Geol170I Solsona Catchillar.docx

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GEOLOGY OF ILOCOS NORTE, PHILIPPINES

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A geologic report submitted in partial fulfillment of the requirements in

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Geology 170 (Field Geology)

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Submitted by:

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Mark Gerome M. Catchillar

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2014-02105

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Submitted to:

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Dr. Leo T. Armada

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Dr. Mario A. Aurelio

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Dr. Allan Gil S. Fernando

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Dr. Jillian Aira S. Gabo-Ratio

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Dr. Betchaida D. Payot

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Dr. Noelynna T. Ramos

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Professor

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Karmina A. Aquino

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Camille Austine O. Muyco

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Ana Marie E. Binuya

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Jayson Gabriel D. Pinza

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Yvonne Ivy L. Doyongan

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Mark Angelo B. Somosa

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Cris Reven L. Gibaga

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Jasmine Consuelo Urquico-Zialcita

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Jose Dominick S. Guballa

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Mirko Alessandro C. Uy

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Ma. Isabella G. Hermo

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Gabriel Theophilus V. Valera

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Paula Naomi S. Irapta

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Barbie Ross Villaplaza

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Ren Thomas C. Marquez

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Richard L. Ybañez

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John Paul A. Mendoza

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Instructors

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National Institute of Geological Sciences

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College of Science

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University of the Philippines

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Diliman, Quezon City

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July 17, 2017

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TABLE OF CONTENTS

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List of Figures ………………………………………………………………………………...iii

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Introduction…………………………………………………………………………………….1

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Background of the Study……………………………………………………………….1

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Objectives…………………………………………………………………………........1

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Scope and Limitations………………………………………………………………….1

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Site Description………………………………………………………………………...2

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Location and Accessibility……………………………………………………..2

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Physiography/Geomorphology…………………………………………….......2

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Climate…………………………………………………………………………2

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Land Use and Vegetation……………………………………………………….3

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Review of Related Literatures………………………………………………………………….4

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Previous Works………………………………………………………………………...4

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General Comparative Stratigraphy……………………………………………………..4

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Regional Tectonics……………………………………………………………………..9

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Methodology.………………………………………………………………………………....11

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Pre-Field………...…………………………………………………………………….11

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On-Site…………...…………………………………………………………………...11

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Post-Field……………………….…………………………………………………….12

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References…………………………………………………………………………………….14

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Figures………………………………………………………………………………………...15

Page

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LIST OF FIGURES

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Figure 1. The Philippine map showing the relative location of the Ilocos Norte Province. Red

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line is 200 km. (Map generated using Google Earth)………………….………………………15

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Figure 2. The map of the Ilocos Norte generated with Google Maps. The red line is 10

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km.……………………………………….................................................................................15

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Figure

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2013)………………………………………………………………………………………….16

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Figure 4. (a) The stratigraphic column provided by Aurelio and Peña (2010) for the Ilocos

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Region. (b) The stratigraphic column of Queaño et. al. (2016) for the Ilocos

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Norte………………………………………………………………….……………………….17

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Figure 5. The Philippines experiences subduction in the Manila Trench to its west, and

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Philippine Trench and East Luzon Trough to its east. Running in between these is the Philippine

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Fault. Map is extracted from Pinet and Stephan (1990)……………………………….………18

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Figure 6. From west to east, the Ilocos Norte Region is consisted of Vigan-Laoag Coastal Strip

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(VLCS), Vintar Median Strip (VMS), and Eastern Strip (ES). The Vigan-Aggao Fault is in

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between the VLCS and VMS while the Abra River Fault bounds the VMS from ES. Map taken

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from Pinet and Stephan (1990)………………………………………………………………..19

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Figure 7. A generalized geologic cross-section of the Vigan-Laoag Coastal Strip and Vintar

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Median Strip (Pinet and Stephan, 1990)………………………………………………………20

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A

table

of

land

use

in

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Ilocos

Norte

(Ecological

Profile,

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INTRODUCTION Background of the Study

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A two-week long field geologic mapping of the Ilocos Norte was conducted by students

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of the University of the Philippines National Institute of Geological Sciences (UP-NIGS) on

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June 10 to 25, 2017. This was accomplished to partially fulfill the requirements of the Geology

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170 class AY 2016-2017. The field work was arranged by the faculty of the institute

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spearheaded by Dr. Leo T. Armada, together with Dr Mario A. Aurelio, Dr. Jillian Aira S.

