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KARSTIFICATION INFLUENCE ON THE DRAINAGE SYSTEM, EXAMPLES FROM THE IRAQI SOUTHERN DESERT

Authors:
  • University of Kurdistan, Hewler, Erbil, Iraq.

Abstract and Figures

The Iraqi Southern Desert is covered mainly by limestone pavement, being mainly composed of Paleocene – Pliocene rocks, which belong to Umm Er Radhuma, Dammam, Euphrates and Zahra formations. The most karstified rocks, however, belong to Dammam Formation of Eocene age. The Dammam Formation consists mainly of limestone, with dolostone, dolomitic and marly limestone, and marl. Some chert nodules or bands occur too within the succession. Morphologically, the Iraqi Southern Desert comprises mainly of flat terrain, which is dissected by dense drainage system, and slopes towards north and northeast. Therefore, the main valleys flow towards north and northeast, with almost parallel courses. However, the course of the valleys within the rocks of the Dammam Formation exhibit strange and abnormal forms, which are not usual in normal drainage patterns. The abnormal forms are like bifurcation of the valleys; downstream and joining again, and circular and crescent forms, besides changing their main flow direction. These abnormal forms are believed to be due to the influence of the karstification, which is still an active process. The karst forms are in circular, oval, polygonal and crescent shapes, with different sizes. The karstification is not only obvious in the drainage forms, but also in the exposed rocks. They exhibit successive and parallel rims, which coincide in shape and direction with the karst forms, indicating continuous karstification. The karstification stages, sizes, types and reasons are mentioned too, with many examples from the abnormal drainage forms.
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Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115

KARSTIFICATION INFLUENCE ON THE
DRAINAGE SYSTEM,
EXAMPLES FROM THE IRAQI SOUTHERN DESERT
Varoujan K. Sissakian
1
, Dhiya'a Al-Deen K. Ajar
2
and Maher T. Zaini
2
Received: 05/ 11/ 2011, Accepted: 09/ 02/ 2012
Key words: Karstification, Karst terrane, Uvala, Iraqi Southern Desert
ABSTRACT
The Iraqi Southern Desert is covered mainly by limestone pavement, being mainly
composed of Paleocene Pliocene rocks, which belong to Umm Er Radhuma, Dammam,
Euphrates and Zahra formations. The most karstified rocks, however, belong to Dammam
Formation of Eocene age. The Dammam Formation consists mainly of limestone, with
dolostone, dolomitic and marly limestone, and marl. Some chert nodules or bands occur too
within the succession.
Morphologically, the Iraqi Southern Desert comprises mainly of flat terrain, which is
dissected by dense drainage system, and slopes towards north and northeast. Therefore, the
main valleys flow towards north and northeast, with almost parallel courses. However, the
course of the valleys within the rocks of the Dammam Formation exhibit strange and
abnormal forms, which are not usual in normal drainage patterns. The abnormal forms are like
bifurcation of the valleys; downstream and joining again, and circular and crescent forms,
besides changing their main flow direction. These abnormal forms are believed to be due to
the influence of the karstification, which is still an active process. The karst forms are in
circular, oval, polygonal and crescent shapes, with different sizes. The karstification is not
only obvious in the drainage forms, but also in the exposed rocks. They exhibit successive
and parallel rims, which coincide in shape and direction with the karst forms, indicating
continuous karstification. The karstification stages, sizes, types and reasons are mentioned
too, with many examples from the abnormal drainage forms.
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____________________________________
1
Expert, Iraq Geological Survey, P.O. Box 986, Baghdad, Iraq
2
Senior Geologist, Iraq Geological Survey, P.O. Box 986, Baghdad, Iraq
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.


