Kennon Limestone


Massive biohermal limestone with associated calcarenite and calcirudite and minor mudstone

Stratigraphic relations

Unconformably overlies the Zigzag Formation along Bued River at Camp 3, Tuba, Benguet area, and unconformably overlain by the Klondyke formation in the Baguio District


Baguio District; Itogon and Mankayan, Benguet


late Early Miocene – early Middle Miocene


240 m at the type locality

Named by

Corby and others (1951)


Butac Limestone (Cervantes-Bontoc area)

The Kennon Limestone unconformably overlies the Zigzag Formation and unconformably rests below the Klondyke Formation at its type locality at Camp 3 along Kennon Road at Km 225-226.  The formation also outcrops on Mt. Sto. Tomas and Trinidad, Benguet.  In the type locality, the formation consists principally of massive cream to buff to dark graybiohermal limestone with associated calcarenites and calcirudites.  The basal portion consists of wackes, including a conglomeratic calcarenite near the base, which contains clasts of volcanic rocks and small amounts of diorite pebbles and cobbles.  Thin lenses of sandstones and siltstones have been observed in the middle section.

Towards the top, the limestone grades into a bioherm-mudstone complex with a thickness of 52 m, which was separately named by Durkee and Pederson (1961) as Twin Peaks Formation.  The reef mudstone at the base of the Twin Peaks grades upward into a mudstone-graywacke sequence.  The Twin Peaks, however, could be considered a member of the Kennon Limestone.

The Kennon Limestone has a total thickness of 240 m at the type locality, including the Twin Peaks member.  Balce and others (1980) give a thickness of 240 m for the limestone north of Trinidad.

Paleontological analyses of limestone samples taken from several localities indicate an age of early Middle Miocene (Tan, 1994).  Maleterre (1989) reports age determinations of late Early Miocene to early Middle Miocene for the Kennon Limestone.

The Butac Limestone in the Cervantes-Bontoc area is considered equivalent to the Kennon Limestone.  This limestone is about 100 m thick and was dated Early to Middle Miocene, probably Middle Miocene (Tf1-Tf2).

Formation sequenceEdit

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