Paleocene Stratigraphy in Aqra and Bekhme Areas, Northern Iraq

The Paleocene Kolosh Formation of Iraq is comprised of flysch deposit of sandstones, marls, shales, intraformational conglomerates and thin beds of arenaceous limestone, deposited in subduction trench, parallel to the suture zone formed by closing of the southern Neotethyan ocean and finally collision between the Arabian, Anatolian and Iranian plates, extended North West-South East, from Mushorah (NW) to Kashti (SW) (van Bellen et al., 1950 and Jassim and Buday, 2006) (Figure 1). Kolosh Formation is coeval with several other formations in other parts of Iraq. These formations are diachronous and define according to lithology. In north Iraq, it is pass to or inter-tongue with algal reef limestone (Sinjar Formation) and reef back reef deposit (Khurmala Formation) (van Bellen et al., 1959), moreover, a different set of paleocene formations are used in central, western and southern Iraq: Aaliji, Akashat and Umm Er Radhumma formations. The complex lithostratigraphy relationships between these units are not suitable for correlation and best resolved by biostratigraphy and sequence stratigraphy.

pelecypod and gastropod. The source of the carbonate rock fragments is believe to be from the underlaying Mesozoic carbonate rock of the Arabian shelf, which are less resistant, accordingly they can not sustain long distances of transportation. The large content of carbonate rock fragments requires high relief and rapid erosion (Pettijohn, 1975).
Chert rock fragments are microcrystalline and cryptocrystalline (Plate 1-6), the grains are mostly angular with sharp to subsharp edges indicated to nearby source, the source rocks should be the radiolarian cherts of the Cretaceous Qulqula series and the carbonate formations include chert nodules.
The metamorphic (Plate 1-7) and igneous rock fragments show low content, indicating to the paucity of these rocks in the source areas, accordingly heavy minerals found with less amount.

Matrix and cement
The carbonate cement form the abundant type of cement in all sandstones of Kolosh Formation, it occurs as microspar and sparry mosaic cement (Plate 1-8). The matrix consist of clayey -silty grains that filled the interpartical vugs (Plate 1-9), it embrace clay minerals in addition to quartz, feldspar and mica minerals.

Sedimentary facies
The studied Paleocene succession in Bekhme section consist of Kolosh and lens of Sinjar formations, while in Aqra section only Kolosh Formation was recognized.

Facies and depositional setting of Kolosh Formation
The Kolosh Formation contains six facies, donated K1 to K6, for which sedimentological and biological evidences are used to determine their depositional environment and bathymetry. Plate 1.

Lime mudstone facies K1
The facies represent thin bedded limestone with thickness ranging between 5 -10 cm, dark grey color. The facies has a mud supported texture and allochems make up to 10% of the total contain (Plate 2-1). The predominant allochems are planktonic foraminifera represented by Parasubbotina pseudobulloides, Praemurica pseudoinconstans and Subbotina triloculinoides. The few miliolid, pelecypod and gastropod are recorded. Extraclasts of quartz and chert are record. The matrix consist of micrite and microspar. Carbonate cement fill the chambers of fossils. The sedimentological and paleontological evidences indicated to deep shelf margin environment of the facies (Wilson, 1975;Flugel, 2004).

Pelloidal lime wackestone facies K2
The facies is characteristically as grey dolomitic limestone with abundance of pelloids amount to 40 % of the total contain. The pelloids are rounded to subrounded shape consist of micrite, it have good preservation (Plate 2-2). The few generally affected by selective dolomitization that forming pelloidal fabric, according to Randazzo and Zachos, (1984), the origin of this type fabric is pelloidal lime wackestone. All the attributes indications subtidal -intertidal of restricted marine shelf (Wilson, 1975;Flugel, 2004).

