Geology of Southern Palawan

A geologic field report submitted to the

Faculty of National Institute of Geological Sciences,

University of the Philippines,

Diliman, Quezon City

In partial fulfillment of the requirements for Geology 170

(Field Geology)

Submitted by:

Jessica Emil B. Compuesto

November 28, 2014

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ABSTRACT

The geology of southern Palawan is composed of imbricated units of Cretaceous ophiolite,

Paleogene Panas Formation and Pandian Formation, Neogene Ransang Limestone and Quaternary

Alluvium. The incomplete Palawan Ophiolite Complex is composed of Beaufort Ultramafic Complex and

Espina Formation. The incomplete Cretaceous ophiolite is found to have patches of Sheeted Diabase Dike

Unit and is intruded by a Monzogranite Intrusive Unit due to an arc magmatism after the Early Oligocene

emplacement. The Eocene clastic sequences composed of Pandian Formation and Early Miocene Ransang

Limestone are mildly metamorphosed. The ophiolite is emplaced over the syn-rift Eocene clastic

sequences, the Panas Formation. An Eocene compressive event due to the northwest dipping subduction

beneath South China Sea, caused the deformation of the clastic sequences together with the Cretaceous

ophiolites. This suggest that Eocene clastic sequences and ophiolite belong to the North Palawan Block

and in the pre-Middle Miocene collision. They were already deformed before the onset of South China Sea

rifting. The onset of Palawan ophiolite emplacement at the end of Eocene is controlled by a thrust-related

metamorphism of the Pandian Formation. The collision of detached North Palawan Block and Philippine

Mobile Belt in the Middle Miocene caused the localized post-kinematic extension affecting the thrust-fold

structures of Eocene clastic sequences and Pandian Formation. This suggests that a continuous convergent

margin affected the southeast margin of the South China Sea between the ends of Eocene to Middle

Miocene. These carbonates, turbidites and shallow marine clastic within thrust fold belts suggest potential

for hydrocarbon generation. With the detailed geologic and structural map generated, new extent for

possible Ni laterite mining is determined.

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TABLE OF CONTENTS

ABSTRACT i

LIST OF FIGURES iii

ACKNOWLEDGEMENT v

INTRODUCTION 1

LOCATION AND ACCESSIBILITY 1

SCOPE AND LIMITATION 2

CLIMATE 4

TOPOGRAPHY AND LAND USE 5

REVIEW OF RELATED LITERATURE 5

REGIONAL GEOLOGY AND TECTONICS 10

METHODOLOGY 13

LOCAL GEOLOGY 16

GEOLOGIC HISTORY 33

DISCUSSIONS 36

CONCLUSIONS AND RECOMMENDATIONS 38

BIBLIOGRAPHY 40

APPENDICES 42

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LIST OF FIGURES

Fig. 1 Location map of Palawan 2

Fig. 2 Location map of study area 3

Fig. 3 Climate map of the Philippines 4

Fig. 4 DEM map of the study area 5

Fig. 5 Geologic map of study area 16

Fig. 6 Cross sections for the transect lines delineated in the geologic map 17

Fig. 7 Beaufort Ultramafic Complex representative outcrop 18

Fig. 8 Beaufort Ultramafic Complex representative hand sample and thin section 19

Fig. 9 Monzogranite Intrusive Unit representative outcrop 20

Fig. 10 Monzogranite Intrusive Unit representative hand sample and thin section 21

Fig. 11 Sheeted Diabase Unit representative outcrop 22

Fig. 12 Sheeted Diabase Unit representative hand sample and thin section 22

Fig. 13 Contact of Espina Formation and Sheeted Diabase Unit 23

Fig. 14 Basalt representative hand sample and thin section 24

Fig. 15 Chert representative hand sample and thin section 24

Fig. 16 Contact between pillow basalt and massive basalt 25

Fig. 17 Panas Formation representative outcrop 26

Fig. 18 Representative hand sample and thin section of Panas Formation 27

Fig. 19 Contact of Panas Formation and Cretaceous Ophiolite 28

Fig. 20 Pandian Formation representative outcrop 29

Fig. 21 Representative hand sample and thin section of Pandian Formation 30

Fig. 22. Stratigraphic Column of the study area 31

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ACKNOWLEDGMENT

I would like to thank the University of the Philippines National Institute of Geological Sciences

for making this Geology 170 2014 fieldwork possible. Thank you to our two great professors, Dr.Carlo

Arcilla and Dr. Mario Aurelio for showcasing us their knowldege and expertise on the field. To our

instructors who helped us in our fieldwork Lea Bron-Sikat, Likha Minimo, Rich Ybanez, Paolo Benavides,

Jace Refran, Dominick Guballa, Sofia Frias, John Dale Dianala, Jasmine Urquico, John Paul Mendoza and

Russel Ong. Thank you Rio Tuba Mining Corporation for graciously funding our fieldwork and

accomodating us with warmest welcome. Thank you to the hospital doctors of the said mining company

for taking care of me when my health was not at its best during the fieldwork. Thank you to the NIGS

drivers who patiently waited after our fieldwork and delievered us safely to our destinations. Thank you to

the staff of NIGS who took care of us providing their services to ease our work. Thank you to the speakers

who gave time to nourish our minds before fieldwork, Prof. Noelyn Ramos and Ms. Betchaida Payot, and

to the UPM doctors and physicians from the University of the Philippines Diliman Health Center. Thank

you to my friend JK Remolador, Lara Hidalgo and Moira Sarmiento for helping me finish this paper.

Thank you to my family, my mother, father, and sisters who helped me prepare financially and

emotionally. To my batchmates who were with me through the midst of fieldwork. Thank you to the

Almighty God for giving us guidance and blessing us safety in our fieldwork.

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INTRODUCTION

The Geology 170 class of 2014 from the University of the Philippines National Institute of

Geological Sciences (UP NIGS) conducted a detailed field mapping of southern Palawan and a

reconnaissance geological survey at northern Palawan from May 2-17, 2014. The field mapping was headed

by Dr. Carlo Arcilla and Dr. Mario Aurelio, professors from UP NIGS. The said activity was also

accompanied by several instructors of institute.

Location and Accessibility

The province of Palawan is situated in the western area of the Philippines with coordinates ranging

from N 8° to 12° and E 117° to 121° as shown in figure 1.

Figure 1 shows the map of Palawan and an inset showing its location in the Philippines. It is 846

kilometers away from Manila, the capital of the country and lies in the southwest of it (Arana, 1949). Its

relief ranges from 100 meters to 1240 meters above sea level (Rollan, 1970). The study area is found in

Figure 1 shows the location of Palawan province in the country belonging to Luzon province. It trends N30°E. It is 100 kilometers long and 50 kilometers width. It is surrounded by Sulu Sea to the east and South China Sea to the west. This map has a scale of 1:20,000.

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the southwest of south Palawan. It is S 60°W and 100 kilometers from Puerto Princesa (straight distance),

the capital of Palawan (Roxas, 1970). It lies within N 8°40” to N8°30” and E 117°15” to E117°15” which

is approximate 682.07 square kilometers as shown in figure 2. This map shows the Canipan quadrangle and

Tagbita quadrangle stitched together. As shown in figure 2, the barangays bounding the study area are

Culasan, Panalingaam Taburi, Latud, Ganipaan, Tagolango, Sumbiling, Taratak, Rio Tuba, Ocayan, Iwahig,

Sandoval and Culandanum.

The study area is accessible by a 1-2 hour plane ride from Manila to Puerto Princesa and a vehicle

ride that lasts for about 6-7 hours to the town of Bataraza. Another way to go to the area is by interisland

boat from Manila to Puerto Princesa which takes about 28 hours. The outcrops in the study area are mainly

accessible by hiking as most of the areas surveyed were mountainous especially in Mt. Bulanjao which can

take about 3-4 hours to hike. The roads established in the municipality of Bataraza and the side areas of the

study were easily accessed by vehicle.

