Iraqi National Journal of Earth Science

The average CIA value for the Injana Formation (Late Miocene) sampled across a section consisting of alternating mudstones, siltstones and sandstones deposited mainly in fresh water environment is rather low value (45.6) indicating the very low level of chemical alteration which the source rocks have suffered which is mainly due to semi-arid to arid climate of weathering and also due to nearby position of the basin of deposition. No overall variation in climatic condition was observed along the section from bottom to top .The variation of major and trace elements involved in this study with mean values of CIA for the sandstone, siltstone and mudstone lithologies was attributed to either mobility of the element concerned (Na, K and Rb) or to gravity fractionation of minerals that host the element or to climate of weathering and deposition (P2O5, Ni, Co & TiO2). Major contribution of recycled argillaceous or clay rich sediments to the Injana Formation do not agree with the results reached in the present study.

Fourteen ground water samples were collected from deep wells from Al-Adnanya –Sinjar area. Major hydrochemical parameters were studied to understand the quality of water. The objective of this study is to map the ground water quality of Injana aquifer and to delineate the areal extent of good and poor water. Two types of ground water were recognized in the study area, according to chemical analysis and utilizing the Hierarchical Cluster Analysis (HCA), bicarbonate type and sulphate type, the sulphate type of water is dominant with high concentration of total dissolved solids, total hardness, magnesium and sulphate comparing with bicarbonate type. Mapping results showed that water occur in Telkasab and Al-Kahtanya (poor quality) is unsuitable for drinking, while water occur in Sinjar, Domise, and Rambosy (high quality) desirable for drinking, and water occur in Al-Adnanya and Al-Jazera are not exceeding the maximum permissible limit for drinking. Dissolution of rocks and salts in soil, ion exchange and limited reverse ion exchange in few parts of the area are the main processes controlling the chemistry of ground water. Based on hydrochemical ratio (HCO3/Cl) 71% of the wells were located in recharge zone and 29 % were located in discharge zone.

The present study deals with the sandstones components of Injana Formation (Late Miocene) in Aqra area, northern Iraq. The Injana Formation consists of cyclic repetition of sandstones and claystones beds. Nineteen samples from sandstone beds were chosen for point counting and petrographic studies. The classification of these sandstone beds are feldspathic litharenite. Petrographic study shows that the sandstones consist of mono and polycrystalline quartz, K- Na feldspar, carbonate and other sedimentary rock fragments, igneous and metamorphic rock fragments and calcite cement. In addition fine- grained clay matrix. The study marked mineralogical immature and physically submature sandstones.
These sediments were deposited under (semi arid-semi humid) climatic conditions. The origin of these sandstones were recycled orogen and dissected arc – transition arc of the collision zone between the passive Arabian plate and the active Turkish-Iranian plates.
These events lead to sedimentary - tectonic intermeshing of the rocks on both plates which were uplifted as high terrains of igneous, sedimentary and metamorphic rocks, which are the source of Injana Formation sandstones.

Three sections of Injana Formation are studied in selected areas at Northern Iraq. Tewenty seven samples of sandstone are chosen for point counting and diagensis studies. The classification of these sandstone beds are feldspathic litharenite. A diagenetic study elucidates the presence of carbonate, iron oxide, clay and silicate cements, as well as compaction, replacement, recrystallization and alteration processes.
Factor analysis shows three main factors controlling the distribution of mineral and rock fragments in sandstones reflecting the type of source rocks and the maturity of the sandstone beds. The first is diagensis , the second is metamorphism of the source rocks, while the third factor is the mechanical erosion of the source rocks. The study of minerals and factor analysis indicate an acidic igneous rocks affected by differential metamorphism of the source rocks with sedimentary rock (carbonate and clastic) and immature texture of sandstone rocks.

The sandstone of Injana Formation (Late Miocene) in Kand anticline consists dominently of carbonate rock fragments, among other types, followed by quartz, feldspars and mica. The ground mass is represented by higher amount of calcite cement in comparison to silica, clay and ferrigenous cements.
Classification of the sandstones indicates their calclithic litharenite type. The source rocks embrace sedimentary, metamorphic and igneous rocks.
The sandstones have been affected by early-diagentic events which mainly include carbonate cement and consequently subduced compaction. The processes of early-mesogentic diagenesis resulted in a decrease of primary porosity with a concomittant increase of secondary porosity during late diagenetic stage due to dissolution of carbonate cement.

Facies analysis of sandstone in the injana formation of kand anticline indicated the presence of : intraformational conglomerate facies (Gm), trough cross –bedded sandstone facies (st), planar cross-bedded sandstone facies (sp), horizontal bedded sandstone facies (sh). Massive bedded sandstone facies(sm), horizontal laminated sandstone facies (fl), ripple cross –laminated siltstone facies (sr) and massive mudstone facies (fsm).
Facies association in the lower part of the succession has affinity to river – dominated delta sequences characterize by small - scale coarsening – upward cycles , while the upper part shows diagnostic thick fining upward sequences of meandering river. Paleocurrent analysis indicates a unidirectional south – south west trend.

Petrographical study of Injana Formation showed that the sandstones are composed of quartz, feldspars, high proportion of rock fragments, other components and carbonate cement. The sandstones are textuarlly, mineralogically immature as lithic arenite.
Petrographic criteria point out that a semiarid–semihumid climate had prevalied during deposition. The affinity to source area validate a back–arc tectonic environment for the source rocks, which was a sequal of the regional continental collision between the Arabian plate (Iraq) and Turkish, Iranian plate; with concomitant uplift and consequent increase in the erosional and depositional rates.

Several diagenetic phenomena have affected the sandstones of Injana Formation. These include: compaction, cementation (manifested by dominance of carbonate cement with minor silica, ferruginous, and gypsum cements), replacement, recrystallization which noticed by the transformation of micritic matrix and fragments to sparry calcite whereas the alteration appeared through change of feldspar to clay minerals. Most of these diagenetic phenomena are related to eodiagenesis and minor rule of mesodiagenesis (alteration and partial recrystallization and cementation ).