Abstract

The Cagayan Valley Basin is a post-Oligocene sedimentary trough in northeastern Luzon Island and is one of the biggest in the Philippines. It attained a fully archipelagic configuration in the Miocene time during which the maximum deposition of marine sediments occurred.

The basin is about 250 km long and 80 km wide and covers an area approximately 20,000 square kilometers. The basement topography is asymmetric with the deepest on the central western part and shoals to the east. Sedimentation was characterized by a rapid turbiditic influx of material in the bathyal depths creating a sequence of normal pelagic sediments and flysch. Organic material in the claystones formed is dominantly land-derived and is high in humic substances.

Preliminary studies are being undertaken to determine the relation between geothermal and geopressure trends and their effect on organic matter and hydrocarbon generation. The compaction of sediments and the drainage of subsurface fluids are deduced from pore-fluid pressure in claystones and a model for the migration pattern of hydrocarbons is constructed.

Hydrocarbons had been generated in the basin and the failure to find commercial deposits is attributed to inadequacy of geologic data from which optimum reservoir rocks can accurately be prognosticated.