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Wawa Formation

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LithologyEdit

Lower sandstone member and upper carbonate member.

Stratigraphic relationsEdit

Unconformably overlies Adgaoan Formation

Type localityEdit

Prosperidad, Agusan del Sur

DistributionEdit

Prosperidad, Bunawan, Talacogon

AgeEdit

Early Pleistocene (NN19) to Late Pleistocene (NN20-21)

Named byEdit

San Jose Oil Company (in BM Petroleum Division, 1966)

DescriptionEdit

The Wawa Formation was named by geologists of San Jose Oil Company for the exposures along Wawa River in Prosperidad, Agusan del Sur. As seen along Wawa gorge, this formation consists of a lower sandstone member and an upper carbonate member. A clear angular unconformity separates the Wawa from the underlying Adgaoan Formation.

Sandstones of the lower member are fine grained and argillaceous and rich in fossils such as pelecypods, gastropods and echinoderm spines. The carbonate member consists of an upper reefal limestone and a lower portion made up of detrital limestone or coral breccia and marls. At Talacogon, over the Guadalupe Anticline, the formation corresponds to a series of thin- and well-bedded sandstones, shales and diatomite bearing mollusks and echinoderms (Quebral, 1994).

A regional angular unconformity clearly separates the undeformed early to late Pleistocene (NN19) from the folded late Miocene to late Pliocene (NN15-16) beds. In Talacogon, this unconformity is clearly uplifted by as much as 100 m (Quebral, 1994).

A possible equivalent of the lower clastic member is the Liuanan Sandstone of San Jose Oil Company (in BM Petroleum Division, 1966), described as a Pleistocene fluviatile sequence of loose and crossbedded sands with gravel lenses outcropping along Liuanan River on the basin's western flank. As reported, the thickness as measured is around 300 m.

This formation was previously considered to be Middle Miocene. However, its age has been revised to Early Pleistocene (NN19) to Late Pleistocene (NN20-21) based on the presence of the nannofossils in the sandstones and marls, such as: Cyclococcolithus leptoporus, Discolithina japonica, Gephyrocapsa ericsonii, Gephyrocapsa oceanica, Helicosphaera carteri, Pseudomiliana lacunosa, Syracosphaera pulchra and Umbilicosphaera mirabilis in the sands and marls. This Pleistocene age is confirmed by the foraminifera Operculintonesa sp. cf. and O. barthschi Cushman from the limestone.

The lower clastic member and upper limestone member of the Wawa Formation probably correspond, respectively, to the Mandog Sandstone (Casasola, 1956) in the Davao Basin and Gamut Limestone (Victoriano and Gutierrez, 1980) in the Bislig-Lianga area.

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