Geology
The crust of northeast Palawan was derived from the Eurasian Plate of mainland China. It is the exposed portion of a microcontinent that drifted southward with the opening of the South China Sea. This microcontinent also forms the shallow water north of Palawan in the Reed Bank-Dangerous Grounds area of the southern South China Sea. Some of the oldest rocks of the Philippines are found in northeast Palawan (Permian-Carboniferous age). Southwest Palawan exposes primarily ophiolitic material (rocks derived from uplifted oceanic crust and mantle). This oceanic material appears to have been thrust upon the continental crust. The transition from "oceanic" ophiolite in the southwest to "continental"-type rocks in the northeast occurs in the area of central Palawan around Ulugan Bay. In the Dalrymple Point area, on the east side of Ulugan Bay, are several exposures showing that the Palawan ophiolite has been thrust on to the continent-derived clastic rocks ("Sabang thrust").
Specific rock types in the "continental" northeast, include clastic rocks (sandstones and mudstones). Good exposures of these rocks types can be found on the main road running along the southern coast east of Puerto Princesa all the way up to Malampaya Sound. These rocks probably formed the continental shelf, rise, slope or even deeper marine deposits on the southeast margin of China prior to the opening of the South China Sea. The Palawan Trench is a deep ocean element of the South China Sea.
Further north, around the Malampaya Sound area and up to the El Nido area, one finds deep marine chert and limestone. Based on the structure of these sedimentary units, it is thought that they formed part of an accretionary prism on the southeast margin of China at a time when that part of China was an Andean-type plate margin (an ocean-continent subduction zone). The chert and limestone were scraped off of an oceanic plate and accreted to the margin of China (again, prior to the opening of the South China Sea). Some of the limestones are also thought to be of olistostromal origin (i.e., they formed in shallow water but were transported to deeper water by submarine slides).
It is interesting to note that the spectacular karst limestones in the St. Paul area and El Nido area that Palawan is somewhat famous for, are of different origin and age. The limestones in the St. Paul National Park east of Ulugan Bay (where the famous Undeground River is located) are relatively young. Based on their fossil content they are assigned an Oligocene-Miocene age (~30 to 15 million years old). These younger limestones formed largely as reef structures on the bit of continental crust that drifted south from China during the opening of the South China Sea. These are the same limestones that host most of the oil and gas that is being extracted offshore in the South China Sea. In contrast, the limestones in the El Nido area are largely Permian in age (~300-250 million years old). They are related to the karst limestones of Vietnam and China.
Intruding these rocks in central Palawan (Cleopatra's Needle area) and northern Palawan (Mount Capoas or Kapoas area) are young granite bodies (true granite to granodiorite) of Miocene age (13-15 million years old based on zircon and monazite U-Pb dating). In the Taytay area of northern Palawan, a young basaltic cinder cone is another manifestation of young magmatic activity. The granitic magmatism and basaltic magmatism are both expressions of what has been identified as a widespread post-South China Sea spreading magmatism that has affected many areas around the South China Sea. Hydrothermal activity associated with mercury mineralization near Puerto Princesa is yet another sign of recent magmatic-hydrothermal activity. Surprisingly though, Palawan is relatively "quiet" in terms of seismic activity. Very few moderate-sized earthquakes are recorded in the area in contrast to the rest of the Philippines east of Palawan which are very seismically active.
Tectonically, Palawan with the Calamian Islands, is considered to be a north-east extension of the Sunda Plate, in collision with the Philippine Mobile Belt at Mindoro.
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