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INTRODUCTION
The Iraqi Southern Desert is one of the most karstified areas in Iraq (Sissakian and
Ibrahim, 2005, and Sissakian et al., 2011). Different karst forms are well developed in the
studied area, which is almost a flat terrain, with desert pavement mainly formed by
limestones, dissected by complex drainage system and characterized by dense karst forms,
which gave the area unique abnormal terrain form. Among the abnormal forms are:
bifurcation of valleys; downstream and joining again forming almost circular, polygonal,
crescent and oval forms, with dense karst forms in the exposed rocks.
Location
The studied area is located in the Iraqi Southern Desert, about 100 Km southeast of
Samawa city, and south of Baghdad about 600 Km (Fig.1). The area is bounded by the
following approximate coordinates and it is about 6250 Km
2
.
Longitude 45 15' 00" 45 45' 00"
Latitude 29 45' 00" 30 30' 00"
Fig.1: Location map of the studied area
Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115
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Aim
The aim of this study is to explain the influence of the karst forms on the drainage system
in the studied area and deduce the genesis of their development in such abnormal density,
as compared to neighboring areas, towards east, south and west.
Methodology and Materials Used
To achieve the aim of this study, the following materials were used:
- Geological, geophysical and topographical maps of different scales
- Land sat and Google Earth images of different scales
- Aerial photographs at scale of 1: 42000
The topographical maps were used to indicate the dimensions of morphological features
and karst forms. Geological maps and reports were used to indicate the surface and subsurface
geology of the studied area and near surrounding, and to correlate them regionally.
Geophysical maps were used to indicate deep seated structures that may have contributed in
development of the karst forms. Land sat and Google Earth images were used to acquire top
view of individual karst form and to indicate the details of the depression rims. Moreover, to
search about recent activities, when compared with the existing aerial photographs, which
were photographed during 1954 1956. Historical books were reviewed to collect any
relevant data concerning the existence of the forms and their development.
Previous Work
Although no much specialized work was done concerning karstification and its influence
on the drainage system, but the hereinafter mentioned work has direct and/ or indirect relation
with this study.
Al-Ani and Ma'ala (1982a and b) executed regional geological mapping of the eastern part
of the Southern Desert in which the studied area is located. They reported about the
karstification in the limestone of the Dammam Formation.
Jassim et al. (1986 and 1990) compiled the Geological Map of Iraq at scale of 1: 1000 000
(1
st
and 2
nd
edits.) and demonstrated the exposed geological units in the studied area.
Al-Kadhimi et al. (1996) compiled the Tectonic Map of Iraq at scale of 1: 1000 000
(2
nd
edit.) and demonstrated the structural zones in the studied area.
Hamza (1997) compiled the Geomorphological Map of Iraq at scale of 1: 1000 000 and
considered the studied area as a karstified region.
Sissakian (2000) compiled the Geological Map of Iraq at scale of 1: 1000 000 (3
rd
edit.)
and demonstrated the exposed geological units, including the large depressions in the
studied area.
Sissakian and Ibrahim (2005) compiled the Geological Hazards Map of Iraq at scale of
1: 1000 000 and included the studied area within the karst hazards region.
Sissakian and Al-Mousawi (2007) reported about the karstification problems in Iraq and
mentioned many examples from the studied area.
Ma'ala (2009a) reported about the geomorphological units in the Iraqi Southern Desert
and mentioned the studied area is within the karst unit.
Ma'ala (2009b) reported about the tectonic evolution of the Iraqi Southern Desert in which
the studied area is located.
Sissakian et al. (2011) reported about the geological hazards in Iraq and included the
studied area within the karst hazards region, and mentioned many examples.
Fouad (2012) compiled the Tectonic Map of Iraq at scale of 1: 1000 000 (3
rd
edit.) and
demonstrated the structural zones in the studied area.
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.

