Full text: Remote sensing for resources development and environmental management (Volume 1)

Figure 1. Location map 
1: emerged area, 2: oceanic crust, 3: active 
subduction, 4: inactive subduction 
To detect structural elements, morphological 
features were used such as wide thalwegs, strong 
deviations in drainage patterns, rectilinear scarps, 
and watershed deviations (Fig. 2a). In Fig. 2c 
structural elements are shown as faults only if they 
separate different geological units, if offsets on 
crests and boundaries can be recognized, or if they 
correspond to known tectonized zones of faults. 
Mapped lineaments are rendered on the images by 
rectilinear thalwegs and fractures. Tonal anomalies 
are less reliable and were not used. Discrete 
anomalies of great extension or strong influence on 
the drainage pattern might indicate buried faults 
associated with lineaments. Sometimes, directions 
of motion can be deduced from associated folds, 
scarps, or deviated crests. However, these 
observations must be confirmed by the stress pattern 
obtained from microtectonic studies in the field. 
Due to the complexity of the region the evaluation 
of folding and imbrication requires more careful 
observations. Hard rocks only once tectonized 
forming herringbones and crests are good indicators 
of local dip. Small crests are generally due to a 
harder layer interbedded in a soft sequence. Its 
geometric aspect might indicate folding and a kind 
of motion when associated with a fault (Rizal 
Fault). Regions with several tectonic phases are 
more difficult to interpret. It seems that the 
first folding can be recognized by bedding, small 
ridges, and fine elements, whereas the second phase 
is often evidenced by the orientation of main 
Palawan island is interpreted as a tectonic ridge 
related to the collision between a volcanic arc and 
the Chinese continental margin which was displaced 
southward during the early Oligocene to early middle 
Miocene opening of the South China Sea. 
Until Eocene times, the sedimentation area of the 
present-day island of Palawan started on the Chinese 
Continental Margin. Southward in the adjacent 
oceanic basin, a first overthrusting of the 
ophiolites was due to Pacific plate movements. From 
late Eocene to middle Oligocene, the rifting of the 
South China Sea is marked (in Reed Bank and North 
Palawan continental area) by tilted blocks bounded 
by normal faults trending N60E (seismic data). 
From Middle Oligocene to Middle Miocene, the 
rifting of the South Sea caused part of the Chinese 
Continental margin to drift southward. 
Concommitently, calcareous deposition occured on the 
tilted blocks previously described. Nowadays, these 
limestones are eroded in the north, overthrust in 
Middle Palawan and underthrust in the south. 
During the Middle Miocene, a north-south collision 
with a volcanic arc (tuffaceous marls and Aba-Aba 
andesites) occured. This major tectonic event 
developed a prism which imbricates Cretaceous and 
Cenozoic sediments deposited along the previous 
margin. Ultra-basic elements, coming from the 
Cagayan Arc are also integrated. Microtectonic 
measurements give a N120E strain direction. Studies 
of the detritai series in the wells offshore from 
North Palawan indicate deposition evolution from 
north to south, accompanied by erosion decreasing 
from NE to SW. This explains the major 
organizational differences between both sides of the 
Ulugan Fault. 
In the late Miocene, the second tectonic event 
( N67E) was induced by movements occurring around 
Mindoro in the Philippines Archipelago. It reworked 
the structures previously elaborated. Left lateral 
shear along N-S faults has been recognized on 
offshore seismic profiles and proved by field work. 
This third tectonic event seems to be of Upper 
Pliocene-Pleistocene age. 
3.1 Lithofacies 
For the entire island, the Quaternary deposits are 
easily distinguished by their flat smooth texture. 
The gray level on the picture is linked to the 
moisture of the alluvium. 
In the southern part of Palawan, the oldest 
sediments are dated from the Paleogene. Thick 
turbiditic series of late Paleocene to early Miocene 
age are strongly tectonized (folded) and imbricated 
with slices of ophiolites, pillow lavas, cherts and 
volcanic breccias of oceanic crust origin. They are 
unconformably overlain by late Miocene-early 
Pliocene series. 
In the Quezon area, several units, dated late 
Miocene-early Pliocene (C. Muller, 1984), are 
differentiated. On top of the series, a brillant 
surface bounded by scarps corresponds to thick 
limestones with marls interbedded (Nc). The 
topographically underneath surface is rough 
(numerous small hills), with a very light grey tone: 
it is related to the reefal limestones often as 
buildup (Nm). A small adjacent plateau is assumed 
to be the westward extension of the one previously 
described (Nc), but boundaries are not very 
understandable and should require acurate field 
data. High limestone ridges in Bulanjao Range are 
attributed to the same formation. They were 
uplifted and slightly tilted before Pleistocene. 
The Paleogene-early Miocene formations are 
considered as a whole since they consist in a very 
thick, quite homogeneous turbiditic sequence. On 
the images, they are hardly distinguished from 
alluvial deposits, but differences in photofacies 
seem to be linked to the proportions of siltstones 
and sandstones. In the southernmost part of the 
island, a detrital unit (Ml) is characterized on the

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