Geomorphological mapping and landform analysis in central Saudi Arabia : with special reference to the characteristics of pediments and fans

Abstract

The aim of this study is to seek for a more detailed understanding of the geomorphology of some parts of Central Saudi Arabia, on the basis of aerial photographic interpretation, field surveys and investigation, and data obtained by field and laboratory analysis. An introduction to the study area is given together with an account of the geology and physiography of Saudi Arabia and especially the study area based upon drilling, field studies, and records from a variety of sources. A procedure for geomorphological mapping is discussed together with a review of the principles, problems, methods, and development of geomorphological mapping. Following these principles and methods, geomorphological maps have been compiled on the basis of the interpretation of air photographs, field surveys, and investigation, and laboratory analysis of surface materials. An attempt has been made to compare the method of geomorphological mapping with the results of landform classification including discussion of the application of the Land System approach to the area. The landform classification has been tabulated and the maps are presented to show the major landform systems and units with sample area showing the smaller units (landform type units) of the landforms. Particle size analysis and pebble shape were employed to give some information about deposition and transportation on selected pediments and alluvial fans. A discussion and critical reviews of relevant literature on the theory of sieving and sedimentation are given, This is followed by an introduction to the procedure for field and laboratory methods of particle size analysis and pebble shape measurements. The terminology for piedmont surfaces is discussed to clarify some of the confusion concerning the use of such terms. This is followed by a review of the theories concerning pediment formation, development, and their relationships to other landforms. The particle sizes of samples taken from pediments and the shapes of pebbles derived from these pediments have been measured, analysed, and discussed in relation to pediment, slope, distance from the mountain fronts and depth. Alluvial fans are another type of the landforms which are discussed in detail. They are well developed in the south-western parts of the study area where they form a series of confluent alluvial fans (bahada). Terminology and the theory of fan formation is discussed on the basis of field investigation and aerial photographic interpretation together with reviews of relevant literature. Size analysis of fan deposits as well as pebble shape are once again used to obtain information about transportation and deposition. Finally these studies are considered in relation to indications of climatic changes within Central Saudi Arabia. Problems of geomorphological mapping and interpretation are discussed and short accounts given of future work needed for detailed understanding of the desert landscape through the regional analysis of the landforms of a part of Central Saudi Arabia (conclusions).