Middle Pleistocene karst evolution in the state of Qatar, Arabian Gulf

Abstract

Karst is a distinctive environment characterized by landforms that are the product of dissolution of surface and subsurface rock by natural water to a greater extent than in other landscapes. It occurs both as surface and underground features (White 1988; Ford & Williams 1989). The highly varied interactions among chemical, physical, and biological processes have a broad range of geologic effects, including dissolution, precipitation, sedimentation, and ground subsidence (White 1984; Trudgill 1985; Ford & Williams 1989; Smart & Whitaker 1991). Diagnostic features such as sinkholes (dolines), sinking streams, caves, and large springs are the result of the dissolving action of circulating groundwater (Ford & Williams 1989; Smart & Whitaker 1991). Karst includes features such as large caves, called as duhul in Arabic. It is an important feature of Eocene exposure surfaces in Qatar as well as some large parts of the Arabian Peninsula (Abul-Haggag 1965; Edgell 1990; Mukhopadhyay et al. 1996). Several substantial caves are known in Qatar, but many have probably been filled with blown sand, or have collapsed to produce some of the thousands of depressions or dolines. The most pronounced topographic features of Qatar are created by the large number (9736) of shallow depressions (Embabi & Ali 1990). Many of these depressions are the surface expression of subsurface collapse structures. Most of them are circular with diameters ranging from a few hundred meters up to ~3 km. Some reach depths of 25 m while others are only a few centimeters deep. Embabi and Ali (1990) related most sinkholes to these depressions. Analysis of the morphometric and spatial distribution parameters of karst depressions reveals that the Qatari karst is represented by broad, shallow depressions with an average density of 1 depression per km2 (Embabi & Ali 1990). The purpose of this paper is to report the geologic evolution of exposed sinkholes in Qatar through an air photo study, field investigations, and petrology.