چکیده:
شرایط اقلیمی از اواخر هزاره پنجم ق.م رو به خشکی گرایید. پژوهشهای دیریناقلیم نیمکره شمالی، به ویژه ایران و کشورهای همجوار، نشاندهنده شرایط اقلیمی نامساعد و وقوع چند دوره خشکسالی شدید از ۴۲۰۰ تا ۳۰۰۰ ق.م هستند. همچنین، بر اساس نتایج مطالعات رسوبشناسی محیطی محوطههای مافینآباد اسلامشهر و میمنتآباد رباط کریم در استان تهران و قرهتپه قمرود در استان قم مشخص شده است که هر سه محوطه در اواسط و اواخر هزاره چهارم ق.م در اثر طغیان رودخانههای همجوارشان، به زیر رسوبات سیل رفتهاند. زمان وقوع این سیلها کاملا با دورههای خشکسالی شدید هزاره چهارم ق.م مطابقت دارند. سیلهای سهمگین ناشی از بارشهای متمرکز و سیلآسا، اصولا یکی از مشخصههای اصلی دورههای تغییر اقلیم و خشکسالی هستند. با شدت گرفتن شرایط اقلیمی خشک، به ویژه از اواسط هزاره چهارم ق.م، جمعیت انسانی در منطقه فرهنگی شمال ایران مرکزی رو به کاهش گذاشت، به طوریکه منجر به یک افول فرهنگی طی عصر مفرغ شد. این پژوهش سعی دارد تا با بهرهگیری از پژوهشهای دیریناقلیم هولوسن و بررسیهای رسوبشناسی محیطی محوطههای باستانی همافق با دوره سیلک III، تأثیرات مخرب تغییرات اقلیمی را بر روی جوامع انسانی دشت تهران و حوضه قمرود-قرهچای، واقع در نیمه غربی منطقه شمال ایران مرکزی، مورد بررسی قرار دهد. همچنین، آنالیز عنصری XRD بر روی رسوبات محوطه مافینآباد نشان دهنده مکانگزینی آگاهانه این استقرارگاه در کنار شاخهای از رود کرج است که در اواسط هزاره چهارم ق.م جریان داشته و به احتمال زیاد، طغیان همین رود موجب تخریب روستای باستانی مزبور شده است. نتایج نشان میدهند که رسوبات این رود، یکی از مرغوبترین خاکهای کشاورزی و سفالگری در سراسر منطقه شمال ایران مرکزی بوده است. بنابراین، به احتمال زیاد، عدم ورود این منطقه فرهنگی به دوره آغاز شهرنشینی، با وجود پتانسیلهای بالای محیطیاش، میتواند در ارتباط مستقیم با وقوع مخاطرات اقلیمی هزاره چهارم ق.م توضیح داده شود.
Climatic conditions have dried up since the late 5th millennium BC. Paleoclimate research in the northern hemisphere, particularly Iran and neighboring countries, shows unfavorable climatic conditions and several periods of severe drought from about 4200 to 3000 BC. Also, based on environmental sedimentological studies on archaeological sites such as Mafin Abad of Islamshahr and Meymanat Abad of Robat Karim in Tehran province and Ghara Tepe of Qomroud in Qom province, it has been determined that all three sites were flooded by neighboring rivers in the mid and late 4th millennium BC. The occurrence of these floods coincided with the severe droughts in the 4th millennium BC. The enormous floods caused by severe centralized rains are, in principle, one of the main features of climate change and droughts. As the drought intensified, especially since the mid-4th millennium BC, human populations in the cultural region of North Central Iran have decreased, leading to a cultural decline during the Bronze Age. This study seeks to study the destructive impacts of climate change on human communities of the Tehran plain and the Qomroud-Gharachay basin, located in the western part of the North Central Iran region, using paleoclimate research of the Holocene age and environmental sedimentological studies on ancient sites contemporary with Sialk III period.
Also, during environmental surveys of the Mafin Abad site, evidence of an ancient stream that was one of the divisions of the Karaj River in the mid-4th millennium BC was discovered. It is probable that the uprising of the same river destroyed the ancient village. XRD analysis on the sediments of this river indicates the deliberate selection of this location for establishment of the important settlement in 5th and 4th millennium BC. According to the sedimentology, the ancient stream has been one of the most valuable mine of pottery clay in the whole of North Central Iran. Previously, there was one of the largest ceramic factories near Mafin Abad, which uses peripheral soil. Also, the existence of very fine and excellent pottery of Mafin Abad, belonging to the Cheshmeh Ali Culture with 3mm thick is another reason to support this hypothesis. Thus, Mafin Abad has great environmental potential for attracting human communities, but has failed to reach the threshold of urbanization.
Mafin Abad and Ghara Tepe in the mid-4th millennium BC and Meymant Abad in the late-4th millennium BC ended their lives. Although it is not yet known exactly where the Meymanat Abad settlement was formed after the Mafin Abad collapse, but because the most recent Mafin Abad cultural material belongs to the early Sialk III6-7b phase and the oldest Meymanat Abad cultural material belongs to the same period, so it is likely that after the end of Mafin Abad due to the flooding of the Siab River which is a branch of the Karaj River, Meymanat Abad has been established, and since the absolute dating of Meymanat Abad indicates the oldest settlement at around 3700 BC, it may be possible to attribute the time to the flood in Mafin Abad. As noted, most of the paleoclimate research confirms the occurrence of a climate change and drought in about 3700-3500 BC. Also, the eventual collapse of Meymanat Abad in the late 4th millennium BC overlaps with the 5.2 ka BP drought event (3200 BC) that continued until the early 3rd millennium BC. From then on, the long cultural decline began in the North Central Iran region and covered the whole Bronze Age. Perhaps one of the most important reasons for the significant decreased of settlements and the existence of only one to two layers of settlement after the Sialk III period was severe climate change. This natural hazards have undoubtedly had profound impacts on the subsistence system of the North Central Iran societies.