Geology: What's in Region I

I found an article from the result of Google search on keywords "Vintar-Aggao Fault". As usual, here's the copy-paste:

http://dvasia.ph/viewgeology.php?region=Region%20I

Geology of the Region: Region I

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  ILOCOS

 

Suyo Schist
Lithology	Greenschist, serpentinite, chert
Stratigraphic relations	Basement of the sequence in Ilocos; Unconformably overlain by the Bangui Formation
Distribution	Suyo, Burgos, Ilocos Norte
Age	Cretaceous (?)
Renamed by	MGB (This Volume)

 

The Suyo schist, exposed largely in Suyo, Burgos, Ilocos Norte, consist of amphibolites, quartz-biotite schist, actinolite-tremolite-talc schist and quartzite, which are mostly in fault contact with serpentinezed peridotite. These rock are probably of Cretaceous age.

The amphibolites schist is light to dark green, fine – to medium-grained and is characterized by planar orientation of green amphibole, chlorite, feldspar and quartz. The rock exhibits usually nemoblastic texture with large bluish green amphibole and prismatic, light colored epdote.

The quartz-biotite schist, consisting dominantly of quartz with lesser amounts of biotite, epidote, gamet, hematite and piedmonite, occurs intimately with the amphibolites schist.

The actinolite – tremolite –talc schist, a product of dynamothermal metamorphism, is structurally confined along the contact of the intensely sheared serpentinized peridotite.

 

Ilocos Peridotite
Lithology	Serpentinized peridotite
Stratigraphic relations	Confined in deformation zones;Unconformably overlain by the Bangui Formation
Distribution	Lapog, Ilocos Sur, Baruyen River and Bangui Ilocos Norte
Age	Cretaceous (?)
Renamed by	Baruyaen formation (Smith, 1924)

 

This peridotite unit is closely associated with reddish radiolarian chert, previously named Baruyen Formation by (Smith 1924) with type locality at Hashimoto and others (1975) believe that the rock at Smith’s type locality at Dungan – Dungan Estate along the Baruyen River is not a true chert but a melangke – like deposit.

This rock unit consist ofa train of relatively small bodies of serpentinites, together with schist, that occur along wife deformation zones (10 – 100 m wide) trending N –S

 

Bangui Formation
Lithology	Sandstone, Conglomerate, Mudstone; Includes olistostrone
Stratigraphic relations	Unconformable over the Ilocos Peridotite; Overlain discordantly by the Magabbobo Limestone
Distribution	Bangui, Baruyen and Lammin area, Ilocos Norte
Age	late Eocene – Late Oligocene
Thickness	Probably exceeds 2,000 m
Named by	Smith (1907)

 

The named Bangui was first used by Smith (1907) for the sandstone unit, with constitutes the  upper member of his Baruyen Series. It is here called Bangui Formation to include not only the sandstone but also the associated conglomerate and shale of Fernandez  and  Pulanco (1967) southwest of pasaleng in northeastern Ilocos Norte. These rock are seen along the road between Baruyen and Pasaleng. In Lammin area , a similar sequence is intercalated with marble. However, the upper and lower contacts of this formation have not been described.

According to Pinet (1990), the Bangui Formation consists mainly of volcanic sandstones interbedded  with varying amounts of conglomerates and mudstones. In  places, the sandstones and mustones are characterized by alternating red and green beds.

Pinet and Smith (1990) have noted an olistosterone unit in the Vintar River section containing serpentinite, radiolarian chert, greywacke, basalt and gabbroic clast.  It sis 200 m thick and exposed over a distance of 20 km. this unit is regarded as part the Bangui formation. This is apparently  equivalent to Baruyen Formation of Smith (1907) with type locality in the Dungan – Dunagan Estate along the Baruyen River Ilocos Norte. It also crops out along Caruan River in Pasuquin. The chert is dirty red, fine-grained, hard and easily break into slabs. Irving and Quema (1948) described the chert as intensely folded, strongly fractured and brecciated.

The marble intercalated with the clastic rocks in Lammin area has been dated Latre Eocene (BMG, 1982). Pinet (1990) reports that recent dating of planktonic foraminera in samples from Pasaleng area and elsewhere indicates ages of Late Eocene (P17) tp Late Oligocene. The thickness of the Bangui formation probably exceeds 2000 m.

