Karstification influence on the drainage system : examples from the Iraqi Southern Desert

الملخص EN

The Iraqi Southern Desert is covered mainly by limestone pavement, being mainly composed of Paleocene – Pliocene rocks, which belong to Umm Er Radhuma, Dammam, Euphrates and Zahra formations.

The most karstified rocks, however, belong to Dammam Formation of Eocene age.

The Dammam Formation consists mainly of limestone, with dolostone, dolomitic and marly limestone, and marl.

Some chert nodules or bands occur too within the succession.

Morphologically, the Iraqi Southern Desert comprises mainly of flat terrain, which is dissected by dense drainage system, and slopes towards north and northeast.

Therefore, the main valleys flow towards north and northeast, with almost parallel courses.

However, the course of the valleys within the rocks of the Dammam Formation exhibit strange and abnormal forms, which are not usual in normal drainage patterns.

The abnormal forms are like bifurcation of the valleys; downstream and joining again, and circular and crescent forms, besides changing their main flow direction.

These abnormal forms are believed to be due to the influence of the karstification, which is still an active process.

The karst forms are in circular, oval, polygonal and crescent shapes, with different sizes.

The karstification is not only obvious in the drainage forms, but also in the exposed rocks.

They exhibit successive and parallel rims, which coincide in shape and direction with the karst forms, indicating continuous karstification.

The karstification stages, sizes, types and reasons are mentioned too, with many examples from the abnormal drainage forms.