GEOLOGY OF THE SOUTHWESTERN MARGIN OF THE CAGAYAN VALLEY BASIN, LAMUT (IFUGAO) AND VILLA VERDE-SOLANO (NUEVA VIZCAYA)

Nathaniel Baluda, Geol 170’00 Class,
Rose Berdin, Joseph Foronda, Neil Macalalad, & Fernando Siringan
National Institute of Geological Sciences, University of the Philippines, Diliman, 1101 Quezon City


ABSTRACT

 

The Geol 170 Class of 2000 conducted basic geologic mapping, covering an area of 423 km², in the towns of Lamut (Ifugao), Villa Verde-Solano (Nueva Vizcaya). Four formations were encountered: the Ibulao Limestone, the Lubuagan Formation, the Balbalan Formation and the Tabuk Formation.

TheVolcanism due to the initial rise of the Central Cordillera in the Early Miocene was reduced to allow the formation of the shallow-marine Ibulao Limestone of the Cagayan Basin. The formation consists of biohermal to biostromal limestones, and forms north-south trending fold ridges. It is characterized by a gradual decrease in bed thickness from the base to the topmost portion.

TheThe continuous rise of the Sierra Madre in the Early Miocene provided the sediments of the Lubuagan Formation. The clastics were deposited in outer neritic to bathyal environment. The lowermost sandstone-siltstone interbeds of the unit were encountered in Brgy. Commonal, Nueva Vizcaya. The Lubuagan formation conformably overlies the Ibulao Limestone.

TheThe Balbalan Formation unconformably overlies the Lubuagan Formation. The base of the unit consists of andesite flow. The clastic sequence includes, from base to top, fine to medium-grained sandstones, siltstones, mudstones, medium to coarse-grained bedded sandstones, breccias and conglomerates. The formation is assigned a Middle Miocene age.

TheThe Tabuk Formation, assigned a Pleistocene age, consists of volcanic plugs, tuffaceous sediments, lahars and terrace gravels. The sediments were derived from the rapidly rising Central Cordillera and Sierra Madre ranges during the Plio-Pleistocene. The formation unconformably overlies the older units.

TheAnalysis of a Middle Miocene to ?Pliocene reverse fault shows a WNW-ESE trending maximum compressional stress (s₁). Quaternary strike-slip and normal faults indicate a NW-SE direction of compression (s₁) and an E-W direction of extension (s₃). The compressional and extensional regimes can be correlated to the movement of the Philippine Fault in Northern Luzon.