GEOLOGICAL SETTING
Geomorphology
The studied area is a flat plain rising gently towards southwest and west, intensely
dissected by valleys, which show different karst forms. The valleys are wide and shallow,
trending generally towards north and northeast, however they exhibit very complex and
abnormal drainage shapes, due to intense karstification. According to Hamza (1997), the
study area is a karst region. According to Sissakian and Ibrahim (2005) and Sissakian et al.
(2011), the study area is a densely karstified area, with different karst forms, which have
different sizes and origins.
Ma'ala (2009a) reported about the geomorphology of the Iraqi Southern Desert and
mentioned the following data.
Chemical Weathering Processes: These are inherited from pre-Miocene phase, and were
continued during Late Miocene Holocene. Some of the subterranean hollows and caves
were enlarged and collapsed during Late Miocene Pleistocene.
Solution Processes: The secondary fractures, which allowed the rain water to percolate,
have accelerated the solutional processes of limestone, and led to produce karst features
(dolines, sinkholes, blind valleys). At the same time, some of subterranean hollows and caves
have been collapsed to produce second phase of collapse sink depressions.
Sinkholes: Areas built-up by limestone are marked by sinkholes, formed due to dissolving
by water (giving a more distinctive type of caves); even underground river channels being
developed. The limestone of Al-Hijara Unit is marked by sinkholes, uvalas, dolines, caverns
and karst valleys. Sissakian and Ibrahim (2005) pointed out that the sinkholes are common
types in the Southern Desert, which are developed due to dissolving of limestone. Sinkholes
are also well developed in the anhydrite land, which can be named as Limestone Pavement
(Bates and Jackson, 1983). It consists of hundreds of sinkholes, which are filled by
polygenetic sediments.
Karst Valleys: These are subterranean passages running in NE direction, developed by
solution of limestones (Eocene). Several of them were collapsed and produced abandoned
valleys, which often end abruptly as blind valley, such as karst valleys.
Stratigraphy
The studied area is covered by Dammam and Zahra formations of Eocene and Pliocene
Pleistocene age, respectively (Fig.2). The two formations are described hereinafter.
Dammam Formation: Is divided into three members: Lower, Middle and Upper (Al-Ani
and Ma'ala, 1982a and b) the age is Eocene. In the studied area, however only the Upper and
Middle Members are exposed. Jassim and Al-Jiburi (2009) reported about the Upper and
Middle Members of the Dammam Formation in the Iraqi Southern Desert depending mainly
on Al-Ani and Ma'ala (1982a and b). Hereinafter is a brief review of the two members.
Middle Member: It is subdivided into four units, as follows (from bottom to top):
1. Upper Huweimi Unit Early Lutetian (Middle Eocene)
2. Shawiya Unit Late Lutetian (Middle Eocene)
3. Chabd Unit Late Lutetian (Middle Eocene)
4. Radhuma Barabak Unit Late Lutetian (Middle Eocene)
Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115
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1. Upper Huweimi Unit: This unit is subdivided into two subunits:
Lower Subunit: It consist of (1 3) m breccia or conglomerate, overlain by
(0.5 2) m hard, well bedded, limestone. The upper part (3 5 m) consists of hard,
well bedded, dolostone and lithographic limestone.
Upper Subunit: The lower part consists of (0.2 1) m of limestone, overlain by
(3 4) m of dolostone, with chert nodules. The middle part consists of (5 6) m of
silicified dolostone. The upper part (4 5 m) consists of well bedded limestone.
The maximum thickness of the Upper Huweimi Unit is about (20 25) m.
2. Shawiya Unit: This unit is exposed as continuous ridge from west of Wadi
Abu Khamssat to the north and northeast of Salman town. It is characterized by high
lateral variation in lithology. It consists of thickly bedded to massive limestone.
3. Chabd Unit: The lower part (15 20 m) consists of limestone, overlain by thinly
bedded, nummulitic limestone, followed by (11 14) m of massive limestone. This
sequence is alternated with (2 3) thin horizons of nummulitic limestone. The middle part
(5 10 m) consists of alternation of thickly bedded, limestone. The upper part (15 m)
consists of thickly bedded to massive limestone.
4. Rudhuma Barabak Unit: It is subdivided into two beds:
Rudhuma Beds: Consist of thinly and thickly bedded, dolomitic limestone,
alternated with cavernous, limestone. The thickness ranges from (12 15) m.
Barabak Beds: Consist of thickly bedded to massive limestone, alternated with
limestone. The thickness ranges from (25 27) m.
Upper Member: It is subdivided into four units, as follows (from bottom to top):
1. Upper Huweimi Unit: This unit is subdivided into two subunits: Lower Subunit:
It consists of (1 3) m conglomerate overlain by (0.5 2) m well bedded, limestone. The
upper part (3 5 m) consists of well bedded limestone. Upper Subunit: The lower part
consists of (0.2 1) m of limestone, overlain by (3 4) m of dolostone, with chert
nodules. The middle part consists of (5 6) m of well bedded dolostone. The upper part
(4 5 m) consists of well bedded limestone The maximum thickness of the Upper
Huweimi Unit is about (20 25) m.
2. Shawiya Unit: This unit consists of thickly bedded to massive limestone, alternated
with thin horizons of limestone and (2 3) horizons of shelly limestone.
3. Chabd Unit: The lower part (15 20 m) consists of massive limestone, overlain by
thinly bedded limestone, followed by (11 14) m of massive limestone. The middle part
(5 10 m) consists of thickly bedded limestone. The upper part (15 m) consists of thickly
bedded limestone.
4. Rudhuma Barabak Unit: It is subdivided into two beds: Rudhuma Beds: Consist of
dolomitic limestone, alternated with cavernous limestone. The thickness ranges from
(12 15) m. Barabak Beds: Consist of thickly bedded to massive limestone, with thin
horizons and nodules of chert, alternated with thickly bedded limestone. The thickness
ranges from (25 27) m.
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.

Fig.2: Geological map of the studied are (after Sissakian, 2000)
Zahra Formation: Al-Ani and Ma'ala (1982a and b) mentioned that the Zahra Formation
in the Southern Desert is composed of (1 3) cycles; it is age is Pliocene Pleistocene.
Generally, each cycle is composed either of alternation of claystone, and limestone or
alternation of claystone, sandstone, and limestone. The claystone beds (thickness of each bed
is 4 5 m) are red conchoidally fractured. The sandstone beds (thickness of individual bed
ranges between 1 4 m) are friable, massive, and medium to coarse grained. The limestone
beds (the thickness is between 0.5 4 m) are hard to very hard, bedded, undulated, highly
jointed, and highly recrystallized. The thickness of the Zahra Formation is (3.50 14.5) m.
Structural Geology
The studied area is located within the Unstable Shelf of the Arabian Plate (Al-Kadhimi
et al., 1996). However, according to Fouad (2012) it is located within the Inner Platform of
the Arabian Plate. The area had not suffered from tectonic disturbances, although Al-Mubarak
and Amin (1983) have mapped many faults in this zone, but not in nearby vicinity of the
studied area. Ma'ala (2009b) reported about the tectonic and structural evolution of the Iraqi
Southern Desert. Hereinafter is a brief review.
The Southern Desert is a part of the northern Arabian Platform, where relatively thin
Phanerozoic sediments cover the Precambrian NW SE and NE SW fractured continental
basement complex. The platform itself is divided into two parts, a stable one to the west
(Southern Desert) and unstable one to the east. The boundary between the two parts of the
platform is taken along Euphrates Fault Zone (extension of Abu Jir Fault Zone).
Depression fill sediments
Zahra and Dibdibba
formations
Dammam Formation
0 20 Km
Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115