Scope and Limitation

The scope of this area is shown in figure 2. The objectives of this study were to construct a lithologic and

structural map of the area and provide a brief geological history of the tectonic events involved in the

formation of the area. The lithologic maps were constructed with aid of the petrographic analysis that was

used for identification of the sample rocks collected during the fieldwork. The majority of the outcrops

were found in the central region of the study area. The collected samples were gathered mainly in the

barangay of Rio Tuba, Sumbiling, Canipan, Latud, Iwahig Range, Panalingaan and Tarusan. There were no

samples collected in the area of Sapa and Ocayan due to its inaccessibility. There were also samples collected

along the roads in the southwest region of the study area.

The geologic history was constructed with the aid of the stratigraphic column that was also

produced from this study. All the data gathered were used to interpret and recommend possible location

of laterite deposits as requested by the sponsor company, Rio Tuba Nickel Mining Corporation.

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Figure 2 shows the location of the study area in Palawan province. It is located in the southwestern portion of the South Palawan. It is bounded by the Sulu Sea to the east and South China Sea to the west. This map has a scale of 1:10,000.

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Climate

The climate of the study area is classified in the scheme used by Philippine Atmospheric,

Geophysical and Astronomical Services Administration (PAG-ASA). Topography plays a major role in

altering the prevailing climate feature of the region (Roxas, 1970). The province is divided into two types

of climate in the Philippines. The west side part is Type 1 which has two pronounced seasons. It experiences

dry season from November to April, and wet during the rest of the year. The maximum rain period is from

June to September. Type III characterized the type of climate in the east part of the southern Palawan. It

is characterized by having no pronounced minimum rain period with a dry season lasting only from one to

three months either during the period from December to February or from March to May. The mean

annual temperature in Palawan is 27-88 degrees Celsius.

Figure 3 Climate map of the Philippines with a close-up view of the Palawan province

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Topography, Surface Drainage and Land Use

The topography of the southern Palawan varies from different places due to the different rock

units (Cabrera, 1986). It consists of high rugged mountain masses with narrow intervening valleys as seen

in figure 4 (Arana, 1949). Slopes have wide summit convexity downslope into concave valleys. The land

surfaces are dissected by small gently sloping gullies. The Canipan area is composed of a terrain with low

ridges that trend in the northeast direction. The ridge line that formed the valley divides the trends of

northeast, north-south, and east-west. The hill and valley topography are distinctly prominent due to the

hogbacks that were formed by steeply dipping resistant rock strata and caused by differential erosion of the

tightly folded sandstone that underlies these ridges (Cabrera, 1985).

Figure 4 DEM of the study area showing its topography

The south eastern portion of Bulanjao ridge has an altitude that ranges from 10 to 100 meters

above sea level. To the northwest the topography rises in relief to a maximum of more than 700 meters

above sea level (Batista, 1970). Areas lying within the rivers of Ilog and Malambunga, show a fairly

rugged topography. A sharp peak with an altitude of 899 meters is the most obvious landmark. Ridges that

trend north-northeast and at altitudes that vary between 400 to 1000 meters contain a very distinctive mantle

of dark brownish soil (Roxas, 1970). The largest stream in southern Palawan is the Iwahig River which is

about 16 kilometers wide. Other large streams are Sumbiling, Rio Tuba, Marangas and Canipaan. All of

these streams except for Canipaan are along the east coast and they originate from the central core of the

ridge. The west coast is composed of short streams. All the streams flow southwestward until they reach

the narrow coastal plains and change direction westward as they go into the South China Sea. The streams

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are used for power supply, natural storage of water, and irrigation for agricultural purposes (Arana, 1949).

The study area is also known for producing crops in the country such as corn, coconut and rice. The study

area is also known for their mineral resources which include nickel, copper, manganese and chromite

(Arana, 1949).

PREVIOUS WORKS

Study on Tectonics

One of the studies about Palawan’s origin is the study conducted by Holloway in 1982 entitled

“The North Palawan Block, Philippines: Its relation to Asian Mainland and role in evolution of South China Sea.” The

North Palawan Block situated in an island arc setting is composed of the Mindoro Island and the northern

part of Palawan Island. The North Palawan Block and the rest of the Palawan Island have two different

origins. The North Palawan Block has been formed back in the Late Paleozoic to the Mid Mesozoic while

the rest of the Palawan archipelago was formed during the Late Mesozoic to Paleozoic. The North Palawan

Block came from mainland Asia that moved southeast and was then attached to the South China Plate. The

Philippine archipelago with the rest of the Palawan Island is believed to have been initiated on the east-

northeast trend to the east of Borneo following a Late Cretaceous readjustment of plate boundaries

(Holloway, 1982).

The rocks found in North Palawan Block are Cretaceous which was an evidence of the Mid

Oligocene break up. After this, there was a substantial sea-floor spreading of the South China Sea that

generated oceanic crust. The sea-floor spreading was terminated leading to the cessation of the subduction

of Palawan Trench. After forming the North Palawan Block, a compressional tectonic event in the Late

Eocene formed the South and Central Palawan. This is formed by a diachronous impingement of crust

against the dipping of northwest Borneo Palawan subduction system. After the opening, the North Palawan

Block and Philippine Mobile Belt collided (Holloway, 1982). This study was supported by two other studies

regarding the tectonic events that involved the Palawan Island. One of these studies is the 2008 study of

Yumul entitled “On Land Signatures of the Palawan Micro-Continental Block and the Philippine Mobile Belt.” This

study supports the idea that there was a collision between the North Palawan Block and Philippine Mobile

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Belt in the early Miocene-Late Miocene after the opening of the South China Sea. More evidences were

presented to support that the North Palawan Block did come from the mainland Asia. This study added

that after the formation of the North Palawan Block, there was volcanism involved and a rifting and drifting

of Palawan southward. South China Sea opened up during the Late Eocene to Early Miocene. The

southward migrating Palawan micro-continental block ultimately collided with the northwestward moving

Philippine mobile belt. It is concluded that the Palawan Ophiolite Complex, a supra-subduction zone

ophiolite, has undergone a relatively high degree of partial melting. They attributed its formation to a post-

rifting, non-collisional setting with the magmatism possibly related to the heating of the Palawan lithosphere

(Yumul, 2008).

The idea of ancient subduction events that Palawan had experienced even before it collided with

the Philippine Mobile Belt is supported by the emplacement of the Palawan Ophiolite Complex in the

Oligocene. The accretion happened in the Middle Jurassic to Early Cretaceous accretionary complex

deposits along the southern margin of mainland Asia. The final event which is expected from arc-continent

collision events was a crustal growth and crustal thickening (Yumul, 2008; Dimalanta, 2008). This collision,

through accretion and crustal thickening, has contributed to the crustal growth of the Philippine archipelago

as well as the geological evolution of the Philippines.

Some of the manifestations of collision are cusping of the overriding plate, forming of volcanic arc

gap, emplacing of ophiolite, incipient back-arc rifting, island rotation and tilting, raising of coastal terraces,

metamorphism, intrusion of igneous rocks and steepening of subducted slab as seen in focal mechanism

solutions. However, the collage of terranes exposed in this part of the Philippines with varying origin

resulted from multiple collisions involving several fragments (Yumul, 2008).

The second study supporting the study is by Dr. Mario Aurelio entitled “Middle to Late Cenozoic

tectonics event in the South and Central Palawan.” Aurelio suggested that the emplacement of the ophiolite

complex over turbidites must have taken place between Late Oligocene and Early Miocene. Aurelio added

that at present, collision is expressed in the form of numerous earthquakes in the western Mindoro Panay

and north Palawan area (Aurelio, 2013). There were other significant studies regarding the formation of

Palawan Island, but overall they suggest that ophiolite emplacement occurred due to tectonic event,

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followed by the sea floor spreading of South China Sea and then followed by the collision of North Palawan

Block to Philippine Mobile Belt.

Study on Metallic Deposits

The Palawan Ophiolitic Complex forms most of the southern and central blocks. It is composed

of thin metamorphic sole of serpentinized amphibolite at the bottom. A thick pile of ultramafic rocks,

which are mostly peridotites, are then found. In this layer, serpentinized gabbros are also found. The next

layer is composed of crustal mafic rocks or diabase rocks. This layer may have intrusions of ultramafic and

felsic crystalline rocks. This is followed by deposition of oceanic sediments, basaltic seamount, and coral

reefs that were accompanied in the obduction. The whole ophiolite complex was down warped and was

then followed by a shallow marine layer of sediments (Mitchell, 1985; Baillie, 2000).

