Download Cenozoic Formations from Erbil to Kore

Salahaddin University
College of Science
Geology Department
Cenozoic Formations
from Erbil to Kore
1-
Upper Bakhtiari Formation (Bai Hassan):
This formation is the youngest formation inIraq.Tectonically located in Foot Hill Zone,It
consists
of
molasses
sediments
(The
term
"molasse"
refers
to
the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in
front of rising mountain chains. The molasse is deposited in a foreland basin)It is largely
made up of coarse and thick fluviatile and estuarine conglomerates, products of erosion of the
rising mountain--ranges-, deposited –mane or more sinking through in front of those
rangesThe formation is composed almost purely of terrigenous clastics from silt size to
boulder conglomerates. In general, the grain size of the clastics increases upward (fining
upward means that the grain size is decreasing upward in the sandstone core/rock/outcrop.
Coarsening upward means that the grain size is increasing upward. In order to deposit coarser,
heavier grains, the hydraulic energy must be higher (faster flowing water) than the energy
required depositing fine grains). (Fig.1)
Conglomerates of considerable thickness are bound on the upper part of the
formationClaystones are reddish brown, pale brown, grayish, in colors, fairly hard when
wellcompacted, usually weathered and fragmented. Variations from claystone to siltstone and
sandstone, horizontally and vertically were observed.
The thickness of the formation is difficult to measure due to wide covered areas of the
formations outcrop. The top of the formation is always weathered. The total thickness of this
formation within the studied region is varying from one place to another and is about 300 to
850m. The lower contact of the formation with underlying Mukdadiya Formation is
diachronous (Buday, 1980); It.is recognized lithologically by the appearance of the first thick
(more than 1m) conglomerate horizon (Sissakian & Youkhanna, 1978).
The age of the formation is mostly Pliocene. There are, indeed, no proofs here if the
formation does not include parts of the uppermost Miocene at the bottom or of the early
Pleistocene at the top.The Upper Bakhtiari formation overlies the Lower Bakhtiari formation.
The contact is probably markedly diachronous, as structures continued to rise throughout the
deposition of these two units.The upper boundary is erosional. The formation is overlain by
terrace gravels and/ or alluvial deposits.
Fig.1 Upper Bakhtiari Formation at Bastora area northern Iraq show coarsen upward
2-
Lower Bakhtiari Formation (Mukdadiya)
Pliocene formation, widespread in northern Iraq,located in Foot Hill Zonethe great thickness
of these molasse-like sediments was deposited in rapidly sinking troughs in front of rapidly
rising mountains. The constituents of the formation are the product of the erosion of these
mountains. Due to this mode of origin the thicknesses' are rather variable.Upper Bakhtiari
formation. This is fixed normally - at the first appearance of the massive conglomerates which
typify the Upper' Bakhtiari in contrast to the sands and grits and pebble beds or the Lower
Bakhtiari.
The formation is exposed in some synclines of the studied such as in the northeastern limb of
the Mirawa (Mawaran) syncline, and the southwestern limbs of Pirmam anticline. The
formation consists of cyclic deposits of clastic material fining upwards. The cycle starts by
claystone, pebbly sandstone and thick layers of the conglomerate, (fig.2) in some other places it
start by pebbly sandstone, thin beds of the claystone and thick beds of the conglomerate.
The lower contact of this unit, with the Upper Fars formation, is marked by the disappearance
of pebbles downwards. This is without doubt a diachronous boundary.
The same can be said for the upper limit, which is with the Upper Bakhtiari formation. This is
fixed normally - at the first appearance of the massive conglomerates which typify the Upper'
Bakhtiari in contrast to the sands and grits and pebble beds or the Lower Bakhtiari.
The thickness of the formation is 500m on the southwestern limb of Pirmam anticline.
Fig.2 lower Bakhtiari Formation at Bastora- northern Iraq show grain size change
3-
Upper Fars Formation (Injana):
Joints form in solid, hard rock that is stretched such that its brittle strength is exceeded (the
point at which it breaks). When this happens the rock fractures in a plane parallel to the
maximum principal stress and perpendicular to the minimum principal stress (the direction in
which the rock is being stretched). This leads to the development of a single sub-parallel joint
set.The formation consists mainly of clastics sediment, which in general coarsens upwards.
