FANDOM


Lithology

Basalt, andesite, pyroclastic rocks, sandstone, shale

Stratigraphic relations

Constitutes the basement of Cagayan Valley basin

Distribution

Western part of northern Sierra Madre; southwest of Divilacan River; Maconacon River, Isabela

Age

Eocene

Previous name

Abuan River Formation (MMAJ-JICA, 1989)

Renamed by

MGB (2004)

Synonym

Dumatata Formation (Huth, 1962), Caraballo Group (MMAJ-JICA, 1977)

Correlation

Mt. Cresta Formation (MMAJ-JICA, 1989)

The Abuan Formation, which was named as Abuan River Formation by MMAJ-JICA (1989), is the oldest formation in the western part of the Northern Sierra Madre and presumably comprises part of the basement of the Cagayan Valley sedimentary sequence. It is a heterogeneous mixture of basaltic to andesitic flows, pyroclastics and sedimentary rocks widely distributed in the southwest part of Divilacan River and northern and western part of Maconacon River. The age of deposition of the Abuan Formation is inferred to be before Early Oligocene, probably Eocene. The thickness of this formation was not indicated by MMAJ-JICA (1989).

The Abuan is probably partly equivalent to the Caraballo Group which was named by MMAJ-JICA (1977) for the volcanic and sedimentary rocks comprising the basement of northern Sierra Madre. This was later renamed by Ringenbach (1992) as Caraballo Formation. Its age was previously presumed by MMAJ-JICA (1977) to be Cretaceous-Eocene, but it was later found to be Middle – Late Eocene (Ringenbach, 1992).

The Abuan Formation may be correlated with the Mt. Cresta Formation which is exposed typically on the slopes of Mt. Cresta and lies scattered on the ridges of the Northern Sierra Madre Range, as mapped by MMAJ-JICA (1989). It is a dacitic complex of lava flows, intrusive rocks, pyroclastics and sedimentary deposits, conformably overlain by the well-bedded Oligocene Masipi Green Tuff of Northern Sierra Madre.

The Dumatata Formation of Huth (1962), which was considered as the basement of the Cagayan Valley sedimentary sequence in BMG (1981), may be regarded as partly equivalent to the Abuan Formation. The Dumatata Formation is composed of an alternation of basic lava flows, partly metamorphosed pyroclastic breccia and tuffaceous sandstone and siltstone. It is about 550 m thick.

Equivalent formation(s):

  • Mt. Cresta Formation - The Mt. Cresta Formation of MMAJ-JICA (1989) is a dacitic complex of lava flows, intrusive rocks, pyroclastics and sedimentary deposits, conformably overlain by the well-bedded Oligocene Masipi Green Tuff of Northern Sierra Madre. It is exposed typically on the slopes of Mt. Cresta and lies scattered on the ridges of the Northern Sierra Madre Range, as mapped by MMAJ-JICA (1989). It may be correlated with the Abuan Formation in northern Sierra Madre.
  • Dumatata Formation - The Dumatata Formation of Huth (1962), which was considered as the basement of the Cagayan Valley sedimentary sequence in BMG (1981), may be regarded as partly equivalent to the Abuan Formation. The Dumatata Formation is composed of an alternation of basic lava flows, partly metamorphosed pyroclastic breccia and tuffaceous sandstone and siltstone. It is about 550 m thick. It is also regarded as partly equivalent to the Dibuluan Formation.

Ad blocker interference detected!


Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers

Wikia is not accessible if you’ve made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected.