Method of paleogeographical analogues in paleohydrological reconstructions

One of the main problems of quantitative paleohydrology is a discrepancy be tween very high (even catastrophic) reconstructed discharges in the paleori vers and the results of the majority of precipitation reconstructions in th e same territory. To resolve the problem it is necessary to find the closes t recent analogue to the hydrological regime of a paleoriver and to calcula te the main hydrological and climatic parameters of the former flow with th e help of this analogue. This approach to paleohydrological reconstructions is the method of paleogeographical analogues based on two assumptions: (1) similar hydrological regimes were characteristic for the paleorivers in si milar paleolandscapes; (2) the hydrological regime of a paleoriver within s ome paleolandscape would be similar to that of a present-day river in the s ame type of landscape. Quantitative paleohydrological reconstruction by pal eogeographical analogy calculates a wide range of paleohydrological and pal eoclimatic parameters, such as maximum discharge and its return period; mea n maximum discharge; mean annual discharge; volume of the floodwave; winter and annual precipitations. A study of the Khoper River paleochannel with a discharge 7 times exceeding the modern one indicates that the paleochannel formation was caused mainly by periglacial conditions with continuous perm afrost and very sparse vegetation, while the rainfall increase was only two -fold. The relative errors in calculations of hydrological parameters for t he present-day rivers using their modern analogues are mainly within +/- 10 %, and up to 40%. The relative errors of palaeohydrological reconstructions are probably closer to the latter value. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.