Marl facies K3
This facies consists of green to dark grey marl, soft beds with thickness ranging between 3 -15 m, embracing thin beds of hard limestone (Plate 2-3). The insoluble residue analysis indicates to carbonate contain of the facies that ranging between (35 -60%). The allochems percentage ranging between (1 -45%). These wide range of allochems content lead to subdivision the facies in to two subfacies:

Highly fossiliferous marl subfacies K3-1
The hard part of the subfacies included to the presence of allochems ranging between 25 -45% of total subfacies content, represent by Paleocene planktonic foraminifera, the washing of 10 gm of soft marl samples indicated to the present of 400 -600 specimen of planktonic foraminifera, the paleontological evidence point to outer shelf -upper bathyal environments of the subfacies, with depth ranging between 150 -225 m ( Gibson, 1989). The inter-tongue of thin beds of hard planktonic foraminiferal limestone with soft marls indicated to the base absent Bouma sequence which is dominated in deep marine basin (van Vliet, 1978).

Poorly fossiliferous marl subfacies K3-2
The allochems of this subfacies represent less than 10% of the subfacies content. Also the washing samples show less than 100 specimens of Paleocene planktonic foraminifera. The subfacies of soft marl embracing thin beds of limestone and dolomitic limestone. The paleontological and sedimentological evidences indicate shallow marine environment extended from inner to middle shelf with water depth ranging between 40 -100 m. (Gibsom, 1989).

Sandstone facies K4
The facies is typically soft greenish grey sandstones, it consist of fine -medium sandstone with thickness ranging between 2 -5m. The grain size decreased upward, it started with structureless massive sandstone contain low percentage gravel grains (2 -3mm in diameter) ranging between 1.00 -2.26% of the total facies contain, these layer followed by laminated silty sandstone and the succession ended by thin bed of mudstone. Vertical burrows were recognized in some bedding planes and segmental warms burrows were recorded at level 60 m (Plate 2-4). Skeletal allochems are dominated by planktonic foraminifera and few benthonic foraminifera of shallow marine environment were recorded in the facies.
The sedimentological and paleontological evidences indicated to the lower part of the submarine fans environment of the facies (Emery and Myers, 2006) or lower part of Bouma sequence (Bouma, 2000;Stelting et al., 2000 andNichols, 2004).

Shale facies K5
The facies is characterized by soft greenish grey shale located at the middle part of the succession of Bekhme section with 17m thick (Plate 2-5), in which allochems dominated by planktonic foraminifera. The facies included low percentage of silt grains, thin beds (>15cm) of hard shale contain high percentage of carbonate cement and lamination structure of alternated silt and clay laminas, which is produced by the oscillated velocity of transportation medium was recognized in the facies.
All the attributes point to levee deposit of submarine fan channels which dominated in the middle part of the submarine fan (Bouma, 2000;Stelting et al., 2000 andNichols, 2004).

Intraformational conglomerate facies K6
The facies has a total thickness of about 2 m at the top of Kolosh Formation in Bekhme section (Plate 2-6), it consist of random distribution intraclasts in calcareous clay matrix. The intraclasts diameter up to 25cm. the sedimentological evidence point to submarine channels depositional environment, in which they transported the sand and pebble grains to the deep marine (Al-Qayim and Salman, 1986;Boggs, 2006), generally these channels found at the upper part of the submarine fans (Nichols, 2004).

Facies and depositional setting of Sinjar Formation
The Sinjar Formation crop out at Bekhme section as a lens of carbonate facies with thickness ranging between (0.2m -11m.) ( Figure 2). Their facies donated S1 and S2, the sedimentological and biological evidences are used to determine their depositional environment and bathymetry.

Rudstone facies (S2)
The facies is typically hard grey to light brown limestone. Their thickness ranging between 0.3m. to 2.5m . The facies consist of bioclasts represented by lime intraclasts, echinoderm, red algae and coral up to 0.5cm in diameter (Plate 2-9 ), in addition to planktonic foraminifera and ostracoda. The allochems content ranging between 10 -25% of the total facies content. The matrix embraces microspar produced by neomorphism. The facies affected by chemical and physical compaction, which indicated by fracturing of fossil and stylolite. Carbonate cement was recorded as granular, drusy and syntaxial cement. The sedimentological and biological evidences indicate to fore reef deposit within marine slope (Wilson, 1975 and Flugel).

