GEOHAZARD, ECONOMIC AND SOCIAL IMPLICATIONS OF SEDIMENTARY-PLUTONIC
STRUCTURE OF BO. BALUYAN, MALALAG, DAVAO DEL SUR
In Partial Fulfillment
Of the Requirements in
Research Methods (ES 106)
Submitted to:
Engr.
Lucio Eduardo V. Pastor
Submitted by:
Abellanosa, Jerahemeel M.
Alconera, Peter Paul M.
Barbacal, Glacy Mae Q.
Benzal, Sheena L.
Buenavista, Allen June B.
De Asis, Deanne L.
Gerodiaz, Daryl Mae M.
Lanit, Leizelle R.
Mantilla, Melvin A.
Notario, Lady Roda G.
Rivera, Michael John A.
Samaniego, Irvin B.
Villanueva, Jonas E.
BS Geology
Third Year
March 2011
Table of Contents
Page
I. Introduction
a. Purpose and Scope
b. Location and Accessibility
c. Topography and Drainage
d. Climate and Vegetation
1
1
2
2
2
II. Geology
a. General Geology
b. Tectonic Genesis
3
3
III. Structures
4
IV. Mineralization
4
V. Geohazard Assessment
5
VII. Social Implications
5
V. Conclusion
7
VII. Recommendations
9
VIII. Acknowledgment
10
IX. References
11
X. Figures
a. Topographic Map
b. Geographic Map of the Region
c. Climate Map
d. Neotectonic Map of Mindanao
e. Geologic Map if Bo. Baluyan,
Malalag, Davao del Sur
f. Documentations
12
13
14
15
16
17
I.
The
Philippines
is
INTRODUCTION
one
of
the
countries
located
in
the
“Pacific Ring of Fire” where tectonic plates are actively moving and
earthquakes,
typhoons,
and
volcanic
activities
are
frequently
experienced. It is formed due to the collision of major tectonic
plates
to
the
Philippine
microplate
in
major
subduction
zone.
Subduction zone is a plate margin where two crusts collide with the
denser crust subducting under the less densed crust. In the east,
the Pacific plate subducts under the Philippine trench and in the
west
is
the
Eurasian
plate
subducts
under
the
Philippine
plate
forming the Manila Trench. A Transform fault is also propagating
from Northern Luzon to Sothern Mindanao called the Philippine Fault
line.
The Philippine trench in the east and the Cotabato trench in
southwest encompassing the island of Mindanao on sea and a Mindanao
fault is present on land trending southeast to northwest.
In Sulop, Davao del Sur, a thrust fault that trends southeast
to northwest passes the formations of sedimentary along the Baluyan
zigzag road. A thrust fault is a low angle reverse fault with the
hanging wall moving upward relative to the footwall. The sedimentary
formations are mainly composed of silt-sandstone-shale with volcanic
intrusions
forming
dikes
and
sills.
Dikes
are
magma
intrusions
cutting across sedimentary beds while sills are magma intrusions
intruding
the
contracts.
Quaternary
Alluviums,
which
are
eroded
rocks, are formed on the lowlands of the area.
The researchers are going to investigate how these structures
and lithologies in Sulop, Davao del Sur will benefit the people
economically
and
socially
as
well
as
to
assess
geohazard
and
precautionary measures.
Purpose and Scope
The authors conducted the field investigation of the thrust
sedimentary-volcanic structure on Bo. Baluyan, Malalag, Davao del
Sur on February 6, 2011. The investigation was purposely conducted
to determine and delineate the general geology and structure of the
2
area, geohazard risk assessment, economical and social implication
brought about by the formation. The data were solely gathered on the
road cuts situated at the Kawayan Hill to Luya Hill on the region. A
1:50,000 topographic map of Padada quadrangle with Sheet No. 4039- I
was used as a reference map.
Location and Accessibility
Bo. Baluyan, Malalag, Davao del Sur is bounded by geographic
coordinates
06°32’27’’
north
latitude
and
125°22’12.9’’
east
longitude (Figure 1). It is southwest of central Davao City and
approximately 45 km distance travel by commercial buses and other
land vehicle for three (3) hours through Davao City – Sta. Cruz –
Digos City – Padada – Sulop National Road (Figure 2).
Topography and Drainage
The topography of Malalag area and its vicinity is typically
planar
terrain
with
some
moderately
steep
hill
distributed
throughout the region. The highest peak in the locale is reaching at
about 800 m above sea level. The region is primarily drained by the
Malalag
river
and
some
of
its
creeks
and
tributaries
northwest
towards the Malalag Bay. Dendritic Drainage pattern is observed in
the region.
Climate and Vegetation
Bo. Baluyan, Malalag, Davao del Sur belongs to fourth (4th)
type
of
rain
condition
which
is
characterized
of
having
evenly
distributed rainfall throughout the year. Tropical cyclones rarely
occur in this region. Vegetation consists mainly of tropical rain
forest trees, shrubs and vines on interior areas. Alluvial plains
are cultivated by palays, corn, bananas, coconut and other fruit
bearing tress for agricultural purposes.
