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ORIGINAL ARTICLE
ASTER mapping of limestone formations and study of caves,
springs and depressions in parts of Sultanate of Oman
Sankaran Rajendran •Sobhi Nasir
Received: 3 October 2012 / Accepted: 13 March 2013 / Published online: 26 March 2013
ÓSpringer-Verlag Berlin Heidelberg 2013
Abstract Caves, springs, and large depressions of lime-
stone karst formations are becoming more attractive tourist
places and have potential importance on socio-economic
development. The present study is a multi-scale point of
view on limestone karst, from the space images to micro-
scopic fabric. Here, the karst features consist of limestone
formations of Cretaceous (Albian–Cenomanian) age of
Tanuf Valley and Tertiary (Late Paleocene–Middle
Eocene) age of Sur region of parts of Sultanate of Oman
which are mapped in the visible near-infrared and short-
wave infrared spectral bands of advanced spaceborne
thermal emission and reflection radiometer (ASTER) using
decorrelated stretch image processing technique and the
occurrences of caves, springs, and depressions of the for-
mations in the field were studied. The decorrelated RGB
images of ASTER spectral bands 8, 3, and 1 discriminated
well the limestone formations and associated lithology. The
limestone formations of Tanuf valley (Natih formations of
Hajar unit) are thick-bedded, massive, shallow marine
limestone and clayey limestone, which have caves and
springs. Large depressions are studied as collapsed struc-
tures at the boundary between Abat formations; they con-
sist of gray to white marly or micritic limestone with chert
nodules and Seeb Formation of bioclastic limestone, cal-
carenite, marl, and sandstone of Sur region. Interpretations
of limestone formations, their occurrences and distributions
of caves, springs and depressions of these regions are
verified and confirmed in the field and studied in the lab-
oratory. Occurrences of more springs and depressions in
the limestone formations of the study sites are interpreted
and located on the Google Earth image. The study proved
the capability of ASTER sensor in mapping of limestone
formations and recommends the technique to other geo-
graphical regions where similar geological questions need
to be resolved.
Keywords Limestone formations Caves Springs
ASTER data Spectral absorptions Sultanate of Oman
Introduction
Nowadays, the caves, springs and the places of large
depressions that occur in carbonate massifs attract more
tourists and emerging tourist places like Oman (Hanna and
Al-Belushi 1996;http://www.alhotacaves.com). Springs
that occur in limestone karst formations play a vital role in
socio-economic cultural development of arid and semi-arid
regions. Caves of carbonate formations are developed due
to the dissolution of water soluble rock which occurred
below the massif surfaces. Large karst depressions are the
geomorphic features formed by the movement of rocks or
sediments into voids created by the dissolution of water
soluble rock (Waltham et al. 2005; Sauro 2003; Williams
2003; Beck 1984). Occurrence of such collapsed structures
depends on the non-cohesive (sand-rich, creating slow
subsidence), or cohesive (clay-rich, creating rapid subsi-
dence) characters of overlying sediments (Sinclair and
Stewart 1985). These karst features occur predominantly in
limestone formations of Tanuf Valley and near Sur regions
of parts of Sultanate of Oman (Fig. 1) and have consider-
able attention to study either for social interest or their
potential socio-economic cultural importance.
Remote sensing technique is proved to map limestone
formations and identify carbonate minerals (Rajendran
S. Rajendran (&)S. Nasir
Department of Earth Sciences, Sultan Qaboos University,
Al-Khod 123, Muscat, Oman
e-mail: sankaranrajendran@yahoo.com
123
Environ Earth Sci (2014) 71:133–146
DOI 10.1007/s12665-013-2419-7
et al. 2011; Corrie et al. 2010; Siart et al. 2009; Jalali et al.
2009; Ninomiya et al. 2005; Gomez et al. 2005; Rowan and
Mars 2003; Abdeen et al. 2001; Sultan et al. 1987). The
reflectance electromagnetic spectrum in the 0.3–2.5 lm
wavelengths provide mineralogical information, especially
carbonate minerals that have diagnostic CO
3
spectral
absorptions near 2.35 lm in the spectrum and can be used
significantly to map carbonate minerals bearing rocks (Mars
and Rowan 2010; Ninomiya 2002; Clark 1999; Hunt 1977).
