Limestone, calcarenite, calcirudite

Stratigraphic relations

Unconformable over volcanic rocks; transitional to Lubuagan Formation


Western flank of Cagayan Valley; traceable from Luna, Apayao to Salegseg, Kalinga; Rizal, Cagayan


Late Oligocene?


546 m

Named by

Durkee and Pederson (1961)


Ibulao Limestone

The Sicalao Limestone was defined by Durkee and Pederson (1961) in reference to the limestone unit on the western flank of the Cagayan Valley which is considered to be equivalent to the Ibulao Limestone. According to Durkee and Pederson (1961) the Sicalao can be traced nearly continuously from Luna, Apayao near the north coast, southward to Salegseg, Kalinga. It rests on volcanic rocks and is transitional to the overlying Lubuagan Formation, designated by Durkee and Pederson (1961) as the Mabaca River Group. The limestone consists mainly of thick beds of calcarenite and calcirudite, becoming argillaceous and thinly bedded at the topmost 20 m. It has an estimated thickness of 546 m as measured along the Anaguan Creek section at Rizal, Cagayan (Durkee and Pederson, 1961). It is dated Early Miocene (T-e4-5) by Durkee and Pederson (1961) on the basis of orbitoid fauna in the limestone but its stratigraphic position suggests a probable Late Oligocene age. It is considered by BED (1986a) and Caagusan (1978) to be coeval with the Lubuagan Formation, which is assigned an age range of Early Miocene to Middle Miocene.

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