GIANT SLIDE DEPOSITS FROM A MESOZOIC FORE-ARC BASIN, ALEXANDER ISLAND, ANTARCTICA

Several very large synsedimentary slide units exist in the well-expose d Mesozoic fore-arc sequence of Alexander Island, Antarctica. The larg est 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 30 0 km3. These units are as large as slide deposits noted by remote sens ing on modern continental margins. The apparent absence of large, anci ent slide deposits is therefore purely a function of exposure. The eno rmous size of these Antarctic examples, in which sheets of partially l ithified sediment, up to 1 km long, have been transported with little or no internal deformation or tilting, emphasizes the care needed in d etermining that even very large outcrops are not allochthonous.