The Upper Miocene Injana (Upper Fars) Formation of Iraq

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Arab J Geosci (2009) 2:337-364
DOI 10.1007/s12517-009-0045-1
The Upper Miocene Injana (Upper Fars) Formation of Iraq:
insights on provenance history
Ali Ismail Abdulla Al-Juboury
Received: 18 August 2008 / Accepted: 14 April 2009 / Published online: 6 May 2009
# Saudi Society for Geosciences 2009
Abstract Petrographic, geochemical, and scanning elec-
Keywords Petrography . Mineral chemistry .
tron microscope analyses of the sandstone and mudstone
Upper Miocene . Iraq . Provenance history
units of the Upper Miocene Injana Formation are presented.
Furthermore, microprobe analysis for amphiboles, pyrox-
enes, garnet, and chromian spinels as common heavy
mineral species present is done to support other results for
better understanding of the provenance history of the Injana
The Upper Fars Formation was originally described in the
Formation. The sandstones of the Injana Formation consist
Fars Province of Iran by Busk and Mayo (1918), but
of terrigenous carbonate lithic fragments as common type
without a type locality in Iraq (van Bellen et al. 1959).
of sedimentary rock fragments in addition to chert,
Accordingly, Jassim et al. (1984) proposed the name Injana
argillaceous, and rare sandstone fragments. They also
Formation to replace the Upper Fars Formation in Iraq and
include metamorphic and igneous lithic fragments, quartz,
defined a subsidiary type section near Injana, at Jabal
feldspars, and mica and generally, the sandstones are lithic
Hemrin South (near the old police station along Baghdad-
arenites and immature. Scanning electron microscopic
Kirkuk Highway, 120 km NE of Baghdad). This recom-
analysis for the heavy minerals shows that they have been
mendation was published by Al-Rawi et al. (1992) and
affected by dissolution due to chemical etching and
adopted by other authors (e.g., Jassim and Buday 2006) and
mechanical abrasion through several surface texture gener-
herein. The Upper Miocene Injana Formation exists in Iraq
ated either in arid and semihumid environment or in
widely; it also extends into northern Syria, Turkey, and over
diagenetic environment. Clay mineralogy of the mudstone
large areas in southern Iran (van Bellen et al. 1959; Jassim
units indicates the presence of illite, chlorite, kaolinite,
and Buday 2006; Fig. 1a). It is basically described as
palygorskite, and illite-smectite mixed layers. Bulk-rock
subcontinental to continental coarse and medium-grained
and mineral phase geochemistry in addition to petrographic
carbonate-rich sandstone alternating with brownish red
data suggest the derivation of the Injana Formation from a
siltstones, mudstones, and marls with rare freshwater
nearby sources with contribution from igneous, metamor-
limestone (van Bellen et al. 1959; Jawad Ali et al. 1988;
phic, and sedimentary provenance mainly from the high
Figs. 1 and 2). Because of its wide distribution, the Injana
lands in the northeastern parts of Iraq which comprise
Formation has been described in numerous papers, books,
mainly the Zagros mountains and the older sedimentary
reports, and academic dissertations (e.g., van Bellen et al.
1959; Basi 1973; Yakta 1976; Yaqub 1977; Al-Sammarai
1978; Buday 1980; Al-Banna 1982; Al-Maroof 1986; Al-
Kurukji 1989; Othman 1990; Al-Juboury 1994; Al-Fattah
2001; Al-Haidary 2003; Al-Rashedi 2005; Mahdi 2006;
Jassim and Buday 2006 and many others), the majority of
A. I. A. Al-Juboury (*)
which focused on geological overviews of the formation
Research Center for Dams & Water Resources, Mosul University,
and/or provided descriptions of its lithofacies, sedimentol-
Mosul, Iraq
e-mail: [email protected]
ogy, and depositional environments.