The Late Miocene (~11 Ma) was the time of the final transition to continental condition,
as collision along the eastern boundaries of the Arabian Plate proceeded, then culminated
through the Pliocene (5.3 Ma). The compression, imposed lateral movement along the
NW SE trending faults, and caused uplifting of the Stable Shelf area, including Safawi Arch
and Dibdibba Basin.
Sissakian and Deikran (1998) showed that the Southern Desert was uplifted since the Late
Miocene with amount of (50 350) m; and exhibits clear bulging with the same trend of the
main lineaments (Ansab Sdair, Amghar Busaiya and Al-Batin). They also deduced that
the rate of regional uplift is about (0.1 0.2) cm/ 100 year, in the area involved.
The Pliocene Pleistocene (5.3 1.8 Ma) was the time of strong influx of terrigenous
debris, from the Arabian Shield, due to the climatic changes. The sediments filled the
aforementioned structural down warped area (Abu Khema Area), which was later on named
as Dibdibba Basin, by Powers et al. (1962). Al-Batin fracture system imposed borders of the
Miocene Pleistocene rock units inside Dibdibba Basin (along eastern slope of Safawi Arch).
KARST DEVELOPMENT AND FORMS
General
The Karst topography is a landscape shaped by the dissolution of a soluble layer of
bedrock, usually carbonate rocks such as limestone (NWE, 2008). In the studied area, the
karst topography is very clear from the existing karst forms, which are formed due to mildly
acidic water action on soluble bedrocks. The karstification in the area has resulted a variety of
large or small scale features. Such different small scale features, like flutes, runnels, clints and
grikes, collectively are called karren or lapiez (NWE, 2008). The medium scale features, in
the area are sinkholes and dolines. Whereas, the large scale features are represented by
limestone pavement and blind valleys. Due to the presence of a lot of sinkholes and dolines in
the area, then the term "Uvalas" can be used (NEW, 2008). Because the subsurface is also
considered in karstification of the studied area, then the term "karst terrane" is used instead of
"karst terrain" (Field, 1999).
Because the karstification process in the studied area is still active, therefore, both
"Holokarst" and "Merokarst" types are present (Fig.3). The former means wholly developed
karst, whereas the latter means imperfectly developed, with some karstic features
(Gams, 2003). The term "Limestone pavement" means karst forms are frequently densely
clustered to dissect larger areas (Ford, 2003). This term can be applied to the studied area
because the area is densely karstified, which gave to the terrain a "shell-pitted appearance".
The developed karst forms range from less than 1 m to few kilometers; in diameter, and from
less than 1 m to less than five meters in depth, most of them are circular, oval and polygonal
in shape, usually with flat banks. However, depths up to 35 m were recorded.
Karstification
The topographic texture and structure of a karst terrain are determined by the lithology,
strength, porosity and structure of the exposed carbonate succession (JNCC, 2008). Different
assemblages of limestone landforms create karst types, which are largely related to the past
climatic environment (during Pleistocene and Early Holocene) in which they have evolved.
Within each type, the geological structure of the host soluble rock determines the patterns of
underground drainage and also influences the surface topography.
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.

Fig.3: Google Earth image showing both holokarst (A) and merokarst (B)
Note the influence of the karst forms on the drainage system,
the course of the valley hardly can be followed
Polygonal karst is a more mature karstic terrain, where dolines have replaced valleys as
the main form, and a polygonal network topographical divides has replaced the drainage
systems of interfluves (JNCC, 2008). In the studied area, such polygonal network of drainage
is formed in main valleys (Figs.3 and 4).
Fig.4: Google Earth image showing polygonal network drainage
1 Km
A
B
B
Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115

The authors believe that the main reason for development of the karst forms in the studied
area is the presence of limestones of the Dammam Formation, which is underlain by Rus
Formation. The latter consists mainly of anhydrite, which is also a soluble rock. The
subsurface extension of the Rus Formation is demonstrated in Fig. (5). However, recently
drilled boreholes in the north and northwest of the studied area indicated that the subsurface
extension is wider, and the studied area is included within the areas where the Rus Formation
underlies the Dammam Formation. The lithological constituent of these two formations
(bedded limestone with spaced fractures and anhydrites, respectively) increases the
dissolution of the rocks, due to subterranean water passages, which was very active during
Pleistocene and partly during Holocene, consequently increases the karstification process. It is
worth mentioning that the limestone and dolomite are dissolved by carbonic acid, at saturation
(thermodynamic equilibrium), concentrations of dissolved calcite will range from 50 gm/ l in
warm surface water to 250 gm/l in deep, cool subsoil water. Rates of limestone solution range
from less than 5 m
3
/ Km
2
/ year in deserts regions to more than 100 m
3
/ Km
2
/ year in rain
forests. Whereas, gypsum dissociates until there are 2500 gm dissolved per liter of water at
25 C (Ford, 2003).
Fig.5: Facies map of the Middle Late Eocene rock units
(Al-Hashimi, 1973 in Ma'ala, 2009a)
Showing the area of anhydrite land in the Southern Desert
44° 45° 46° 47° 48°
3
33°
32°
31°
30°
29°
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.