In 2001, a study by Baillie entitled “Soils and Land Use on Lithologically diverse Ophiolitic Alluvia on the

plain of Palawan, Philippines” focused on the ophiolite sequence with the use of soil profiles. Baillie concluded

that the mixtures of soil are from the ultramafic rocks of the extensive ophiolite sequences. He concluded

that the ultramafic clays support only stunted vegetation and are poor agricultural soils.

Their infertility is due to locally variable combinations of drought, susceptibility to fire, imbalances

in the cationic nutrients, heavy metal toxicities, and phosphorus fixation. However, these components have

been separately identified only in the northern part of the study area. It was recommended to further study

the Palawan ophiolitic soil in the rest of the island. Baillie concluded that in the section that has been

geologically mapped, there are small outcrops of highly serpentinized amphibolite. The most extensive

outcrops are of ultramafic rocks, especially peridotites. There are also mafic and felsic crystalline rocks, and

patches of sedimentary rocks (Baillie, 2001).

These ultramafic rocks found in Palawan developed as a lateritic regolith. They contain

economically significant concentrations of Ni (nickel) in one or more horizons, and these units are

commercially known as the “Ni laterite.” (Butt and Clutzel, 2013) Nickel enrichment in the laterite profile

is largely derived from olivine or serpentine of ultramafic rocks, which are mostly peridotites. The peridotite

bedrock under climatic and topographic conditions that favor the ultimate removal of all the least soluble

elements (Fe, Al, Cr, and Ti) developed the nickeliferous laterite deposits. The ultramafic parent bedrocks

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of Palawan that developed nickeliferous laterite soils are very different in comparison to other laterite soils

because the process of weathering plus the conditions in the country is also extreme (Golightly, 1981).

The Ni laterite profiles have two ore types, an oxide component and either a hydrous silicate or a

clay silicate component. These two types of laterite profiles have different processing requirements which

s why mining companies tend to achieve only one style of mineralization (Butt and Clutzel, 2013). Nickel

laterite ores account for 60% of global nickel supply. Saprolite, the layer with the most content of Ni in a

laterite profile, comprised 80% of the total thickness of a profile. These profiles have developed under

intensive weathering with humid tropical to sub-tropical conditions, under present and or past climatic

regimes (Butt and Clutzel, 2013) like the Philippines. Nickel laterites occur in strongly weathered regions.

These conditions are typical of laterite processes on cratons and less active accretionary terranes (Butt and

Clutzel, 2013) like Palawan Island.

In 1970, a study conducted by Roxas under the Mines and Geoscience Bureau determines the

economic value of the nickeliferous laterite, copper, garnierite, and chromite prospects in Southern

Palawan. They concluded that garnierite’s are better grades of nickel and about a grade of 1.533% found in

the nickeliferous laterites. In the same year, another study was conducted by Bautista under the request of

Rio Tuba Nickel Mining Corporation and reported that the area in Bulanjao is about 1.31% nickel and 37%

iron from the weighted average of the laterite and saprolite layers combined. However, the area was also

found to have garnierite floats with 5.25% nickel. This laterite soil is derived from a serpentinized rock

(Bautista, 1970). In 1971, another study was conducted by Bautista with Apelo and found that there are

also nickel laterite deposits in Aborlan Palawan with a range of 0.70%-0.84% nickel and 17.70%-23.20%

iron.

In 1949, a reconnaissance geological survey under the Bureau of Mines and Geosciences by Arana

was conducted leading to the conclusion of other minerals present in Palawan like chromite, zinc, iron, and

especially a significant percent of guano and phosphate. This is also supported by another study in 1984 by

Cabrera who also found sites with high values of guano and phosphate. Sulfide however is not massively

widespread as concluded by John in his exploration in 1963.

In 1976, a team was sent by the Bureau of Mines and Geosciences to the Palawan province to

conduct a reconnaissance geological survey of all the mineral resources found in the province. It was

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concluded that there are many nickeliferous laterite deposits in the area especially in the municipality of Rio

Tuba. Rio Tuba has nickel laterite reserves consisting of 19.9 million tons of 2.15% nickel. Iron reserves

are also found to have 27.8 million tons. There were also large amount of laterite deposits in Narra Palawan.

The study also concluded that the province is rich in deposit of silica sand, marble and limestone. As well

as iron, copper, and manganese minerals.

In 1967, Santiago’s study on the mercury Deposit in Puerto Princesa. He found out that mercury

there have reached a value that is economically useful. In 2001, another study was conducted by Baillie

about the soil involving the ophiolitic alluvia. The soil’s data confirm that the Palawan southeastern coastal

plain is lithologically heterogeneous. For each catchment, the soil pattern can be interpreted as a sequence

of increasing weathering and leaching with present elevation, age, distance of transport, and reworking of

different types of alluvium. The degree of reworking and types of soil are related to the landforms, thus soil

survey is less problematic than in the ophiolitic uplands (Baillie et al., 2000). This implies that area are not

favorable to cultivation are left unoccupied. Substantial properties and consideration to their different

combinations of soil limitations will be needed to develop them in a sustainable way (Baillie et al, 2000).

With the Palawan tectonic setting, its hydrocarbon potential is also introduced by Aurelio (2013).

Palawan has many potential for metalliferous minerals, nickeliferous laterite soil and hydrocarbon

generation.

REGIONAL GEOLOGY AND TECTONICS

In between the western margin of the Philippine plate and the southeastern portion of the Eurasian

plate is where the whole Philippine archipelago is situated. The Philippine plate and Eurasian plate

subducted under the Philippine archipelago westward and eastward respectively. It is in a trapped zone in

between two active subducting systems (Aurelio, 2013). The main Palawan Island is northeast–southwest

trending and is made up of two blocks: the northern Palawan block made up of continent-derived

sedimentary and metamorphic rocks and the southern Palawan block made up of oceanic-derived rock

formations, as exemplified by the Palawan Ophiolite Complex (Yumul, 2008). Palawan Island is located in

the southwestern region of the Philippine archipelago. It is also situated at the south-eastern margin of the

South China Sea (Willies, 1950). It is composed of ranges, shelves, ridges and offshore basin (MGB, 1986).

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Palawan is an old mountain range that is arched by compression until now. It is also generally more

seismotectonically stable as compared to the other islands in the Philippines (Aurelio, 2013). Palawan, with

the Zambales range of Luzon, and the islands of Lubang, made the outline of the South China Sea basin

(Willies, 1950).

North Palawan Block

The North Palawan Block trending northeast is separated from the island of Mindoro by Mindoro

strait. This is comprised mainly of the sedimentary and metasedimentary of Paleozoic and Mesozoic rocks

of continental affinity that is also comprising the Calamian Island, Cuyo Island ot the east, western Mindoro,

and northwest tip of Panay. North Palawan Block is made up of Reed Bank, the Spratley Island and the

shallow part of South China Sea. It is believed that this was once a piece of East Asia mainland that drifted

away from southeast Asia in the Early Tertiary (Holloway 1981).

Central and South Palawan

This is believed to be a tectonic melange comprising of peridotite and gabbro with an extension of

ultrabasic rocks along with the Paleogene clastic sediments. An accretionary wedge lie adjacent to Palawan

with thrust verging northwest. The wedge is underlain, beneath a southeast dipping thrust by Lower

Miocene Carbonate and beneath this, are the Lower Cretaceous sediments. Middle and Upper Miocene

sediments blanket the accreted wedge and extends through the Reed Banks, Spratley Island and various

shoals comprising the southern part of South China Sea (Holloway 1981). There are unconfimities in this

region due to the rifting of the North Palawan block from mainland East Asia. The Upper Oligocene to

Lower Miocene Carbonate platform are found to be extending in central and south Palawan. In this area

also lies the projected axis of Palawan Balabac Island ridge (Mitchel, 1985).