Arab J Geosci (2009) 2:337-364
Fig. 1 a Location map showing the Mesopotamian Basin in Iraq and
section), 12 Habaniya). Also shown is an isopach map of Late
simplified Late Miocene lithofacies distribution after (Bolton 1958;
Miocene-Pliocene; Injana, Mukdadiya, and Bai Hassan formations in
Dunnington 1958; Buday 1980; Jassim and Karim 1984; Ziegler 2001;
Iraq (after Dunnington 1958), distribution of Injana outcrops in Iraq
Jassim and Buday 2006). b Location of 12 studied sections (1 Khand,
(after Bolton 1958), and tectonic provinces (after Numan 1997)
2 Sheikhan, 3 Aqra, 4 Bashiqa, 5 Aski Kalak, 6 Bastora, 7 Hasarok,
8 Sinjar well KH 8/9, 9 Makhul, 10 Hemrin north, 11 Injana (type
This paper starts with a general survey of several of
Heavy minerals are separated from 25 sandstone samples
these previous studies. It then examines in greater detail the
from both sections by the traditional gravity method using
petrography, geochemistry, and mineralogy of the Injana
bromoform (CHBr3, specific gravity 2.89). Heavy minerals
Formation in Iraq as implications for provenance history.
from the very fine to medium (63-250m) size fraction
were separated in order to avoid the worst effects of the
varying density, shape, and size of different heavy minerals
Sampling and methodology
in causing hydraulic differentiation (Hubert 1971). Three
hundred grains from each sample were counted as
The present study takes into consideration 12 sections in
described by Mange and Maurer (1992). The surface
northern and central Iraq for the study (Fig. 1b), whereas
textures of the studied heavy minerals are studied by
section 1, Khand, and section 4, Bashiqa (Fig. 2), were
scanning electron microscopy.
studied in detail. From these two sections, 75 samples were
collected from the sandstones (53 samples) and mudstones
(22 samples) for petrographic, mineralogical, and geochem-
Paleogeography and lithostratigraphy
ical analysis. Selected samples were analyzed by scanning
electron microscopy (SEM; using Camscan MV 2300 SEM
The paleogeographic setting of northern Iraq was highly
with a calibrated energy dispersive X-ray analysis system)
affected by the collision of the Arabian and Eurasian plates
and X-ray diffraction (using D8 Advance [Bruker axs] with
and their related effect on the accumulation and disturbance of
Cu- radiation). Geochemical analysis of major and trace
the sedimentary cover. In Late Miocene-Pliocene time, major
elements, for selected samples, was made using a Siemens
thrusting occurred during collision of the Neo-Tethyan
SRS 303 X-ray fluorescence spectrophotometry, whereas
terranes and the Sanandaj-Sirjan zone with the Arabian Plate.
microprobe analysis for selected heavy minerals were done
This event resulted in the uplift of the High Folded, Northern
using CAMEBAX microprobe. All these analyses took
Thrust Zone, and Mesopotamian zones (Figs. 1 and 3).
place at the Mineralogical and Geological Institutes of
During the Late Miocene and Early Pliocene, a close of
Bonn University, Germany.
the Neo-Tethys Ocean by the collision of the Arabian and

Arab J Geosci (2009) 2:337-364
Fig. 1 (continued)
Eurasian plates (Central Iran and Turkey, Turkish/Iranian
After the end of the Middle Miocene, the sea started
Plate; Fig. 3) took place, and the Zagros and Taurus
its final regression from the Iraqi territory leaving
Mountain belts started to be uplifted (e.g., Buday and
behind as it regressed a trail of shoreline marine clastics
Jassim 1987; Al-Sharhan and Nairn 1997). Between these
represented by the basal part of the Injana Formation
two tectonic events, starting in the Late Eocene and
(Middle Fars, this term has been considered previously
continuing through the Miocene, crustal loading and flexure
for the basal part and is no longer used with geological
of the eastern Arabian Plate formed the broad and shallow
survey and now is representing the lower part of the
Mesopotamian Basin as a NW-oriented foreland basin
Injana Formation) followed behind by fluviatile sedi-
(Jordan 1981; Allen et al. 1986).
ments deposited on the newly emerged land areas. Both

Arab J Geosci (2009) 2:337-364
Fig. 2 Composite lithologic section of Injana Formation in the Khand (a) and Bashiqa (b) sections (see Fig. 1 for locations). It also illustrates the
depositional setting, higher-order sequences, and sample locations