The ASTER on board the earth observing system (EOS)
TERRA platform offers relatively improved spatial, spec-
tral, and temporal resolutions and has the spectral bands 8
and 14 characteristics to the diagnostic CO
3
absorption
facilitates to map carbonate rich formations (Rajendran
et al. 2011). Understanding its capability, in the present
study, the mapping of limestone formations of Cretaceous
(Albian–Cenomanian) age of Tanuf Valley (Fig. 1a, b; Site
1) and Tertiary (Late Paleocene–Middle Eocene) age of Sur
region (Fig. 1a, c; Site 2) of parts of Oman are carried out
using the visible near-infrared–shortwave infrared (VNIR–
SWIR) spectral bands of ASTER by decorrelated stretch
digital image processing technique. The interpreted images
are verified in the field for the occurrences of limestone
formations. The occurrence and distribution of caves,
springs, and depressions of the limestone formations of
these regions are studied. Review of literature shows that a
meager study has been attempted on the application of
remote sensing technique in mapping of limestone forma-
tions which are associated with these features and no study
has been carried out for the said study regions.
Spectral characteristics of carbonate minerals
Carbonate minerals have favorable spectral absorption
characteristics for remote identification. The reflectance
spectrum of limestone formation depends on the carbonate
minerals composition of its surface, which is usually a
mixture of the whole formation mineralogy and weathering
or alteration of minerals. Comprehensive spectral absorp-
tion-compositional studies can provide important insights
to the causes of spectral variations and quantitative data for
use in the interpretation of optical remote sensing data
(Rajendran et al. 2011; Mars and Rowan, 2010; Corrie
et al. 2010; Ninomiya et al. 2005; Rowan and Mars 2003).
The spectral library plots of major carbonate minerals
stacked from the USGS Spectral Library for minerals (Envi
4.8) are given in Fig. 2. The carbonate minerals such as
calcite (CaCO
3
), dolomite [CaMg (CO
3
)
2
], and siderite
(FeCO
3
) show significant useful narrow absorption features
around 2.35 lm [shown by the vertical line in Fig. 2;
correspondence to band 8 (2.295–2.365 lm) in ASTER
b
Tanuf •
•Al Hamra
Al hoota •
•Bahla
a
•Sur
Site2
Site1
Study sites 1 and 2
c
Wadd •
•Paleo sink
Fig. 1 Shows aregional geology and structural map of the Oman Mountain area (after Robertson and Searle 1990), band cthe ASTER FCC
image (RGB bands 3, 2, and 1) illustrates the carbonate massifs of Tanuf Valley (Site. 1) and the region near to Sur (Site. 2), respectively
134 Environ Earth Sci (2014) 71:133–146
123
data] due to C–O bonds (Mars and Rowan 2010) in their
compositions. The calcite and dolomite (end members of
series) minerals can be distinguished and identified by
variations in their absorptions between 2.33 and 2.45 lm
(Kuosmanen et al. 2000; Mars and Rowan 2010; Combe
et al. 2006). The iron carbonate, siderite shows absorption
near 2.3 lm due to C–O bonds and broad absorption
around 1.1 lm due to the presence of ferrous contents.
Based on the spectral absorption characters of such
minerals, the mineral bearing rock types are discriminated
over satellite data using several image processing methods
including false color composites, band ratios, decorrelation
stretching, and principal components analysis (Rajendran
et al. 2011; Corrie et al. 2010; Ninomiya et al. 2005;
Ninomiya 2002; Sultan et al. 1987).