Biostratigraphy
The studied rocks of Kolosh Formation exposed in Bekhme area are characterized by abundant well preserved planktonic foraminiferal assemblages, washed residues of Bekhme section were investigated from common diverse planktonic foraminifera to be used as biostratigraphic tools for investigating the marine setting of the formation. Twenty species belonging to six genera were identified in Kolosh Formation, the stratigraphic distribution of these species indicated two biozones and four subzone of the early Paleocene age (Danian) ( Figure 5), these zones and subzones are correlated with similar ones established by other authors as shown in Table 2 and Table 3. The zonal scheme (P zones) followed in this study is that of Blow (1979). The zones and subzones are described in ascending orders as follows:
Boundaries: the zone bounded at the base by the disappearance of the Late Cretaceous planktonic foraminifera and the disconformity with the underlying Tanjero Formation. The top of the zone is placed at the first appearance of the Praemurica uncinata ( Bolli).
Characteristics: The zone is characterized by the presence of cancel planktonic foraminiferal species in the lower part. The easy distinguished and dominated of (Parasubbotina pseudobulloides) make it favor in the biostratigraphic studies (Bolli, 1966, Toumarkine & Luterbacher, 1985, Molina et al., 2005, Arenillas et al. 20042006). Accordingly the biozone was subdivided into four subzones, these subzones are from base to top:
Boundaries: The subzone bounded at the base by the first appearance of the Parasubbotina pseudobulloides (Plummer). The top of the subzone is placed at the first appearance of the Subbotina triloculinoides (Plummer).
Thickness: The subzone is 5 m. thick.
Boundaries: The subzone bounded by the first appearance of the nominated taxon and ended by the first appearance of the Praemurica inconstans (Subbotina ) and Globanomalina compressa (Plummer).
Boundaries: The subzone bounded by the first occurrence of the nominated taxa and the initial appearance of the Praemurica trinidadensis (Bolli).
Boundaries: The lower boundary is defined by the first occurrence of the nominate taxon. The upper of this subzone is placed at the first appearance of Praemurica uncinata ( Bolli).
Boundaries: The base of the zone is defined by the first occurrence of the nominate taxon. The top of the zone is identified by the disappearance of the early Paleocene planktonic foraminifera at the disconformity with the overlying shallow marine carbonate rock of Khurmala Formation.

Sequence stratigraphy
The sequence stratigraphic analysis of Paleocene deposits (Kolosh and Sinjar formations) in Bekhme section interpreted four depositional sequence, designated Kolosh sequence 1 to 4 ( Figure 6 ), The sequence, which vary in thickness from (13 -66 m.) are described in terms of sequence boundaries (SB), lowstand system tract (TS), lowstand fan (LSF), transgressive system tract (TST), maximum flooding surfaces (MFS) and highstand system tracts (HST). As discussed in the final sections of this paper, correlations of depositional sequences and isochronous surface must be based on correlative biozones and follow the most recent conventions of the International commission on stratigraphy (ICS) as documented in Gradstein et al. (2004).

Kolosh sequence 1
The sequence 58 m. thick, begins with the deposition of (2 m.) of facies (K4), their content point to lowstand fans by turbidity currents. It is overlying the deep marine deposit of the Tanjero Formation (late Cretaceos age). This is followed by marls (subfacies K3-2 and Lower part of K3-1) accompanied by an increased abundance and greater diversity of planktonic foraminifera that represent the TST. The MFS is positioned in the middle of subfacies K3-1, where the maximum number of species is recorded.

Plate 3. Figure listing
The HST is characterized by the upper part of subfacies K3-1 followed by subfacies K3-2 and capping limestone beds (Facies S1 and S2), both the lower and the upper contacts are interpreted as SB Type-1. The sequence spars about 2.8 my. The age of the MFS as calculated from biozone is (63.6 Ma) at interval (24 m.), according to Gradstein et al. (2004) (Figure 6 ).

