JJees Volume 5, Number 2, December. 2013 ISSN 1995-6681 Pages 45- 52 Jordan Journal of Earth and Environmental Sciences Dissolution Cavities of Karren type in the Algal Limestone Member of Al Bayda Formation, Sector (3), Wadi Az Zad, Al Jabal Al Akhdar, NE Libya Omar B. Elfigih 1,* and Mohamed Y. Elgheriani 2 1 Assistant Professor, Petroleum Geologist, University of Benghazi, Faculty of Science, Department of Earth Sciences 2 Geologist, University of Benghazi, Faculty of Science, Department of Earth Sciences, Received 23 April, 2013; Accepted 9 Nov., 2013 Abstract The study area of Wadi Az Zad is characterized by landforms of relatively stepped terraced escarpment and karst isolated hills.At least three distinct karst features are recognized in the selected measured traverses in the surface exposure of the Algal Limestone Member at Wadi Az Zad which are: Groove karren, Circular karren, and Kluft karren. Histograms of the Algal Limestone Member at the studied traverses (T1-T3) have revealed some relationships of the recognized karren types with their elevation, lithology, topography and number of karrens or density variations. For instance, the observed densities of these surface cavities vary widely from high density of about (5.2-15.8) karren/m 2 for circular type which is found to be associated with flat area and grainstone facies, to an intermediate density of about (1.6-3.2) karren/m 2 for groove type which is found to exist mostly in relatively slope areas and in mudstone facies, and eventually to low density of about (0.5-1.5) karren/m 2 for kluft type which is found to be associated with relatively fractured (heavily jointed) and of wackstone – packstone facies. These surface dissolution cavities are evident to be associated with lithologic and structural characters of the Algal Limestone facies in the study area. © 2013 Jordan Journal of Earth and Environmental Sciences. All rights reserved Keywords: Al Jabal Al Akhdar, Algal Limestone, Karren, Wadi Az Zad * Corresponding author. e-mail: oelfigih@yahoo.com. 1. Introduction Karst features are the foremost examples of surface water erosion on this planet. The sculpturing and removal of limestone rocks is predominantly by solution, aided in some cases by soil transmission or piping, eventually causing collapse. Surface karst features are small landforms created by solution of the surface of the rock (Selby, 1985). In general, also karst landforms (minor and major) are best developed in limestone and dolomites. Karst surface morphologies exist at a variety of scales. Inevitably then, a wide variety of geomorphological techniques and methods are employed in karst morphometric analysis (McIlroy de la Rosa, 2012; McIlroy de la Rosa et al., 2012). Carbonate rocks of Algal limestone member in sector (3) (Fig.1) crop-out over approximately (75%) of the study area, and are characterized by surface features which are formed mainly through surface runoff and aided by integrated conduit flow systems through surface joints and even porous, leached grainstones. We observed and measured karst features in Wadi Az Zad; we were constrained by conditions of the exposures to measuring features of the limestone surface rather than of land surface. In general, we found that the solution features on the surface of the limestone are smaller than dolines or caves of meso-karren type (Eren et al., 2010) and too small to create permanent depressions in the overlying sediment cover because the rate of dissolution is certainly much slower than the rates of surface phenomena like intensive bioturbation. The high density (number/unit area) of small solution features (karren types) on the surface of the Algal Limestone Member and sparse land- surface depressions or sinkholes are, in part, a consequence of the differences in lithology, structure, runoff, and the mechanism of dissolution of the various facies types of this limestone. The objective of this study is to outline some of the diagnostic surface karst features in the Algal Limestone Member of sector (3), and to reveal their relationship to lithological changes and minor structural features.