Reconstructing the Sequence of Discharge and Paleotemperature of Jajroud Basin Based on Geochemistry and Sedimentology of Terraces.

Terraces are important archives for paleontology. In this research, the paleotemperature changes and discharge frequency of Jajroud basin in the northeast of Tehran have been investigated based on the sedimentology and geochemistry characteristics of the reservoirs. First, the sediment samples were analyzed with calcimetry, EC, XRF, and PH techniques, and then these data were correlated with the indices of salinity, chemical weathering, acidity, and maturity of the sedimentary layers of the defenses. The results show three periods of flow rate changes, during the alternation of cold and warm periods. One is at the peak of the glacial period when the accumulation of precipitation in the form of snow and ice in the mountainous part of the basin brought about a decrease in discharge (before the Holocene). In the second stage, by passing from the glacial period to the warm period (about 11 to 8 thousand years ago), Jajrud has experienced its highest flow. Because the melting of glaciers has been accompanied by rainfall. These conditions have also led to severe floods. The existence of very coarse-textured layering in the early Holocene Terraces is the result of the dominance of these conditions. In the third stage, the dominance of recent warm and dry conditions (8 thousand years ago until now) has been associated with the lack of glacial and the decrease in river flow. Because today Jajrud discharge is only supplied by rainfall and the occurrence of periodic floods is also a direct result of exceeding the thresholds of the intensity and duration of rainfall. Recent floods have also occurred in the lower reaches of the Jajrud basin and affect only the area of the Rote sub basin to the outlet of the basin. The findings indicate that the geochemical studies of the reservoirs can provide valuable data to recover the dynamic changes of flow and discharge during the Quaternary period and can be generalized to other similar basins. [ABSTRACT FROM AUTHOR]