Satellite data and methods
ASTER sensor is a multispectral imaging system, launched
during December 1999 travels in a near circular, sun-syn-
chronous orbit with an inclination of approximately 98.28,
an altitude of 705 km and a repeat cycle of 16 days. It
measures visible reflected radiation in three spectral bands
(VNIR between 0.52 and 0.86 lm, with 15-m spatial res-
olution) and infrared reflected radiation in six spectral
bands (SWIR between 1.6 and 2.43 lm, with 30-m spatial
resolution). It records the data in band 3B (0.76–0.86 lm)
with a backward looking angle that enables the calculation
of digital elevation models (DEM). In addition, it measures
emitted radiation in five spectral bands in the thermal
infrared region between 8.125 and 11.65 lm, with 90-m
spatial resolution (Fujisada 1995). The increase of spectral
bands in the SWIR region (one spectral band for Landsat
Fig. 2 USGS spectral library plots for minerals show the absorptions
differences in the spectra of major carbonate minerals
Sites of spring (waterhole)
Sites of cave
Jka-b
JSA
0 5k
57°25’E
57°25’E
23°05’N
23°10’N23°10’N
23°05’N
N
Fig. 3 Geology of Site. 1 (Ministry of Petroleum and Minerals 1992)
Environ Earth Sci (2014) 71:133–146 135
123
versus six spectral bands for ASTER) enhances the surface
mineralogical and lithological mapping. In the present
study, 14 ASTER Level 1B spectral bands date of April 07,
2007 for Site 1 (Fig. 1b) and April 07, 2004 for Site 2
(Fig. 1c) obtained from NASA Land Processes Distributed
Active Archive Center User Services, USGS Earth
Resources Observation and Science (EROS) Center
(https://LPDAAC.usgs.gov) are used. The data were
delivered in a Tag Image File Format which provides files
for each band containing the imagery and an ASCII text
.met file containing the metadata. The imagery was
checked and found in the cloud cover of 0 % and for sensor
errors, such as banding and other geometric distortions.
Both the data were supplied in terms of scaled radiance at-
sensor data with radiometric and geometric corrections
applied. Data were georeferenced in the UTM projection
and for the WGS-84 ellipsoid. The nine VNIR–SWIR
spectral bands were chosen and processed to the region of
interest to map the limestone formations using ENVI (4.8)
and ArcGIS (10) softwares. Mapping of limestone
formations of the study sites is carried out by decorrelation
stretch digital image processing technique. Interpreted
images of Site 1 and Site 2 are verified in the field, and
traverse-based samples were collected for laboratory
studies during May and September, 2012. The regional
geological maps (Ministry of Petroleum and Minerals
1992) available in the scale 1: 250,000 were used to verify
the processed remote sensing data. The samples collected
from the field are studied further using a microscope and
PIMA SP infrared spectrometer at the Department of Earth
Sciences, Sultan Qaboos University to determine the major
minerals and spectral properties of limestone formations.
The spectrometer is fabricated for field spectroscopy by
Integrated Spectronics Pty Ltd., Australia. It identifies and
analyzes the spectral signals of rocks and minerals in the
wavelength ranges from 1,300 to 2,500 nm with PIMA
VIEW software (version 3.1). The spectral resolution of the
instrument is *7 nm. It has a built-in wavelength cali-
bration target plate and is capable to measure spectra from
10 s to around 5-min speed.
Site.2, chosen area for image analysis
N
PTR
jsb
05k
59°10’E
22°40’N 22°40’N
22°30’N
22°30’N
59° 10’E 59°20’E
59° 20’E
Fig. 4 Regional geology in and around of Site. 2 (Ministry of Petroleum and Minerals 1992)
136 Environ Earth Sci (2014) 71:133–146
123
Geomorphological and geological setting
The major geomorphological units of the Site 1 (Figs. 3,
1b) are represented by structural hill (side of Jabal Akhdar
anticline, Fig. 1a) and intramontane valley. The carbonate
massifs are widespread over the hill area of the side of
Tanuf Valley having slope environments. Occurrences of
caves, springs (marked as waterhole) and dissected drain-
ages are evidenced in this carbonate massifs (Waltham
et al. 1985; Ministry of Petroleum and Minerals 1992;
Hanna and Al-Belushi 1996). In Site 2 (Figs. 4and 1b), the
landscape is typically characterized by summit plateau
bounded by steep structural hill slopes, which grade to
wide piedmonts areas. Here, the large depressions occurred
as collapsed structures. Geologically, the Site 1 consists of
the major rock formations of Hajar units (Autochthonous
shelf sediments), Hawasina, and Samail nappes (Allo-
chthchonous units; Fig. 3). The Sahtan and Kahmah group
formations of Jurassic to Albian age of Hajar Units
occurred in the NE of the area. The Shams Formation, Nahr
Umr Formation, Natih Formations, and Muti Formation of
Albian to Santonian age of Hajar units cover most of the
central part of the area. All formations of the Hajar Units
are limestone-rich carbonate massif formations. The Hajar
units are thrust over by the formations of Hawasina nappe
and Samail nappe and deposited by post-nappe Quaternary
formations.
