Document Type : علمی - پژوهشی
Faculty of Earth Sciences, University of Shahid Beheshti
2 Institute of Earth Sciences, Geoogical Survey of Iran, Tehran
Institute of applied Sciences, Geoogical Survey of Iran, Tehran, Karaj
University of Goettingen, Germany
University of Payamnoor, Yasouj
Faculty of Geography, University of Tehran
Abstract: In this research we tried to investigate the respond of high part of Zagros Mountains to past climate change by studying a 300cm core was extracted from Lake Gahar. This region is as an important biome of oak forest of Iran. Then the aim of this investigation is to detect past climate condition by palynology and modeling. According to the pollen percentage diagram of Lake Gahar (Fig. 3, 4, 5), four main local pollen assemblage zones consisting of two older zones GHA(depth of 300 to 210 cm), GHB (210 to 65 cm depth) and two more new zones GHC (depth 65 to 30 cm) and GHD (depth 30 to 0 cm) were identified. For interpretation the pollen diagram we reconstructed the annual mean precipitation and temperature data over 40000 years by MCM (Macrophysical Climate Model). By calculation the Z-score index four major thermal and moisture period found in Gahar region: 1- Cold and dry period (40000-30000 Yr. B.P) 2- Warm and dry period (30000-20000Yr. B.P) 3- Cold and wet period (20000-11900 Yr. B.P) and 4- Warm and dry period (11900-now Yr. B.P). The indices and our data showed that two zones GHA and GHB beyond depth 300-60cm may have been exposed to cold and wet period around 20000-11900 Years B.P..The mentioned zones have vegetation of forest- steppe with dominant species of oak trees. It seems that the disappearing of arboreal pollen, especially Quercus at a depth of 50 and 60 cm at the boundary between the two zones GHB and GHC is associated with unfavorable conditions for plant growth during the last glacial period. There are also upland herbs pollen types such as Poaceae crealia types and polygonium, and also arboreal pollen such as Corylus, Juglans, olive and Vitis can be considered as evidence of the destruction of the region as a result of anthropogenic effects and heavy grazing and farming operations. It is approved that consecutive period of cold/wet and warm/dry period in the past climate of Gahar region by comparing the results with other lakes in the north west of Iran.
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