues have taken another look, their results coming from a cruise in 1995 by the research ship Polarstern. The impact left a distinctive 'signature' of geological layers, very like that of the Chicxulub impact. Lowest in the 'impact' sequence is a thick layer of disordered rubble, full of chunks of rock up to 50 cm across: this layer represents the large-scale disturbance immediately after the impact as the ten-megaton blast ripped up the ocean floor. This layer took around four hours to settle after the blast. Smaller particles, such as grains of sand, took longer to settle, explaining why this layer was found immediately above the rubble layer. Capping the whole sequence is a thin layer of very fine sediment, dispersed over a wide area. This would have contained fine-grained material (including vaporized asteroid) flung high into the air and which took days or months to settle out. This layer contained the iridium.
by Henry Gee
UC Davis Geology Department
Ooops, probably this one:
http://www.freerepublic.com/focus/news/1197396/posts
http://www.freerepublic.com/focus/bloggers/1248406/posts
http://www.freerepublic.com/focus/news/1641966/posts
http://www.freerepublic.com/focus/chat/1643681/posts