期刊名称：Science et changements planétaires / Sécheresse
印刷版ISSN：1147-7806
电子版ISSN：1777-5922
出版年度：1991
卷号：2
期号：1
页码：26-39
出版社：John Libbey Eurotext
摘要：Author Yann Callot Géodynamique des milieux continentaux, Université P. et M. Curie (Paris VI), PICG 252 : Évolution passée et future des déserts, Tour 26-16, 4e étage, 4 place Jussieu, 75252 Paris cedex 05. Page(s) : 26-39 Published in: 1991 The Great Western Erg (Grand Erg Occidental) began to form during the Plio-Pleistocene. A vast, contoured aeolian structure then came into being and has been re-used by successive arid phases since then. On the Erg’s northern border, the great length of time this aeolian activity lasted caused the hollowing out of vast, enclosed depressions of hydro-aeolian origin formed by the wearing of rock by water, and deflation of the fragmented matter. Since the Plio-Pleistocene, the same shapes have been re-used by each consecutive arid phase, and, consequently, reconstituting them is impossible. The Erg’s massiveness is unusual (lack of sand-free interdune corridors) making it so distinctly inpenetrable. It can be divided up into three parts: a) an eastern part where, integrated into the Erg’s contoured structure, the dunes are made up of a continuous, coarse and ancient sandy mass forming large domes upon which living dunes of finer sand are superposed; b) a western, and more recent, part not integrated into the Erg’s contour where the dunes are made up of fine sand alone, and; c) a central part where the two dune structures combine. The Great Western Erg is thus a polygenic erg. During the Holocene, rising water from the continental land forming the Erg’s substrate formed numerous lakes of variable salinity in the enclosed depressions on the Erg’s border. Other water, diluted in the sand of the Erg’s great dunes, formed small paleo-lakes in between the large sandy domes in the eastern part of the Erg. The study of lacustrine deposits shows that they appeared towards 11 000 BP and disappeared around 3 000 BP with maximum humidity occurring between 9 000 to 5 000 BP and drying out occuring during two millennia, from 5 000 to 3 000 BP. The differences between lakes, able to form or dry out during the same time period, lead one to question the validity of paleoclimatic interpretation of sedimentation in lakes of this size when considered in isolation; only the study of a whole group of lakes will allow local topographical and hydro-logical influences to be avoided and hence reconstitute paleoclimatic evolution on the thousand-year scale.
