The outcrops of Scala Dei (Colombo, 7 980) and Guadalope-Matarraña (Cabrera, 1983) alluvial systems are located in the SE sector of the Ebro basin. These alluvial systems were developed during the Palaeogene between the mountain front of the Iberian Chain-Catalan Coastal Ranges, and the Los Monegros (Cabrera, 7983) lacustrine system. The proximal alluvial materials correspond to thick conglomeratic levels with different geometries showing diverse types of progressive unconformities (Colombo and Vergés, 1992).
The distal materials interfingered with lacustrine deposits correspond mainly to ochre and reddish lutites intercalated with some small tabular or lenticular sandstone rock bodies. The intermediate deposits are characterized by large amounts of sandy rock bodies, with symmetric or asymmetric transverse geometries, placed between tabular lutites and sandstone flat layers. Their geometries are lenticular and well differentiated with respect to their wings of lateral expansion which are infrequent. The planimetry of these lenticular bodies shows more or less straight segments separated by bends with a low curvature radius. Their mean sinuosity is low, although on rare occasions it is possible to find some bodies with a high sinuosity. The real meandering geometry is very uncommon. The study of several of these sandy bodies and their lateral edges allows us to define two basic architectural units. The lower unit corresponds to the filling of the initial incision and occupies approximately between the half and three quarters of the sandstone body total thickness. The upper unit is placed on the previous one and remains usually confined by the lateral banks The lenticular sandy bodies which are well-known in the literature as "Caspe- type palaeochannels" provides some information on the early stages sedimentary evolution of a distributive drainage system. When a low sedimentation rate In the interchannel sectors exists, this sedimentary information can be lost by the reworking of the initially deposited materials. This type of paleochannels are very common in the type area (distal areas of the Guadalope- Matarraña System) as. in other more distant zones with a different age (marginal-distal areas of the Seal a Dei System) in the Les Garrigues area. Depending upon their sedimentological features and palaeogeography these palaeochannels could be characteristic o f distal tracts o f alluvial systems developed in a semiarid to arid climate, in a general context with a high topographical gradien