Chemistry of Karstification
The chemistry of the karstification includes two processes: The main one is dissolution
mechanism by carbonic acid, whereas the secondary one is dissolution mechanism by sulfide
oxidation (Wikipedia, 2009).
Main Dissolution Mechanism, Carbonic Acid: The carbonic acid that causes the karst
forms is formed as rain passes through the atmosphere picking CO
2
, which dissolves in
water. The sequence of reactions involved in the limestone dissolution are the following:
H
2
O + CO
2
→ H
2
CO
3
Ca CO
3
→ Ca
2+
+ CO
3
2
CO
3
2
+ H
2
CO
3
→ 2 HCO
3
Ca CO
3
+ H
2
CO
3
→ Ca
2+
+ 2 HCO
3
This is the main dissolution mechanism of calcium carbonate in limestone.
Secondary Dissolution Mechanism, Sulfide Oxidation: The oxidation of sulfides leading
to the formation of sulfuric acid can also be one of the corrosion factors in karst formation. As
O
2
-rich surface waters seep into deep anoxic karst system it brings oxygen, which reacts with
sulfide present in the system (pyrite or H
2
S) to form sulfuric acid (H
2
SO
4
). Sulfuric acid then
reacts with calcium carbonate causing increased erosion within the limestone formation. This
can be summarized by the cascade of the following reaction.
H
2
S + 2 O
2
→ H
2
SO
4
(sulfide oxidation)
H
2
SO
4
+ 2 H
2
O → SO
4
2
+ 2 H
3
O
+
(sulfuric acid dissociation)
CaCO
3
+
2 H
3
O
+
→ Ca
2+
+ 2 H
2
CO
3
+ 2 H
2
O (calcium carbonate dissolution)
CaCO
3
+
H
2
SO
4
CaSO
4
+ H
2
CO
3
(global reaction leading to calcium sulfate)
Ca SO
4
+ 2 H
2
O → CaSO
4
. 2 H
2
O (hydration and gypsum formation)
Although no sulfides were found on surface, in the studied area, but such reactions may
occur in subsurface rocks, where the Rus Formation consists mainly of anhydrite. Such
reaction exists in "Kebritiyah" vicinity (Fig.1), southwest of the studied area, where native
sulfur occurs in a sinkhole, as byproduct of bacterial action with the groundwater, indicating
the aforementioned chemical (sulfide oxidation) reaction.
Stages and Dating of Karstification
The studied area includes three stages of karstification, as it is clear from the existing karst
forms, especially the circular forms. Figure (6) shows a main valley with two circular forms
(A and B). The outer one (A) is a mature karst, which affected on the shape of the valley. The
second one (B) is more than half circle, which means the dissolution is not completed and the
collapse of the roof is not completed yet. Whereas, in the eastern rim of the outer circle; at (C)
the third stage of karstification is still in progress and no collapse has occurred yet. This is
clear from the successive rims formed along the bank of the valley. Such successive rims
however, also could be formed due to a land slide, but the height of the cliff which is only
(2 3) m does not permit for sliding. Another indication for the continuity of the
karstification process is shown in Fig. (7), where concentric rims are well developed in
a sinkhole.
Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115

Fig.6: Google Earth image showing three stages of karstification
Fig.7: Google Earth image showing continuous karstification process,
indicated by the three concentric rims (A)
1 Km
B
N
0.25 Km
N
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.

The following event is another indication for continuation of the karstification phase.
On 5/ 3/ 1944 a large sinkhole was formed in limestone beds of the Dammam Formation
(Eocene), after collapse of the roof forming beds, near Al-Shbicha police post, which is
located 300 Km south of Baghdad. The collapse continued for a month, the local people, few
kilometers from the formed sinkhole felt the sound of the collapse, whereas the local people
from much farther areas from the formed sinkhole felt ground shocks. The diameter and the
length of the sinkhole are 33 m and 27 m, respectively. The estimated volume of the collapsed
rocks, by a petroleum geologist is 1 230 000 m
3
(Sossa, 1966).
In this study, the climatic changes during Pleistocene and Holocene (Jado and Zofl, 1978)
and the duration of each climatic period are considered in estimating the age of the
Karstification. In calculating the humid and arid phases during Holocene and Pleistocene with
the supposed time span for each (Gradstein et al., 2004), then the following intervals can be
seen (Table 1).
Table 1: Climatic changes and durations within Quaternary Period
(Jado and Zofl, 1978)
Quaternary
Years
Climate
Holocene
6 000
arid
Late Pleistocene
17 000
35 000
arid
semi-arid
Middle Pleistocene
1 100 000
arid to semi-arid
Early Pleistocene
Pliocene
3 500 000
semi-arid
semi-humid
The time spam, starting from Early Pleistocene, which is 1 800 000 Ma (Gradstein et al.,
2004) where the first semi-humid phase had started, during Quaternary, will suit with the
estimated starting karstification phase in the studied area. However, if the Late Pliocene is
considered, then the karstification age will be 3 500 000 Ma.
The authors believe that the karstification process started from Early Pleistocene and is
still in process, as indicated from the shape and forms of the karst features (Figs.6, 7 and 8).
The successive rims with almost uniform patterns, indicate continuous collapsing of the
bedrock due to dissolution of the limestones, till the roof will collapse, forming a new
sinkhole. However, Ma'ala (2009a) claimed that the karstification started from Late Pliocene,
he attributed his assumption to the age of the Zahra Formation (Pliocene Pleistocene),
which is deposited in some karst depressions. The authors are in accordance with Ma'ala
(2009a) when the sediments of the Zahra Formation fill the karst forms, only.
Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115

