Giant slide deposits from a Mesozoic fore-arc basin, Alexander Island, Antarctica

Several very large synsedimentary slide units exist in the well-exposed Mesozoic fore-arc sequence of Alexander Island, Antarctica. The largest single exposure, which is at least 440 m thick and more than 21 by 6 km in area, forms part of a unit that has a volume of as much as 300 km (super 3) . These units are as large as slide deposits noted by remote sensing on modern continental margins. The apparent absence of large, ancient slide deposits is therefore purely a function of exposure. The enormous size of these Antarctic examples, in which sheets of partially lithified sediment, up to 1 km long, have been transported with little or no internal deformation or tilting, emphasizes the care needed in determining that even very large outcrops are not allochthonous. November 1993