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Gabo-Ratio, Dr. Betchaida D. Payot, Dr. Allan Gil S. Fernando, Jayson Gabriel D. Pinza, Ana

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Marie E. Binuya, John Paul A. Mendoza, Richard L. Ybañez, Mirko Alessandro C. Uy, Ren

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Thomas C. Marquez, Paula Naomi Irapta, Mark Angelo B. Somosa, Yvonne Ivy L. Doyongan,

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Cris Reven Gibaga, Gabriel Theophilus Valera, Camille Austine O. Muyco, Karmina A.

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Aquino, Jose Dominick S. Guballa, Barbie Ross Villaplaza, and Jasmine Consuelo Urquico-

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Zialcita.

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Before the field proper, the class was divided into four camps that would be based on

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different municipalities and cities in the province. The places each camp was situated in were

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Solsona, Burgos, Pinili, and Laoag. The faculty was divided into each camp equally.

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Objectives of the Study

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The objectives of this study were to collect rocks, structural readings, and other relevant

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data from outcrops in the region. This would be used to create lithologic, structural, and sample

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index maps that were to be synthesized to form a detailed geologic map, cross-section, and

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stratigraphic column of the area. With these, the tectonic and geologic history of the area could

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be established.

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Scope and Limitations

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The study was conducted in the Ilocos Norte province located in the northwest part of

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Luzon, Philippines (Figure 1). It is geographically located in between 17043’ and 18029’ north

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latitudes and 120025’ and 120058’ east longitudes (Ecological Profile, 2013). It is bounded in

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the east by the provinces of Cagayan and Apayao, in the southeast by Abra, in the south by

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Ilocos Sur, and in the west by the South China Sea.

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In the region, the class conducted field work in the municipalities of Adams, Bacarra,

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Badoc, Bangui, Banna, Burgos, Carasi, Currimao, Dingras, Dumalneg, Marcos, Nueva Era,

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Pagudpud, Paoay, Pasuquin, Piddig, Pinili, San Nicolas, Sarrat, Solsona, and Vintar. Cities of 1

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Laoag and Batac were also included. As supplementary to these, some teams were sent to the

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municipalities of Sinain in Ilocos Sur, and Sta. Praxedes and Claveria in Cagayan.

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Although the goal was to cover the whole province, some obstacles were encountered that

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challenged this. In many rivers, boulders, water level, and lack of passage inhibited teams to a

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certain distance of traverse. In road traverses, some outcrops were heavily weathered. Since

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there were significant places in the region that were not traversed due to either lack of outcrops

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or presence of obstacles, outcrop patterns were used to close the map.

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To identify the lithologies present in the area, hand samples were identified using relevant

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diagrams prior to the return to the institute. These were rechecked later on with petrographic

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microscopes.

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Site Description

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Accesibility

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The heart of the Ilocos Norte, Laoag City, is around 500 km, northwest of Metro Manila

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(Ecological Profile, 2013). It can be reached through land or air from Metro Manila. In terms

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of land transportation, different buses offer transport to different municipalities and cities in the

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province. Approximately, the bus ride takes 10 to 12 hours from Metro Manila to Ilocos Norte.

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Other than the buses, the only option is private transport.

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Physiography/Geomorphology

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The Ilocos Norte has a total area of 3,622.91 km2 (Ecological Profile, 2013). Its map is

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shown in Figure 2. The province sits on a wide plain to the west of the Central Cordillera range.

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13 mountains, however, are located in the region. The highest of these is Mt. Sicapoo (2360 m)

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and the lowest is Mt. Simminublan (1472 m).

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Ilocos Norte’s coastline stretches from Badoc up to Pagudpud at a distance of 155.37 km

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(Ecological Profile, 2013). From here on, the vast South China Sea bounds the province.

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Consequently, several rivers of the province drain to this. One of this is the Laoag River which

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has the largest drainage area of 1343.96 km2 and a length of 33.15 km.

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Climate

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The Ilocos Norte’s climate is classified into Type I according to the Corona Classification

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(Ecological Profile, 2013). This means that the region experiences two major seasons. One of

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these is the dry season from November to April and the other is the wet season from May to 2

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October. Generally, the region experiences a northward wind direction. In terms of temperature,

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it has an average of 23 to 30oC.

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Land Use and Vegetation

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The province’s land is used in different ways. The usage of which is shown in Figure 3.