Arab J Geosci (2009) 2:337-364
Fig. 3 Late Miocene-Pliocene
paleogeography (modified after
Jassim and Buday 2006)
illustrating the main
stratigraphic units deposited
during this time period
these facies are recognized in the Injana Formation
Dibdibba Formation (Upper Miocene-Pliocene) exposed
(Jassim and Karim 1984).
in southern and central parts of Iraq (Fig. 3) consists of a
Injana Formation characterizes basically by a clastic
mixture of gravel and sand. In the northwestern part of
sequence that consists of fining upward cyclothems of
Iraq, especially in Sinjar area, the formation exists
carbonate-rich sandstones, siltstones, and claystones depos-
scarcely and covered by thick alluvial fan deposits. The
ited dominantly in fluvial, coastal, and near-shore river
formation was deposited in fluviatile environment with a
environments (Al-Banna 1982; Al-Juboury 1994). The
general current flowing from southwest to northeast, i.e.,
sinking of the basin can be noted from Middle Miocene
the source area could be the Arabian Shield to the
as indicated by gradual change in the deposition from
southwest (Al-Rawi and Sadik 1981). The upper part of
claystones, silty claystones, and fine sandstones (in the
the Injana Formation consists of molasse type sediments
upper part of the Fatha Formation) to the sedimentation of
of cyclic alternations of fining-upward sequence, whereas
clastics (mainly sandstones of Injana Formation) through
the lower part taken as a transitional zone (Basi 1973;
Pliocene which caused the deposition of coarse clastics of
Buday 1980). But the general sequence tends to be
Mukdadiya (formerly Lower Bakhtiari Formation) and then
coarsening upward, which may related to increasing
coarser clastics of Bai Hassan (formerly Upper Bakhtiari
tectonic activity in the type area (Basi 1973).
Formation) filled it. The derived materials came from the
Figure 1b illustrates the combined thickness of the
rising Zagros basin (Sissakian and Youkhana 1978).
Upper Miocene Injana and the Pliocene Mukdadiya and
The Injana Formation crops out in the northern,
Bai Hassan (formerly Bakhtiari) formations. The thick-
eastern, and central Iraq and trending in NW-SE
ness of the Injana Formation varies and reaches
direction but loses its identity probably in the Dibdibba
2,000 m in places. The formation lies in the foothill
Formation, in south Iraq (van Bellen et al. 1959). The
zone area, but interrupted by the Mosul High where the

Arab J Geosci (2009) 2:337-364
Fig. 4 a Regional correlation
between the Tertiary formations
in Syria, Iraq, Kuwait, and Saudi
Arabia (after James and Wynd
1965). b Regional correlation in
the Middle East by Goff et al.
(1995) based on Haq et al.
(1987). c Sequence interpreta-
tions and correlations for Iraq
after Jassim and Buday 2006. In
the present study, the Injana
Formation is interpreted as a
third-order depositional se-
quence of Late Miocene
(Serravallian) age