 

Magabbobo Limestone
Lithology	Micritic limestone, calcarenite, minor argillite
Stratigraphic relations	Unconformable over the Bangui Formation; Overlain by the Bojeador formation
Distribution	Vintar River near Barangay Megabbobo East Laoag City
Age	Late Oligocene – early Miocne
Thickness	Undetermined
Previous name	Megabbobo Formation (Pinet, 1990)
Renamed by	MGB (this volume)

 

The Meggabbobo Formation (here renamed Meggabbobo Limestone) was defined by Pinet (1990) for the narrow limestone body exposed along Vintar River East of Laoag near barrio Megabbobo. The limestone bodies are disposed along the Vigan – Aggao Fault, which defines the contact between the coastal and the median units of Pinet (1990). The formation is consist of two members: a lower white, massive micritic limestone with sea urchins and hexacorals and an upper reddish calcarenite with reworked micrites and buff – colored argillites. It rests discordantly  over the volcanic sandstones of Bangui Formation. The angular discordance was not observed but only indicated by differences in attitude. Pinet (1990) reports  ages ranging from Early Oligocene to early Middle Miocene (P20 – N9). However, its age probably ranges only from Late Oligocene to Early Miocene. Samples dated late Early Miocene. Samples dated late Early Miocene to early middle Miocene age probably belong to the Dagot Limestone.

The thickness and nature of the upper contact of the formation were not described by Pinet (1990).

 

Bojeador Formation
Lithology	Conglomerate, greywacke, shale, limestone and associated volcanic flows and pyroclastic
Stratigraphic relations	Unconformably underlain by Bangui Fomation and Suyo schist; intruded by quartz diorite
Distribution	Vintar, Ilocos Norte and northeast of  Vigan, Ilocos Sur
Age	Early Miocene
Thickness	500 m
Previous name	Bojeador Agglomerate and Tuff (Irving and Quema 1948)
Renamed by	MGB (this volume)

 

This formation   was originally named Bojeador Agglomerate and tuff by Irving and Quema (1948) for the rocks at Cape Bojeador, Northwestern Ilocos Norte. The unit rest uncinformably over the olistostrome of the Bangui Formation, serpentinites and schist (BMG, 1981). It includes the conglomerate, greywacke, shale, limestone and associated basic flows and pyroclastics of Fernandez  and Pulanco (1967) exposed of east Vintar, Ilocos Norte and northeast of Vigan, Ilocos Sur. The conglomerate is thick with poorly sorted pebbles and cobbles of angular to subrounded andesite, basalt and limestone set in a sandy and slightly calcareous matrix. The sandstone and shale are well-bedded, cream to buff and locally slightly recrystallized.  It is intruded by diorite of probable late Early Miocene age.

The Bojeador Formation was previously estimated to be about 500 m thick and dated Early to Middle Miocen, in which case, it could be partly contemporaneous with the Dagot Limestoen (describd below). However, considering the overall stratigraphy of the region. It could be confined toEarly Miocene and partly equivalent to the Zigzag formation of Central Cordillera.

 

Dagot Limestone
Lithology	Reefal limestone, calcarenite, biosparite, minor calcareous volcanic conglomerate, particularly at the base and middle section
Stratigraphic relations	Not reported
Distribution	Meridionally distributed from the vicinity of Laoag City through the summit of Mt. Dagot in La Paz, hilltops east of Solsona Basin down to the Abra River Valley
Age	late Early Miocene to early Middle Miocene
Thickness	Undetermined
Renamed by	MGB (this volume)

 

Limestone bodies of Early to Middle age exposed in several places in the Ilocos belt are correlated with the Kennon Limestone with type locality along Kennon Road at Canp 3, in the Bagiou District in Central Cordillera (Pinet, 1990). These limestone bodies are distributed along a roughly meridional line extending for 200 km from the vicinity of Laoag in the north down to Bagiouo District Liestone occupies the summit of Mt. DAgot in LA Paz and one of the hilltops east of Solsona Basin and Constitutes a north – south trending backbone of a dome southeast of Bangued. South of Bagued, this formation drops to Abra River valley west of barrio Luba.

The formation as described by Pinet (1990) is a reefal platform with algae, shells, milliolids and benthic foraminera. Two common facies are light – colored,  fine – grained calcarenite and reddish biosparite. Calcareous conglomerates at the base and the middle section are volcanic in character. The top of the formation corresponds to limestone breccias grading into a sequence of alternating sandstone – mudstone. The contacts of the limestone with the underlying and overlying formations were not reported. Microfossils indicate a late Early Miocene to early Middle Miocene age.

 

Pasaleng Quartz Diorite
Lithology	Quartz diorite
Stratigraphic relations	Intrudes Bojeador Formation and older units
Distribution	Pasaleng, Pagudpud and areas in Northeastern Ilocos Norte
Age	late Early Miocene to early Middle Miocene
Renamed by	MGB (this volume)

 

Quartz diorite bodies intruding Cretaceous, Paleogene and Early Miocene units were mapped by Fernandez and Pulanco (1967) in northeastern Ilocos Norte. The intrusive unit is designated here as Pasaleng Quartz Diorite for the exposures in Pasaleng, Pagudpod. The rock is leucocratic, coarse – grained and composed principally of quartz, feldspar and chloritized amphibole. A late Early Miocene to early Middle Miocene age was assigned to this intrusive unit based on its correlation with the Itogon Quartz Diorite Complex in the Central Cordillera.

