干旱区生态环境知识资源中心

Southern Tunisia is dominated by early to middle Triassic continental sandstones inter-bedded with shales and conglomerates followed by late Triassic shallow marine carbonates, lower Jurassic evaporates, and upper Jurassic to lower Cretaceous elastic sedimentary rocks. These constitute the Dahar Plateau (which is part of the Ghadames Basin and it is the focus of this study) that was developed in association with regional uplift of the Saharan Platform. Efforts in mapping the details of surface geology in southern Tunisia are hindered by the lack of continuous bedrock outcrops, where some of the formations are buried under the sand of the Sahara Desert. Remote sensing data including multi-spectral optical (Landsat Enhanced Thematic Mapper (ETM+) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)), radar (RADARSAT), and Digital Elevation Models (DEMs) extracted from the Shuttle Radar Topography Mission (SRTM) data are used to trace along strike continuity of different lithological units as well as mapping morphologically defined structures in southern Tunisia. Landsat ETM+ and ASTER Red-Green-Blue (RGB) color combination images (both band and band-ratio images) have been used for the identification of various lithological units when they are exposed on the surface. On the other hand, RADARSAT images have been utilized for tracing geological formations and geological structures that are buried under thin (similar to 1 m) sand. Fusion of optical and radar remote sensing data using Color Normalization Transformation (CNT) has been effectively implemented to further identify lithological units and geological structures. Hill-shading techniques are applied to SRTM DEMs to enhance terrain perspective views and to extract geomorphological features and morphologically defined structures through the means of lineament analysis. Results from remote sensing analysis are in good agreement with results obtained from in situ investigations including geological mapping and seismic exploration. Identifying lithological and structural features using remote sensing studies incorporated with surface and sub-surface geological investigations in southern Tunisia can aid exploration for new oil and gas fields. Such an approach of integrating remote sensing and in situ geological studies can be successfully adopted in other parts of North Africa and arid regions in general. (c) 2005 Elsevier Ltd. All rights reserved.