The dominant color of the clastics is red color,consists of sandstone& mudstonefig. (3) The
mudstone is occasionally silty with some thin horizons of interbedded siltstone, which are
reddish brown. Soft to fairly hard, weathered in some places usually covered by soil, this is
silty and sandy. Fracturing and Jointing are well developed in the sandstone fig. (4). the
sandstones are rich in sedimentary structures among them, mud balls; cross bedding(ross beds
can tell geologists much about what an area was like in ancient times. The direction the beds
are dipping indicates paleocurrent. The type and condition of sediments can tell geologists the
type of environment (rounding, sorting, composition), ripple marks (Current ripple
marks, unidirectional ripples, or asymmetrical ripple marks are asymmetrical in profile, with
a gentle up-current slope and a steeper down-current slope. The down-current slope is
the angle of repose, which depends on the shape of the sediment. These commonly form
in fluvial and aeoliandepositional environments, and are a signifier of the lower part of the
Lower Regime. Ripple cross-laminae forms when deposition takes place during migration of
current or wave ripples); and burrowings are common,Figs. (5&6)
The upper contact of the formation islower Fars formation is conformable which is
recognized in the field by the uppermost limestone horizon the lower contact with lower
Bakhtiari Formation at this area.
Fig.3-Upper Fars Formation at Banaman
Fig.4-Join and fracture in upper Fars Formation
Fig. 5 -Cross bedding in upper Fars Formation
Fig.6- Ripple mark at Fars Formation
4-
Lower Fars Formation (Fatha):
The Lower Fars is well defined formation in the northern parts of the country;the age of the
formation is Middle Miocene and the unit, according to Ponikarov at (1967).
Geomorphologically the formation forms hilly area with continuous ridges of thick limestone
forming cuesta and hogback features around most of the anticlines.
The formation in this area consists mainly of limestone and marls with lenses of
gypsum (fig.7) as in the southwestern limb of Safin anticline. The claystone is the main
constituent of the formation; the claystone is soft fragmented into small chips, occasionally it is
silty conchoidal fracturing is common in the claystone. The limestone is also one of the main
constituents of the formation. It is light gray, white, light brown, hard, well bedded, some of
beds are fossiliferous, and fossils are mostly shells of Pelecypods and gastropods. Others are
recrystallized, sandy limestones are common, more towards the lower parts of this formation,
and some of the limestone beds are underlain by green marl or marly limestone.
The lower limit of the formation in northern Iraq is marked by a' prominentconglomerate,
known informally as the Basal Fars Conglomerate (upper Fars Formation)
The lower contact of this formation with the underlying Pila Spi Formation is
unconformable marked by presence of basal conglomerate, the thickness of this basal
conglomerate ranges from 1 m as in the case of Pirmam anticline to 2.5m in the Bina-Bawi
anticlines.
Figure (7) Lower Fars Formation near Pirmam anticline
5-
Pila Spi Formation:
The formation consists mainly of limestones, which are crystalline, dolomitic, clayey or
chalky. The color is white, creamy, light gray, and well bedded (fig.8). Sometimes it is seen as
continuous high ridges surrounding the anticlinal structures with very common flat iron
morphology, while in the other places it forms the carapace of main body of the anticline as in
case of the Pirmam Anticline.
The lower most part of this formation consistsof conglomerate, which marks theunconformable
contact with the underlying Gercus Formation fig. (9). this conglomerate consists of chert
pebbles, chalcedony, flint, jasper, some igneous rocks and limestone also occur. The maximum
thickness of the conglomerate beds reaches up to 10m, such as near Shaqlawa City.
The thickness of the formation is highly variable, generally increasing toward the
southeast and south of the studied region and it ranges from 5m up to 90m. The formation is
deposited in a lagoonal environment (Bellen et al, 1959). The upper" and / or “middle" Eocene
age is accepted.
