ABSTRACT
The stratigraphic record of Holocene alluviation in the intermontane Qara Su Basin, central west Iran (34°N, 47°E) is dominated by four overbank mud units and four soils, labelled II-V and A-D, in order of increasing age. Unit I is modern alluvium. In numerous lowland cutbank sections, unit V, with thick soil D on it, is truncated by a paleochannel up to 2 m deep, occasionally flanked by a level, eroded, channel-border zone. The paleochannel contains a structureless, poorly sorted, matrix-supported, muddy sand gravel, unit IVa, interpreted as the product of a single, brief, basin-wide, catastrophic flood. There is no evidence of comparable earlier or later Holocene events in the basin.
Chronological evidence, drawn from associated archeological occurrences and comparison of the alluviation record with palynological records of Holocene vegetation-climate change in the Zagros Mountains, indicates that deposition of the exposed alluvium began in the early Holocene, and converges on a date for the flood between 200 and 1850 A.D., with justifiable preference given to a date between ca. 950 and ca. 1250 A.D.
The flood is most simply attributed to the stalling of a Mediterranean winter ‘low’ over the basin, the hydrological effect of which may have been enhanced by basin conditions changed as a consequence of a sudden political disruption, perhaps the Mongol conquest.
