عنوان مقاله [English]
The archaeological site of Mafin Abad, located in the central part of Islamshahr city and 3 Km to the south of Mafin Abad village, was excavated under the supervision of Ahmad Chaychi Amirkhiz in two seasons in 2005 and 2006 (Maps 1-2). Moreover, they have dug some trenches around the site for environmental sedimentology. Findings concerning prehistoric pottery in Mafin Abad are contemporary with cultural periods of Sialk II to Sialk III4-5. However, a few pieces of pottery belonging to Sialk III6-7b are found as well. Sedimentological data shows that a layer of dense sedimentary soil, on a grey and black layer, is covered by Sialk III4-5 pottery, which suggests flood events of an ancient river near the site. Mafin Abad had probably changed to a basin catchment for a relatively long time. Paleoclimate studies show that despite the overall optimum climatic conditions during the Mid-Holocene in the westerly-dominated regions in West Asia, this period is punctuated by episodic dry spells, particularly during the fourth millennium BC. Such abrupt climate variability has probably been accompanied by extreme weather events, such as severe droughts and torrential rains which have potentially led to river overflows and massive floodings in the plains and alluvial fans. Detachments in habitats of the Tehran Plain in the late Sialk III4-5 period and the reduction of settlements in Sialk III6-7b and Sialk IV periods, and then, the cultural decline of the Bronze Age in North Central Iran, may be associated with the climate changes during the latter half of the Mid-Holocene.
Due to its special geographical location, the effect of the air circulation system, subtropical high pressure, and other factors, Iran generally has a semi-arid to the arid climate and a semi-desert to desert nature. The cultural region of North Central Iran overlaps with two large basins of the Salt Lake and the western part of the Central Desert. Most of the prehistoric sites belong to the Salt Lake basin. In this part, several sub-basins are resulting from the permanent rivers of Jajroud, Karaj, Qarachay, and Qomroud. The mentioned rivers and their branches have formed the main pattern of human settlements since the Neolithic period in the cultural region, because these human societies needed sufficient water resources for permanent settlement and agriculture and animal husbandry, as well as industrial activities and, finally, the formation of government and civilization. Climatic changes have had devastating environmental effects, disrupting the development and cultural transformation of ancient societies; Severe hurricanes, heavy rainfall, severe prolonged droughts, heat waves, and cold spells are some of the outcomes of climate change. Climate change in arid and vulnerable regions such as North Central Iran has had dire consequences for water-based human communities.
The archaeological site of Mafin Abad, located in the central part of Islamshahr city and 3 km to the south of Mafin Abad village, was excavated under the supervision of Ahmad Chaychi Amirkhiz in 2005 and 2006. Prehistoric pottery found from the layers of Tepe Mafin Abad was contemporary with cultural periods of Sialk II to Sialk III4-5. Also, a few pieces of pottery belonging to Sialk III6-7b were found on the surface. it is worth mentioning that the area of this site at the time of the excavations was 5.5 hectares, which was one of the largest settlements in North Central Iran in the Chalcolithic Age. During the excavations, six trenches were also excavated for environmental sedimentology around Tepe Mafin Abad called A to F. The A to C trenches were dug in the western part of the hill, side by side, along the northwest, at a distance of approximately 10 meters from each other. Also, Trench D was excavated in the southwest, Trench E in the south, and Trench F in the southeast of the site. The main question of this study was about how the environmental changes in this area in the chalcolithic period. We also sought to answer the questions of whether climatic events and natural hazards contributed to the decline of the prehistoric cultures of North Central Iran? What were the climatic conditions of the Chalcolithic Age (4200-3000 BC) like?
This research is based on environmental sedimentology studies of the prehistoric site of Mafin Abad, Islamshahr (Figurs. 1-2). The stratigraphic report of each of the excavated sedimentary trenches along with the features and contents of each layer are presented in full. Also, to analyze the findings, archaeological information of the Chalcolithic Age of North Central Iran and paleoclimate research of Greenland (GISP2), Iran, and neighboring regions have been examined. The Middle Holocene covers approximately 8200 to 4200 years ago. This period in the cultural region of North Central Iran includes the cultural periods of Sialk I, II, III, and IV. Although in the first half of the Middle Holocene, in general, warm climatic conditions (in different areas with a decrease or increase in humidity) prevailed, but from about the beginning of the fourth millennium to the second half of the third millennium BC, frequently, abrupt climate change has occurred, causing severe droughts or torrential rains in various regions. Flood-based sedimentary strata in the ancient cities of Ur, Shurupak, and Kish in Mesopotamia from the mid-fourth millennium BC to the early third millennium BC may indicate the occurrence of climatic hazards associated with climate change. This evidence has been obtained from the C and D sedimentological trenches of Mafin Abad site belonging to the mid-fourth millennium BC. Paleoclimate research in Lake Maharlou in Fars province shows a very dry period between 3700 to 3500 BC. Studies of Lake Neor in Ardebil province determine a significant increase in drought and dust flux during the fourth millennium BC. Proxies of Lake Kongor in the Gorgan plain show the dry conditions from about 3700 BC to the end of the fourth millennium BC. The results of research in Katalekhor Cave in Zanjan indicate the existence of dry conditions in the early and late centuries of the fourth millennium BC. Also, high-resolution paleoclimate research of Soreq Cave shows the very dry climatic conditions between 3700 and 3600 BC (Figur. 3).In the archaeological studies of North Central Iran, it is clear from the datings of most sites, except for a few, that habitation in them lasted until the late Sialk III4-5 and the early Sialk III6-7b, and other sites, since the Sialk III6-7b are set up. In sites that, according to the systematic survey, have pottery of all layers of Sialk III, it is impossible to assume with complete certainty the continuity without interruption of dwelling.
According to sedimentological studies, in Trench D, a thick, dense layer of sediment (3.5 m thick) covered a layer of gray soil with Sialk III4-5 pottery, which probably indicates the flooding of an ancient river near this site (Figurs. 1-2). Paleoclimate studies show that despite the overall optimum climatic conditions during the Mid-Holocene in the westerly-dominated regions in West Asia, this period is punctuated by episodic dry spells, particularly during the fourth millennium BC. Such abrupt climate variability has probably been accompanied by extreme weather events, such as severe droughts and torrential rains which have potentially led to rivers overflowing and sink the plains and alluvial fans. The settlement gap in the Chalcolithic villages of the Tehran Plain in the late Sialk III4-5 period and the decreasing trend of settlements in Sialk III6-7b and Sialk IV periods, and then, the cultural decline of the Bronze Age in North Central Iran may have been related with the climate changes during the second half of the Mid-Holocene. It is worth noting, according to archaeological studies in Alborz and Qazvin provinces, the number of bronze and iron age settlements in these areas is more than Tehran plain. So we can say that probably the abrupt climate change of the late Middle Holocene has changed the pattern and spatial distribution of settlements in the western part of the cultural region of North Central Iran, and shifted the settlement from arid to semi-arid areas and more favorable climates.
Environmental sedimentology in archaeological sites can acquaint us with natural events and climate change in antiquity. The results of these studies can also be effective in understanding the causes of cultural changes in prehistoric societies. This study identifies the climatic conditions of the fourth millennium BC and the dry climatic events of the Chalcolithic era and reveals the destructive effects of natural hazards associated with climate change. So far, no research has been conducted with the approach of studying climatic events in the decline of Sialk III culture in North Central Iran.