Arab J Geosci (2009) 2:337-364
formation relatively thin, which measure about 600 m as
basement faults reactivated throughout the Cenozoic Zagros
Orogeny not only within the Zagros fold and thrust belt but
The deposition of fluviatile Injana (Upper Fars) Forma-
also on the Arabian platform. This model also suggests that
tion in the foreland basin of Iraq in the Upper Miocene
the propagation of deformation front due to the collision
marked the end of marine conditions in northern Iraq. This
between Arabian and Iran-Turkey plates and reactivation of
gradual change from marine to continental sedimentation
basement faults controlled syntectonic sedimentation in the
shows itself as a common feature of the deposition in
Zagros foreland basin. Uplifting due to folding and faulting
foreland basins (Allen et al. 1986). The evolution of the
in these areas affect on the thickness variation of the Late
basin fill in a foreland basin system in terms of sedimentary
Miocene-Pliocene succession. However, abrupt increase in
environment, succession thickness, and vertical trends
thickness of Aghajari (Injana) and Bakhtiari (Mukdadiya
depends strongly on the degree of compressional tectonic
and Bai Hassan) formations in Kirkuk embayment refers to
activity (Munoz-Jimenez and Casas-Sainz 1997). As the
a considerable subsidence of this area than its surroundings
foreland basin develops and fills with sediment, the main
(Motiei 1993).
trend is that of shallowing and coarsening of the sediment.
Figure 4 summarizes various chrono- and sequence
The Middle Miocene Fatha Formation (formerly Lower
stratigraphic interpretations and correlations of the Injana
Fars Formation) underlies the Injana Formation gradation-
Formation and bounding units. Figure 4a indicates the age
ally, whereas the formation overlain by the Mukdadiya
assignments and regional correlations from James and
(formerly Lower Bakhtiari Formation). The contact is also
Wynd (1965) and Goff et al. (1995). According to eustatic
gradational, conformable marked by an appearance of
curve of Haq et al. (1987; Fig. 4b), the Injana Formation
gravel-bearing sandstone of Pliocene age (van Bellen et
forms a base of third-cycle megasequence in 3.3 sequence
al. 1959; Jawad Ali and Khoshaba 1980; Al-Rawi et al.
of early Late Miocene age. The Serravallian age can be
interpreted by Jassim and Buday 2006 for the Injana
Formation (Fig. 4c). In the Late Miocene, the main tectonic
event is the Alpine collision and final folding and thrusting
Regional setting
with common regression in sea level (Fig. 4c). The Injana
Formation could be correlated also with the lower part of
The Injana Formation is widely exposed in Iraq mainly in
the Dibdibba Formation in south part of Iraq and in Kuwait,
northern and central parts. The formation also exists in
while the age correlative in Saudi Arabia is the Hadrukh
Syria (where it still named Upper Fars, Ejel and Abdul
Formation (Lababidi and Hamdan 1985).
Rahim 1974), in Turkey (the Siirt Series is the correlative
In Iraq, based on stratigraphic position, the Upper
units, Brinkmann 1976), and in Iran (where the name Upper
Miocene age is considered for the Injana Formation. A
Fars being abandoned and the Aghajari Formation replaced
lack of detailed studies on age determination can be noticed
it, James and Wynd 1965).
due to nonabundance and not well preservation of fossils
In the Miocene, shallow marine sediments covered the
within the clastic succession of the Injana Formation,
northern Arabian Plate with the exception of the tectoni-
whereas in Syria, the accepted age is the Upper Miocene-
cally affected zones along the northern and eastern margins
Lower Pliocene (Messinian-Zanclean). Therefore, the
of the Plate (Ziegler 2001). During Late Miocene, the
formation is diachronous in age (Lababidi and Hamdan
renewed nappe activity in southern Turkey, Selmo and
Upper Fars (Injana) Formations red-bed clastics spilled
onto the shallow marine carbonates platform carbonates
(Silvan-Germik formations, Middle Miocene, the equiva-
Lithofacies and depositional settings
lent of the Fatha, Lower Fars Formation in Iraq; Ziegler
The lithofacies association of the Injana formation in Iraq
In Iran, the Aghajari Formation consists of sandstones
by many workers and in the present study has revealed that
and siltstones in a fining upward point-bar and flood-plain
two sequences could be recognized for the deposition of the
sequence and overlies by Bakhtiari Formation which
formation, the lower being the transitional facies between
comprises massive conglomerate deposited in braided
the underlying marine evaporitic Fatha (Lower Fars)
rivers on proximal alluvial fans in a piedmont zone (Elmore
Formation, and the continental (fluvial) facies in the upper
and Farrand 1981). A tectonosedimnetary model proposed
part of the Injana Formation (Fig. 2).
by Bahroudi and Koyi (2004) for the Lower Miocene
The transitional facies overlies the last gypsum bed of
Gachsaran Formation explains the characteristics of sedi-
the underlying Fatha Formation. Generally, it consists of
mentation in the Late Miocene-Pliocene Aghajari and
coarsening-upward sequence of very fine sandstones, silt-
Bakhtiari formations. This model has assumed that the
stones, and mudstones with thickness range from 25 to

Arab J Geosci (2009) 2:337-364
130 m in north and northeastern Iraq. Rock units within
individual cycle are characterized by fining-upward se-
quence consisting of coarse sediments that are mainly
medium-grained sandstone of rapid sedimentation overly-
ing erosional lag deposits. Bioturbation common in this
facies can be interpreted by scattered and tabular burrows
that may form by pelecypod activity. This type of
burrowing is common in tidal and lacustrine environments
(Swinbanks and Murray 1981).
The tidal sequence of the lower transitional unit of the
Injana Formation has been studied in detail in Hemrin
mountain area of central Iraq (Jawad Ali et al. 1988; Al-
Kurukji 1989; Jawad Ali and Hadi 1989) and in many
sections of Injana Formation in northern Iraq (Al-Banna
1982). Similar conclusions have been reached by many
researchers on this unit in other parts of north and central
parts of Iraq. Two main subenvironments could be observed
in the transitional unit according to lithology and sedimen-
tary structures: intertidal and subtidal. The latter one is
further divided into ebb and flood-dominated channel
This sequence started with gray marl rich in pelecypods
and interbedded with thin limestone lamina at the base
(Fig. 2b) and overlain by very fine sandstone, siltstone, and
mudstones with common bioturbation. Several medium-size
grain sandstone beds occur each of 30 cm thick. The contact
between these beds generally is erosional with small mud balls
of 1.5 cm diameter. Small-scale cross-bedding oyster is
occasionally observed. Above this succession fine sandstones
and claystone with few marl lenses occur containing planar
and trough small-scale cross bedding. An overall coarsening-
upward cycling could be distinguished (Fig. 2b). This
deposition refers to tidal-dominated deltaic deposition
(Reineck and Singh 1980; Miall 1996).
The main characteristic features of the observed subtidal
subenvironment include the fining-upward sequence. This
sequence commonly overlies an erosional (scoured) base
and started with medium- to coarse-grained sandstone
including large-scale trough cross bedding. This facies is
overlain by medium-grained sandstone with planer cross
bedding followed by fine-grained sandstones with common
horizontal cross-stratification (Fig. 2).
The upper fluvial facies is dominated by sandstones with
subordinate siltstones and mudstones. Sandstones generally
are medium to coarse grained at the base and very fine
sandstones and siltstones at the top of the sequence forming a
fining-upward sequence. The observed sedimentary structures
in the coarser sandstones are dominated by medium to large
trough cross bedding, whereas planar cross bedding and ripple
laminations are common in the upper finer clastics (Fig. 2).
Generally, the characteristic features of these sand-
stones suggest fluvial channels filled with point bar
sands (Miall 1996). This fluvial deposition can be divided