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REVIEW OF RELATED LITERATURE Previous Works

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Ilocos Norte has been the subject of many studies since 1900s. One of these is the

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exploration of Pinet and Stephan (1990) in which they mapped and analyzed in detail the

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Philippine wrench fault system in the Ilocos foothills. This led to a better understanding of the

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tectonic evolution of the area and its relation with the Philippine Fault. Aurelio and Peña (2010)

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have also conducted recent exploration in this area as well as compiled previous studies to come

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up with the most updated stratigraphic column of the Ilocos Region in their 2nd Edition of the

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Geology of the Philippines book. However, a more recent study by Queño et al. (2016) has

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come up with a different interpretation of the geology of the area and has presented a new

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stratigraphic column. Together with this, they have also proposed that the tectonic mélanges

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found in Ilocos Norte are equivalent to all mélanges found in the western side of the Philippines.

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General Comparative Stratigraphy

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The study area, the Ilocos Norte, is part of the Ilocos-Central Luzon Basin (Aurelio and

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Peña, 2010). Several formations are provided by Aurelio and Peña (2010) in this area but recent

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studies of the region by Queaño et. al. (2016) have refined these and even proposed new ones.

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The following formations comprise the two stratigraphic columns in Figure 4 that are put in

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comparison with the data gathered by the class.

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Suyo Schist, named by Aurelio and Peña (2010) from the Suyo Metamorphics of the

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Bureau of Mines and Geosciences (1981) (as cited in Aurelio and Peña, 2010), is widely

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distributed across Suyo, Burgos, Ilocos Norte. It is composed of amphibolite, quartz-biotite

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schist, actinolite-tremolite-talc schist and quartzite. This formation is the basement of the

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sequence in Ilocos. It is unconformably overlain by the Bangui Formation and is speculated to

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be of Cretaceous in age (Aurelio and Peña, 2010).

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The amphibolite schist of this formation is light to dark green in color that is fine- to

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medium-grained and is composed of green amphibole, chlorite, feldspar and quartz in planar

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orientation (Aurelio and Peña, 2010). It typically exhibits a nematoblastic texture accompanied

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by large bluish green amphibole and prismatic, light-colored epidote.

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The quartz-biotite schist is composed mainly of quartz with few amounts of epidote,

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biotite, hematite, piedmontite and garnet (Aurelio and Peña, 2010). It occurs closely with the

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amphibolite schist. 4

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The actinolite-tremolite-talc schist, formed through dynamothermal metamorphism, is

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found along the contact of the heavily sheared serpentinized peridotite (Aurelio and Peña,

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2010).

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The llocos Peridotite is composed of relatively small bodies of serpentinites, together

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with schists and few gabbros, that occur along N-S to N30oE trending deformation zones that

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are 10 to 100m wide (Pinet and Stephan, 1990, as cited in Aurelio and Peña, 2010). One of

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these zones can be traced approximately 140 km from Lapog, Ilocos Sur to Bangui, Ilocos

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Norte. This unit is probably Cretaceous in age and is unconformably overlain by the Bangui

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Formation.

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This rock unit is intimately associated with a reddish radiolarian chert that was previously

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named by Smith (1924) (as cited in Aurelio and Peña, 2010) as the Baruyen Formation, with

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type locality at the Dungan-Dungan Estate along Baruyen River, Ilocos Norte. However,

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Hashimoto and others (1975) (as cited in Aurelio and Peña, 2010) believe that this chert unit is

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a mélange-like deposit, and not a true chert as what Smith has proposed.

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Dos Hermanos Mélange is the unit which amalgamates the Suyo Schist and the Ilocos

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Peridotite into a single formation as fragments, serving as the basement rock of the region.

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Recent studies conducted confirm these two to be associated with one another (Queaño et. al.,

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2016). Its type locality is found in the Dos Hermanos Island, Ilocos Norte. In here, the mélange

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is composed of cobble to boulder, angular to sub-angular clasts of serpentinized peridotite,

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chlorite schist, quartzo-feldspathic schist, muscovite schist, actinolite schist, and quartz mica

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schist that are in a sheared, greenish, course-grained sandy matrix. Its contact with the upper

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formations, the Bangui Formation and the Pasuquin Limestone, is found at the Vintar River

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wherein it is in thrust contact with the former while it is in unconformable contact with the

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coralline limestone of the latter. According to Queaño et. al. (2016) this formation is a tectonic

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mélange that was amalgamated to northwest Luzon at around Early to Middle Miocene based

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on correlations with mélanges found in Central Visayas (Yumul et. al, 2003 as cited in Queaño

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et. al., 2016).