 

Batac Formation
Lithology	Thinly bedded sandstone and shale conglomerate
Stratigraphic relations	Not reported
Distribution	Batac, Ilocos Norte and northeast of Vigan, Ilocos Norte
Age	late Middle Miocene to Late Miocene
Thickness	Undetermined
Named by	Pinet (1990)

 

The Batac formation is sequence of thinly – bedded sandstone s and shales named by Pinet (1990) for the exposures around Batac. Pinet exposed along the road between the Pinili and Nueva Era, which could be part  of the Batac. Is consist of conglomerates with clast of limestone  accompanied by sandstones and mudstones with minor tuffs and andesite. The sandstones  are slightly  volcanic in character. The stratigraphic relations of this formation with  respect with the other formations were not described by Pinet (1990). However, the Liliputen Formation probablt constitutes the basal formation of the Batac Formation although Pinet (1990) has noted differences in the intensity of deformation between the Liliputen and Batac Formation.

Pinet (1990) presumes the age of the Liliputen to be probable late Middle Miopcene to early late Miocene (NN11) for the BAtc formation of Pinet (1990). Here, the age of Batac Formation  as a whole is considered late Middle Miocene to Late Miocene. In terms of regional correlation, this is equivalent to the Klondyke Foramtion of Central Cordillera.

 

Pasuquin Limestone
Lithology	Limestone with minor calcareous; Conglomerate, calcirudite, calcarenite
Stratigraphic relations	Discordantly overlies folded Bangui Formation; unconformable over Bojeador Formation
Age	late Miocene
Thickness	late Miocene
Previous Named	Pasuquin Arenaceous Limestone (Smith, 1907
Renamed by	MGB (this volume)

 

The Pasuquin Limestone was called Pasuquin Arenaceous Limestone by Smith (1907). This exposed along Pasuquin River, northeast of Pasuquin, Ilocos Norte. According to Pinet and Stephan (1990), this limestone forms the summit of a hillock east of Magabbobo where the nearly horizontal limestone overlies the folded Bangui formation with a prominent angular unconformity. It has also been observed to rest unconformably over the Bojeador Formation east – northeast of Vigan.

It is well – bedded, light cream to light buff, porous and sandy in some places. The basal portion is described by Pinet (1990) as a conglomerate facies consist of calcirudites, calcarenites and fossiliferous limestone. It is around 200 m thick. Paleontologic dating indicates a late Miocene age for the formation. This formation appears to be equivalent to the Mirador Limestone in central Cordillera and Labayug Limestone in La Union.

 

Laoag Formation
Lithology	Sandstone with interbeds siltstone and Claystone and occasional reefal limestone and limestone breccias
Stratigraphic relations	Not reported
Distribution	Laoag, Ilocos Norte
Age	late Early Pliocene to Pleistocene
Thickness	Undetermined
Previous Name	Laoag Marls Beds (Smith, 1907)
Renamed by	Irving and Quema (1948) as Laoag Calcareous Sandstone
Renamed by	MGB (this volume)

 

Smith (1907) first named the sedimentary rocks exposed along the highway between Bacarra and Laoag, Ilocos Norte as Laog Marl Beds. Irving and Quema (1948) renamed the rock unit Laoag Calcareoous Sandstone. It is here called Laog Formation.  The formation is made up of flat – lying sandstone with interbeds of siltstone and claystone and occasional reefal limestone and limestone breccias towards th top. These are predominantly sandy well – bedded cream to buff calcareous rocks. Some conglomerate beds contain abundant shell and other molluscan, as well as wood and leaf, fossils. Pinet (1990) reports a dating of late Early Pliocene to Pleistocene age for the fossilferous beds of this formation.

 

Uplifted Coral Reefs
Lithology	Coral reefs
Stratigraphic relations	Unconformable over the Bojeador Formation and Pasuquin Limestone
Distribution	Coast of  Ilocos Norte
Age	Late Pleistocene
Thickness	Up to 30 m
Named by	Smith (1907)

 

Smith (1907) recognized two levels of raised coral reefs along the shores of Ilocos Norte: one elevated 30 m high; the other, about three to four meters above the high tide level. At Cape Bojeador, these reef lie over the Bojeador Foramtion and the Pasuquin Limestone. These reefs are consolidated coral fragments and other calcareous debris, Irving and Quema (1948) gave alate Quaternary age of these reefs.