mainly Tertiary rocks and Quaternary soils (Al-Rawas et
al 1992).
It is widely recognized that the formation of the smectite
group is greatly influenced by the composition of the
parent rocks. Van der Merwe (1964) has indicated that
the decomposition of basic and ultrabasic igneous rock
can result in the formation of residual soils containing
montmorillonite. Basic and ultrabasic igneous rocks are
well represented in Northern Oman by the wide spread
exposure of late Cretaceous Semail ophiolite (Figure 1).
Musandam
Peninsula
GEOLOGY OF THE
OMAN MOUNTAINS
EXPLANATION
SEMAIL OPHIOLITE — OCEAN CRUST
A AA À
~~] HAWASINA COMPLEX — BASIN
AA AA
ME suvem croup - store
—À A A A.
(ID ARABIAN CARBONATE PLATFORM |
-:— DIRECTION OF NAPPE EMPLACEMENT
P km
HAWASINA
WINDOW
Figure 1. Geological Map of Oman Mountains Showing
the Semail Ophiolite (Watts, 1990).
The Semail ophiolite has been weathered at various
periods in geological time and the weathering products
are now contained within a range of Tertiary rocks and
Quaternary soils. Thus there are a number of materials in
Northern Oman which may be identified as having
swelling potential. These are Bentonitic Mudstones,
Marls and Silty Mudstones, Argillaceous Dolomitic
Limestones, Altered Conglomerates and Desert Fill. All
of these materials, except the desert fill, tend to form
impersistent bands within mainly Tertiary conglomerates
and limestones.
The climate in Oman is arid, with evaporation rates
higher than the annual rainfall, so that there is almost
always a moisture deficiency in the soils and rocks.
Supply of water from any source is thus liable to cause
ground heave over any soils or rocks possessing swelling
potential.
Al-Rawas (1995) reported that the mineralogical
investigation conducted on samples from Al-Khod and
Al-Murtafa’a has shown that smectite is the predominant
32
clay mineral. Nevertheless, Kaolinite, illite and swelling
chlorite clay minerlas are also present in these soils and
rocks in small percentages. Chemical analysis has shown
that Na and Ca cations are predominant while
magnesium and potassium cations are present in small
percentages. The microfabric tests conducted on the
same samples revealed that the microfabric of the Omani
expansive soils and rocks consists of dense clay matrices,
although — clay-granular matrices are observed
occasionally.
3. SATELLITE DATA AND PRELIMINARIES
Data from two satellites have been used in the current
phase of the research. They are Japanese Earth
Resources Satellite (JERS) and Landsat (Thematic
Mapper, TM). The pixel sizes of these images are
18m.sq and 30m.sq. respectively. The available spectral
bands of JERS are tabulated below ; Landsat bands are
well reported in literature and are not repeated here.
Table 1. Spectral Bands of JERS 1
1 0.56 0.08
2 0.66 0.06
3 0.81 0.10
5 1.655 0.11
6 2.065 0.11
7 2.190 0.12
8 2.335 0.13
The spectral response generally reported in literature for
study of soils are of limited use in this case. This is
because the type of information being sought is a buried
phenomenon and there is no clear understanding of the
resultant spectral response.
The soil sustains only a very specific class of vegetation.
Also the surface takes a special look being subject to
characteristic periodic minor and uneven swelling due to
limited infrequent rainfall. All these- the soil, surface
texture and vegetation- together are likely to result in a
class which should permit multispectral classification.
3.1 Histograms
Histograms of all the bands were plotted to see if their
distribution is suitable enough for application of the
more important supervised classification technique,
namely the maximum likelihood classification technique.
These are given in Figure 2. The data structure seems
good enough for the purpose. The distributions are
however slightly skewed, for which apparently there is
no explanation.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
mean brightness values (8-bit scale}
CO) — CT 0H 0 A CT peed es