3
II. Geology
a. General
The main lithologic unit in the area are interlingering of
thrusted sedimentary rocks and volcanic intrusions. It was generally
referred to as Sulop Formation (Milanes, 1981). The formation was
redefined to include andesite intrusive and Mal clastics by the same
author.
The sedimentary beds are composed of detrital rocks such as
sandstone, conglomerate, shale, siltstone and chert. The sandstone
is typically of medium to course grained size, which is well sorted,
compacted, and has greasy black appearance that could be mistakenly
thought as basalt. It is moderately jointed and fractured. Veins and
stingers
of
infills
the
quartz
and
fractures
calcite,
of
the
ranging
sandstone
at
about
rocks.
1-5mm
size,
Conglomerate
is
predominantly of couble to boulder ( 64- 256 mm) size sandstone
clasts. It is thickly bedded and exhibits spheroidal weathering. The
shale
is
well
sorted,
moderately
compacted
and
has
a
brownish
sediments. The siltstone predominantly composed of quartz grains
that have been baked sideways relative to shales.
Consequently,
the
extrusive
rock
is
chloritized
porphyrtic
andesite which is moderately to deeply weathered. It is composed
chiefly of augite, plagioclase feldspar, amphibole, biotite and some
traces of muscovite.
b. Tectonic Genesis
The Sulop formation is part of the Padada- Malalag Sub basin
which is assumed to act as the catchment basin is geologic past. The
sediments are bedded, well sorted and compacted, signifying a marine
depositional environment, even though traces of marine fossils are
not found. The region was uplifted as a result of the compressional
force acting on the eastward by the Saranggani Trench towards west
and the Cotabato trench towards northeast (Figure 4). The andesite
rocks intruding the clastic rocks is of Late Miocene age (7.25-11.61
4
mya) that is younger to the sedimentary sequence which is of Late
Oligocene age (23.03-28.4 mya).
The Sulop formation forms the bulk of the Saranganni Ridge
System and was conformable to Bauyan Formation (MGB, 2004)
III. Structures
The general structure of the region is thrusted sedimentary
layers and andesite bodies. The thrust fault is located at the
eastern part of the Saranggani Penisula trending at NW-SE direction.
Chaotic exhumation and upliftment of the rocks resulting to the
formation
of
fault
block
mountains
and
hills.
Furthermore,
the
intrusion of andesite body had also contributed to the upliftment of
the region. Irregular bed dippings downward results the jointing of
andesite and sandstone bodies.
Fault traces, passing on andesite bodies, are aided by the
formation of fault gouge is about 8-9 inch in thickness. The gouge
signifies occasional movement of the fault in geologic time. It is
reddish to brown in color which signifies stains in oxidation. The
structure reveals also of anticlinal folds that strike at N 19’ W
and dips at NE 54’. According to Milanes(1981), the clastic sequence
in
the
region
occupies
the
different
flank
of
the
Saranggani
Anticinorium.
Quartz
and
Calcite
veins
infills
the
moderately
fracture
andesites and sandstone which is pervasively seen near the fault
zones.
IV. Mineralization
Economic minerals are not typically distributed and identified
on
the
implies
Chlorite
deposits
region.
a
But
magmatic
is
a
and
the
occurrence
composition
common
mineral
commonly
with
of
the
ore
mineralizing
associated
occurs
“chloritic”
solution.
with hydrothermal ore
with epidote,
adularia and sulfide minerals (Hulburt, 1985).
andesite
sericite,
5
Furthermore, occurrence of veins and stringers, calcite and
quartz, in the area signifies replacements of mineral chemistry
brought about by hydrothermal activities of the magmatic intrusions.
In
addition,
presence
of
small
amount
of
chert
also
indicates
hydrothermal solutions associated in volanics (Huwang, 1980)
The presence of reddish stains in weathered andesites and
especially in gauge materials may indicate minute metallic deposits
in the region.
V. Geohazard Assessments
The Sulop formation is elevated at about 200m -800m terrain.
Geomorphically, it is relative at young-stage cycle reflecting to
high
denulation
process
to
occur
on
the
region.
The
lithology,
mostly consists of detrital sedimentary rocks and intrusive, is
dipped
almost
vertically
jointed,
fractured,
possesses
imminent
along
the
spheroidally
danger
to
road
and
the
ways.
deeply
traveling
The
presence
weathered
vehicles
and
of
rocks
human
infrastructures. Rock and debris fall will mostly likely to occur.
Landslide exposures are observed with no tress and shrub growing.
Slope failure will likely occur as the slope support is curbed
for road ways construction. Talus deposits alongside reflect the
pervasive weathering of the rocks. This also may possess dangers in
prolonged duration of rainfalls. Since the region has type 4 climate
pattern, the weathering of the rocks will be high.
The
thrust
fault
possesses
also
dangers
when
displacement
occurs generating earthquakes that will trample down unstable rocks
and debris causing landslides.