Palawan Trough

The northwest Palawan shelf extends 60 to 80 kilometers offshore Palawan. This characterizes that

the Palawan trench is inactive since the Mid Miocene which lies northwest of the shelf and extends to the

southwest. This is also called the Palawan trough (Holloway, 1981). The Palawan trough is believed to

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cause the subduction of proto South China Sea in Paleogene. However, since it terminates in the Luconia

Shoals in Northwest Borneo Trough, it makes the interpretation questionable (Aurelio, 2013).

Offshore Northwest Palawan

The offshore Northwest Palawan is made up of Upper Jurassic or Lower Cretaceous limestone,

tuffs, volcanic rocks and sandstone overlain in angular unconfomity by nearly Upper Eocene fine grained

sandstone, siltstone, claystones with minor tuffs and a local conglomerate. In this area, the Nido Limestone

is found. The Nido Limestone is made up of Oligocene to Lower Miocene but with Upper Eocene

carbonates. The Nido Limestone lies unconformably over Eocene and Upper Jurassic. It is overlain

conformably by a succession of calcareous slate, siltstone, sandstone, micritic limestone and local igneous

class conglomerate of Early Middle Miocene Pagasa Formation. The Matinloc formation above a Mid

Miocene unconformity, consists of a conglomeratic sandstone with siltsone and claystone of Late Middle

to upper Miocene. The Ulugan Bay fault as a major boundary between continental rocks and ophiolites

with melange as a sinistral strike slope fault formed during collision of Palawan and Palawan Trough mid

Tertiary (Holloway 1982).

South China Sea

The eastern part of South China sea is underlain by a sediment mantled oceanic type crust created

along an easterly trending spreading center between Mid Oligocene and Early Miocene. The western part

of South China Sea basin is overlain by a thinned continental crust. This is believed to be due to the breakup

of Asia on North Palawan Block from Oligocene. This is followed by the Cretaceous rifting (Mitchel, 1985).

Northwest Borneo

A geological strike controls the pattern of the collision between the North Palawan Block and the

Palawan trough. The Bacungan lowlands are composed of gabbros and its default system of the Bacungan

and Irataga tectonic windows. The St. Paul limestones have a trend of northeast. Its highest elvation is 1028

m and this is situated within the Babuyan Island. The karst topography has an internal drainage system. In

Saban, an underground river is found. The limestones are from Upper Permian. In the east of Babuyan

lowland, the highest elevation is the Cleopatra’s needle with an elevation of 1063 m. The coast is trending

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southeast-northwest and the watershed is trending northwards. The eastern margin of Rizal river is trending

northward and is composed of quartzite ridges that rise abruptly from alluvial deposit (Hamilton, 1977).

Sulu Sea

The Sulu Sea basin is a Paleogene fore arc basin subsequently titled with post subduction sediment.

This is believed to be a represented passive margin sedimentary deposited in the southeast margin of North

Palawan Block. The southeast of Sulu Sea is where the Cagayan Ridge is found. The Cagayan Ridge with

an elevation of 150-200 kilometers is cut by the Negros Trench in the north. The southeast of Sulu Sea is

made up of Mid-Tertiary oceanic crust. It subducts in the southeast-east in Sulu and Negros trench during

the Miocene. The northwest of Sulu is composed of a thick subhorizontal succession of Upper Miocene to

Recent Sedimentary. Found below this is an angular unconformity of Upper Mesozoic to Lower Miocene

sedimentary rocks (Hamilton,1977).

METHODOLOGY

There were a total of five fieldwork days: May 5- 6, May 10-11 and May 14. Each fieldwork day required

the 18 groups to accomplish a daily traverse map on their designated area. On field, if a group finds it

difficult to produce a compass tape or compass pace traverse due to steep slope, the group needs to locate

themselves using the GPS coordinates. In flat area, compass tape traverse was most likely used. The traverse

data were directly plotted on the 1:5000 maps. Along the traverse, if an outcrop was found, the outcrop

locations are highlighted in the maps. It was scrutinized and was then given an outcrop description. The

outcrop description included the outcrop features from afar, its dimension, its direction, GPS coordinates,

and its appearance. If beds were identified, the strike and dip measurements and other structure

measurements were gathered. Sampling was done by locating where the fresh part of the outcrop is exposed.

With the use of hard pick, fresh fist-sized samples were then collected. At least three samples per outcrop

were collected. The samples were described with the help of hand lens. A field identification and sample

number were given to the sample rock before leaving the outcrop. The sample name format include the

region of the area, the map grid based on the topographic map given by the Mapping Committee, peg’s

name, day of the fieldwork, outcrop number and sample number. In the sample naming, SP stands for

southern Palawan. The peg’s name in the sample format was only composed of their first three letter for

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easy recall. After the traverse of the designated area was done, each group reported what they have observed

to the class. The class plotted the data into the Lithologic Map, Structural Map and Geologic Map to

overview the accomplishments for the day. From that, the class planned out the next designation of each

group. With a total of five days, the class finished the mapping of Canipan quadrangle. The majority of

the outcrops were found in the central region of the study area specifically in Mt. Bulanjao Range and

barangay Sandoval. Most of the outcrops are widely exposed in the mentioned areas.

The lithologic maps created, used the data from petrographic analysis. Petrographic analyses were done

with the use of a polarizing microscope. There were a total of 117 rock samples collected. The sample rocks

were cut into thin sections and using a microscope with plane polarized light and cross polarized light

feature, the rock thin sections were identified based on their transmitted light properties. With the maps

generated and the data gathered, a geologic history was created to confirm or debunk some of the previous

work on the geology of southern Palawan.

With all the information, the class was required to submit an aerial geologic research paper about

the entire fieldwork. This was the main objective of the study which was to report the data and produce

interpretation. Construction of this data and interpretation need the consensus of the class.

LOCAL GEOLOGY

The areas mapped are within the combined quadrangles of Canipan and Bulaloc. These are

pertaining to the area from N 8°31” to 8°46” and E 117°19” to 117° 30”. In the north of the study area in

Taburi, the interbedded sandstones comprising Panas Formation are located. It extend to the northeast of

the study area in barangays of Panalingaan and Culandanum. The Panas Formation is also found in Brgy.

Sandoval in the east and Brgy. Latud in the west of the study area. Barangays in the south area namely Sapa,

Sumbiling, Canipaan, and Ocayan also belong to the Panas Formation. The massive sandstones in the

northeast in Brgy. Tarusan composed the Pandian Formation. The limestone in Brgy. Iwahig in the east

composed the Ransang Limestone. The ultramafic rocks of Beaufort Ultramafic Complex, basalt and chert

of Espina Formation, Monzogranite Intrusive Unit and Sheeted Diabase Unit were found in the old mining

site in Brgy. Rio Tuba in the center of the study area near Brgy. Taratak. The study area covered a total of

seven (7) formations and rock units with eight (8) different rock types as shown in the geologic map.

15

The oldest rock unit in the study area is the Palawan Ophiolite Sequence. It is composed of the

Beaufort Ultramafic Complex, and Espina Formation emplaced in the Cretaceous. This is accompanied by

the Monzogranite Intrusive Unit and Sheeted Diabase Unit. In the Early to Late Eocene, the Panas and

Pandian formations are emplaced. This is overlain by the Ransang Limestone in the Late Oligocene to Early

Miocene Age. The rest of the study area is composed of Quaternary Alluvium

16

Figure 5 Geologic map of southern Palawan

17

Figure 6 Cross sections of the study area with transect lines delineated in the geologic map

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EARLY CRETACEOUS

PALAWAN OPHIOLITE SEQUENCE

The Palawan Ophiolite Sequence is emplaced in a volcanic arc-continent fragement setting as

nappes in the Early Cretaceous (Aurelio, 2013). Palawan Ophiolite Sequence includes the Beaufort

Ultramafic Complex, and Espina Formation. The Palawan Ophiolite Sequence ranges about 300 kilometers

along the trend of the island and has a maximum width of 30 kilometers (Pena, 2008). Included in the

Palawan Ophiolite Sequence are the Monzogranite Intrusive Unit and patches of the Sheeted Diabase Unit.