Arab J Geosci (2009) 2:337-364
Fig. 5 Photomicrographs of selected sandstone samples of Injana
talline quartz grains (Qp), chert (Lch), carbonate (recrystallized) lithic
Formation. a Monocrystalline (Qm), both well rounded and angular,
fragments (Lc), and rare occurrence of secondary silica cement
and polycrystalline quartz (Qp) grains; squeezed argillaceous lithic
(arrow), pores (p). d Well-rounded carbonate lithic fragment (Lc)
fragment (La), metamorphic lithic fragment (Lm), note the presence of
and sever alteration of plagioclase feldspar to clay minerals (arrow).
plagioclase feldspar (arrow) partly replaced by carbonate and common
Dissolution of unstable grains resulting in secondary porosity (p).
chert (Lch) and pores (P). b Both fresh (black arrows) and altered
Samples S4 and 11, section 4--Bashiqa. See Fig. 2 for sample location
feldspar (white arrow) grains with rounded quartz (Qm). c Polycrys-
into meandering and braided river environments and their
zontal laminas of silty and muddy sandstone and, finally,
subenvironments, namely, channel lag deposits which
the flood plain subenvironment as represented by massive
include intraformational conglomerate at the base of
mudstone unit.
fluvial cycle. This channel lag deposits may represent
the high-stand sequence at the beginning of new fluvial
cycle (transgressive sequence system track; Fig. 2). The
Petrography and diagenesis
fluvial cycle includes point bars deposition as indicated
from the presence of trough, planar, and rippled cross-
Sandstone framework petrography
bedded sandstone units and terminated by massive mud-
stones and siltstones. Crevasse splay subenvironment is
Petrographic investigation with the help of modal analysis
recognized by massive sandstone interbedded with hori-
for the estimation of the composition of sandstones indicate

Arab J Geosci (2009) 2:337-364
Fig. 6 Photomicrographs showing the main constituents and diage-
calcite (red colored) and filling veins in quartz (white arrow), clayey-
netic processes of the Injana sandstones. a Chert of microcrystalline
ferruginous cementing materials (black arrow), rounded carbonate
(Lch) and radiolarian (black arrow) types; rounded carbonate lithic
lithic fragment (Lc), argillaceous lithic fragment (La), well-rounded
fragment (white arrow), mono (Qm)- and polycrystalline quartz (Qp),
and angular monocrystalline quartz grains (Qm), and feldspar (F).
and altered feldspar (K). b Angular monocrystalline quartz (Qm),
Partial and complete dissolution of unstable grains (feldspars and lithic
rounded carbonate lithic fragments (Lc), and microcrystalline chert
carbonate fragments resulting in secondary porosity (P), sometimes
fragment (Lch). c, d Stained sample with alizarine red S, note the red
the porosity is selective as it dissolves part of fossil (Fs)). Samples S9
color for calcite cementing materials. Replacement of quartz with
and 16, section 1--Khand, see Fig. 2 for sample location
that they are mainly lithic arenites. Injana sandstones
fine-grained and angular to subrounded. Some of them are
generally are fine grained, moderately to well sorted. The
well rounded (Fig. 5a), representing reworked quartz.
sandstones are composed of three main detrital constituents
Straight to slightly undulose extinction is present, suggest-
(Table 1).
ing a plutonic igneous origin. Quartz grains may be with or
Quartz (Q) generally is less in the studied samples with a
without inclusions. The most common inclusions represent
mean value of 9.7 (10.37 and 9.03 for Khand and Bashiqa
zircon, rutile, iron oxides, and vacuoles that are distributed
sections, respectively; Table 1). Both monocrystalline
in oriented or random pattern suggesting a metamorphic
quartz (Qm) and polycrystalline quartz (Qp) occur through-
and plutonic igneous origin (Folk 1974; Pettijohn et al.
out the sequence. The Qm is generally medium- to very

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