image by symetric ridges (attributed to thick
sandstone beds) alternating with smooth areas (more
silty strata). This is attributed to the early
Miocene. At this level, no indication reveals if
the arrangement of the ridges is related to tectonic
imbrications or to a fan delta sedimentation process
with further uplift. Undated series are refrered to
as MP on the map. They correspond to a very flat
rough surface, in slightly datted light gray level
on the image. This is the case for the detritai
series in the NW area of the foothills along the
western flank of the Central Range. The light gray
siltstones of the turbiditic sequence (Pga) sampled
in the Quezon area are of late Paleocene to late
Eocene age (C. Muller, 1984). On the images, the
same characteristics (plain area with a slightly
rough surface and no erosional feature) can be
observed east of the Bulantao Range. Therefore,
these terrains are attributed to the same sequence.
All these units are equivalent to the detritai
Crocher formation in northern Borneo (Sabah region).
The ophiolitic complex (0) forms the highest
relief of the Central Range. The ophiolites are
most probably of early Cretaceous age compared to
those dated in Sabah (North Borneo). The Unit
referred to as M on the map occurs as a very flat
area, with alluvial deposit aspects. Since
ophiolites can be observed in the field, the lack of
relief on Landsat images suggests a melange.
Therefore, an argillaceous matrix would produce the
flat appearance while the ophiolites would be too
small to be detectable.
In central and southern North Palawan (Aborlan
River, Ulugan Bay and north of it up to the
Malampaya Sound) thick clastic series of late
Cretaceous age (Muller, in preparation) are exposed.
They are strongly tectonized and locally slightly
metamorphosed. These alternating sand and
siltstones with some thin graphitic layers were
deposited along the former Chinese continental
margin. On both MSS and radar documents two main
photofacies correspond to this sequence:
1. The UKS-unit forms high mountains with
brilliant surface (around Cleopatra Needle).
2. The UKM-unit occurs as strongly dissected and
highly fractured plateau with a velvety appearence
(region of Roxas).
These differences on satellite imagery can be
linked to local differences in the degree of
metamorphism and/or to the greater amount of
sandstones in the area of Cleopatra Neddie which are
more resistant to erosion. The crests outlined in
the western part correspond to particularly thick
sandstone beds: The St. Paul shelf limestones
(Pgb), of late Oligocene-early Miocene age, occur as
a wide plateau on the image. In the area of Ulugan
Bay they are present also as small elongated slices
trending N20E, perpendicular to the first
compressional phase. The same formation is known
from offshore wells NW off Palawan. Offshore from
South Palawan this carbonate platform is covered by
overthrust accretionary wedge.
Massive granodiotite intrusions, considered as
late Miocene in age in comparison with Sabah, occur
at Linapacan Island, Mount Capoas and Cleopatra
Neddie. It is not excluded that there are some other
small intrusions in this region. These formations
form high relief but elevation induces artefacts in
vegetation so that their boundaries cannot be drawn
precisely.
In North Palwan, Permian to Jurassic formations
occur from Bay Point to Cabuli Island. On MSS
imagery this is rendered by a very peneplanated
surface, that is homogeneous in medium grey so that
only very few morphological features can be of help
in evaluating lithological or structural changes.
In the field, early Jurassic limestones and
sandstones (Frontaine) and Cretaceous detritics are
tectonically imbricated with radiolarites (with
slate and tuff intercalations) of Triassic age.
Paleozoic is mentioned at Bacuit Island, Miniloc
Island and north of El Nido. Two series are
described: limestones (with fusulinas, algae,
crinoids) and a clastic sequence (sandstone, tuffs,
calcareous sandstones).
3.2 Tectonic features
It is quite difficult to detect the oldest
structural features as reactivations by further
tectonic phases have alterated them. Hence, mainly
in the northern part of Palawan, the superimposition
of at least three folding events plus the strong
peneplanation make imbricated structures impossible
to perceive on a 1:500 000 scale. The same problem
occurs with the very thin early to middle Miocene
imbrications.
Abnormal contacts can easily be mapped when the
difference in hardness and colour of the two
juxtaposed units is great (as ophiolites and
detrital) but their vergence can be deduced only
from field observations.
Regional fracture analysis reveals five domains of
main directions:
- South of Quezon: Due to the nature of the rocks
(mainly ophiolites and elastics) fracturation is
very badly expressed. The main trends are N40-N170,
N60, N30, N135.
- Between Queron and Ulugan Bay: Major trends are
N45-N60, N160.
- Cleopatra unit: N10, N37, N65, N105.
- Roxas unit: N20-30, N60-70.
- North or Malampaya sound: N-S, N30, N60, N120.
The young N-S fault direction was more distinctly
detected by remote sensing interpretation compared
with previously published maps.
The Ulugan fault, a major fault in the strongly
N-S sheared zone, is clearly recognized in the
bathymetry, coastal line and on aerial photographs.
However, there is no clear evidence of this fault on
satellite imagery. This might be due to sub-recent
conglomerates and alluvial deposits which conceal
its manifestation.
The Rizal fault separates two lithological units
(referred to as UKM and UKS) and is outlined by a
broad rectilinear thalweg. Bent crests interpreted
as folded beds in its vicinity confirm the
hypothesis of a left lateral shear zone. This might
be interpreted as a satellite of the Ulugan Fault to
which it runs parallel. At Imuruan Bay some
complications occur due to the interference with
N30E right lateral strike slip faults or reverse
faults.
A very dense fracturation pattern with a N30E
direction affects the UKM unit. It seems to be
linked to the N67E compression of the second
tectonic phase.
The N60E trending major fractures which affect
south and central Palawan may be interpreted as
tension fractures of this second tectonic event.
South of Cleopatra Needle, strong deviations of
the drainage pattern suggest a major fracture zone
trending N100E. This element, unshown on previous
maps, could be related to the second tectonic event
(as sinistral shear zone) reactivated during the
third one (as a dextral shear zone). Many
hypotheses require further field observations.
The folding processes can be evidenced only in the
"UKS unit". Here, herring bones and bed-tracks
reveal an axial intense and penetrative folding
which could be related to the first folding event.
The Curvature of the main ridges and their asymmetry
108
suggest
to a late
South-eas
Quaterna!
roughly
faults,
important
explained
theo veri
faults a
Ulugan ar
C0NCLUSIC
REFERENCE
Balce, G.
map of tl
Floyd,
interprel
Indonesi
Fontaine,
Calamian
News Let1
Fricaud, I
la marge
Thesis. F
Hashimoto
of the P
geologicc
Paleontol
Holloway,
relations