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Bangui Formation is a unit that is unconformable over the Ilocos Peridotite, or over the

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Dos Hermanos Mélange based on a recent study (Queaño, 2016), and is overlain discordantly

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by the Magabbobo Limestone (Aurelio and Peña, 2010). According to Pinet (1990) (as cited in

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Aurelio and Peña, 2010), it is composed dominantly of volcanic sandstones interbedded with

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differing amounts of mudstones and conglomerates. Some sandstones and mudstones are

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characterized by interchanging of red and green beds. In a section along the Vintar River, Pinet 5

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and Stephan (1990) (as cited in Aurelio and Peña, 2010) noted an olistostrome unit of the

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formation composed of serpentinite, radiolarian chert, graywacke, basalt and gabbroic clasts.

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According to Queaño et. al (2016), conglomerates of this formation are composed of pebble to

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cobble sized basaltic to andesitic clast in a grayish sandy matrix. It is 200 m in thickness and is

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exposed over a 20-km distance. Apparently, this unit is equivalent to the Baruyen Formation of

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Smith (1907). In terms of its chert, it is observed to be dirty red in color, fine-grained, hard and

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easily breaks into slabs. Irving and Quema (1948) (as cited in Aurelio and Peña, 2010) noted

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that it is intensely folded, strongly fractured and brecciated.

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The name Bangui was coined by Smith (1907) (as cited in Aurelio and Peña, 2010) and

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was intended to only indicate the sandstone unit of the upper member of his Baruyen Series. It

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is termed as Bangui Formation to include not only the sandstone but also the associated

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conglomerate and shale of Fernandez and Pulanco (1967) (as cited in Aurelio and Peña, 2010)

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located in the southwest of Pasaleng, Ilocos Norte. These rocks also crop out along the road

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between Baruyen and Pasaleng. In the Lammin area, a similar unit is intercalated with marble.

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This marble has been dated Late Eocene (BMG, 1982) (as cited in Aurelio and Peña, 2010). On

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the other hand, Pinet (1990) (as cited in Aurelio and Peña, 2010) dated the planktonic

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foraminifera in samples to be of Late Eocene (P17) to Late Oligocene in age. The thickness of

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the Bangui Formation is hypothesized to be more than 2000 m.

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Based on the olistotrome unit and associated sandstones displaying features of the Bouma

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sequence, the Bangui Formation is considered to be formed in a deep sea environment (Queaño,

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2016).

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Magabobbo Limestone, also referred as Magabobbo Formation, is defined by the narrow

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limestone unit found along Vintar River, near barrio Magabbobo (Pinet, 1990 as cited in Aurelio

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and Peña, 2010). This unit is disposed along the Vigan-Aggao Fault. It is made up of two

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members: a white and massive micritic limestone composed of sea urchins and hexacorals in

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the lower part, and an upper reddish calcarenite composed of reworked micrites and buff-

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colored argillites. It discordantly overlies the volcanic sandstone of the Bangui Formation and

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is overlain by the Bojeador Formation. According to Pinet (1990) (as cited in Aurelio and Peña,

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2010) this formation ranges from Early Oligocene to early Middle Miocene (P20 - N9).

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However, it is probably only of Late Oligocene to Early Miocene since samples that are of late

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Early Miocene to early Middle Miocene maybe of Dagot Limestone (Aurelio and Peña, 2010).

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Bojeador Formation, originally named Bojeador Agglomerate and Tuff for the rocks at

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Cape Bojeador, northwestern Ilocos Norte (Irving an Quema, as cited in Aurelio and Peña, 6

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2010), is a unit overlying the olistotrome of the Bangui Formation, serpentinites, and schists.

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It is composed of conglomerate, shale, graywacke, limestone, and associated basic flows found

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along the east of Vintar, Ilocos Norte, and northeast of Vigan, Ilocos Sur (Fernandez and

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Pulanco, 1967 as cited in Aurelio and Peña, 2010).

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The Bojeador Formation age was previously determined to be at around Early to Middle

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Miocene. However, the region’s general stratigraphy suggests it to be limited to Early Miocene

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(Aurelio and Peña, 2010). This formation is also considered to be partly equivalent to the Zigzag

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Formation of Central Cordillera.

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Suyo Formation is a relatively new formation consists mostly of marine turbidites (Queaño, 2016). It has an age of Early Miocene.

