تشکیل و تکامل خاک های رخنمون شده مناطق باستانی کنارصندل و دقیانوس در شهر جیرفت، استان کرمان

خاک ها به عنوان اجزای مهمی از مکان های باستانی تشخیص داده می شوند و عموما به عنوان نشان گرهای چینه شناسی مورد استفاده قرار می گیرند. هدف از این مطالعه، بررسی میکرومورفولوژی و کانی شناسی رس بخشی از مکان های باستانی دقیانوس و گورستان های باستانی کنارصندل (بستر قدیم و جدید هلیل رود) و ترکیب اطلاعات به دست آمده در زمینه خاک شناسی و باستان شناسی و نیز هم پوشانی مناسب اطلاعات به منظور شناخت بهتر وقایع گذشته می باشد. به همین منظور تعداد سه خاک رخ در نقاط باستانی منطقه حفر شد و پس از نمونه برداری از اعماق مختلف، آزمایش های فیزیکی و شیمیایی، میکرومورفولوژی و کانی شناسی رسی روی آنها انجام گرفت. در بررسی نتایج کانی شناسی رس، وجود کانی های کائولینیت، ایلیت، کلریت، اسمکتیت و پالی گورسکیت تایید شد. نتایج میکرومورفولوژی، حضور نوعی فسیل جلبک کاروفیت که نشان دهنده محیط آب شیرین تا لب شور در عصر دونین تا حال حاضر می باشد را در خاک رخ دقیانوس نشان داد. هم چنین بررسی مقاطع نازک، وجود بلورهای گچ عدسی شکل و به صورت صفحات درهم قفل شده در خاک رخ های کنار صندل، به ویژه بستر جدید هلیل رود و عدم وجود گچ در خاک رخ دقیانوس را تایید کردند. این موضوع می تواند به دلیل تاثیرپذیری منطقه کنار صندل از سازندهای نئوژن و گچی بالادست و رژیم بالارونده آب زیرزمینی باشد. وجود پوشش های قوی رس و کلسیت در اطراف حفرات، به ترتیب نشان گر شرایط تکامل بالاتر در خاک رخ دقیانوس و بستر جدید هلیل رود بود. احتمالا به دلیل تاثیرات هلیل رود بر بستر قدیم خود در طی زمان های طولانی، تکامل پایین تر این خاک رخ در منطقه مشاهده شد. نتایج رده بندی خاک در منطقه باستانی دقیانوس، وجود افق آرجیلیک که نشان دهنده بیشتر بودن رطوبت قابل دسترس در گذشته است را اثبات نمود.

Genesis and Evolution of Exhumed Soils in Konarsandal and Daqyanous Archaeological Sites, Jiroft Area, Kerman Province