The occurrences and spatial distributions of different
rock formations in and around of Site 2 are given in Fig. 4.
The Site 2 mainly consists of the sedimentary formations of
Tertiary and Quaternary age underlined by the Allochtho-
nous units such as Hawasina and Samail nappes (Fig. 4).
Here, Simsima Formation (end of Cretaceous) is overlined
by the Abat Formation, Musawa Formation, Jafnayn For-
mation, Rus Formation, and Seeb Formation of late
Paleocene–early Eocene age. All formations are rich in
limestone variety of rocks. The entire Tertiary formations
are enveloped by Quaternary formations that consist of
coastal deposits to recent wadi alluvium. Here, the large,
oval- and crescent-shaped depressions occurred as col-
lapsed structures in the Tertiary Group of formations
(Ministry of Petroleum and Minerals 1992).
ba
Fig. 5 Decorrelated RGB images of ASTER spectral bands 8, 3, 1 of aSite 1 and bSite 2 shows the limestone formations in pink color (refer
the legend of Figs. 3,4)
Environ Earth Sci (2014) 71:133–146 137
123
Mapping of limestone formations
The occurrences and spatial distribution of limestone for-
mations are mapped by decorrelation stretch digital image
processing method, studying the spectral sensitivities of
carbonate minerals (as discussed above in Sect. 2) of the
formations using ASTER spectral bands 8 (2.295–2.365
lm), 3 (0.78–0.86 lm), and 1(0.52–0.60 lm) for Site 1 and
Site 2. Among the three bands, the band 8 responds to
the presence of carbonate and hydroxyl bearing miner-
als of the limestone formations. Band 3 serves to charac-
terize the general albedo of the materials to highlight
certain silicate minerals associated with the formations
and band 1 contains information relating to the presence of
iron minerals associated with the formations or tecton-
ized harzburgite. The technique is well discussed by
Gillespie et al. (1986), Rothery (1987a,b) and Abrams
et al. (1988), which is based on principal components
transformation of the acquired data. The transformed
channels here are themselves contrasted, stretched, and
arbitrarily assigned to primary colors for display as a color
composite image.
The images of decorrelated ASTER bands 8, 3, and 1 of
the study sites are given in Fig. 5. Almost all limestone
formations occurred in Tanuf Valley (Figs. 1b, 3,5a) and
Sur region (Figs. 1c, 4,5b) of the parts of Oman are dis-
criminated well. The formations are mapped and are cor-
relatable to the available geological maps (Figs. 3,4). The
limestone formations of Tanuf Valley namely Shams
(Kshs), Nahr (Knu), Natih (Knt1 and Knt2), and Muti
(Kmu
cg
)Formations of Albian to Santonian age are well
delineated within Hajar units. The occurrence and spatial
distribution of formations are shown distinctly by pink
color in the decorrelated RGB image (Fig. 5a). The other
formations associated with massifs, such as Hawasina and
Samail post-nappe units, are discriminated by pale blue and
dark green colors, respectively. The limestone formations
have the occurrences of springs and caves (Figs. 3,5a) and
their locations are star marked on the interpreted image
(Fig. 5a). These features were studied and discussed in the
field in the following section. The Natih formations are
major oil producing formations in Oman and featured by
the occurrences of Al Hota and Al Fallah caves (Hanna and
Al-Belushi 1996; Frans et al. 2002). The decorrelated RGB
image of Site 2 of Sur region (Fig. 5b), which consists of
the Tertiary group formations, namely Abat (Eab), Musawa
(Emw), Jafnayn (Ejf), Rus (Ers), and Seeb (Ese), are dis-
criminated too well similar to Site 1. The occurrence and
spatial distribution of such carbonate formations are shown
by similar pink color. Interpretations of image show the
occurrences of large depressions at the boundary between
the Abat and Seeb Formations (Figs. 3,5b). The locations
of such depressions are star marked on the interpreted
image (Fig. 5b). The image processing method applied on
ASTER spectral bands (8, 3, and 1) are proved beneficial in
the discrimination of limestone formations of the study
sites.
