A GRAVITY STUDY OF THE NUKHAIB DEPRESSION AREA, WESTERN DESERT OF IRAQ

Abstract

The studied area, which includes the Nukhaib Depression extends from Wadi Ubaiyadh in the south to Wadi Ghadaf in the north. The depression is marked by the outcrops of a N – S strip of alluvial fans. The gravity field as observed on the Bouguer anomaly map, scale 1: 500 000, is found to decrease by 8 mGal over the area. This reduction in gravity is argued to be related to a widespread subsurface solution, which has reduced the average density of subsurface rocks. The gravity map further shows local undulations, which when isolated, produce positive and negative anomalies that are distributed irregularly over the whole area including the depression strip. These anomalies are interpreted as due to variations in the intensity of subsurface solution, which reflects the local nature of rocks. Intense solution at some locations forms local subsurface basins of dissolved, broken and collapsed rocks of average low density. It was found that these basins cause topographic down warping. Some of these basins occur below parts of the depression. The alluvial fans are thought to have been formed over these depressed topographic locations. It is emphasized that solution basins are not confined to the depression's outlines only and, as such, these outlines should be reviewed and so should the naming of Nukhaib graben.