USING LANDSAT IMAGERY FOR GEOLOGIC MAPPING IN REMOTE DESERT REGIONS, SAHARAN WEST AFRICA

The Proterozoic Atar Group, East-Central Mauritania, preserves a reef-to-basin transition. This transition represents a rapid facies change from a stromatolite-dominated carbonate reef to organic-rich basinal shales (20% TOC) devoid of carbonate. Field research is planned for winter, 2002 and aims to reconstruct the reef-to-basin transition within a sequence stratigraphic framework in order to investigate the role of differing carbonate precipitation environments on reef development. However, existing maps are at a scale of 1:5,000,000 and are of poor quality. In such remote regions, successful field study depends on timely identification of promising outcrops for section measurement and sample collection, and definition of logistical access routes. Maps produced from satellite images can serve as adequate reconnaissance geologic maps in areas where base maps are lacking, access is difficult, or ground truth is minimal. Reconnaissance mapping by remote sensing is therefore both cost effective and time efficient.

Here, we identify and establish a sequence of mappable units directly from LANDSAT imagery, using draft maps constructed from aerial photographs to identify key features in the region of interest. LANDSAT imagery is particularly suited for this project because the uniform scale and minimal distortion of images make mosaic compilation easier. We constructed a mosaic of two LANDSAT scenes, clipped a subscene corresponding to the reef-to-basin transition, and optimized the raw LANDSAT data for geologic mapping, using available techniques for image restoration, image enhancement, and information extraction. Currently, we are applying spatial enhancements on combination images, thus improving the resolution of original LANDSAT TM color images (30 m) to ~15m resolution. With image processing, the resultant geologic map clearly shows significant geologic features at a much-improved scale.