Time Constraints on the Evolution of Southern and Central Palawan Island, Philippines from On- and Offshore Correlation of Miocene Limestone Formations. (Charles Hutchison Memorial)

Steuer, Stephan¹; Franke, Dieter¹; Meresse, Florian²; Savva, Dimitri²; Pubellier, Manuel²; Mouly, Benoit³; Auxietre, Jean-Luc³
¹Economic Geology of Energy Resources, Federal Institute for Geosciences and Natural Resources BGR, Hannover, Germany.
²Laboratoire de Géologie, Ècole Normale Supérieure, Paris, France.
³Total/EP/GSR/PN/BTF, Paris, France.

The link between the deformation of southern and central Palawan Island and the deformation of the adjacent offshore wedge is poorly studied. The wedge is a continuation of the Palawan fold and thrust belt and bounds the Borneo-Palawan Trench to the Dangerous Grounds and to Palawan Island. A key parameter for understanding the formation and development of this wedge is the Upper Miocene to Lower Pliocene Tabon Limestone. With an age of ~9 to ~4 Ma, this limestone sequence overlies unconformably the offshore wedge. A detailed biostratigraphic correlation of the Tabon Limestone along the SW Palawan shelf, using well data, combined with detailed investigations onshore southern and central Palawan, revealed a time-and space-transgressive development of these limestones. They are progressively younging towards the West. We infer that the formation of the Tabon limestone is directly linked with the development of the wedge that tectonically controls the formation of this carbonate platform. This constrains the time for the final phase of the formation of the Palawan thrust belt. After the end of the compression and wedge formation in the lower Early Pliocene the wedge underwent a phase of thermal subsidence.

The beginning of the thrust belt formation is constrained by the so called Nido Limestone, which was deposited after the breakup of the South China Sea (~35Ma) until the Early Miocene. Age data available from offshore wells give an age of 28 - 25Ma near the base of the Nido Limestone. While cropping out onshore north Palawan, these limestones were overthrusted by the wedge in southern and central Palawan. Seismic images show a gentle dipping of these carbonates towards the east. It is also visible in the seismic, that these limestones are only slightly affected by the wedge formation.

We can deduce that the wedge did not reach the southern and central Palawan area prior to ~18Ma. Using the Tabon Limestone, which seals the wedge, as time constraint we state that the development of the wedge in the south Palawan area started in the upper Middle Miocene (~12Ma) and continued developing towards the west until the upper Late Miocene to Early Pliocene (~5Ma).

After the wedge propagation stopped, the wedge front collapsed in several places due to gravitational sliding.

Southern and central Palawan was formed in a second pulse of compression and uplift in the Late Pliocene. Investigations on onshore outcrops give indications to a working spleothem since ~1.2Ma.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012