|
Present work aims at defining, by means of lineament analysis from satellite imagery, the geo- struc- tural scenario of the upper Inland Niger Delta (Mali Republic), trying to match main results of previous investigations. The study region has been for a long time examined for geomorphologic and hydrological studies. These researches have highlighted major steps in the quaternary evolution of the Middle Niger valley. In 1929, Furon provided a preliminary description of the ancient hydrographic pattern of Niger Delta. In 1965, Tricart outlined on the basis of geological field suney that, only hypothesising post- Cretaceous tectonic events, it could be possible to give insight into some meaningful regional drainage changes. In 1982, Simon et al. compared geophysical and classical geological documents with digital satellite data, pointing out the existence of linear features related to deep structures, never revealed by classical photointerpretation works. In 1983, McIntosh presented a reconstruction of the geomorphological evolution in the last 20,000 years, mostly related to palaeoclimatic oscillations. In 1987, Guerre and Sow have performed an hydrogeological research in the area, by interpreting geological, hydrological and geophysical data collected during field surveys. In 1988, Jacobberger, by analysing satellite data, confirmed, within the Azauoad dunes field north of Tombouctou, the oc- currence of abandoned river channels, already pointed out by Palausi(1955). Present research has concerned a 70,000 sq. km wide area, Iying between the city of Mopti (to the south), the Faguibine lake (to the north), the city of Tomboutctou (to the west) and the town of Lere' (to the east), including most of the Upper Inland Niger river Delta. The analysis has been carried out by processing the MSS bands of the two Landsat subscenes covering the study area in different dates, corresponding to dry and wet seasons. The Landsat MSS bands have been geometrically corrected and georeferenced with respect to a UTM grid, locating Ground Control Points in the available topographic maps. These images have been then processed by convolving them with suitable spatial low-pass and directional filters, enhancing structures with peculiar wavelengths and trends. Particular attention has been driven on removing the imprints of surface features such as sand dunes which may be considered noise in this study. The obtained lineament spatial distribution has been checked with already mentioned literature information and, where possible, geophysical and topographic data, with the aim of providing an improved structural interpretation of recent hydrographic network changes.
|