Kolosh sequence 2
Sequence 2, 66m. thick, commence with the deposition of facies (K4) that deposited by gravity flow of the shallow marine sediment to accumulate in the deep marine as LSF. It is followed by facies (K5), their lower part showing increasing water depth upward indicated by the increasing of planktonic foraminifera percentage, it is represented the TST of the sequence. The middle of facies (K5) (at 80 m.) is picked as the MFS, where the planktonic foraminifera percentage reach maximum (35%) in the facies. The upper part of (K5) followed by subfacies (K3-2), both display a shallow environment upward, suggesting the HST of the sequence. The sequence spans less than (1 my), the upper SB is Type 2 (Figure 6).

Kolosh sequence 3
This sequence begins with the deposition of the facies (K 3-1), It is lower part show increasing of diversity and percentage of the planktonic foraminifera assigned to the TST.
The MFS is represented at the middle of subfacies (K3-1) where the planktonic foraminifera percentage decreasing and followed by subfacies (K3-2) as the HST, the upper SB is Type-1.

Kolosh sequence 4
Facies (K6) represents the LSF of this (13m.) thick sequence, (Figure 6). It is followed by subfacies (K3-2) and part of subfacies (K3-1) showing increasing water depth and the TST with a retrogradational stacking pattern. The MFS occurs at interval (163m.) within subfacies (K3-1), the upper part of the (K3-1) and the overlying subfacies (K3-2) reflect decreasing water depth and the HST with a progradational stacking pattern. The upper boundary is SB Type-1 below the shallow marine deposit of Khurmala Formation.
The four sequence of Paleocene form a third -order sequence with a total thickness of about, duration of approximately (3.8 my.) and MFS at interval (24m.), and (63.6 Ma).

Correlation to Aruma sequence
In central Arabia, Aruma Formation subdivided into three informal members Khanasir limestone, the Hajajah limestone and the Lina shale members (Phillip et al., 2002), They interpretated the khanasir member as Aruma sequence 1, hajajah member as Aruma sequence 2 and 3 and Lina member as Paleocene age Aruma sequence 4. the maximum flooding surface of Aruma sequence 4 may correlate with Kolosh third orders MFS. Sharland et al. (2001) consider MFS Pg10 as late paleocene and positioned it in the base of Kolosh Formation; But in the global planktonic foraminiferal Biozone (P4), which is younger than the studied section in the time scale of Gradstein et al. (2004) MFS Pg10 has an age of 58 Ma, this age appear too younger to correlate with the third order MFS of Kolosh in Danian.

Correlation to global maximum flooding surface
The 3 rd order Kolosh sequence can be correlated with European Danian transgressive surface of Gradstein et al. (2004), which lies within the planktonic foraminifera biozone (P1b), also it can tentatively correlated with Danian 3 rd order sequence (TP1) of Blake Plateau, of the eastern united state (Schlager, 1992