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Dagot Limestone is a limestone unit correlated with the Kennon Limestone in Central

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Cordillera (Pinet, 1990, as cited in Aurelio and Peña, 2010). This is distributed from Laoag in

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the north up to the Baguio District in a meridional line for 200 km. It caps the summit of Mt.

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Dagot in La Paz, as well as a hilltop east of Solsona Basin. It also forms the north-south trending

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backbone located southeast of Bangued. In the south of Bangued, it is found in the Abra River

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valley, west of barrio Luba.

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Dagot Limestone is a reefal formation with shells, benthic foraminifera, miliolids, and

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algae (Aurelio and Peña, 2010). The two facies it consists of have reddish biosparite and light-

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colored, fine-grained calcarenite. Found at its base and middle sections are calcareous

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conglomerates that are volcanic. Above these, a limestone breccia is grading into a sequence

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of interbeds of sandstone and mudstone. Although its stratigraphic relations were not reported,

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microfossils found suggest a late Early Miocene to early Middle Miocene age.

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Pasaleng Quartz Diorite is a unit earlier mapped by Fernandez and Pulanco (1967) (as

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cited in Aurelio and Peña, 2010) in northeastern Ilocos Norte, and later named by Aurelio and

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Peña (2010) based on the rocks at Pasaleng, Pagudpud. In their study, it was found to intrude

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Cretaceous, Paleogene, and Early Miocene units. The nature of the unit is leucocratic and

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course-grained with a composition of quartz, feldspar, and chloritized amphibole. It is

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correlated with the Itogon Quartz Diorite Complex in Central Cordillera. Based on this, its age

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is probably of late Early Miocene to early Middle Miocene.

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Batac Formation, named by Pinet (1990) (as cited in Aurelio and Peña, 2010) based on

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the exposures found in Batac, is a sequence of thinly-bedded sandstone and shales. In a road

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between Pinili and Nueva Era, exposures of it were found but defined separately by Pinet (1990) 7

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(as cited in Aurelio and Peña, 2010) as the Liliputen Formation. In it, conglomerates with clasts

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of limestones, slightly volcanic sandstones, and minor tuffs and andesites were found.

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Although the Batac Formation have no reported stratigraphic relations, its Liliputen part was

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thought to be its lower section. In connection to this, the age of the Batac Formation as a whole

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is late Middle Miocene to Late Miocene based on Pinet’s (1990) (as cited in Aurelio and Peña,

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2010) dating for the Liliputen Formation (late Middle Miocene to early Late Miocene) and the

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nannoplanktons found (Late Miocene-NN11) in his separate Batac Formation. This formation

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is the equivalent of the Klondyke Formation in Central Cordillera.

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Pasuquin Limestone, formerly called Pasuquin Arenaceous Limestone (Smith, 1907 as

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cited in Aurelio and Peña, 2010), is a unit cropping out along the Pasuquin River, northeast of

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Pasuquin, Ilocos Norte. Its contact with the Bangui Formation is found at the summit of a

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hillock east of Magabobbo where it overlies the folded clastics with a well-defined angular

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unconformity. In the east-northeast part of Vigan, on the other hand, the Pasuquin Limestone

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is found to unconformably cap the Bojeador Formation.

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The Pasuquin Limestone is well-bedded, light cream to buff in color, and sandy and

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porous at times. It also has a conglomerate part with carbonate matrix and clasts of serpentinite

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(in some places) in its basal section (Pinet, 1990 as cited in Aurelio and Peña, 2010). Its upper

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facies, on the other hand, is composed of calcirudites, calcarenites, and fossiliferous limestone.

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Based on its fossils, its age is of Late Miocene and it is said to be equivalent to the Mirador

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Limestone in Central Cordillera, and the Labayug Limestone in La Union.

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Bojeador Volcanics is composed of andesitic lava flows and pyroclastic rocks (Queaño et. al., 2016). It is assigned an age of Early Pliocene.

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Laoag Formation, formerly named as Laoag Marl Beds (Smith, 1907 as cited in Aurelio

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and Peña, 2010) and Laoag Calcareous Sandstone (Irving and Quema, 1948 as cited in Aurelio

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and Peña, 2010), is a sedimentary unit exposed along the highway between Bacarran and Laoag,

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Ilocos Norte. It is a sequence of flat-lying sandstone with interbeds of siltstone and claystone,

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and at times, reefal limestone and limestone breccia going up. These rocks are mostly well-

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bedded sandy calcareous units with a cream to buff color. In places, conglomerate beds have

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numerous shell and other molluscan, wood, and leaf fossils. According to Queaño et. al. (2016),

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this formation is associated with deltaic facies. An age of late Early Pliocene to Pleistocene is

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assigned to this formation (Pinet, 1990 as cited in Aurelio and Peña, 2010) but Queaño et. al.