BEAUFORT ULTRAMAFIC COMPLEX

DISTRIBUTION

The Beaufort Ultramafic Complex is widely exposed in the ridge of Mt. Bulanjao and Brgy. Rio

Tuba. These are high rugged areas located in the middle of southern Palawan. The total area bounded by

this formation is about 10 kilometers thick and 12 kilometers wide.

The Beaufort Ultramafic Complex is also distributed near the Okayan River and near the streams in area

of Taratak. Small area of the east in Latud also comprised the Beaufort Ultramafic Complex. The

distribution of this formation and the other formations are also presented in the lithologic and sample map

located in the appendix. Shown in figure 7 is a representative outcrop of Beaufort Ultramafic Complex

found in the upper region of Mt. Bulanjao. The outcrops under this formation are massive and extensive.

Figure 7. Located in N 8°33”'52’ E 117°22”43.59’ in Mt. Bulanjao, Rio Tuba. An outcrop showing limonite layer on top, underlain by a saprolite layer and serpentinized peridotite. The outcrop is jointed with strike and dip readings of N80W, 27NE and N10W and 70NE

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They are brown to dark red in color. The outcrops are highly vegetated and highly weathered. The outcrops

are comprised of peridotite bedrock at the bottom, overlain by a saprolite layer. On top, the limonite layer

is found.

PETROLOGY AND PETROGRAPHY

The Beaufort Ultramafic Complex is composed of four lithologies namely pyroxenite, dunite,

harzburgite and peridotite which are highly serpentinized (Pena, 2008). Serpentinized basalt, arkosic wacke,

serpentine, chalcedony and claystone are also found in some part of this area. Most of the rocks are

serpentinized and there are rocks found to be chloritized. It is not determined which rock is the most

abundant of all.

This is a hand sample (figure 8) from an outcrop near the representative outcrop previously

mentioned. This is identified serpentinized dunite. The hand sample is orange to green in color with black

splotches and it is very weathered. The hand sample is medium-grained and have equiangular grains. Shown

in in the right of the image is the thin section of the sample. Its textures are holocrystalline and

microcrystalline. The serpentine exhibited mesh texture. It is mainly comprised of serpentinized olivine.

Other component are too small to identify.

FIELD RELATIONS

The Beaufort Ultramafic Complex is overlain by the Espina Formation. The rock found to be in

contact with the Espina Formation are serpentinized peridotites. The contact is located in the northeast of

Latud and northwest of barangay Rio Tuba. This can be seen in the cross section of transect line 5.

Figure 8 Sample Number 91 Hand sample and thin section in 4.4 mm field of view. Located in N 8°33”46’ E 117°22”39’. Identified to be a serpentinized dunite.

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STRUCTURES AND LOCAL DEFORMATION

The rocks are prone to chemical weathering due to the climate. The soil derivatives of this

formation formed the laterite deposits in the Mt. Bulanjao. Structures found in the Beaufort Ultramafic

Complex are extreme joint patterns, fractures in the outcrops, fault gouge and mineral veins signifying that

Beaufort Ultramafic Complex is deformed. The joints strike direction is northwest and dip northeast. The

joints are extensive in the outcrops. These structures are post-depositional structures that have affected all

the member lithologies of the ophiolite sequence. Even though there is the presence of arkosic wacke, there

were no sedimentary structures found.

AGE AND CORRELATION

This is correlated to the Paly Serpentine in northern Palawan and Smooth Hill Ultramafics in

Balabac Island. This is dated Early Cretaceous using the Osmium-Rhenium dating method by Santos in

1997 and similar to the age determined by MMJA-JICA in 1988 (Pena, 2008; Aurelio, 2013).

MONZOGRANITE INTRUSIVE UNIT

There are no studies yet reporting the existence of this identified granite intrusion in the study area

thus establishment of this unit is proposed in this study. The name is Monzogranite Intrusive Unit because

it is suggested that this unit intruded the diabase unit.

DISTRIBUTION AND STRUCTURES

These monzogranite rocks are found in the southwest of Brgy. Sandoval, near the Umawi River

and in the northeast of Rio Tuba. This unit extend about 3 kilometers long and 2 kilometers wide. The

monzogranite rocks are also found in the path of the Umawi River. The extent of this unit is then inferred

from the river path. The topography of the area is high and rugged. The representative outcrop is massive

Figure 9 Massive and extensive outcrop of the Monzogranite Intrusive Unit located in Brgy. Sandoval with coordinates N 8°37.76” E 117° 24.806”

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and extensive. It is highly weathered and highly vegetated. It is located near the Umawi River. It is about 8

meters high and 36 meters width. This outcrop shown in figure 9 is reported to have conjugate joints. Veins

or dikes of light green rocks are also found in the outcrop. It was concluded that granite intruded the

diabase rock. Evidence of cooling was found in the granite and might be an evidence that the granite is

younger than the diabase.

PETROLOGY AND PETROGRAPHY

This is the monzogranite identified to be present the outcrop shown in figure 9. The hand sample

is fine-grained and light grey in color. There is also a secondary growth of chlorite. It is diamagnetic. The

thin section shows the three major components of this rock. It is composed of plagioclase, alkali feldspar

and quartz. Both plagioclase and quartz have grains that are about 1mm size and composed 80% of the

rock. The plagioclase possessed a myrmekitic texture. It can also be distinguished by its lath-liked shaped.

The alkali feldspar composed the rock about 20%. It is granophyric and the size of its grains is about

0.7mm. Other minerals found in small amount are chlorite and opaque minerals. The quartz and alkali

feldspar have obscure shape as shown in the thin section. It has a holocrystalline texture and inequigranular.

FIELD RELATIONS, AND AGE

It is unconformably overlying the basalt of Espina formation. This is shown in cross section of

transect line 5. The structures found in the outcrop are fractures, conjugate joints and mineral veins. Age

of this unit is not yet determined but since it is presented to be an intrusive unit of the Cretaceous ophiolite,

it is not later than Late Oligocene.

Figure 10 Hand sample and thin section of the monzogranite sample number 115 located in N 8°37.76” E 117° 24.806” in Brgy. Sandoval. The thin section is under 4.4mm field of view.

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SHEETED DIABASE UNIT

DISTRIBUTION AND STRUCTURES

The sheeted diabase are located in the east portion of barangay Sandoval near the quaternary

alluvium. It is not mappable to be presented as a new formation. It is also not too small to be ignored thus

this is presented as patches in the basalt of Espina Formation.

The diabase outcrops are found in the river of Sandoval. It is color black from afar and it is highly

jointed. The outcrops are highly vegetated. They are also highly weathered and highly jointed. Its attitude

is N50E, 40SE.

PETROLOGY, PETROGRAPHY, FIELD RELATION AND AGE

The rock types of this unit are composed of andesite and diabase. Shown in figure 11 is the contact

between the andesite dike and diabase dike. The andesite is unconformably overlying the diabase. The

andesite is light grey in color. The hand sample of one of the outcrops belonging to the Sheeted Diabase

Figure 11. Shown in the left is the diabase outcrop in Sandoval with coordinates N8°36.326” and E 117° 24.116” ’ and on the right is the andesite dike and diabase dike located in N8°37.120” E117° 24.458”

Figure 12 Hand sample and thin section of sample number 11 located in E117°23.981” and N 8°37.727”. The thin section is under 4.4 mm field of view.

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Unit is shown in figure 12. It is dark green to gray in color. It is fine-grained and chloritized. The diabase

representative sample is composed of 40% plagioclase, 35% clinopyroxene, 10% quartz, and 10% opaque

minerals. It is identified to be a highly chloritized diabase. The plagioclase are the lath shaped minerals and

the quartz are the anhedral grains. The age of this unit is not yet determined but it is not later than Late

Oligocene.

ESPINA FORMATION

DISTRIBUTION

The Espina Formation of Late Cretaceous is the last member of the Palawan Ophiolite Sequence.

Espina Formation was first named by Basco in 1964 due to its locality (Pena, 2008). The Espina Formation

is distributed in the area of Brgy. Sandoval and in the ridge of Mt. Bulanjao. It is about 1000 meters thick.

