The ergs of the Atacama's marginal desert, Chile

The morphology of these ergs, their interaction with topographical preexisting conditions and their formative pulses are studied. These landforms are not present coastal features, but internal basin and range system, whose structure is a set of basin dune expansion fans connected among them by valley

dune belts. The expansion fans are formed principally by akle systems and the belts, by transversetransgressive sets and complex linear dunes. Fiveformative pulses are observed in these sand seas, represented by linear, transverse-transgressive and akle patterns. As evidenced by their morphoscopic

and mineralogical properties, sands were supplied by ancient marine beaches, yardang formative deflations and the nearest principal river valley. Because the interaction between sand drifts and the pre-existent basins, the formative pulses,are represented both in principal basin stores and bypass landforms among basins. Because the isotopic age of the corresponding marine terraces, the formative pulses are thought to have operated during a long time, in the Pleistocene and perhaps the Holocene, so that bypass linear dunes are polyfasic landforms, including a present pulse. Among the elements on theory of ergs of

mountainous deserts, have been observed the effect of variable winds on linear dunes of bypass and akle assemblages, the relations between yardang and formative processes in dunes and the dual structure (valley and basin) of the ergs. This important assemblage of landforms is a Fomenschatz of Mortensen,

in the sense of morphogenetic treasure.