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(2016) consider it to be of Late Pliocene only. 8

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The Uplifted Coral Reefs of the region are divided into two levels: one with an elevated

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height of 30m, and the other with an elevation of three to four meters above the high tide level

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(Smith, 1907 as cited in Aurelio and Peña Aurelio and Peña, 2010). It is composed of

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consolidated coral fragments with calcareous debris. Its stratigraphic relation with the Bojeador

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Formation and Pasuquin Limestone was found at Cape Bojeador, and it was noted to overlie

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the two. The assigned age to this unit is Late Quaternary (Late Pleistocene) (Irving and Quema,

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1948 as cited in Aurelio and Peña, 2010).

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Regional Tectonics

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The Philippines is a tectonically active region wherein it is considered as one of the few

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island arcs in which both sides experience subduction (Figure 5) (Queaño et. al., 2006). To its

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east, the West Philippine Basin is being subducted to the Philippine Trench, and this even

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extends up to the East Luzon Trough. On the other side, the South China Sea is being subducted

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in the Manila Trench. These zones are the ones responsible for the absorption of the collision

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of the Eurasian and Philippine plates at the Taiwan-Luzon-Mindoro Belt (Pinet and Stephan,

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1990). In the middle of these subduction zones, the left-lateral strike-slip Philippine Fault is

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located which runs for more than 1300 km from Mindanao to north Luzon (Figure 5) (Allen,

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1962; Rutland, 1968; Acharya, 1980; Hamburger et al., 1983; Maleterre, 1989 as cited in Pinet

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and Stephan, 1990). In the island of Luzon in the north, several N-S trending morphostructural

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units are found. These units are disrupted by the N150E Philippine Fault segment and this led

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to the understanding that the study area, the Ilocos Norte, is equivalent to the Central Valley

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Basin in the south (Pinet and Stephan, 1990).

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The study area is a region composed of two main faults that are related to the braided

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system of the Philippine Fault. These are the Vigan-Aggao Fault to the west and the Abra River

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Fault to east (Figure 6). In the presence of these faults, the Ilocos Norte region is divided into

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three tectonic strips (Figure 6). From west to east, these are the Vigan-Laoag Coastal Strip, the

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Vintar Median Strip, and the Eastern Strip.

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The Vigan-Laoag Coastal Strip is composed of an ultramafic basement overlain by a thin

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sedimentary deposit (Figure 7) (Pinet and Stephan, 1990). The basement is made up of

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serpentinized peridotites tectonically mixed with Cenomanian red radiolarian cherts and

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metamorphic rocks of the Suyo schists. An intrusive body that is granitic in nature cuts through

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this. Above this basement is an unconformable sedimentary cover of the Bojeador Formation.

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Overlying these older rocks is the Pasuquin Formation’s limestones. Laoag Formation sits on

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top of these formations. This strip is bounded to the west by the Manila Trench and to the east 9

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by the Vigan-Aggao Fault. Historically, this unit was a bathymetric high during most of the

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Eocene to Miocene period (Pinet and Stephan, 1990).

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The Vintar Median Strip is composed of thick, predominantly clastic, sedimentary

4

sequence (Figure 7) (Pinet and Stephan, 1990). It is bounded to the west by the Vigan-Aggao

5

Fault and to the east by the Abra River Fault. This strip comprises the following formations:

6

the Bangui Formation, Magabobbo Formation, Kennon Formation, Liliputen Formation, Batac

7

Formation, and the Pasuquin Formation. It also contains the Solsona Basin, a 30km long and

8

15km wide topographic depression. In its west, deposits of calcareous arenites with shell

9

fragments are exposed. Interbedded with these are vertical dipping limestones dated to be at

10

around the Pliocene age. These are quite similar to those of the Laoag Formation.

11

The Eastern Strip is bounded to west by the Abra River Fault and to the east by the Central

12

Cordillera range. It is characterized by Eocene to Middle Miocene volcaniclastic sequence

13

associated with andesitic and basaltic flows and intruded by Oligocene to Miocene gabbros,

14

diorites and granodiorites (Pinet and Stephan, 1990).