Fig.8: Google Earth image showing successive rims in Zahra Formation
indicating continuous collapsing of the roof,
note the dense karst forms on the flat area (A)
and the developed doline in (B)
KARSTIFICATION INFLUENCE ON THE DRAINAGE SYSTEM
The studied area is gently sloping towards north and northeast, therefore, the main valleys
flow north and northeastwards. However, this main flow direction is often not followed by the
main valleys. Due to dense karstification, the main courses of valleys have different directions
with some abnormal drainage forms, such as bifurcation of valleys; downstream and their
junction again after certain distances. This is an exceptional drainage form (pattern),
indicating the presence of karst forms, either totally developed or under process. Figure (9)
shows a good example of abnormal valley, the main trend of the valley is towards northeast
(A), but it changes to NW SE (B) and ends in a circular depression (C). Moreover, the main
valley exhibits many bifurcations in its course before changing its direction to NW SE.
Another example of abnormal valley course is shown in Fig. (10), where the main valley
exhibits many polygonal and circular forms in its course. Moreover, each polygonal and/ or
circular form exhibits abnormal tributaries that have also abnormal forms, as compared to
a normal flowing valley. Such forms could not be developed unless the course of the valley is
under the influence of karstification, which had developed these abnormal forms, like
bifurcation of the valley downstream (A), polygonal forms (B), circular form with parallel
rims (C), in Fig. (10).
A
B
N
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.

Fig.9: Google Earth image showing abnormal valley course, note the change in the flow
direction (NW SE) and development of many circular and polygonal forms
due to karstification
Fig.10: Google Earth image showing abnormal valley due to karstification.
Note the bifurcation of the valley downstream in point (A),
polygonal forms in points (B), circular form with parallel crescent forms in point (C)
N
A
B
C
0.25 Km
A
C
B
B
N
Iraqi Bulletin of Geology and Mining Vol.8, No.2, 2012 p 99
115

Figure (11) shows another abnormal drainage system, where the course of the valley
hardly can be followed. The main flow direction is towards north and northeast, which can be
seen in point (A), but it changes its flow trend to different directions with abnormal forms.
Fig.11: Google Earth image showing abnormal drainage. The main valley trend is
towards NE, in point (A), abnormal forms in the points (B, C, D and E)
DISCUSSION
The studied area is covered by carbonates of Dammam and Zahra formations; the former
is densely karstified, due to high solubility and permeability of the carbonates, which
contributes in increasing the circulation of the water. The two formations are underlain by
anhydrite of the Rus Formation. During Pleistocene and even Late Pliocene, the climate in the
studied area was wet with high rainfall intensity, this had caused dissolution of the carbonates
in surface exposures, and in subsurface. Therefore, subterranean passages were developed and
enlarged continuously leading to collapse of the roofs and evolution of karst forms.
Because the karstification is very dense, in the studied area, therefore, the rock surface
could be considered as limestone pavement. The dens karstification had and is still
influencing on the drainage system, which shows abnormal forms, as compared with normal
drainage systems. Among the abnormal forms of drainage systems are: bifurcation of the
valleys; downstream and their junction together to form circular or polygonal shapes,
development of concentric and successive rims in the exposed rocks, the rims have the same
orientation of the already developed karst forms. Moreover, polygonal shapes are developed
in the valley courses, which indicate dens karstification of the bedrocks.
The karstification started most probably in Early Pleistocene, as indicated by the
concentric rims and multiple circular forms on the exposed rocks. However, the karstification
could be since Late Pliocene, as indicated from the presence of rocks of Zahra Formation
of Pliocene Pleistocene age.
B
C
D
E
N
Karstification Influence on the Drainage System Varoujan K. Sissakian et al.