Depositional environment and sedimentary model
The sedimentary evidences of Kolosh Formation clastic deposit indicated to submarine fan environment that spilled over in the narrow Ne-Tethys onto the passive continental margin of the Arabian plate from the active margins of the Iranian and Anatolian plates (Numan, 1997).
The Kolosh Formation is widely distributed in the subsurface and at outcrop in parts of northern Iraq, and is coeval with several other formations in other part. These formations are diachronous and defined according to lithology; for examples: marine marl and marly limestone (Aaliji Formation), reef and back reef (Sinjar and Khumala formation) and clastics (Kolosh Formation) (Dunnington, 1958;van Bellen et al., 1959 andGoff, 2006). These formations can pass below, above and inter-tongue with one another. Fig. 7. Mud-rich, submarine fan model (modified from Bouma, 1997 andDeVay et al., 2000) www.intechopen.com The lower boundary of Kolosh Formation in Bekhme section was mentioned as a disconformity K/T boundary with the underlying Tanjero Formation. It is followed by 2m thick of sandstones facies (K4) contains gravel grains of shallow marine deposit bypasses the middle and outer shelf and ended up in the outer fan imprinting the usual turbidite sole marks. (Al-Qayim andSalman, 1985 andBouma, 2000).
Grey to olive green thick marl beds facies (K3) bearing fine silt and planktonic foraminifera deposited in continental slope at the edge of submarine fan lobes, where the turbidite current speed diminished and the foraminifera rainfall dominated, these unit continue until another influx of turbidite sandstone (Facies K4) is introduce or carbonate thin bed (Facies K1) where deposited as a result of short-lived phase of pelagic sedimentation dominated, when the sea level relatively stagnate and the turbidity current laterally switching to built a new lobs leaving the previous lobes area with carbonate production conditions. The cycles of marl and carbonate beds represent the lowest part of the outer fan (Figure 7).
Interfingering lens of Sinjar Formation was identify in the top of marl -limestone cycles, ranging in thickness between (0.2m -11m), it consist of boundstone facies (S1) and rudstone facies (S2) their depositional environment point to organic build up -fore reef deposit within marine slope.
Four cycles of Bouma sequence are overlying the lowest part, these cycles deposited by turbidity current that bypasses the mid fan and deposited their bedload as a sheet sands or depositional lobes (Bouma, 2000). Each cycle commence with deposition of sandstones (facies K4), which consist of massive badly sorted sandstone were representing Ta interval of Bouma sequence (Bouma et al., 1985). Td and Te interval can be found overlaying Ta interval directly, Tb and Tc interval are difficult to identify or may be eroded by the next gravity flow coming from the same distributary, eroded parts of the underlying deposit (Bouma et al. 1985 andBouma, 2000). A number of layers are stack on top of one another as a sheet sand layers this part of the section representing the lowest part of the mid fan and the upper part of the outer fan ( Figure 7). ( Reading, 1986;Bouma, 2000;Kirschner andBouma, 2000 andNichols, 2009).
Seventeen meter of shale beds overlying the package of sandstones layers, it is silty rich partly laminated shale beds (Facies K5) embrace thin siltstones -fine sandstones characterized by parallel lamination and highest porosity, which is generally well cemented, the sand to shale ratio of the shale beds is low, and the carbonate material of the sandstone beds were ranging between 32 -44% of the total content, it make the thin siltstones-fine sandstones hard and easy recognized in the field. A block of coral bearing limestone bed of 0.8m. thick and 4m. width ( Figure 8) is embedded within the shale facies. It is sliding from the upper part of the shelf as a result of active turbidity current and storms originate from the tectonic earthquake. The shales -sandstones layers deposited in the mid fan as levee and over bank deposit (Figure 7). (Darling and Sneider, 1992;Basu and Bouma, 2000;Bouma, 2000;Steling et al., 2000 andNichols, 2009).
The upper succession of Kolosh Formation in Bekhme section embraces poorly fossiliferous marl facies (K3-2 ) characterized by low P/ B ratio, benthonic forams represented Lokhartia spp., Rotalia spp., eponids spp. and Quinqueloculina spp. These genera were indicated to shallow marine environment (inner -middle shelf) (Berggren, 1974;Petters,1978 andLeckie andOlson, 2003), The present of lokharitia point to regional regression during late Paleocene  (Berggren, 1974). Marl facies embedded a layer of conglomerate facies (K6) contains intrabasional (preigenetic) clasts. It is interpreted to represent the distal toe deposit of flows debouching from a main feeder canyon at the foot of the slope (Browne et al., 2000). The sedimentological evidences of the upper succession indicated to the upper fan sediment (Figure 7).
The Kolosh formation in Aqra section is 40m thick, The variable thicknesses of the two sections are due to the bathymetry of the Kolosh basin which is a result of the inherited anticlines of Cretaceous age. Aqra section consists of alternated thick marl facies (K3-2), it is very poorly fossils, representing by few bad preserved benthonic forams only, and pelloidal lime packstone facies (K2) ), the succession is pale grey color. The sedimentological and biological attributes indicated to semirestricted platform (Flugel, 2004) and represented upper fan deposit.