15

During the late Middle Miocene, extensions of the Philippine Fault became active in the

16

Ilocos Norte region (Pinet and Stephan, 1990). In the area of Central Cordillera, a quiescent

17

tectonic period was recorded during the latest Miocene to Early Miocene (Rigenbach et. al.,

18

1990, as cited in Pinet and Stephan, 1990) which is correlated to the study area as the deposition

19

of the Pasuquin limestones both in the Vigan-Laoag Coastal Strip and the Vintar Median Strip.

20 21 22 23 24 25 26 27 28 29 10

1 2 3 4

METHODOLOGY Pre-field The class was divided into three committees for the pre-field activities. These are the accommodation, mapping, and supplies committees.

5

The accommodation committee was in charge of the place where each camp will stay as

6

well as the necessary miscellaneous. It was also the team that coordinated with concerned

7

municipalities and cities of the province.

8

The supplies committee was the group that provided the necessary materials for the

9

upcoming field. It was the responsible committee that coordinated with the Supplies Office of

10

the institute that provided the hard hat, vest, picks, and Brunton compass necessary for the

11

actual field work.

12

The mapping committee was the in-charge group for the traverse and base maps of the

13

class. Several computer programs were used by the team to cater different parts of the maps.

14

For roads and rivers, Google Maps was used and the file was saved as shapefiles. Lineaments

15

were traced using the digital elevation model (DEM) generated from an Interferometric

16

Synthetic Aperture Radar (IFSAR) and saved as shapefiles as well. The contour lines were also

17

produced from the DEM and saved as shapefiles. For the boundaries of each barangay, data

18

from PhilGis was used. All these shapefiles were synthesized using QGis to create both the

19

traverse and base maps.

20

The traverse map produced by the committee is in a 1:10000 scale. It was printed in A4

21

and had a geographic coordinate system and a datum of WGS 84, in degrees units. The base

22

maps, on the other hand, are in a 1:50000 scale and printed in A0. It has the same coordinate

23

system and datum.

24

On-site

25

Each camp was divided into groups spearheaded by pegs that would serve as the main

26

responsible per each group. On site, the base maps were used as guides in plotting of data for

27

the structural and sample index locations. The traverse maps provided by the mapping

28

committee in the pre-field were used to plot the traverse and outcrops of each team during the

29

actual field work.

30

During the actual field work, descriptive characteristics of outcrops found were obtained.

31

Together with this, rock sampling, structure measuring using a Brunton compass, and picture 11

1

taking were done. These data were later synthesized every after field in a camp discussion and

2

database.

3

For two weeks, two class synthesis were held to compare, contrast, and compile data of

4

each camp. These were held every last day of each week.

5

Post-field

6

Back in the institute, the class were divided into four committees, each has a different

7

task to process the data collected during the field work. These four are the Figures, Pictures,

8

and Structures Committee, the Thin Section Preparation and Petrography Committee, the

9

Stratigraphy and Paleontology Committee, and the Mapping and Cross-section Committee.

10

The Figures, Pictures, and Structures Committee handled the sorting and treatment of the

11

pictures taken using photoshop and PowerPoint features. The processing of structures, on the

12

other hand, were done with the help of Georient computer program. Features such as domes

13

and folds were determined through the structural readings done by Brunton compass in the

14

field. Lastly, figures that were deemed relevant were produced by this committee.

15

To assess the rechecking and precise identification of rock samples gathered from the

16

field, the Thin Section Preparation and Petrography Committee were tasked to spearhead the

17

preparation of thin section slides for the class. The committee facilitated members of other

18

committee in preparing the slide of each rock assigned to them for petrographic analysis. It also

19

provided the specifications of the petrographic report to be presented by each student.

20

To treat sedimentary rocks for paleontological analyses, the Stratigraphy and

21

Paleontology Committee handled the work. There were two types of rocks that were processed:

22

limestones and calcareous mudstones.

23

For limestones, preparation of these started with treatment of hydrogen peroxide solution

24

to dissolve organics. After which, the solution was heated to facilitate the dissolution process.

25

It was then sieved to exclude unwanted particles such as mud-sized sediments. The remaining

26

powder was oven-dried overnight. After drying, the sample was sorted to benthic and

27

planktonic foraminifera in accordance with Graham and Militante (1959) using a picking needle

28

under binocular microscope. The sorted grains were then stored in cavity slides that were

29

surrendered to Dr. Leopoldo De Silva for identification.

