Introduction

The last and shortest geological period is the Quaternary. One of the most important features of this period is irregular climate changes. The evidences and legacies of this unique period began and continues about 2.5 million years ago, and the last part of this period that has continued until now is the Holocene period.Today, Iran's playas are in arid conditions, but the geomorphological and sedimentological evidences of these areas have indicated significant changes in their climatic and natural conditions in the Quaternary. In this period glacial and interglacial condition in high latitudes and high mountains of mid-latitudes in areas far from the lands covered with ice, the level of lakes rose and there were lakes in the closed basins of arid or semi-arid areas today as well. Many studies conducted on the Holocene and Quaternary climate in Iran have pointed to dry and cold climatic conditions in the glacial period and relatively humid and warm in the interglacial period. Some authors have also proposed the event (rainy period) and assumed that the amount of precipitation is greater during the glacial period. Some scientists also attach importance to the increase in rainfall during that period and consider the changes in these areas to be caused by the cooling of the air and decrease in evaporation, and instead of rainy periods, they use the term cold periods. The simultaneity of rainy or cold periods of low latitudes with glacial or interglacial periods of high latitudes in different regions is one of the topics that is of interest to researchers.



Methodology

This research was carried out in Masileh,Depression which covers of Qom, Isfahan and Semnan provinces.The method of this research is the examination of geographical data and information, field studies, laboratory and remote sensing.The purpose of this research is to determine the extent of the Pluvial Lake of hill Mesileh including (Hoz-e-Sultan Basin, Mareh Basin and Salt Lake) based on geomorphological evidence (lacustrine terrace) in the Quaternary. In the field studies, the presence of a lake terrace in a specific area, the height of the levels was determined and samples were taken from their surface for laboratory analysis.This depression is located between the southern elevations of Middle Alborz in the north, the volcanic elevations in the west, the heights of Tafarsh and Kashan in the south and southwest, and the desert plain in the east of a large triangular area. Inside this triangle, there are basins and holes, which includes the salt lake, the Hoz-e-Sultan Basin, and the Marah basin. The maximum height of this basin is 3588 meters (Karkas peak) in the southern heights and the minimum is 800 meters in the salt lake.



Results and discussion

The studied watershed consists of 9 smaller sub-basins with an area of 18639 square kilometers. Hoz-e-Sultan playa with an area of 69.60 square kilometers, Hoz-e- Mereh with an area of 27.90 square kilometers and salt lake with an area of 1865 square kilometers are located in this basin. The exploratory terrace in Mesila basin at an altitude of 805 meters above sea level shows the extent of the paleo lake, which has an area of 6190 square kilometers, which includes each salt lake, Hoz-e- Mareh and Hoz-e- Sultan. This range shows that in the paleo climatic periods, when the dominance of rainy conditions was accompanied by a decrease in evaporation, these three basins were shared by a single lake. Based on these results, based on the height of its bottom, 802 meters above the sea level, the lake had 3 meters of water at the time of its expansion. Also, according to the height of the playa floor of Hoz-e- Sultan, which is 799 meters above sea level, this playa had 6 meters of water as a result of the extent of the said lake, and the salt lake with a floor height of 786 meters above sea level had 19 meters of water as a result of the extent of the said lake. The results of grain measurement and calcimetry analyzes of the sediments collected from the studied area have shown a peaceful sedimentation environment in the past and are proof of an ancient lake environment in this area.



Conclusion

Many studies conducted on the Holocene and Quaternary climate in Iran have pointed to dry and cold conditions in the glacial period and relatively humid and warm in the interglacial period. Some authors have also proposed the event (rainy period) and assumed that the amount of precipitation was greater during the glacial period. Some scientists also attach some importance to the increase in rainfall in that period and consider the changes in these areas to be caused by the cooling of the air and decrease in evaporation, and instead of rainy periods, they use the term cold periods. The simultaneity of rainy or cold periods of low latitudes with glacial or interglacial periods of high latitudes in different regions is one of the topics that is of interest to researchers. Mostofi and Feri's studies show that first the water enters the Mareh reservoir, and after it is filled, it enters the Hoz-e-Sultan reservoir from the last two reservoirs, and when the water rises a few meters in the Hoz-e-Sultan reservoir, it returns to the Mareh reservoir. The overflow of these two basins is discharged into the salt lake (Mostofi and Feri, 1959). These studies also confirm the possibility of the existence of this integrated lake, as well as Krinsley's studies also indicate the existence of Pluvial lakes in the central Iran regions in the past, which have led to the current situation and the loss of the lakes due to climate change and has left playas in central Iran.