The Mid-Upper Jurassic olistostrome of the west Philippines: a distinctive key-marker for the North Palawan block

Abstract

A field survey in North Palawan shows that this part of the island is mainly occupied by a chaotic clastic sequence in which several facies are distinguished; namely turbidite and slump deposits, pebbly mudstone, thick coarse sandstone and olistostrome, with exotic blocks of Permian or Triassic chert and limestone, Mid-Upper Jurassic Limestone, acidic lava and volcanoclastic rocks. Callovian to Lower Kimmeridgian radiolarian assemblages have been discovered from the mudstone matrix. Combining our new results with previous stratigraphic data, it is likely that the olistostrome with exotic blocks is followed by late Cretaceous-Eocene (?) turbidites. The same kind of olistostrome is known from the Calamian, Mindoro, Panay and Carabao islands. We propose that this olistostrome can be used as a distinctive criteria of the Palawan block. Comparisons of the age range of the matrix and the nature of the olistoliths suggest that the Palawan olistostrome can be correlated with the Sanbosan zone of S.W. Japan and central Ryukyu. To the south, such an Upper Jurassic olistostrome has not yet been recognized, though it is probably present below the chert-spilite formation of Borneo.