Table 1 Geographical locations of springs and caves
Locations of spring Latitude Longitude
WH1 23°706.9400N57°2705.6700E
WH2 23°8033.9400N57°2806.8600E
WH3 23°9013.0200N57°24021.1300E
WH4 23°8057.2200N57°24015.5000E
WH5 23°8046.6300N57°23058.6000E
WH6 23°9013.6900N57°23029.9900E
WH7 23°8028.0800N57°23028.6400E
WH8 23°7049.2800N57°24033.9100E
WH9 23°7032.6500N57°23044.9400E
WH10 23°6043.3700N57°2403.3300E
WH11 23°6031.0200N57°24015.7500E
WH12 23°5054.7200N57°23057.5300E
WH13 23°6017.2600N57°22038.3200E
WH14 23°6016.4400N57°22023.1600E
WH15 23°6022.3900N57°2202.5900E
WH16 23°9023.9600N57°20012.1500E
WH17 23°9028.6000N57°20011.8500E
WH18 23°8046.0100N57°18038.7700E
WH19 23°1004.8700N57°18046.2300E
WH20 23°9033.2600N57°17056.0900E
WH21 23°9032.3400N57°17053.1500E
WH22 23°8039.8600N57°17045.5900E
WH23 23°8039.5900N57°17049.3700E
WH24 23°9040.6700N57°15059.3300E
WH25 23°1008.7500N57°15017.5800E
WH26 23°9055.1200N57°1502.0900E
WH27 23°1006.0600N57°14051.9400E
WH28 23°10010.4400N57°1403.4200E
WH29 23°9037.4600N57°23042.9000E
WH30 23°9058.5700N57°15043.5800E
WH31 23°10021.2300N57°1607.1500E
WH32 23°9042.9300N57°1705.1100E
WH33 23°9051.6800N57°17012.3000E
WH34 23°9045.3500N57°17036.7200E
WH35 23°1002.2800N57°19030.3400E
WH35 23°1002.2800N57°19030.3400E
WH36 23°9039.0000N57°20020.7200E
Caves
Al Hota cave 23°606.0300N57°2206.2000E
Al Fallah Cave 23°4055.6000N57°21015.9800E
138 Environ Earth Sci (2014) 71:133–146
123
a
Spring
h
c
Al Fallah Cave
Visitors Entrance
Joints
b
Limestones
d
Black pebble
limestones
e
Lining of solution
features
f
Occurrences of
leached fossils
g
Fossil coral
Fig. 6 Field photographs in and around of Tanuf Vally shows athe
steep dipping of the Natih formations, bthe massive and smooth
surface Natih formations, cthe Al Fallah cave in Natih formations,
dthe black pebble in limestone, ethe lining of solution features in
dolomites, fthe occurrences of fossils on the surface of dolomites,
gthe dissolved coral filled with sediment occurred in carbonate
massif observed under the microscope (nicols crossed 259), and hthe
spring in the lower part of Natih formations
Environ Earth Sci (2014) 71:133–146 139
123
Field evidences and laboratory studies
Systematic field verifications on interpreted image of Site 1
and Site 2 are carried out and traverse-based samples were
collected. The occurrences of carbonate massifs and asso-
ciated rock types of Tanuf Valley and Sur region dis-
criminated on the image by difference in tones are verified
at several locations. The samples used in the laboratory
studies are described in Table 1. At Tanuf Valley, the
Natih formations (Knt1,Knt2) of Hajar units are shelf
carbonate sedimentary rocks deposited during Albian to
Cenomanian age widespread over a large area from the
base of Tanuf valley (Hanna and Al-Belushi 1996; Frans
et al. 2002). In the field, these are dipping steep and
developed slope to the side of Tanuf Valley (Fig. 6a). The
Knt1 formation is thick and its surface is massive and
smooth (Fig. 6b) compared to Knt2 formation, which may
be due to the presence of high contents of dolomite formed
by dolomitization. The formations consist of gray to black
limestone and dolomites (Table 1; Vandeginste and John
2012; Breescha et al. 2006; Frans et al. 2002; Pratt and
Smewing 1990; Filbrant et al. 1990). These are massive
