Publications

The Upper Oligocene Cebu Limestone In Central Philippines represents the early sedimentary fill of the Visayan Basin, which opened during the mid - Oligocene. The Cebu Limestone, which spans a period of about 3 Ma, has a total thickness of ~2130m It consists of alternating siliciclastic and carbonate intervals from which three depositional sequences, numbered from I to 111, have been identified.In Sequence I (NP25 nannoplankton zone), a thin limestone bed set separates the transgressive lagoonal mudstones from the overlying highstand beach system. This limestone is composed mainly of larger foraminifera1 test concentrations. Sequence I1 has a basal transgressive limestone bed set. This limestone represents thin ramp carbonates characterized by winnowed larger foraminiferal-coral floatstones in the downramp reaches and larger foraminiferal-oncoidal floatstones in the lagoonal area. The early highstand is represented by offshore mudstones to coastal sandstones, whereas a thick succession of ramp carbonates was deposited during the late highstand. A relative sea-level fall subjected the shallow ramp carbonates to limited karstification and dolomitization. Sequence III (uppermost NP25 to NN1) commences with limited deposition of shelf margin wedge limestones above this karstification surface. During the ensuing transgression, partial drowning of the distal ramp initially occurred. In a later stage, complete drowning of the ramp is marked by the abrupt contact with the overlying mudrocks.Shallow ramp carbonates were preferentially deposited during transgressions (Sequence 1: 11, and 111) or Iate highstands (Sequence 11) probably due to the trapping of siliciclastics in coastal areas. Siliciclastics occur in all systems tract types.