The Klondyke (Middle Miocene to early Late Miocene) and Amlang Formations (late Late Miocene) make up a sequence of over 5,000 meters-thick, mostly clastic rock units that are well exposed on the southwestern flank of the Luzon Central Cordillera. The Klondyke Formation which conformably underlies the Amlang Formation. generally consists of coarse clastic rocks of polymictic conglomerate, conglomeratic sandstone, fine-grained to coarse-grained sandstone and flow breccias interbedded with thin to medium beds of shale and siltstones. The Amlang Formation, on the other hand. is a rhythmic alternating deposit of sandstones and shale or sandstone-siltstone-shale,

Workers and students have assigned various ages and given palaeoenvironmental interpretations to these rock units. particularly the Klondyke Formation. This study was thus initiated based mainly on calcareous nannofossils of the Klondyke and Amlang Formations, to determine their age and depositional palaeoenvironments. The objective for refining the formations` age and palaeoenvironment is part of the continuing project to understand the complex sedimentological history of the northeastern margin of the Central Valley basin bordering the Central Cordillera of Luzon Island.

Biostratigraphic determination was carried out using predominantly calcareous nannofossils on over 277 samples collected from 11 study sections. Foraminifera was largely used to support calcareous nannofossil evidences and for reconstructing palaeoenvironments. ln addition. palynological examination was attempted on a few selected samples. particularly those that yielded neither calcareous nannofossils nor foraminifera but are critical to the delineation of palaeoenvironnient. The biostratigraphic interpretation based on calcareous nannofossilsi planktonic foraminifera and larger foraminifera followed zonal schemes presented by Martini (1971), Blow (1969 & 1979) and Adams (1970 & 1984), respectively. Likewise, reference to Bolli et al. (1975) was made. The nomenclature of Hedgepeth (1957), Murray (1973), Berggren (1978) and lngle (1980) was adopted for palaeoenvironmental interpretation.

Integrated calcareous nannofossil, foraminiferal and stratigraphic analyses indicate the age of Middle Miocene to early Late Miocene (NN5-NN10/N9-N17) for the Klondyke Formation and late Late Miocene (NN11/NN17) for the Amlang Formation. Additionally, the pattern of distribution ofthe calcareous nannofossils and the associated foraminiferal assemblages and lithofacies support the interpretation that the two formational units belong to a submarine fan system ranging in paleodepths from middle sublittoral to bathyal.