Deltaic Cycle of the Upper Shale Member of the Zuhair Formation in Luhais Oil-Field, SW Iraq
Saad M. Ashoor* and Badir Albadran**
*Southern Petroleum Company, Basrah, Iraq.
**Department of Geology, University of Basrah, Iraq.
Five core samples and logs of the upper shale member of the Zubair Formation were studied. These cores were collected from five wells drilled in Luhais oil-field, southwest Iraq. The study reveals that the upper shale member represents one deltaic cycle. The cycle is a regressive of a construction phase, which is responsible for the progradation of the delta. Depending on the texture, sedimentary structures, petrography, and gamma ray, seven facies were distinguished. These facies are, from bottom to top; facies (I) clayey sand of distributary mouth bar in the delta front, facies (2) sandstone, cross-bedded, of distributary mouth bar in the delta front. facies (3) sandy clay, bioturbated of bay in the delta front. facies (4) medium to coarse sandstone cross-bedded, of distributary channel in the delta plain, followed by a medium sandstone layer. Facies (5) black organic clay rich in plant debris of swamp and marsh of delta plain. Facies (6) dark grey marlstone massive with pyrite nodules followed by thick layer of highly fissile dark grey shale, then massive marlstone again, it might be considered that it is the starting moment of a transgressive phase. Lastly, facies (7) beige with disseminated pebbles of shale of the underlying layer and siliceous pebbles from other sources. This is a transgressive phase in a prodelta.