30

For calcareous mudstones, the smear slide preparation of Bown (1998) was used as

31

reference. The rock was first powdered using mortar and pestle. It was then smeared onto a 12

1

cover slip with water and toothpick. After this, it was dried over a heat plate. The glass slide

2

was then applied with mountant to hold the cover slip. The cover slip was then mounted onto

3

the glass slide and put under UV light for 24 hours. After 24 hours, the slide was observed under

4

a petrographic microscope for identification of calcareous nannofossils with guidance of

5

taxonomic classification provided by holotypes in Perch-Nielsen (1985) with supplementary

6

information from Bown (1998).

7 8

The Stratigraphy and Paleontology Committee was also the group that refined the stratigraphic columns based on the dating of fossils found.

9

The Mapping and Cross-section Committee was the group that produced the geologic

10

map and cross-section of the class with the synthesis of the data from all other committees. In

11

the post field activities, the committee refined lineaments using traced features in geotiff files

12

from PHIVOLCS. These are saved as shapefiles and compared to field data for final tracing.

13

The cross-section hand-drawn was scanned and digitized using MapInfo and photoshop. The

14

geologic map was scanned and digitized as well using MapInfo and then its layout was done in

15

ArcMap. For the sample location map, the data collected by the class were plotted using

16

earthpoint.us. This converted the excel files into kmz files that were saved as shapefiles using

17

Global Mapper. The layout of the map was done using ArcMap.

18 19 20 21 22 23 24 25 26 27 28 29 13

1

REFERENCES

2

Aurelio, M. A., & Peña, R. E. (2010). Geology of the Philippines. Mines and Geosciences

3

Bureau, Quezon City, 25, 71-78.

4

Bown, P. R., Young, J. R. 1998. Techniques. In P. R. Bown, Calcareous Nannofossil

5

Biostratigraphy (pp. 16-28). British Micropalaeontological Society Poblications Series,

6

Chapman and Hall/Kluwer Academic Publishers.

7 8

Ecological Profile [PDF]. (2013). Ilocos Norte: Office of the Provincial Planning and Development Coordinator.

9

Perch-Nielsen, K. 1985. Cenozoic Calcareous Nannofossils. In H. Bolli, J. Saunders, & K.

10

Perch-Nielsen, Plankton Stratigraphy 428-554. Cambridge: Cambridge University Press.

11

Pinet, N., & Stephan, J. F. (1990). The Philippine wrench fault system in the Ilocos Foothills,

12

northwestern Luzon, Philippines, Tectonophysics, 183(1-4), 207-224.

13

Queaño, K. L., Marquez, E. J., Dimalanta, C. B., Aitchison, J. C., Ali, J. R., & Yumul, G.P.

14

(2016). Mesozoic radiolarian faunas from the northwest Ilocos Region, Luzon,

15

Philippines and their tectonic significance. Island Arc.

16 17

Queaño, K. L., Milsom, J., Ali., J. 2006. Peculiar geometry of northern Luzon, Philippines: Implications for regional tectonics of new gravity and paleomagnetic data. Tectonics.

18 19 20 21 22 23 24 25 26 27 14

1

FIGURES

2 3

Figure 1. The Philippine map showing the relative location of the Ilocos Norte Province. Red

4

line is 200 km. (Map generated using Google Earth)

5 6

Figure 2. The map of the Ilocos Norte generated with Google Maps. The red line is 10 km. 15

1 2

3

Figure 3. A table of land use in Ilocos Norte (Ecological Profile, 2013)

(a)

16

1

(b)

2

Figure 4. (a) The stratigraphic column provided by Aurelio and Peña (2010) for the Ilocos

3

Region. (b) The stratigraphic column of Queaño et. al. (2016) for the Ilocos Norte.

17

1 2

Figure 5. The Philippines experiences subduction in the Manila Trench to its west, and

3

Philippine Trench and East Luzon Trough to its east. Running in between these is the Philippine

4

Fault. Map is extracted from Pinet and Stephan (1990).

18

1 2

Figure 6. From west to east, the Ilocos Norte Region is consisted of Vigan-Laoag Coastal Strip

3

(VLCS), Vintar Median Strip (VMS), and Eastern Strip (ES). The Vigan-Aggao Fault is in

4

between the VLCS and VMS while the Abra River Fault bounds the VMS from ES. Map taken

5

from Pinet and Stephan (1990).

19

1 2

Figure 7. A generalized geologic cross-section of the Vigan-Laoag Coastal Strip and Vintar

3

Median Strip (Pinet and Stephan, 1990)

4 5

20