Introduction: Several archaeologists believe that there is a relationship between cultural residuals, human beings, and soil. Soil related factors such as age index, climate change, and paleoclimate are important in archaeology. Soils could be accounted as records of invaluable information. Appropriate compiling of these data cause better understanding of soil and landscape genesis, and human activities in the past. There are two distinguished archeological sites of Daqyanous (Islamic Era) and Konarsandal (before Islamic Era) in Jiroft area. Besides, Konarsandal site is surrounded by old and new Halilrood channels. Since no data about the comparison of soil evolution in the mentioned archeological sites were available, the present research was conducted to compare soil evolution of archaeological sites using soil classification, clay mineralogy, and micromorphology in Jiroft area.،Materials and Methods: soil samples were collected from three different archaeological sites including new channel of Halilrood (pedon 1), old channel of Halilrood (pedon 2) and, Daqyanous (pedon 3). The samples were airdried and sieved (2 mm). Routine soil physical and chemical analyses including pH, EC, soil textural class, soluble sodium, calcium, and magnesium, and gypsum and calcite contents were performed. The studied pedons were classified using Soil Taxonomy system according to morphology, laboratorial results, and field observations. The clay minerals were determined by Xray diffraction (XRD) method after carbonates, organic matter, and Fe were removed using Jakson (1965) and Kittrik and Hope (1963) procedures. Ten undisturbed samples were selected for micromorphology studies and thin section preparation.،Results and Discussion: Pedon 1 is affected by Halilrood River sediments, that is why an old soil together with a young soil was formed. Salinity and SAR in the old soil were higher than the upper young soil. A textural discontinuity was found between the old and the young soils. Natric, calcic, and gypsic horizons were found in pedon 1 and caused a Typic Natrargid to be formed in new Halilrood channel. Natric horizon due to high Na cation was formed in pedons 1 and 2. On the other hand, salic, natric, and cambic horizons formed a Typic Haplosalid in pedon 2 (old Halilrood channel). High salinity and SAR in the upper layers caused salic and natric horizons to be formed. Pedon 3 with argillic horizon is an old polygenetic soil. Available humidity in the past caused removal of carbonates from upper layers that followed by clay illuviation and argillic horizon formation. Salinity and SAR in this soil were low and a heavy texture was found in pedon 3. Since pedon 3 showed cambic, argillic, and calcic horizons, it was classified as Arenic Haplargids. Calcium carbonate, gypsum, Fe oxides, and clay coatings were among dominant micromorphological features observed in the studied pedons. Konarsandal archeological site is located in the lowlands of Jiroft plain downward Rabor and Baft elevations. Lenticular gypsum crystals could be attributed to the solution of upward Neogene formations and groundwater close to the surface which evaporates due to capillary. Powdery calcite, Feoxides, and clay coating and infilling of gypsum in pore spaces of pedon 1 were observed by micromorphological investigations. Diffused clay coating around pore spaces is explainable by high sodium content and Natric horizon formation. Lenticular, interlocked plates, and infillings of gypsum were observed in pedon 1. However, gypsum with irregular shapes and low content was investigated in pedon 2. This is due to location of this pedon in Halilrood old channel. That is why pedon 2 affected by Halilrood during long periods of time is unstable and shows less evolution compared to pedon 1. Irregular and lenticular forms of gypsum show weak soil development due to low rainfall, high evaporation, and excess salt. High NaCl is reported as a requirement for lenticular gypsum formation. This form of gypsum is supported by high salinity in pedons 1 and 2. High Na and natric horizon formation in pedons 1 and 2 caused dispersion of clay and ceased formation of clay films around pore spaces. Gypsum was not found in pedon 3 during filed and laboratory studies. Besides, gypsum was not observed by micromorphological observations. Clay and calcite coatings and calcite infillings were among the micromorphological features observed in pedon 3. Calcite coating on clay coating in this pedon could be attributed to the climate with more available humidity in the past followed by an arid climate. Carophyte algae fossil was only observed in pedon 3. Kaolinite, illite, chlorite, smectite, and palygorskite clay minerals were determined by Xray diffraction. Palygorskite is highly related to the parent material and climate. Pedogenic palygorskite formation from transformation of 2:1 clay minerals and/or neoformation is reported by several studies.،Due to the impact of paleoclimate with more available humidity, palygorskite was not found in Daqyanous archeological site. It seems that higher humidity in the past did not allow palygorskite formation or transformed it into smectite. Chlorite and illite are originated from parent material. Evidences of pedogenic mica minerals in arid and semiarid environments were also found which is due to K fixation among smectite layers. Smectite with pedogenic origin is also reported by Sanjari et al. (29) in the study area. Chlorite, illite, and kaolinite clay minerals seem to be originated from parent material in the present study.،Conclusion: Laboratories analyses and micromorphology observations clearly showed weak development in Konarsandal pedons compared to high evolution of soils in Daqyanous archaeological site. The same results were also found for unstable surfaces of pedons 1 and 2 compared to stable surface of pedon 3. The stable surface provided the accumulation of clay and calcite coatings around the cavities and the formation of argillic and calcic horizons indicating high soil development. Results of the study showed polygenetic formation in soils. Soils in old Halilrood channel show high salinity and Na adsorption ratio compared to other two pedons under study.