and karstified due to the circulation of water (Hillga
¨rtner
et al. 2003; Sattler et al. 2005). The occurrences of Al Hota
and Al Fallah caves are occurred within these formations
(Fig. 6c; Hanna and Al-Belushi 1996). They are the
Fig. 7 Google Earth true color satellite image shows the locations of spring in the carbonate massifs at Anuf Valley (inset shows the springs of
location WH1, WH10, WH20, WH21 and WH27)
Table 2 Geographical locations of depressions
Locations of depression Latitude Longitude
S1 22°29023.3300N59°16050.7100E
S2 22°30052.6500N59°1606.4600E
S3 22°31039.6100N59°16019.8200E
S4 22°33012.3100N59°1602.5000E
S5 22°34010.8300N59°16025.2800E
S6 22°34045.3400N59°16028.5200E
S7 22°3600.5000N59°1600.1100E
S8 22°37010.1100N59°15018.9000E
S9 22°38040.9500N59°14052.5100E
S10 22°40034.7400N59°18015.5800E
S11 22°4305.7700N59°1805.3700E
S12 22°45047.5500N59°15038.0800E
S13 22°47045.0000N59°13055.5800E
S14 22°43030.3800N59°8051.4300E
S15 22°5400.3100N59°5027.5300E
Bimmah waterhole 23°207.7200N59°4021.5900E
140 Environ Earth Sci (2014) 71:133–146
123
e
Friable Tertiary formation
Collapsed structure
h
Massif bioclastic
limestone
g
Harzburgite
c
b
Feldspar
Quartz
d
Pyroxene
Serpentine
Chromite
a
Megabreccia
f
Highly fractured
limestone formation
Fig. 8 Filed photographs shows the occurrences of athe megab-
reccia of Aqil formation in filed and bunder microscope (nicols
crossed, 159), cthe tectonized harzburgite of Samail nappe in field
and dunder microscope (nicols crossed, 259) of Tanuf Valley, and
efriable Tertiary formations, fand glimestone massifs, and hthe
collapsed structure of Sur region
Environ Earth Sci (2014) 71:133–146 141
123
c
Massive carbonates
Impression of
dissolutions
Bimmah Waterhole
d
e
Marl
g
Bioclastic limestone
Chlorite
f
h
Calcite
Dolomite
Shell fragments
b
Depression and
Structures
Massive
carbonates
Striations due to
subsidence
Depression and
Structures
a
Massive
carbonates
Fig. 9 Shows aand bthe depressions (S1 and S5 in Fig. 5b) and
massive carbonates over the Google image (not to scale), cthe
photographs of massive carbonates with dissolution imprints, dthe deep
waterhole (Bimmah), ethe marl in the field and fthe marl under the
microscope (nicols crossed 259), gthe massive bioclastic limestone in
the field and funder the microscope (nicols crossed 259) of Sur region
142 Environ Earth Sci (2014) 71:133–146
123
occurrence of speleothems in caves (http://www.alhota
caves.com) and solutional karst features in the limestone
surface, such as black pebble limestones (Fig. 6d), lining of
solution features (Fig. 6e), extensive dissolution, missing
fossilized zones, and leached fossils surface (Fig. 6f; Jones
and Smith 1987; Wright 1982) are observed in the field.
Under the microscope, the dissolved corals filled with
sediments (Fig. 6g) are observed. The occurrences of
springs are evidenced (Fig. 6h) in parts of Natih formations
(Knt1). The survey made with the local people, confirms
that these are being used for domestic and irrigational
purposes. Visual interpretations of true color Google Earth
images (http://www.google.com/earth/index.html) of the
region show the occurrences of more springs (WH1–
WH36) in the barren exposures of massif formations and
are located in Fig. 7. The geographical locations of the
caves and springs of the region are given in Table 2.