VI. Social Implication
Due
to
elevated
topography
of
the
region,
resorts,
restaurants, and other socially enriching businesses is of good
economic market to be established in the area. The paranomic view of
the Malalag Bay, Davao Gulf, Malalag- Pujada sub basin will surely
generate income of interested and entice the people to appreciate
6
and
admire
nature
and
the
Philippines
as
a
whole.
Religious
congregations and meditative groups can also consider this place for
reflection, relaxation and outdrawing of themselves to the world and
its stresses.
7
VII. Conclusion
Based on the observations and assessments, the authors have
drawn the following conclusions:
1. Bo. Baluyan, Malalag , Davao del Sur constitutes generally
of
interlingering
of
thrusted
sedimentary
rocks
and
porphyritic andesite intrusions.
2. Sedimentary beds are composed of detrital rocks such as
sandstone, conglomerate, shale, siltstone and chert.
3. Sulop formation is part of the Padada- Malalag Sub basin
which is assumed to act as the catchment basin is geologic
past.
The
region
was
uplifted
as
a
result
of
the
compressional force acting on the eastward by the Saranggani
Trench
towards
west
and
the
Cotabato
trench
towards
northeast.
4. The andesite rocks intruding the clastic rocks is of Late
Miocene
age
(7.25-11.61
mya)
that
is
younger
to
the
sedimentary sequence which is of Late Oligocene age (23.0328.4 mya).
5. The thrust fault is located at the eastern part of the
Saranggani
exhumation,
Penisula
trending
upliftment
and
at
NW-SE
intrusion
direction.
of
Chaotic
andesitic
rocks
results to the formation of fault block mountains and hills.
6. Thrust faults and fault gouge is present generating the
anticlinal folded structures.
7. The occurrence of the “chloritic” andesite and the veins &
stringers
implies
an
hydrothermal activities.
ore
mineralizing
solution
and
8
8. The presence of jointed, fractured, spheroidally and deeply
weathered rocks possesses imminent danger to the traveling
vehicles and human infrastructures. Rock and debris fall
will mostly likely to occur.
9. Due
to
elevated
topography
of
the
region,
resorts,
restaurants, and other socially enriching businesses is of
good economic market to be established in the area.
9
VIII Recommendations
Based on the observations and assessments, the authors have
drawn the following recommendations:
1. Irregular
downward
dippings
and
jointing
of
rocks
in
the
region posses imminent danger. Engineering techniques such as
concrete walls, bolts, etc. should be applied in areas of weak
zones to prevent falls, slips and mass movements reducing the
hazard of the area.
2. Curbing
along
the
roadside
should
be
minimized
to
prevent
destabilization of the rock that may lead to mass movements.
3. Road signs such as landslide areas, debris falls, zigzag roads
among others should be placed as warning signs for the road
users to be aware.
4. From time to time, local geologist and the residence of the
region should observe any minute mass movement in order to
mitigate and reduce hazards in the locale.
5. Possible exploration for economic deposits in the region or
near the region may be done due to the presence of chloritic
andesite and veins and stingers.
6. Location of establishments, housing and settlements should not
be located in geohazard areas.
7. Resorts, restaurants, and other socially enriching businesses
is of good economic market to be established in the area.
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XI. ACKNOWLEDGEMENT
The authors would like to express their deepest gratitude
to the following persons and institutions who in one way or another
have contributed in realization of this field study: To the office
and personnel of Mines and Geosciences Bureau Region XI for lending
information on the local geology of Padada, Davao del Sur; To our
respective families, for their consent, financial and moral support;
To Mr. Jose D. Madrona, for his imparted knowledge, untiring efforts
and guidance in the field; To
Engr. Lucio Eduardo V. Pastor, for
his guidance, supervision and assistance in making this research
paper, and
the people of Bo. Baluyan, Padada for their peaceful
welcome; To Kent Albiso, Lemuel Libres, and El-Jedidiah Villacampa
for their shared insights on the region visited; and to the unseen
God, for His protection and guidance and giving this opportunity to
study the marvels and beauty of His creation.
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REFERENCES
Mines and Geosciences Bureau(MGB) Region XI Davao City, April
1992,Geology
and
Mineral
Resources
of
Davao
del
Sur
Huang, W.T. 1950, Petrology, Classification of Sedimentary Rock,
Chert, pp. 297, 1950
Hurlbut, C. Jr.1985, Dana’s Manual of Mineralogy, Desciptibe
Mineralogy, Chlorite, pp. 445
13
Figure II
Geographic Map of Region XI
Bo. Baluyan,
Malalag , Davao
del Sur
14
Figure III
Climate map
Type I. There are two pronounced seasons: The dry season (from
November to April) and wet season (rest of the year).
Type II. There is no dry season under this classification, with a
very pronounced rainfall from November to January.
Type III. Seasons are not very pronounced. It is relatively dry from
November to April, and wet during the rest of the year.
Type IV. Rainfall is more or less evenly distributed throughout the
year under this classification.
15
Figure IV
Neo Tectonic Map of the Mindanao