Das Chalus-Tal und seine Terrassen.

Studien zur Landschaftsgliederung und Landschaftsgeschichte des mittleren Elburs (Nordiran)

Abstract

The north flank of the central Elburz shows an exceptionally strong areal differentiation both vertically and horizontally. In the example of the Chalus Valley it is possible, using a geological foundation, to distinguish five sub-regions whose geologic and geomorphologie individuality is accentuated by differences in their respective plant covers: a) the source area formed in easily-eroded Tertiary marls, whose rounded hilltops are covered by a loose rock-steppe vegetation (more than 2400 m) b) the southerly valley of the river breaking through the Paleozoic of the central zone, and whose steep gorge sides and ravines are covered by mountain woodland of Quercus-Carpinus (2400-1000 m) c) the Marzanabad basin, excavated in Mesozoic lime stones and marls, distinguished in climatic-ecologic terms through its dryness and in plant-geographic terms as a transitional region between mountain woodland and low land forest (1000-400 m) d) the narrow northerly valley incised into Cretaceous limestones with humidity-loving subtropical lowland forest (400-20 m) e) the Chalus delta fans, whose extensive silt-covered gravel areas have been stripped of their forest cover and taken in for rice fields (less than 20 m). This sub-regionalisation of the Caspian mountain flank, is typical for large parts of central Elburz. The geologic structure and chain structure are the preconditions for this clear zonation which is strengthened and refined by macro and mesoclimate. The Chalus terraces, to the extent that their numbers and classification are obviously similar to other valleys of the Elburz north flank, are significant in dating the Pleistocene and postglacial climatic and landscape history of north Persia. Since it appears possible to follow the physiognomically dominant 40-60 m terrace level in the mountains up to the end moraines of the Würm (?)-age Takht-e-Sulaiman glaciation and to correlate it in the confluence area with the 48 m NN high-water mark of the Caspian Sea, an early Würm-age formation must be regarded as probable. From this, however, follows a further, at least two-fold, climatic deterioration, corresponding to the two lower gravel terraces (20 m, 10 m). Therefore a three fold division of the Würm cold period can be assumed for the central Elburz. In addition, the possibility of an older (Riss [?]) glaciation should not be rejected out of hand. Thick, tightly-conglomerated gravel banks, most ly covered by the 40-60 m level, have been incised by the Chalus at various points and dip under the recent valley floor. Riss-Würm interglacial tectonics indicate a displacement of these older gravels while the undisturbed deposition of the younger group of terraces allows one to assume tectonic peace since the Würm. The widespread distribution of low 2-3 m and 1 m terraces indicates that minor climatic variations have occurred in post-glacial times.