The Mesopotamian Paleontology researches..

Article

Paleontology

Abdul-Mutalib H. Al-Marsoumi*

College of Science, Basrah University, Basrah-Iraq
 

   The rocks which belong to the Pre-Cambrian Era were not exposed on the Iraqi territories, nevertheless, the geophysical investigation confirm their existence at great Depth. The depth of Basement rocks in the Mesopotamia ranges between 7-9 km which is a part of the Nobiou Arabian platform.

    Stable shelf conditions have prevailed in the Mesopotamia since Paleozoic and early Mesozoic time, with the rate of subsidence and sediment supply resulting in very thick shallow water sequence dominated by platform carbonate, During the Lower Paleozoic (Cambrian, Ordovician, and Silurian), the dominance were for the invertebrate faunal assemblages especially the Trilobite. In Iraq these life were not recorded  owing to the missing of the Cambrian and large part Ordovician ages in Iraqi stratigraphic column, Khabour Quartzite shale Formation (Ordovician) represents the oldest formation exposed in  northern Iraq, this formation as well as Pirispiki red beds Formation  contain trace fossils which is believed to be related to the Trilobite (Cruziana). The Middle East area were uplifted during the Silurian period due to Caledonian Orogeny, i.e become positive area, therefore, it is highly affected by erosion. So no sediments belong to this period were recorded in Iraq. Gaar'a Formation (Permocarboniferous) represents the oldest exposed formation Western Desert Iraq, lithologically consist of alternation of finning upward sandstone and claystone, most of claystone beds contain plant remains.

   Chiaser Formation re-resents the oldest formation sunked by the S.O.C drilling team in well Diwan 1, southern Samawa town, this formation characterized by the presence of small bethonioc form. Lagoonal and restricted basin are dominated during Triassic period (Korachine and Galikhan Formation) lithological consist of dolomitic limestone and anhydrite, the faunal assemblages are rare  and almost absence owing to the hypersalinity of the basins. During Lower Jurassic the conditions continue as in Triassic, Upper Jurassic period comprises the Qutaina, Najmah, and Sargelu Formations, the faunal assemblages are pelagic, mollusca and rare echinods. Most fossils are of invertebrate types. The cretaceous periods marked at its beginning by the widespread break due to the Kimmerian movement in the area nearby the geosynclines. The Lower Cretaceous ended with another break caused by Austrian phase of Alpine folding.

 Tertiary formations are the most widespread formations on the surface and in subsurface sections throughout almost all the structural units in Iraq. However, the Tertiary sediments have small areal extent in the high folded and imbricated and northern thrust zone units. The Paleocene-Lower Eocene period southern Iraq is characterized by the faunal assemblages reflecting the nreitic marine near shore to lagoonal environments, this period ended with regression, uplift and erosion during Lower Eocene. The Late Lower Eocene-Upper Eocene period , this period mainly represented by Damam Formation southern Iraq lithologically consist of porous  moderately dolomitized limestone some times chalky, and mainly nummulitic-alveolina limestone. The Oligocene group sediments are almost missed southern Iraq. The middle Miocene period represented by Fat;ha Formation, this formation is well known in Iraq with high thickness in its northern part, but in southern Iraq it has a limited thickness, lithologically consist of marl , limestone and Gypsum, reflecting a lagoonal environment of deposition. Fossils were found rarely. This is due to the hypersaline character of the basins. The assemblages are composed mostly of minute Foraminifera mainly milliolids, beside Ostracoda were more frequently found too. The Upper Miocene – Pliocene period is characterized by the progressive changes from marine sedimentation to lacustrine and fluviatile one. This period is represented by Dibdibba Formation which composed of sand and gravel of igneous rocks with white quartz pebbles, gypsum presents as cemented materials. Fossils remnants occur mainly in the lower part of the formation. Unfortunately they were not investigated at all. Dibdibba Formation covered unconformably by sandy soils.        

*Phd: Abdul – Mutalib Hasson Mohammed Al-Marsoumi

     E-mail: abdmars@yahoo.com