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Sagada Formation

Lithology

Lower member– limestone, biomicrite, biosparite

Upper member – red and green mudstones with minor conglomerate

Stratigraphic relations

Conformably underlain by the Malitep Formation in Bontoc area, and overlain by the Balili Formation in the Lepanto mine area in Mankayan, Benguet

Distribution

Cervantes-Bontoc Road; Sagada, Mountain Province

Age

Late Eocene – Early Oligocene

Thickness

>200 m and may reach 400 m.

Previous Name

Sagada Limestone (Maleterre, 1989)

Named by

MGB (this volume)

Synonymy

Tineg Formation (MMAJ-JICA, 1977), ApaoanVolcaniclastics (Garcia, 1991), Columbus Formation (Maleterre, (1989)

The Sagada Formation was originally described by Maleterre (1989) as Sagada Limestone for the pre-Miocene limestone in the Cervantes-Bontoc area.  He divided it into three members, namely: a lower member with a thickness of 100-200 m, consisting of thinly bedded limestone, biomicrites and biosparites; a 100-m thick middle member of well-bedded red and green mudstones with minor conglomerate; and a 5-m thick upper member made up of volcanic biomicrite.  However, Ringenbach (1992) considers the upper member as part of the overlying Balili Formation, so that the Sagada Formation is left with only two members: a lower limestone member and an upper clastic member.  The best sections are exposed west of Bontoc, on the Cervantes-Bontoc road, between Sabangan and Bauko.  This formation shows a gradational and concordant contact with the Malitep Formation along Sabangan River.

A large part of the Sagada Formation apparently corresponds to the Tineg Formation of MMAJ-JICA (1977, 1980) and BMG (1981).  This was described as a sequence of pyroclastic rocks with intercalated dacitic flows, sandstones, mudstones and limestone mapped in Abra area (where it was originally recognized), Kalinga-Apayao and Bontoc area.  It was estimated to be 300-400 m thick in Abra area, but presumably attains a thickness of 1,500 m in Bontoc area.  The 200-m thick limestone body in Sagada, which MMAJ-JICA (1980) included as part of its Tineg Formation, is probably the same as the limestone of the Sagada Formation described by Maleterre (1989).  The ApaoanVolcaniclastics of Garcia (1991) could also be equivalent to the upper member of the Sagada Formation.

Maleterre (1989) reports a dating of Late Eocene to Early Oligocene age for the Sagada Limestone.  MMAJ-JICA (1980) dates the limestone at Sagada as Late Oligocene.  Garcia (1991) reports an Early Oligocene dating by Maac for radiolarian from red beds of the ApaoanVolcaniclastics obtained from Level 670, Tubo area.  Here, the age of the Sagada Formation is regarded as probable Late Eocene to Early Oligocene.

The lower limestone member of the Sagada Formation is correlated with the Columbus Formation farther southeast.  The type section of the Columbus Formation is along an unnamed tributary of Agno River (Maleterre, 1989) and outcrops are limited on hilltops east of Agno River.  The formation consists of thinly laminated biomicrite, which shows volcanic clasts in places.  It is about 200 m thick and is dated Oligocene, probably Early Oligocene.


  • Preceeded by - Malitep formation</li>
  • Succeed by - Central Cordillera Diorite Complex</li>
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