It is found in high rugged areas and along the river. The outcrops belonging to Espina Formation are highly

weathered and highly vegetated. They are black to dark green in color. They are massive and extensive.

They are highly jointed. Shown in figure 13 is the contact between basalt and diabase. As seen in the cross

section number 5, the Espina Formation is overlain by the sheeted diabase unit.

Figure 13. The contact between basalt and diabase unit located in Brgy. Sandoval with coordinates N 8°37.76” and E 117°24.806”

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PETROLOGY AND PETROGRAPHY

The Espina Formation is composed of spilitic basalt with intercalated sandstone and chert. Figure 14

shows one of the basalt located in the ridge. The hand sample is black in color. Its texture is aphanitic and

it is identified to be basalt in the field. The thin section on the right confirms it is a basalt. The thin section

shows the major component of basalt is plagioclase.

It is hypocrystalline, inequigranular, aphanoporphyritic, and amygdaloidal in texture. The plagioclase

composed 46.72% of the rock have lath-shaped, euhedral, idiomorphic grains. Pyroxene is about 1.37%

and the grains are subhedral to anhedral that is xenomorphic. The opaque minerals is about 6.57%. It is

anhedral, xenomorphic with size of about 0.06mm. Larger compared to the other minerals in 0.1mm. The

glass is about 15.03% which appear as dark brown in color. Quartz is 24.32% and occurred as amygdules.

The chlorite found is about 4.37% surrounded by the quartz grain. It is euhedral, idiomorphic and about

0.6mm. The remaining 1.64% goes to the calcite that occurred as veins. In figure 15, a representative sample

chert is shown.

Figure 14. Hand sample and thin section of basalt sample 93 located in Mt. Bulanjao with coordinates E117°24.22” N 8°37.5” The thin section is under 4.4mm field of view

Figure 15. Hand sample and thin section of sample 2 in Brgy. Sandoval with coordinates N8° 38'6.4” E117° 25' 44.2”. This is identified to be a metachert. The thin section is under 4.4 mm field of view

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The cherts found in the Espina Formation are reddish to brownish in color in the hand sample. It did

not effervesce in the field. It is composed of 20% megaquartz, 75% microquarts and 5% chalcedonic quartz.

The sample is reported to have veins of megaquartz and chalcedonic quarts exhibiting a microfolds.

FIELD RELATIONS AND STRUCTURES

Shown figure 16 (left image) is the contact between pillow basalt and massive basalt. On the right

image is the contact between chert and basalt. The pillow basalt is also unconformably lyng on the massive

basalt. The chert is unconformably lyng in the basalt. The structures found in this unit are joints and mineral

veins signifying a post depositional structures. There were no sedimentary structures found in the

sedimentary rock under this unit.

AGE AND CORRELATION

Espina Formation is correlated to the Boayan Formation in northern Palawan and Irahuan

Metavolcanics in central Palawan (De los Santos, 1959). It is unconformably underlain by the Panas

Formation and the Ransang Limestone (Pena, 2008). This can be seen in the cross section 4 and 5. The age

is determined using the radiolarians found in one of their chert sample by MGB in 2004 (Pena, 2008). There

were no fossils found in the collected samples of chert.

Figure 14. On the left is the contact between the pillow basalt and massive basalt. Located in N8°36.346” E 117°24.084” and on the right is the contact between chert and basalt located in N8°38”53.3’, E117°25”45’’

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PANAS FORMATION

DISTRIBUTION

Panas Formation was first named by Casasola in 1965 due to its locality in Panas Creek near Iwahig

River (Pena, 2008). In the study area as seen in the geologic map, it extend from southwest-west-northeast.

It is found in Panalingaan, but the west of Panalingaan is made up of Pandian Formation. It is also located

in Iwahig River, Tagbita, Latud, Taburi, Culandanum, Sandoval, Ocayan, Sumbiling and Canpinaan. It is

also found in Mt. Bulanjao in the west part of the Beaufort Ultramafic Complex and Espina Formation.

These are high rugged areas. It is about 1500 meters thick.

This is a representative outcrop of Panas Formation. It appears to be part of a folded sequence. Red

rocks are effervescent that are identified to be calcareous mudstone. Alternating colors of the fold are

possibly due to change of oxidizing conditions. Limb of a possible fold of cherty mudstone is seen.

Figure 17 this is the representative outcrop of Panas Formation located in Culandanum River at N8° 38.404” E117° 25.424”

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PETROLOGY AND PETROGRAPHY

Panas Formation is composed of sandstone, mudstone, siltstone, shale and conglomerate. The

interbeds are composed of highly indurated and sparsely fossiliferous sandstone and shale. Shown in figure

18 is a hand sample of a Panas Formation outcrop identified to be a quartz sandstone.

The hand sample is yellowish in color. It is fine to medium-grained and the grains are angular. This is

composed of 42.6% quartz, 42.6% feldspar, 12.7% matrix and 2% opaque minerals. The final identification

for this is arkosic sandstone. The sandstones found in the Panas Formation generally have high content of

quartz and feldspar.

FIELD RELATIONS

Panas Formation is unconformably lying over the Espina Formation and intertoungues with Ransang

Limestone. This can be seen in the cross section 1, 3, 5, 6 and 7. Shown in Figure 19 is the contact between

Panas Formation and the laterite deposit of the Palawan Ophiolite Sequence. Found on the left side is the

mudstone which have quartz vein. The lateritic soil is found on the right side. Below is the contact between

interbedded sandstone of Panas Formation and peridotite of Beaufort Ultramafic Complex. This shows

that the Cretaceous ophiolite was emplaced over the Eocene turbidites (Panas Formation).

STRUCTURES

There was a bedding plane observed in a sandstone outcrop in Culandanum. It has a strike and dip of N60E

and 57SE respectively. Few faults were measured. These faults seem to have a direct relationship with the

faults found in the ophiolite sequence.

Figure 18 Hand sample and thin section of sample 14 found in Brgy. Sandoval with coordinates E117° 23.043 “ N 8°36.136”. The thin section is under 4.4 mm field of view.

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Figure 19 shows the contact between the mudstone and laterite with coordinates N 8° 33.184” E 117° 21.546” in Brgy. Sumbiling. The outcrop is generally weathered, and highly vegetated. It has roots on top of it. Below image is the contact of the sandstone and peridotite. This contact is located in N 8° 33.221” E117° 21.530” in Brgy Sumbiling.

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AGE AND CORRELATION

The outcrops (as shown in figure 19) are generally weathered and vegetated. It exhibit folding

and tilting of beds. Its age was determined by BMG using the foraminifera Globorotalia velascoensis (Cushman)

and Globigerina gravelli Bronnimann, indicative of Paleocene to Early Eocene age (Pena, 2008). This is

supported by the sandstone that were dated (sample 55) and shows that it contains coccolithophores that

are dated Eocene of age (see appendix for reference).

PANDIAN FORMATION

DISTRIBUTION

The Pandian formation is found in the west of the study area, the Balansungan peak extending

southwest near Taburi. It passes the Tagbita River, Nipa River and Colby River. In the east, it occupies the

Matalingajan Rage up to the north in Brgy. Tarusan. It is also seen in the eastern flank of Bulanjao, Tarusan,

Labog, Marirong-Tagusao, Punang, Lamican, Malinao and Mariquit Island. It is about 1500-200 meters

thick. It was named by Casasola in 1956. Shown in figure 18 is the representative outcrop of Pandian

Formation. This outcrop from afar is brownish in color.

Figure 20 Seen in this outcrop are the yellow lines showing the tilting of beds of the outcrop. This is located in Tagbita area with coordinates N8° 45”58.2’, E117° 26” representing the Pandian Formation.

30

The outcrop shows 2 major layers. The top layer is lighter in color compared to bottom layer. The

outcrops under Pandian Formation are generally massive. The outcrops are highly weathered, highly

vegetated and exhibit tectonic deformation like tilting of beds and folding.

PETROLOGY AND PETROGRAPHY

Pandian Formation is composed of massive sandstone, shale and conglomerate. This is mainly composed

of the massive sandstone that is arkosic in nature and porous. They are accompanied by indurated dark

gray mudstone and silty shale interbeds.

