Karstification and Tectonic Effects on the Drainage Trend in the Southwestern Part of Iraq

Abstract

The extreme southwestern part of Iraq forms a flat terrain, but densely dissected by valleys that flow in different directions with different types. The exposed rocks are horizontally lying, mainly of carbonates of Ratga Formation; Eocene in age; however, eastwards Cretaceous rocks are exposed of different formations; also mainly carbonates with some intercalations of fine clastics and marls. The concerned area is intensely karstified; exhibiting different karst forms and sizes. It is also intensely parted by lineaments of different orientations, which have controlled the drainage style and flow direction. Tectonically, the concerned area lies within the Outer Platform (Unstable Shelf) of the Arabian Plate. Structurally, apart from two main normal faults of E - W trend and intense jointing and lineaments; no other features exist in the area. The intense karstification, presence of lineaments and neotectonic activities has controlled the trends of the valleys forming very complex water shades and basins that locally interfere with each other. These abnormal drainage style and different flow directions of the valleys are studied and correlated with the regional tectonic frame of the region. Moreover, we have used subsurface data; such as groundwater flow directions and geophysical data to indicate the reasons for existing of abnormal drainage style and flow directions of surface water.