SUBSURFACE GEOLOGICAL STUDY ON AL-SAMAWA REGION SOUTH OF IRAQ

Abstract

The project area of about (11550) square kilometers was located to the southwest of Samawa City in Al-Muthana Governorate. It was mapped by the detailed geological mapping project on scale 1:25000 during the period between 2009-2014. The exposed rocks belong to many formations with different types of Quaternary sediments, ranging in age from middle Eocene to Pliocene- Pleistocene.They include (from older to younger): Dammam, Euphrates, Nfayil, Zahra formations and Quaternary sediments. During the process of surface geological survey, 17 boreholes had been drilled with rock core recovery ( one borehole for each sheet scale 1:25000 ) with depths reach to 150 meters, to study and link the surface geological data with subsurface geological data also to study the subsurface stratigraphic sequence and lithostratigraphy by making boreholes correlation,, upon completing the drilling process, two others formations appeared, Rus Formation ( Early Eocene ) and Umm Er-Rudhma(Late Paleocene) in addition to the formations mentioned before. Geomorphogically, the project area is generally flat with some undulation. The main geomorphlogical unites are Dundational, Fluval, Soluation and Aeolian origin. The drainage pattern is usually centripetal and dendritic. Structurally, mapped area is located in the stable shelf of the Arabian shield within Al-Salman Sub- Zone. Many of the faults those were set in the previous study were canceled in our present drilling and mapping project. Four water wells were drilled, to study the hydrogeological and hydrochemical conditions of the area. Pumping test was carried out for these wells drilled within Euphrates and Dammam formations to calculate the hydraulic coefficients of aquifer. The results indicated that the aquifer has a very high transmissivity,due to the presence of fractures and channels within its rocks, which gave a high discharge. Geophysically, the present work represents a documentation of geophysical works; gravity and radiometric, executed in the Southern Iraqi Desert (Al-Salman Quadrangle). The gravity survey aims to studying, in more details; some impressive anomalies appeared in Bouguer map. On the other hand, the radiometric survey has different aims. It aims to measure the distributions ofthe U235, K40, Th and Dose rate, of some predefined anomalies and also to measure the level of cesium (Cs137) contamination. It also aims to detect the differences in radiometric levels between the adjacent exposed lithologies that may be useful in geological mapping.