The sandstone is mostly made up of quartz and feldspar. The arkosic sandstones are primarily made up of

quartz making it light in color. The alkali feldspar in large percent comprised the sandstone too. They are

also made up of matrix, cement and lithic fragments. Some contain fossils. The black minerals are the lithic

fragments. This is identified to be a fault breccia. It is cream in color. It effervesce with hydrochloric acid.

The minerals are mostly calcareous in nature. It is identified to be a limestone breccia on the field. The thin

section shows that it is mainly composed of quartz which are sub-angular and the rest are cement. The

cement has more sparite than the micrite. There are no feldspars, no lithics, and no matrix in this sample.

FIELD RELATIONS, STRUCTURES, AGE AND CORRELATION

The Pandian Formation is unconformably overlying the Panas Formation. This can be seen in the

cross sections provided especially in cross section 1. It is found to have folding and faulting. The early

study determined this formation to be Middle to Late Miocene by Casasola. Later studies that include

Casasola (1956), Martin (1972) and BMG (1981) determined in with Oligocene age. MMAJ-JICA (1990)

Figure 21 shows hand sample and thin section of the fault breccia located in Tagbita with coordinates N 8° 38”5' E117° 28”24.5' Sample number 31. The thin section is under 4.4 mm field of view.

31

determined to be in Early Oligocene. But in 1977 Gamboa, found an Eocene foraminera from the shale

they collected. Pandian is dtermined to be Eocene of age.

RANSANG LIMESTONE

DISTRIBUTION

The Ransang Limestone was named by Martin in 1972 for the carbonate exposures in Barrio

Ransang, Quezon. This limestone rock unit is located in Iwahig. It is in the east portion of southern Palawan

along with other formations like Panas and Pandian. However there were no contacts found in this area.

PETROLOGY AND PETROGRAPHY

The Ransang Limestone formation are composed almost of micritic limestone.

This sample has a light grey color due to the felsic minerals composing it. The grains are medium-sized

grains. Since it effervesce in cold HCL this sample is identified to be a calcareous medium-grained sandstone

in the field. The thin section clearly present the thin section composing only of micrite thus this is further

identified to be a calcilutite limestone.

FIELD RELATIONS, AGE AND CORRELATION

Ransang Limestone is conformable overlying the Pandian formation. This is presented in cross

section number 5. It is determined to be Early Miocene (Pena, 2008). Studies before by Maac and Agadier

(1988) found foraminifera test classified as Spiroclypeus and Lepidocyclina species that suggest an Early

Figure 22 Hand sample and thin section of sample 69 located in Iwahig. It is under 4.4 mm field of view.

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Miocene age. The Ransang is correlative to the St. Paul Limestone onshore and Nido Limestone in offshore

northern Palawan (Pena, 2008).

SUMMARY OF STRUCTURES

The structures found within the study area are generally fractures in outcrops. Joints and faults

were grouped based on their lithologies of their respective rock units. There were folds and faults found in

the sedimentary units. Fractures and mineral veins were dominant in the non-sedimentary rock unit.

Deformation occurred more than once in the study area. There were major rifting and convergence that

happened causing the bedding planes to have their present attitudes. A table of structures is found in the

appendix.

GEOLOGIC HISTORY

CONTINENTAL RIFTING

Tectonics in southeast margin of South China Sea (Late Cretaceous)

The mainland Asia moved southeast and attached to the South China Sea margin (Holloway, 1982).

In the South China margin, an oceanic basin was formed due to the attenuation of crust. In the south of

this oceanic basin is where the small paleo-Palawan is placed (Aurelio, 2012). This small paleo-Palawan is

an accretionary prism composed of chert-limestone-clastic as part of mainland Asia (Yumul, 2009). The

Upper Paleozoic to Jurassic sedimentary succession composing the paleo-Palawan is also called Jurassic

olistostrome (Aurelio, 2012). Before the opening of South China Sea, the depocenters responsible for the

Upper Cretaceous to Eocene sedimentary successions were located in the continental margin of southern

China. This continental margin is inactive as the sedimentary succession is still being deposited. These two,

the oceanic basin and continental margin are in thrust contact (Suzuki, 2000). Thus the South China Sea

continental margin is composed of the Cretaceous ophiolite, oceanic and arc rocks. The North Palawan

Block which is still part of mainland Asia (Yumul, 2008) is composed of Eocene oceanic crust. Palawan

therefore is continentally derived unit that includes clastic, carbonate and igneous from mainland Asia

(Aurelio, 2012). The Cretaceous ophiolite involved the Beaufort Ultramafic Complex and the Espina

Formation. The Eocene turbidites is the Panas Formation.

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Formation of Rift Structures

The south-eastern edge of the South China Sea, North Palawan Block and proto-South China were

subjected to continuous convergent tectonics. This was induced by the continuous south-eastward

movement travel of these rifted blocks and their approach to Philippine Mobile Belt (Aurelio, 2013). The

margins then rifted that produced fault bounded tilted basins. These resulted to the asymmetric basin

deposition. When the Upper Cretaceous ophiolite and Eocene succession in the continental margin became

active, it drifted from the South China continental margin when the South China Sea opened (Suzuki, 2000;

Zamora, 2009; Aurelio, 2013). This resulted to the collision between converging masses of similar densities

(North Palawan Block and Philippine Mobile Belt arc in the north), and to the subduction and obduction

where crustal densities differ (proto-South China and Philippine Mobile arc) (Yumul, 2008). This caused

the deformation in the Beaufort Ultramafic Complex, Espina Formation and Panas Formation.

Subduction in Palawan Trench (Late Eocene)

The Upper Cretaceous Palawan Ophiolite and Eocene turbidites subducted in the paleo-Palawan

Trench in the Late Eocene to Early Oligocene (Suzuki, 2000). This subduction event formed the east-

northeast-southwest trending fold axis and south dipping axial plane, the D1 deformation (Suzuki, 2000,

Hall 2013).

Emplacement of ophiolite in south of mainland Asia (Early Oligocene)

Subduction and obduction happened emplacing the Cretaceous ophiolite thrust from the collision

of south Palawan southward over the turbidite oceanic fragment derived filled with syn rift clastic sequence

(Aurelio, 2012; Yumul, 2009). This caused the Beaufort Ultramafic Complex and Espina Formation to be

found in the Panas Formation.

OCEANIC SPREADING AND MULTIPLE EPISODE OF SUBDUCTION

Opening of South China Sea (Mid Oligocene)

The opening of the South China Sea happened in the Mid Oligocene to Early Miocene about 32

to 12 million years ago (Holloway, 1982; Aurelio 2013). Opening of South China Sea basin was triggered

by approach of hot region responsible for the spreading in West of Philippine Basin (Honka, 2002).

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Subduction in Palawan trough (Late Oligocene)

After opening, subduction along Palawan trough occurred (Hall, 2013). In the Late Oligocene,

there was heating and rifting of continental crust in East of South China Sea (Pineda, 1992). Partial melting

occurred and this served as an evidence of the supra subduction zone of ophiolite (Yumul, 2008). When

the subduction stopped, intrusion of granite happened cutting the D1 deformation structure due to rifting

(Suzuki, 2010). During collision of Cagayan Arc, the Pre Mezosoic granite was intercalated with Mesozoic

sedimentary rocks (Hall, 2013). Margin rifting ceased and mild metamorphism happened causing the

indurated sandstone and siltstone known as the Pandian Formation. This cannot be older than Early

Oligocene (Aurelio, 2013). This caused the granite and diabase to be found in the Cretaceous Ophiolite.

The diabase was formed first before the granite rocks.

Subduction in Palawan Trough stopped (Early Miocene-Middle Miocene)

Extensive shallow marine area persisted followed by deposition of platform carbonic sequence

topped in places by shelfal reefs. General subsidence ensued after erosional event causing the Palawan to

remain shallow and allow deposition of carbonate. Deep marine clastics accumulated in this basin and

formed the turbiditic sequence. Then carbonate buildup occurred (Aurelio, 2013). This serve as the mark

of the final approach towards subduction zone (Zamora, 2009). Palawan trough is covered by Middle

Miocene to Recent deposits suggesting that subduction along Palawan Trough ended before Middle

Miocene (Suzuki, 2000). However other studies suggest that it ended in Early Miocene (Hall, 2013).