CONCLUSIONS
The following can be concluded from this study:
The studied area is densely karstified, due to the presence of limestones of the Dammam
Formation, which is underlain by the Rus Formation, which consists mainly of anhydrite
and limestone.
The studied area is formed of limestone pavement, including "holokarst" and "merokarst"
forms.
Three karstification stages were recognized in the studied area.
The influence of karstification on the drainage system is clearly developed in the area, as
indicated from abnormal features, like bifurcation of the valleys downstream, presence of
successive parallel and concentric rims near depressions or valley banks, and different karst
forms of different shapes.
The karstification started most probably during Late Pliocene, accelerated during Early
Pleistocene, and is still in process.
ACKNOWLEDGEMENT
The authors highly acknowledge Mr. Hayder H. Taha for his skill work in presentation
of the Google Erath images and other figures in the text. The comments of Mr. Sabah
Y. Yacoub, which amended this article, are highly appreciated.
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About the authors
Mr. Varoujan K. Sissakian graduated from University of Baghdad in 1969
with B.Sc. degree in Geology, and M.Sc. in Engineering Geological Mapping
from I.T.C., the Netherlands in 1982. Currently, he is working as the Head of
Geology Department in GEOSURV and was nominated as Expert in 2005. He
has 118 documented reports in GEOSURV's library and 52 published articles
in different geological aspects. His major fields of interest are geological
hazards, geological maps and the stratigraphy of Iraqi territory. He is the
Deputy Vice President of the Middle East Subcommission of CGMW, Paris,
since February 2010.
e-mail: varoujan49@yahoo.com
Mailing address: Iraq Geological Survey,
P.O. Box 986, Baghdad, Iraq
Mr. Dhiya'a Al-Deen K. Ajar graduated from University of Baghdad in
1997 with B.Sc. degree in Geology, and joined GEOSURV in 2001, working
in the geological mapping groups. He was the project manager of Samawa
Geological Mapping Project. Currently, he is M.Sc. student in Baghdad
University.
e-mail: dialdeen2006@yahoo.com
Mailing address: Iraq Geological Survey,
P.O. Box 986, Baghdad, Iraq
Mr. Maher. T. Zaini graduated from University of Baghdad in 1994 with
B.Sc. degree in Geology, and joined GEOSURV in 1999. He got M.Sc. in
Structural Geology from University of Baghdad in 2006. Currently, he is
working as Project Manager of a mapping field group. He has 5 documented
reports and published articles. His major field of interest is structural geology.
e-mail: mahirzaini@yahoo.com
Mailing address: Iraq Geological Survey,
P.O. Box 986, Baghdad, Iraq
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Al-Salman Depression is one of the largest karst forms in the Southern Desert of Iraq. It is of doline type, being formed in carbonates of Dammam Formation of Eocene age. The length of the depression is 20 Km, whereas, the width is variable, it is (6.5, 10 and 4.5) Km, in the northern, central and southern parts, respectively, whereas, the depth ranges from (5 – 35) m. The Iraqi Southern Desert is one of the most extensive karstified areas in Iraq. Different types and forms of karst were developed with different sizes. Among the karst forms is Al-Salman Depression. The main reason of karstification is the presence of the carbonates of the Dammam Formation, which are underlain by the Rus Formation (Early Eocene); it consists mainly of anhydrite with limestone interlayers. The Pleistocene Period witnessed wet climate in the studied area, which had contributed in the karstification of the Iraqi Southern Desert, in which karst forms have played a big role in development of special landscape, which is characterized by special drainage system and enormous amount of closed depressions and blind valleys. Originally, Al-Salman Depression was consisting of three main depressions, which merged together due to karstification, head ward erosion and collapsing parts of the rims. The presence of the sediments of Zahra Formation (Pliocene – Pleistocene) in the Salman Depression indicates Pliocene and most probably uppermost Late Miocene age for the depression that has developed due to karstification and collapsing, which are still active processes. This age and genesis hold good for all those large depressions in the Iraqi Southern Desert.
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p class="Abstract">The purpose of this research is to mapping cavities in karst area in Temurejo Village, Karangrayung, Grobogan using geoelectric resistivity method and dipole-dipole configuration. Measurement consist of six lines using Multichannel S-Fields geoelectric instrument. Apparent resistivity data processing use two software, Res2DInv ver. 3.56.22 and Voxler 4.0. The result is lithology of the research location can be interpret consist of sand-silt, carbonate-silt rock, carbonate-sand rock, and carbonate rock with resistivity range 15,3-4919 Ωm. There are resistivity value anomaly in line of 1,2,3,4,5, and 6 on the carbonate rocks layer, the value is more than 4949 Ωm which can interpret as a cavity. On the first line, cavities are at depths of 20 m and 12 m, on second line are at depths of 17 m and 12 m, on third line is at depth of 19 m. Cavity continuously at depth of 18 m on fourth, fifth and sixth lines. This cavities at the depth >23 m beneath eath surface.</p
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The contact between the uplifted and subsided areas that represents the Neotectonic movements, which are presented by mean of contours, in West of Iraq, are revised and reconstructed. The contours, previously, were constructed depending on the contact between Fat'ha and Injana formations, which represents the last sea level during the Middle Miocene. The contours, in West of Iraq, are reconstructed depending on the top of the Nfayil Formation that is the equivalent of the Fat'ha Formation. Previously, the contours, in the extreme western parts of Iraq, where the Injana Formation is not exposed, were constructed depending on the bottom of the Zahra Formation. In this study, these contours are canceled, because the Zahra Formation is proved to be of Pliocene – Pleistocene age, therefore it is younger than the considered contact. The re-constructed contours, which are hypothetical, have different values, shapes and extensions, as compared to the previously constructed contours. The calculated rate of uplifting has changed too, depending on the values of the re-constructed contours. Many features indicating Neotectonic movements were recognized. Majority of them are related to active faults, dislocated drainage system and their control. These are indicated mainly using remote sensing techniques.
