Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Synthetic geological map obtained by remote sensing
An application to Palawan Island
F.Bénard & C.Muller
Institut Français du Pétrole, Rueil-Malmaison, France
ABSTRACT: This project was undertaken to compensate for the lack of new data for the blanks of maps and to
link spot datings due to bad outcrops on Palawan Island. A synthetic map of all the available data, including
new field work and datings, is based on remote-sensed documents. Good results were obtained using
black-and-white prints of Landsat MSS (band 7). Faults N60E on the E. coast show a recent normal movement,
and the sinistral movement of the meridian zones is confirmed by field work. The geological units shown on
the preexisting maps are identified and separated into subunits characterized on remote-sensed documents by
their morphology - texture - tone properties. These subunits are superimposed on the geological units. This
map suggests new hypotheses for further investigations on both the tectonic and lithological aspects.
RESUME : Cette étude a été entreprise pour pallier le manque de données récentes, les lacunes des cartes et
pour uniformiser les datations rendues ponctuelles par les difficultés d'affleurement de l'Ile de Palawan.
Une carte synthétique, s'appuyant sur les données de télédétection homogénéise les données préexistantes et
inclue les résultats de travaux de terrain récents accompagnés de nouvelles datations. Des images noir et
blanc de Landsat MSS (bande 7). L'interprétation, visuelle sur agrandissements au 1/500 000 s'appuie
essentiellement sur la morphologie. Deux directions majeures ressortent : l'une à N60 avec un mouvement normal
récent sur la côte Est ; l'autre méridienne de jeu senestre récent confirmé sur le terrain. Pour chaque unité
lithologique cartographiée, des figurés représentent les zones caractérisées, sur images, par leur homogénéité
en morphologie, texture, teinte, reflet de variations lithologiques. Cette carte récente suggère de nouvelles
hypothèses pour les études ultérieures tant eh tectonique qu'en lithologie.
INTRODUCTION
This study is part of the "Geodynamics of SE Asia"
program undertaken several years ago by the Institut
Français du Pétrole. The aim of remote-sensing
interpretation is to obtain more geological and
structural information by using this method in
regions covered by dense vegetation, difficult of
access to the field, and to supplement field
observations which have been more or less restricted
to coastal regions. Revised age determinations of
sedimentary sequences are based on investigations of
calcareous nannoplankton.
Palawan (Fig. 1) is a narrow elongated SW-NE
trending island (about 470 km long) which is part of
the Philippines Archipelago. It is bounded to the
north by the South China Sea and to the south by the
Sulu Sea. The island is predominately mountainous
reaching its greatest altitude at 1953 m (Cleopatra
Needle). The slopes of the mountain ranges are
narrow and steeper to the NW, reflecting the
asymmetry related to NW vergent overthrusts.
Located in an equatorial zone, it is covered by
dense vegetation and rocks undergo strong
alteration. MSS data are the only remotely-sensed
information available for Palawan island. It can be
shown that good results are obtained with careful
physiographic studies. The geological map is a
synthesis of remote-sensing interpretation combined
with previous data from the literature mainly L.
Fricaud, 1984 and field survey, J. Letouzey, 1985.
This island is covered by three Landsat images
(number 125-52, 125-53, 126-54). Sets from
different dates were used (see references). Due to
cloudy and hazy conditions, only band 7 gave useful
information. Swath number 29 (center 10'36 lat,
119°42 long) taken by the synthetic aperture radar
on board the SIRA shuttle was also studied. It
covers a narrow transect of the island south of
Mount Capoas.
1 METHODOLOGY
All geological and structural information was
reported on transparent overlays placed on black and
white prints. The same method can be applied to MSS
and radar images, even if the elements detected are
different in each case (Floyd and Sabins, 1983).
Particular attention was paid to physiographic
elements. Exemples given in Fig. 2 demonstrate how
this kind of information extracted from satellite
imagery can be interpreted in terms of geology.
Results are compiled on a 1:500 000 scale map with
Lambert Conformal Conic Projection (0NC number
L 11). To minimize difficulties related to dense
vegetation in these tropical areas, attempts have
been made to recognize "photofacies" representing a
homogenous area on remotely sensed documents. It is
characterized by specific criteria such as
elevation, drainage pattern, landforms, texture,
tone, etc. These characteristics are the results of
interaction between lithology, tectonics, elevation
and vegetation.
On a first map all photofacies recognized were
represented. Some of their characteristics may
provide information on the lithology (hard or soft,
bedded, heterogeneous, etc.). By comparing this
document with other available geological data from
the literature and field work, it was possible to
compile the synthetic geological map on which the
main sample locations are also shown. Accurate
geological boundaries can be drawn if there is a
possible correlation between the "photofacies"
detected and a geological unit having a known
lithology. This comparison with given data is
important for interpreting the photofacies
characteristics (hardness, structural fabrics). If
two formations are different in age but similar in
lithology, they have a same "photofacies". In this
case, formation boundaries from previous maps are
shown as dotted lines. However, such problems can
be solved only by detailed field work.
