Geology

Foreshore rocks on Capsalay

10 February 2019

Although politically part of the Philippines, Palawan and the Calamian Islands, and also the Sulu Archipelago and the Zamboanga Peninsula in western Mindanao, are part of two protruding north-eastern arms of the Sunda Plate. They are not on the Philippine Mobile Belt but are colliding with it. The inactive Palawan Trench marks the subduction boundary between the Palawan microblock and the Spratly Islands plateau of the South China Sea basin.
The Palawan microcontinental block separated from the southwestern coast of the Asian continent (southwestern Taiwan) during the formation of the South China Sea in the Oligocene to Miocene times.

The Palawan microcontinent consists of Upper Paleozoic to Mesozoic rocks belonging to oceanic plate stratigraphy or a subduction complex composed mainly of Permian to Upper Jurassic chert, Middle Jurassic to Cretaceous clastics, and limestone blocks of various ages. Basaltic blocks and Cretaceous shallow marine sediments occur locally on the microcontinent.

Rocks adjacent to the Capsalay view deck

Geologically the province is divided into distinct areas bounded by the Sabang Thrust, which bisects the island north of Puerto Princessa. Northern Palawan comprises variably metamorphosed pre-Cretaceous sedimentary sequences

The following abstract is from Raschka, H & Nacario, E & Rammlmair, Dieter & Samonte, C & Steiner, L. (1985). Geology of the ophiolite of Central Palawan Island, Philippines. Ofioliti. 10. 375-389:

 The central part of Palawan Island is composed predominantly of ophiolitic rocks stretching for approx 100 km in a SW-NE direction. This complex fills the requirements of a complete ophiolite. It is built up of a basal tectonized peridotite that consists mainly of foliated harzburgite and dunite; this grades upward via foliated troctolite to the gabbro unit that is generally foliated but exhibits massive, isotropic fabrics in its highest level. The uppermost unit of the ophiolite sequence is formed by pillow basalts with associated cherts. Microgabbro dykes cut the whole sequence, whereas pyroxenite and dunite dykes are restricted to the peridotite unit, and plagiogranites to the upper gabbro unit. A sheeted dyke complex is missing. Chromite stringers and bodies are associated with dunite. The ophiolite is overlain by flyschoid sediments, either deformed or undeformed, the palaeontological age of which ranges from late Cretaceous to Oligocene. They are covered by younger shallow water sediments. Intensely foliated rocks of mainly basaltic origin are associated with the peridotite contacts towards flyschoid sediments and pillow basalts with cherts. They are metamorphosed in amphibolite and greenschist facies. K/Ar determinations on amphibole and mica yielded isotopic ages of approx 40 m.y.

Softer foreshore rocks at Villapenya, on the western side of Pagdanan Bay.

Fossils

Fossilised vertebra from marine mammal found on Capsalay beach