عنوان مقاله [English]
Introduction: Soil studies have been used as complementary data in archaeological investigations. Review and acceptance of papers focusing on the use of micromorphology in archaeology were discussed and agreed in the 12th International Micromorphology Meeting in Turkey (8). Morphology, physicochemical, clay mineralogy, and micromorphology investigations may provide invaluable data about the way ancient people used to live, the source of soil that was used for pottery and architecture, the reason of degradation or existence of monuments, and the suitable soil for the restoration of monuments. On the other hand, the restoration of our ancestor's monuments could be better performed if soil data and micromorphology techniques are used.
Materials and Methods: The present research was conducted to study the ancient and restored sections of Konar Sandal historical (5000 YBP) citadel, South Jiroft, Iran. The area under study located 30 km south of Jiroft in the Halilrud cultural area. Samples were collected from both ancient (3 samples) and restores (1 sample) sections of the citadel. Representative samples (3 from the ancient and the other from the restored sections) were also collected for clay mineralogy and micromorphology (undisturbed samples) investigations after physicochemical analysis performed on all samples. Routine physicochemical analysis performed on the air-dried samples that were passed through a 2 mm sieve.
Results and Discussion: Results of the study showed that the clay percentage of the ancient section was rough twice the restored section. On the other hand, soluble salts were about 3 times higher in the restored section than the ancient section. High salinity and solubility of salts caused restored sections to have lower resistance to environmental variations of the recent years. It seems that saline and gypsiferous soils close to the citadel were used for the restoration of Konar Sandal citadel. However, no gypsum was found in the thin section of the ancient section. Besides, Na monovalent cation plays an important role in the dispersion of soil particles compared to divalent Ca cation. Results of this study showed that soil with low clay content and high salinity was used for restoration recently. On the other hand, soils for construction of ancient sections with higher clay and lower salinity (compared to restored sections) were probably transferred from another area by our ancestors. Besides, pottery pieces to provide more stickiness and charcoal for more resistance to environmental variations were also used to construct the raw bricks in the old (5000 YBP) monument.
Illite, chlorite, smectite, and kaolinite clay minerals were found in the samples from the ancient section (Fig. 3). Palygorskite, quartz and trace amounts of sepiolite were only found in the restored sections together with the previously mentioned clay minerals (Fig. 4). The absence of palygorskite in the ancient samples may prove the presence of paleoclimate with more available humidity in the area because palygorskite is unstable in humid environments and transforms to smectite. It seems that palygorskite has a pedogenic origin in the area.
Micromorphological observations showed that the organic matter in the groundmass of the ancient samples (Fig. 6 a, b) is the reason for stability in this section. The same conclusion was also reported for samples of Bam citadel by Farpoor (4). Lenticular and interlocked plates of gypsum were found in the restored section (Figs. 6 c, and 7 a, b). Gypsum crystals were not observed in the thin sections of ancient samples. Calcium carbonate nodules were also observed in the ancient section (Fig. 7c). It seems that additives such as pottery pieces together with calcium carbonate have probably increased the stability of raw bricks through time.
Conclusion: Physicochemical properties showed more salinity in the restored compared to ancient sections and micromorphology showed gypsum crystals only in the restored samples. Besides, clay content and organic matter in the ancient section are about twice the restored section. Meanwhile, pottery pieces and charcoal were also found in the ancient section. These seem to be a reason for higher stability of ancient sections against environmental variations compared to restores sections with low clay content and high gypsum and more soluble salts that were degraded in 5 years. Illite, chlorite, kaolinite, and smectite clay minerals were investigated in both sections, but palygorskite and quarts were only found in the restored section. Results of the study clearly showed that soil data might be used as a helpful technique in archaeology studies and projects.