CONTINENTAL ARC COLLISION

Palawan North Block moved to Philippine Mobile Belt (Middle Miocene)

After the subduction in Palawan trough, the Palawan North Block collided with Philippine Mobile

Belt. This resulted to more rift sedimentary successions (Aurelio, 2012). This also caused more collision

and thrusting (Hall, 2013). The Palawan Ridge as a part of North Palawan Block rifted east and south from

South China Sea (Pineda, 1992). The Philippine island arc together with Manila trench drifted westward as

seen from the occurrence of north-northwest-south-southeast trending folded structures.

35

The collision between North Palawan Block and Philippine Mobile Belt is seen in the Miocene

south Palawan sandstone which were derived from North Palawan metasedimentary and metamorphic

basement rocks (Suggate, 2013). Paleo-Palawan arc begun to subduct into the Manila trench (Suzuki, 2000).

In the Late Miocene, the deposition of collision-sealing carbonates occurred. In the Pliocene,

general subsidence ensured after erosional event (Aurelio, 2013). Palawan remained shallow that allowed

deposition of carbonate. In present time, tectonic regime remains convergent at northeast margin of

Palawan towards Mindoro and Panay (Aurelio, 2013).

DISCUSSIONS

EVIDENCES OF EACH FORMATION

The Cenozoic tectonic events that led to the formation of south Palawan can be summarized into

the following: before, during and after the opening of South China Sea margin. Before the opening of South

China Sea, the Cretaceous ophiolite sequence was emplaced over the Eocene turbidites.

This can be seen in their contacts shown in the cross sections. Based from the seen deformations

of the Cretaceous ophiolite and Panas Formation, these two had undergone more than one deformation.

One of the deformations these two had undergone took place before the rifting of the South China Sea.

This can be seen in the major folds in the outcrops seen in Panas Formation. There was an Eocene

compressive event in Mid Cretaceous to Late Paleogene due to the northwest dipping convergent margin

of southeast of South China Sea. Another evidence is the presence of chert in the Espina Formation. The

cherts are due to the localized thrust slope during the rifting (Pineda, 1992; Honka, 2002). The syn rift

structures in the Mezosoic basement rocks filled with syn rift basins are all evidence of the rifting (Aurelio,

2013). Thus Cretaceous ophiolite and Eocene turbidites were already deformed even before the opening.

The syn rift basins were then filled with deep marine clastics that formed the turbiditic sequence. Carbonate

buildup occurred then. This is an evidence of deep water basinal environment (Aurelio, 2013). This

environment is the probable reason for the serpentinization and chloritzation of the Beaufort Ultramafic

Complex and some of the basalt in Espina Formation. These are also evidence of potential hydrothermal

ore deposits. When the South China Sea opened, an arc magmatism occurred that metamorphosed the

Pandian Formation in the Early Oligocene. The arc magmatism can also be the reason for the presence of

36

the granite and diabase. The boundary between the Cretaceous ophiolite and clastic in Late Oligocene are

general thrust features due to the sea floor spreading and not controlled by transform faulting (Pineda,

1992). This can be seen in Pandian and Cretaceous outcrops. After the opening of the South China Sea,

the collision of North Palawan Block and Philippine mobile belt occurred. This further enhanced the

deformation that happened. These are exhibited in the micro fold in the outcrops. There was an

obliqueness of collision between north-south of North Palawan Block and northwest southeast Asia margin

in the compressive event in Miocene that makes the north very distinct from south Palawan. This is

enhanced by the movement of the Philippine Mobile Belt to its present location. This produced thrusting

in Palawan. Thus the Ultramafic Beaufort Complex represents the true boundary of north Palawan to south

Palawan (Pineda, 1992). The collision of North Palawan Block and Philippine Mobile Belt also caused

localized extension. Evidence of Palawan North Block to Philippine Mobile Belt is the emplacement of

Sibuyan ophiolite complex (Dimalanta, 2008). With the compressive event in Eocene and extensional in

Miocene, Palawan is a site of superposed tectonic and not a simple accretionary model (Pineda, 1992). It

involves both extensional and compressional event.

Figure 21 shows the stratigraphic column of the study area. The Palawan Ophiolite composed of

Beaufort Ultramafic Complex, Monzogranite Intrusive Unit, Sheeted Diabase Unit and Espina Formation

served as the basement rocks. The Panas Formation and Pandian Formation intertoungues one another

with Pandian on top of Panas. This is followed by Ransang Limestone and Quaternary Alluvium on top.

37

MINERAL RESOURCES

The laterite soil found in Southern Palawan has been studied to have a high grade percent of nickel

as well as iron specifically the Beaufort Ultramafic Complex. This could be supported that the saprolite and

limonite layers found in the ridge of Mt. Bulanjao have very strong colors. The limonite has very brownish

color and the saprolite exhibits very reddish brown color. This soil color is a possible correlation to its

grade. Thus the soil are of great value due to its metal content. They are of high grade due to the fact that

their plates where these outcrops belong have undergone a lot of tectonic events. From the emplacement

up to their current position, these events contributed to how much weathered these soil are. Adding up to

these tectonic events is the current condition in the Philippines making these soil into higher grade. The

constant change of climate and abundance of vegetation. Another evidence for their high grade are the

highly serpentinized rocks abundant in this area. This is related to how much these rocks have undergone

Figure 21 shows the stratigraphic unit of the study area.

38

intense weathering. This study then suggests that the whole extent of Beaufort Ultramafic Complex is a

good source for laterite mining.

CONCLUSIONS

This study concludes the tectonic events that happened in the Middle to Later Cenozoic that

formed the rock units in the study area. (1) The continental rifting of south Palawan happened wherein the

ophiolite was emplaced over the turbidites even before the opening of the South China Sea (Aurelio, 2013)

as seen in the cross section of the study area as same to the other previous work claiming it. (2) The rock

units of Beaufort Ultramafic Complex, Panas Formation and Pandian Formation are therefore part of the

North Palawan Block. They were already deformed even before the onset of the opening due to the

continental rifting. (3) The Monzogranite Intrusive Unit on the Espina formation was formed not later than

Late Oligocene. This is due to an arc magmatism that occurred when the South China Sea started opening.

(4) The sheeted diabase rock unit found in the Espina Formation is an evidence of crustal extension that

occurred during the rifting. When South China Sea oceanic margin opened in Late Oligocene, it caused

more folding and thrusting of the ophiolite and clastic sequence. The Eocene turbidites were then mildly

metamorphosed forming the Pandian. (5) After that the Palawan Continental Block moved toward

Philippine Mobile Belt as continental arc collision. This caused localized extension. The deformations are

not only due to regional compression but also of extensional (Hall, 2013). (6) Emplacement of Limestone

happened due to the basin formed by the over thrusting of ophiolite to the Eocene turbidites. Overall the

tectonic setting that formed southern Palawan makes it a good source of hydrocarbon (Aurelio, 2013). This

study concludes that the whole extent mapped as Beaufort Ultramafic Complex is a good source for Ni

laterite mining. There are of high grade based from the evidence found such as abundance of garnierite and

serpentinized rocks in the area of Mt. Bulanjao. There are also joints and other structures found in the

Eocene turbiditic sequence thus a possible source for hydrocarbon. The Eocene sedimentary sequence

might be the possible entrapment of the hydrocarbon.

39

RECOMMENDATIONS

This study recommends to determine the extent of granite and sheeted diabase. The units should be

further investigated to determine other information such as its age, and contact between other rock units.

This study also recommends to conduct geophysical survey such as magnetics and gravity survey to

delineate fault in the Panas Formation and Pandian Formation. Other geophysical surveys such as electrical

resistivity, ground penetrating radar and induced polarization is highly recommended as well. The

determination of the grade of laterite on the top of Mt. Bulanjao ridge is also highly recommended of this

study.

40

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