Figure (8) well bedded limestone of Pila Spi Formation at Pirmam anticline
6-
Gercus Formation:
The formation consists of red clastic rocks, which are mainly claystones, siltstones, and
sandstones with thin horizons or lenses of conglomerate that vary vertically and laterally.
This formation is of Middle Eocene age (Buday, 1980), is exposed in all the mapped structures
of the studied region. It generally forms steep slopes below the hard limestones of Pila Spi
Formation, Soft rocks are the main constituents of this formation; hence it is dissected by a
dense drainage pattern, which forms parallel rills and galleys, When the slopes are gentler the
rocks are mainly weathered and covered by red soil.
The main rock type of this formation is the claystones, which are reddish-brown, brown and
rarely violet, rich in iron oxide nodules. Limestone horizons may occur within this formation.
These limestone beds represent short-lived marine incursions and are supposed to be equivalent
of the Avanah Formation of Middle Eocene (Sissakian and Youkhanna, 1978).
Thickness of this formation In Safin Anticlines the thickness of this wide spread formation
becomes 120m. Underlying formation and details of contact the formation covers Kolosh
formation. The contact appears to be gradational, Overlying formation and details of contact The Pila Spi limestone formation
Fig. (9) Contact between Pila Spi & Gercus Formations near ShiraSwar area
7-
Khurmala Formation:
This formation, found as a series of ridges around most of the anticlinal structures in the
studied region, belongs to the Early Paleocene - Early Eocene time span (Bellen et al., 1959). It
consists of limestone which is dolomitic, crystalline, and fossiliferous. Fossils found within this
formation are some large gastropods whose lengths reach up to 20cm. The color of the
limestone beds is yellow, in some localities creamy, well bedded, the thickness of individual
beds ranges from 0.5-3.0m, and the beds are relatively hard, because they are overlain and
underlain by soft materials (clastics). They always form ridges and scarps over the whole area.
At the vicinity of Shaqlawa town, one or two horizons of limestone occur, with one horizon of
clastics. The thickness there is 3-12m, but it starts thickening toward the southeast and
northwest of the studied region. In the southwest limb of the Harir Anticline the thickness of
this formation become 8-15m.
Fig. (10) Khurmala Formation at Korea area
Fig. (11) Fossiliferous limestone of Khurmala Formation in ShiraSwar
8-
Kolosh Formation:
This formation is exposed in all the structures of the high folded zone, within the
mapped region. Generally it forms gently elevated areas, which are dissected by dense drainage
system, due to the predominance of the soft rocks in the formation. The formation consists of
clastic rocks that are dark gray and black in color. The rocks are shales, claystones, sandstones,
siltstone with conglomerate. The age of this formation is Paleocene - Lower Eocene (Bellen et
al., 1959).
The sandstone beds are generally dark gray or black in color, friable, medium to coarse
grained with very small amount of quartz grain. They consist mainly of dark minerals with
large amount of clayey cementing materials. The thickness of the sandstone beds ranges from
0.25m up to 3m. Occasionally they are pebbly; the pebbles are small in size, not more than 23cm. The conglomerate beds have thicknesses of about1-2 m with pebbles, not more than 4cm
in size. The pebbles are mainly of limestone and cherts, spherical in shape, sorted and rounded.
They are poorly cemented with sandy and clayey materials, and occasionally bituminous. The
shales and claystones of this formation are soft papery and fragmented, and are weathered. The
thickness of the formation is variable and increases southeastwards. In Shaqlawa its thickness
ranges between 140 and 180m. In the upper part the formation consists in most localities of thin
layers of marly limestone, marls, and shales with thicknesses of 3-5m. Dolomitic limestone
beds representing the Khurmala Formation are interbedded within the Kolosh Formation.
In Safin anticline the appearance of thin bedded sandstone is considered to be the contact
between this formation and underlying Shiranish Formation (Hana, 1993). The upper contact of
the Kolosh Formation is gradational with the Khurmala Formation, The total thickness of the
Kolosh Formation is variable; it increases towards southeast of the investigated region
Figure (12) Kolosh Formation