GRAVITY EVIDENCE OF WIDESPREAD SOLUSION BELOW SALMAN AREA, THE IRAQI SOUTHERN DESERT

Abstract

The area of study is (80 × 100) Km in dimensions and lies to the immediate NE of the town of Salman in the Southern Desert. The topography is flat with sporadic sediment – fill depression of which the Salman Depression is the largest and most conspicuous. The Bouguer map of the area, is characterized by a number of local anomalies having closed contours. These gravity highs and lows have various shapes and dimensions with an average amplitude of one mGal. These anomalies can be grouped into two broad long highs enclosing a zone of gravity lows. These groups are elongated in an E – W direction. Various workers have shown that solution of calcareous and evaporitic rocks in the Southern Desert by groundwater has been active since the early Miocene times. The subsurface geology of the present area consists of almost horizontal succession of Limestone (the Late Eocene Dammam Formation) underlain by evaporates and limestone of the Late Eocene Rus Formation, which in turn underlain by more than 400 m of limestone of the Paleocene Umm Er Radhuma Formation. Such lithology is highly susceptible to solution by continuously running water. The aim of the present work is to relate the observed gravity anomalies to possible underground solution hollows and channels with attempts at estimating depth, dimensions and trends of such channels. No tectonic sources for the anomalies are feasible as the entire successions are regular and structurally conformable with no sign of any trend.Detailed interpretations of the local residual anomalies have indicated the existence of an interconnected E – W trending channel of irregular boundaries occurring at a depth of about 50 m below the surface. It varies in width between 20 and 40 Km and in depth extent up to 60 m.