Detailed study and investigation of these features in the
entire formations of Hajar units of this region using high
spatial resolution satellite data may provide significant
useful information to the socio-economic and cultural
development of this region. The other rock types, such as
megabreccia (TRKaq
b
) of Aqil formation of Hawasina
nappe and tectonized harzburgite (TH) of Samail nappe
(post-nappe units) associated with Natih formations, are
verified in the field and the samples are studied under the
microscope. The field structure of megabreccia (Fig. 8a)
exhibits coarse mosaic texture and pale blue in color on the
image (Fig. 5a) which is easily distinguishable from its
associated rocks. Under the microscope, the minerals of the
rock show angularities (Fig. 8b). The harzburgite is inter-
preted from dark green in color (Figs. 5a) on the image and
tectonized in the field (Fig. 8c). Under the microscope, the
major minerals, such as serpentine and orthopyroxene
(Fig. 8d), are studied. Chromite is observed as minor
phases.
In the field, the limestone formations of Site 2 are friable
(Fig. 8e), fractured and massifs, occurred in different
thicknesses (Fig. 8f). The image interpretations of Abat
Formations that consists of gray to white marly or micritic
limestone with chert nodules and overlined by the Seeb
Formations, consists of bioclastic limestone (Fig. 8g),
calcarenite, marl, and sandstone are verified in the field.
The occurrences of large depressions as collapsed struc-
tures (Fig. 8h) at the boundary between Abat and Seeb
formations are observed (Fig. 9a, b). The region exhibits a
wider plateau at the top and a steep slope at the boundary.
The collapsed breccias and extensive dissolution on the
c
Sandstone
d
Quartz
Iron matrix
Feldspar
weathered
Dolomite
b
Dolomite
a
Fig. 10 Photographs of Sur region shows the occurrences of adolomite in the field and bunder the microscope (nicols crossed 259),
csandstone in the field, and dunder the microscope (nicols crossed 259)
Environ Earth Sci (2014) 71:133–146 143
123
carbonate massifs are observed in the field. The depres-
sions are developed due to the movement of Seeb forma-
tions into voids created by the dissolution of water in the
limestones of Abat formations. Here, the bioclastic lime-
stones occurred as massive formations (Fig. 9c). The
region is also featured by a deep water hole (Bimmah)
developed by the collapse of limestone cavern (Fig. 9d).
The samples of marl (Fig. 9e), massive bioclastic lime-
stone (Fig. 9g), dolomite (Fig. 10a), and sandstone
(Fig. 10c) collected from the field are studied in the labo-
ratory. The microscopic study of such samples shows the
presence of more chlorite minerals in the marl (Fig. 9e, f),
bioclasts in the bioclastic limestone (Fig. 9g, h), minerals
of dolomite (Fig. 10a, b), and sandstone (Fig. 10c, d).
Under the microscope, the etched carbonate cements are
studied. The grain boundaries are marked by sharp, iron-
stained border, a zone of micrite that contains some iron
staining (Jones and Smith 1987; Wright 1982). Study of the
true color Google Earth image shows the occurrences of 15
large depressions along the boundary in and around this
region. The geographical locations of the depressions are
given in Table 3.
Further, the samples collected from the field are studied
for the understanding of the image characters of limestone
formations by measuring the spectral reflectances using
PIMA SP infrared spectrometer. The spectral plots of
selected samples of Tanuf Valley (Sample nos. AH1, AH2,
AH3, AH5, and AH5a) and Sur region (Sample nos. Sr3,
Sr5, Sr6, Sr9, Sr10, Sr12, Sr15, and Sr16) are given in
Fig. 11. Almost all the samples showed strong absorptions
around 2.3 lm and confirmed the presence of carbonate
minerals namely calcite (CaCO
3
; Fig. 11a), dolomite
[CaMg(CO
3
)
2
; Fig. 11b], and siderite (FeCO
3
; Sample no.
Sr. 9, marl sandstone). The montmorillonites [(NaCa)
0.33
(AlMg)
2
(Si
4
O
10
)(OH)
2
.nH
2
O] are detected with carbonate
minerals in the marl samples. It shows a strong absorptions
feature around 1.4 and 1.9 lm in the infrared wavelength
regions (Fig. 11c) due to the presence of hydroxyl mole-
cules in its contents. The selected plots of calcite, dolomite,
and montmorillonite minerals are given in Fig. 12 to
compare the absorption differences of minerals. It shows
that the samples containing high content of calcite have
strong absorptions compared to the samples consisting of
dolomite and montmorillonite which have moderate to
poor absorptions. The absorptions of dolomite and mont-
morillonite are due to the presence of magnesium and
hydroxyl molecules in its contents, respectively.
