رسوبات کواترنری و استقرارهای پارینه‎سنگی در حاشیه شمالی دشت کویر مرکزی؛ معرفی محوطه‌ های پارینه‌ سنگی شورقاضی و سردره

رسوبات دورۀ کواترنری همچون سایر ادوار زمین شناسی همواره در حال دفن و بایگانی داده های باستان شناختی و اقلیمی و محیطی بوده اند. بنابراین، می توان گفت رخساره های رسوبی کواترنری بخشی از میراث برجای مانده برای باستان شناسی است که شواهد مربوط به محیط انسانی، چشم انداز، و تغییرات اقلیمی را در خود حفظ کرده است. برخی مدل های پراکنش انسان ریخت ها و گروه های انسان مدرن، از افریقا به شرق آسیا، حاشیۀ شمالی دشت کویر مرکزی ایران را یکی از گذرگاه های این پراکنش معرفی می کند. وجود محوطه های پارینه سنگی در این محدوده نیز نشان دهنده چنین موضوعی است. در پژوهش حاضر به بررسی روابط بین چشم اندازهای رسوبی کواترنری در حاشیۀ شمالی دشت کویر مرکزی ایران و محوطه های پارینه سنگی در این پهنه پرداخته و برخی دلایل احتمالی حضور انسان ریخت ها و انسان مدرن در این پهنه بررسی می‌شود. همچنین، به کمک اطلاعات موجود از محوطه های پارینه سنگیِ یافت‌شده در حاشیۀ شمالی دشت کویر مرکزی، از دید بستر و فرایندهای دخیل در شکل گیری محوطه ها، چند بررسی پیمایشی در این پهنه طراحی و انجام شد که نتیجۀ آن کشف دو چشم انداز نویافتۀ پارینه سنگی در پایین دستِ مخروط ‌افکنه های ایوانکی و جاجرود، به ترتیب به نام های سردره و شورقاضی، بود. این دو چشم انداز پارینه سنگی و مجموعه دست ساخته های سنگی یافت‌شده از آن ها در این نوشتار به طور خلاصه معرفی می‌شوند.

Quaternary Deposits and the Paleolithic Sites on the Northern Edge of Iranian Central Desert: Introduction of the Newly-found Paleolithic Sites of Shour-e Qazi and Sar-Darreh

The northern fringes of the Iranian Central Desert (NICD) is a long corridor created due to the proximity of the Alborz Mountains to the north and the Central Desert to the south. For the first time, one of the present authors (HVN) highlighted the importance of the NICD as one of the routes for the dispersal of human populations from Africa to East Asia during Pleistocene epoch. In recent years, huge surface scatters of lithic artifacts have been found at openair Paleolithic sites of the region such as Soufi Abad, Delazian, Mirak, Chahe Jam, and Zaviyeh, with Mirak being the only excavated site. Sedimentological analysis in Mirak indicates that due to climatic fluctuations, the NICD had been frequently visited by human populations through millennia, especially during MIS 3. According to these results, the presence of cultural Pleistocene deposits could be expected for the other Paleolithic sites mentioned, the identification of which is difficult due to some complications. For instance, among other factors, the alluvial fans of the southern Alborz and the infiltration of their sediments to the region has caused the covering of Pleistocene deposits by recent Holocene ones and the Pleistocene outcrops are only seen in some spots across the region. Thus, it could be assumed that there are more Paleolithic sites across the NICD which are buried beneath newer sediments, agricultural lands, and urban facilities. This paper is an attempt to study the Quaternary surface deposits in the region and to assess their relation to the presence or absence of Paleolithic relics. In doing so, two questions arise, as the following:To what extent has the presence of Paleolithic human population been influenced by the environmental featues across the region?Which types of surface deposits are more talented for possessing the evidence of Paleolithic relics across the NICD?2. Materials and MethodsThe NICD extends along Semnan to Markazi Provinces in eastwest axis. The Paleolithic sites of the region, including Zaviyeh, Masileh, Moghanak and Ochounak, Soufi Abad, Delazian, Mirak and Chahe Jam are investigated from sedimentological aspects. An integral part of the present study is the comparative sedimentological analysis of the landscapes which requires frequent field visits. Field activities include pedestrian surveys and direct observations of sedimentary features of the Paleolithic landscapes and also, the landscapes with no reported Paleolithic evidence. The geomorphological features of the region are including vast pediplains, rolling hills, nebkha and nonnebkha mounds, river terraces and seasonal canal beds, and sections created by civil construction projects. The photos were taken in order to compare the features to each other and to the Geological maps of the region. Duringin conducting the comparative analysis, in addition to using geological maps and satellite images, the results of other laboratory and field studies in the region were also used (library research method). Finally, based on the information collected, some pedestrian surface surveys were designed in the NICD, which resulted in the discovery of two openair Paleolithic landscapes, namely, Shoure Qazi and Sar Darreh.3. Results and DiscussionAs mentioned above, the sediments of newer periods could usually cover and hide the Paleolithic remains and make them inaccessible. Thus, before choosing the area of study, the type of sedimentary environments should be considered in terms of the visibility of cultural remains. In general, sedimentary environments are divided into three groups in terms of erosion and sedimentation, as the following: erosional environments, accretion environments, and balanced environments. In erosional environments, erosion rate is heavier than sedimentation. In water erosion environments (e.g., erosional pediments), due to the relatively high energy, the possibility of moving, transporting and washing the archaeological material is usually high. Thus, it is better such environments are not considered a priority in pedestrian surveys; albeit in such environments, the sections and walls of water canals may sometimes expose the traces of archaeological material. On the contrary, in aeolian erosional environments, due to the lesser energy than water, only finegrained particles are usually transported and larger rubbles and pieces of rocks (including stone artifacts) remain in the form of desert pavement. Such environments are suitable for pedestrian surveys; the examples of which could be seen in Delazian, Mirak, Soufi Abad and Chahe Jam. In accretion environments (e.g., modern floodplains), the sedimentation rate is higher than erosion, which causes the burial of cultural artifacts. As a result, it is better not to prioritize such depositional environments. In the socalled ldquo;balanced environments rdquo; (e.g., interior of cave spaces, or playas), the rates of sedimentation and erosion are rather equal. In such instances, the archaeological remains are likely to remain visible for a protracted period of time without being buried. Such environments are also of significance for pedestrian surveys.4. ConclusionIn response to the first question, it seems the latitudinal diversity in topography and ecosystems in the region, the availability of freshwater in the form of permanent or temporary water bodies, the possibility of longitudinal movement due to the similarity of environments in the eastwest axis, as well as the advantages of open landscapes in the region are among the most important factors that played roles in attracting human populations to the NICD. In responding the second question, one could look for two types of environments. The windmade desert pavements are one of those two, which bear surface lithic artifact scatters mixing with natural pebbles and rubbles. In such environments, some nebkha mounds are sometimes seen which could help to hold archaeological deposits against the wind power, like what is the case for Mirak. The second environments which are of significance for pedestrian survey are the dorsal ends of alluvial fans and the pediments located upstream of the local streams and in the upper margins of the playas; since in one hand, such zones have been largely overlooked for residential and agricultural uses due to their relative dryness and the higher degree of soil salinity, and on the other hand, due to the decrease in slope, the energy of water is reduced in such zones and as a result, the chances of erosion in archaeological deposits and the transportation of lithic artifacts are less here.