The Euphrates Formation (Early Miocene) is wide spread formations in central western part of Iraq. It consists of basal conglomerate, well bedded, grey, fossiliferous and hard limestones (Lower Member), chalky like dolomitic limestone, white and massive, green marl, and deformed, brecciated dolomitic limestone and well bedded undulated limestone (Upper Member). The thickness of the formation Iraq is 35-110 m. The uppermost part of the Euphrates Formation includes Brecciated Unit. The fragments (size 1 – 3 cm) are semi angular to semi rounded, consist of very finely crystalline, silicified limestone, arranged in systematic form, which is parallel to the deformations and undulations that are present in both the brecciated mass and the overlying Undulated Limestone Unit. These characteristics of the fragments indicate that the breccia is not formed due to break in sedimentation, but it is syn-sedimentary breccia. The genesis and deformation style of the breccia is discussed in this study. The results indicate the seismic effect on the development of the breccia, during the deposition, which means syn-sedimentary origin of the breccia, most probably due to tectonic unrest, which has caused seismic shocks in the depositional area; such sediments are called "seismites".