Conclusions
In the present study, the limestone karst formations of Tanuf
Valley and Sur regions are discriminated well by the dec-
orrelated image processing methods using ASTER spectral
bands 8, 3, and 1. The discriminations are carried out based
on the spectral sensitivity of carbonate minerals which have
Table 3 Shows the locations and descriptions of selected samples collected from the field
No. Locations Field descriptions Laboratory minerals descriptions
Latitude Longitude Types Characters Microscopic Spectrometer
At Tanuf Valley
AH1 23°0404700N57°2101600E Dolomite Massive Rich in dolomite, calcite Dolomite
AH2 23°0404700N57°2101400E Clayey
Limestone
Clay, friable Clay minerals Montmorillonite, calcite
AH3 23°0502200N57°1905300E Dolomite Massive Rich in dolomite, calcite Dolomite
AH5 23°0601300N57°2201000E Limestone Friable Rich in calcite, dolomite Limestone
AH5a 23°0601700N57°2200400E Limestone Massive Rich in calcite, dolomite Limestone
At Sur Region
Sr3 22°3005300N59°1700200E Limestone Massive, Rich in dolomite, calcite Dolomite
Sr5 22°2804700N59°1605200E Marl limestone Massive, friable Cemented, calcite, clay
minerals
Montmorillonite, dolomite
Sr6 22°2900400N59°1604300E Marl limestone Friable Calcite, clay minerals Montmorillonite, calcite
Sr9 22°2803200N59°1803200E Marl sandstone Loose and friable,
ferrugenous
Sharp, iron-stained
border, zone of
micrite, chlorite
Montmorillonite, siderite
Sr10 22°3005000N59°1602500E Limestone Massive Calcite, dolomite coral Dolomite
Sr12 22°3004400N59°1901200E Limestone Massive Rich in dolomite, calcite Dolomite
Sr15 22°3803600N59°2002600E Marl Limestone Massive, friable, bioclasts Calcite rich fossiliferous Calcite
Sr16 22°3900900N59°2005000E Marl Limestone Loose and friable Calcite, clay minerals Calcite, montmorillonite,
tremolite
144 Environ Earth Sci (2014) 71:133–146
123
CO
3
absorption near 2.35 lm in ASTER band 8. The inter-
pretations of limestone formations and associated lithologies
of sites are comparable with the available geological map.
The limestone formations of Albian–Cenomanian periods of
Cretaceous age of Tanuf Valley are associated with the
Hawasina and Samail nappes whereas, the limestone for-
mations of Tertiary age (late Paleocene to early Eocene) of
Sur region are associated with Hawasina and Samail nappes
and Quaternary formations. Caves, springs and large
depressions that occurred in limestone formations in the sites
are studied in the field and the more occurrences of springs
and depressions are interpreted and located on the Google
Earth image. The samples collected from the field are studied
in the laboratory and the mineralogical and spectral char-
acters of carbonate formations are confirmed. Thus, the study
of mapping of limestone formations of the study sites using
ASTER spectral bands by decorrelated stretch image pro-
cessing method demonstrates the capability of ASTER
sensor; and thus, the technique presented in this work could
be applied to other geographical regions where similar
questions needed to be resolved.
Acknowledgments The authors are thankful to NASA Land Pro-
cesses Distributed Active Archive Center User Services, USGS Earth
Resources Observation and Science (EROS) Center https://
LPDAAC.usgs.gov) for providing the ASTER data. The study is
supported by Sultan Qaboos Internal grant IG/SCI/ETHS/12/02. The
helps extended by Mr. Abdulla Al-Fahdi and Mr. Badar Al-Waili,
Department of Earth Sciences, SQU are thankfully acknowledged for
extending their valuable help in the preparation of thin sections and
support. Authors are very much thankful to the anonymous reviewers
and the editor of the journal for their valuable reviews and providing
constructive comments and suggestions that have helped to present
the work lucidly.
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