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The recorded geological hazards in different parts of Iraq are of 15 types. Although they are not well recorded and documented, but still a series of Geological Hazard Maps at scale of 1: 250 000 is compiled in the State Company of Geological Survey and Mining (GEOSURV) that covers the whole Iraqi territory in 39 quadrangles. Moreover, Geological Hazards Map of Iraq at scale of 1: 1000 000 is compiled too. Each of those maps is enclosed by a report in which the existing geological hazards are documented, zoned and ranked. Except the data of GEOSURV, and seismicity and meteorology, almost no other geological hazards data are available, in Iraq. This study depends mainly on the aforementioned maps, beside the available data concerning the geological hazards, like historical books, journals and field observation. Each type is zoned according to its Time of Occurrence and Intensity of Damages caused, consequently a weight is given, which differs in different areas, in Iraq, for the same type. The geological hazards are ranked according to the given weights, their distribution and total scored weights, in different parts of Iraq are demonstrated statistically. For each of the 15 recorded types of the geological hazards, examples are given, with documented damages in properties and lives lost. The damages and lives loss are also statistically demonstrated. Many hot spots were found in different parts of Iraq. The most dangerous and effective geological hazard was found to be the floods, in rivers and valleys, whereas the least effective one was found to be the Tectonic active areas. Two new classifications for the geological hazards are introduced. The natural radiation hazards are excluded from this study.
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The recorded geological hazards in different parts of Iraq are of 15 types. Although they are not well recorded and documented, but still a series of Geological Hazard Maps at scale of 1: 250 000 is compiled in the State Company of Geological Survey and Mining (GEOSURV) that covers the whole Iraqi territory in 39 quadrangles. Moreover, Geological Hazards Map of Iraq at scale of 1: 1000 000 is compiled too. Each of those maps is enclosed by a report in which the existing geological hazards are documented, zoned and ranked. Except the data of GEOSURV, and seismicity and meteorology, almost no other geological hazards data are available, in Iraq. This study depends mainly on the aforementioned maps, beside the available data concerning the geological hazards, like historical books, journals and field observation. Each type is zoned according to its Time of Occurrence and Intensity of Damages caused, consequently a weight is given, which differs in different areas, in Iraq, for the same type. The geological hazards are ranked according to the given weights, their distribution and total scored weights, in different parts of Iraq are demonstrated statistically. For each of the 15 recorded types of the geological hazards, examples are given, with documented damages in properties and lives lost. The damages and lives loss are also statistically demonstrated. Many hot spots were found in different parts of Iraq. The most dangerous and effective geological hazard was found to be the floods, in rivers and valleys, whereas the least effective one was found to be the Tectonic active areas. Two new classifications for the geological hazards are introduced. The natural radiation hazards are excluded from this study.
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Karstification is a common phenomenon in different parts of Iraq, where large areas are involved, causing severe damages to infrastructures and occasionally life losses. The main Karstified rocks are limestone and gypsum. The latter is restricted to the Fat`ha Formation, which covers considerable parts of Iraq, especially in the Al-Jazira vicinity. Whereas, the former is exposed in different formations that are exposed almost every where. Among the involved formations are Euphrates, Anah, Dammam, Ratgah, Pilaspi, Aqra – Bekhme, Qamchuqa… etc. Among Quaternary deposits, the gypcrete is another potential deposits that are highly karstified after being in contact, shortly, by water. The gypcrete also covers considerable parts in Iraq. Beside the economic lost caused due to karstification, some death causalities are also recorded. Moreover, in the Western Desert, karstification plays big role in miss leading the stratigraphic position of different horizons within different Jurassic and Cretaceous formations, making them in very complex situation, although they are in horizontal (not folded) position.
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The available geological information including stratigraphic sequence, unconformities pattern, drill-hole data, structural elements have been integrated to infer the tectonic and structural evolution of the Iraqi Southern Desert. The Southern Desert is a part of the northern Arabian Platform, where relatively thin Phanerozoic sediments cover the Precambrian NW – SE and NE – SW fractured continental basement complex. The platform itself is divided into two parts, a stable one to the west (Southern Desert) and unstable one to the east. The boundary between the two parts of the platform is taken along Euphrates Fault Zone (extension of Abu Jir Fault Zone). The Paleozoic sequence is reduced in the Southern Desert. Its composition and development is still unknown. The Mesozoic cover characterized by significant carbonate deposition with interspersed clastic episodes and is marked by few gaps in Campanian – Maastrichtian. However, the Cenozoic sequence displays gradual retreat of the sea and final transition to the continental conditions. The main structural element is Safawi Arch, which initiated in Late Triassic – Early Jurassic. The sedimentation pattern through the most of the Mesozoic era was a reflection to a fluctuating sea level and periodical movements of Safawi Arch. In the Tertiary, the main tectonic activities were periodical uplift and downwarp along the southeastern slope of Safawi Arch during Late Oligocene and Miocene periods which reactivated of Al-Batin fracture system, as well are contributed to formation of the Dibdibba basin and terminated by a limited right lateral strike – slip movement on Euphrates Fault Zone in Pliocene – Pleistocene period. Finally, conclusive evidences on the nature of Al-Batin fracture system were introduced.
The middle part consists of (5 – 6) m of silicified dolostone. The upper part (4 – 5 m) consists of well bedded limestone. The maximum thickness of the Upper Huweimi Unit is about
  • Of
m of dolostone, with chert nodules. The middle part consists of (5 – 6) m of silicified dolostone. The upper part (4 – 5 m) consists of well bedded limestone. The maximum thickness of the Upper Huweimi Unit is about (20 – 25) m.
This unit is exposed as continuous ridge from west of Wadi Abu Khamssat to the north and northeast of Salman town. It is characterized by high lateral variation in lithology
  • Shawiya
  • Unit
Shawiya Unit: This unit is exposed as continuous ridge from west of Wadi Abu Khamssat to the north and northeast of Salman town. It is characterized by high lateral variation in lithology. It consists of thickly bedded to massive limestone.