Detrital serpentinite from the Guajira Peninsula, Colombia

Small lenses of detrital serpentinite, completely surrounded by massive serpentinite, occur within a sequence of Mesozoic phyllites and metasiltstones in the Cerros de Parashi area, Guajira Peninsula. These lenses, which are as much as 30 m thick, consist of poorly sorted breccias that grade irregularly upward into bedded serpentinite sandstone and shale. Graded bedding is well developed in the sandstones, and channel structures and cross-bedding are also common. Two chemical analyses of serpentinite sandstone and shale show them to be of normal serpentinite composition. The original detrital serpentine minerals in these rocks were lizardite and chrysotile, but they have been partially replaced by antigorite during a period of upper greenschist facies metamorphism. The detrital serpentinites were formed by large submarine turbidity currents or mudflows, and the massive serpentinites surrounding them are believed to have been emplaced by gravity sliding.