Volume 6 Article informations Lithofacies and depositional environments of the Hawaz formation, Murzuq basin, SW Libya Eman AB. Moh. Taktek a,* Abstract Middle Ordovician Hawaz Formation is represents the primary reservoir rocks in Murzuq Basin, in J oil field consists of a 550 feet thick succession made of fine-grained quartz-arenite displaying a variable degree of bioturbation. This J oil field study is an integration approach and it is based on 235 feet thick of slabbed cores photographs from well J4- NC186, with core samples, petrography, wireline log data, and conventional core analysis of the Hawaz siliciclastic sediments. The Hawaz Formation was deposited in wave-dominated shoreface and shelf environments. The stratigraphical and sedimentological characteristics of the Hawaz Formation in the study area in the Murzuq Basin are attributed to shoreface and shelf facies associations within which some 9 facies have been distinguished. The lower part of the cored section of the Hawaz Formation is dominated by the outer and inner shelf facies associations. The outer shelf association is dominated by mudstone whereas the inner shelf association is dominated by siltstone/sandstone. This variation probably corresponds to variations in water depths and energy levels on the shelf. Storm deposits of sand grade are restricted to the inner shelf association. These were deposited immediately below fairwater wave-base and represent shallower water and higher energy than the outer shelf association. In the lower shoreface the wave effect is very weak and, as a consequence of this, fine to medium grain sands dominant in this zone, intercalated with layers of laminated mudstone, both showing abundant bioturbation and trace fossils. Key words: Lithofacies, reservoir rock, Bioturbation, Murzuq formation, Libya