Foraminiferal analyses of Cenozoic strata of Central Valley, Luzon and southern Iloilo, Panay, indicate a general planktonic zonation for the middle and later Cenozoic which is similar to that recognized in equivalent strata of other tropical areas of the world.

There is generally parallel basinal development in Central Valley and Iloilo beginning in the Late Oligocene-Early Miocene interval. The cycle commenced with shelf conditions and orbitoidal facies giving way upward and with time to increasingly deeper-water facies of the bathyal zone. Maximum water depths of at least 1,000-2,000 meters were attained during the Miocene as indicated by Pullenia bulloides, Osangularia bengalensis, Laticarinina pauperata, and others. The parallel history in the two areas stops in the Late Miocene when Central Valley experienced prominent basin-filling and a transition to shallow-water paralic facies. In Iloilo, deep basinal conditions prevailed into the Middle Pliocene before basin-filling occurred.

The more complete planktonic sequence is that of Iloilo. Late Oligocene time is suggested by Globigerina ciperoensis in at least one part of the basin. Early Miocene is represented by a lower Globigerina dissimilis zone and an upper Globoquadrina rohri zone. Middle Miocene time is indicated by a lower Globorotalia fohsi fohsi left-coiling zone giving way upward to the right-coiling populations of Globorotalia fohsi robusta and Globorotalia menardii (primitive form). From bottom to top, the Late Miocene zones include a basal Globoquadrina dehiscens advena zone, a Globoquadrina altispira altispira zone (top of occurrence), a Globigerina nepenthenes zone (top of occurrence), and at the top a Globoquadrina altispira globosa-Globoquadrina dehiscens dehiscens zone.

Early Pliocene populations are characterized by Sphaeroidinella dehiscens dehiscens and Globigerina eggeri. Middle Pliocene populations lack these but include an abundance of Globorotalia truncatulinoides and Globorotalia menardii. Pulleniatina obliquiloculata is common to abundant in the Middle and Early Pliocene and rare in the Late Miocene. It is dominantly right-coiling in the Middle and most of the Early Pliocene, left-coiling at the base of the Pliocene, right-coiling and rare in the latest Miocene, and mostly left-coiling and very rare below.

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