ژئوشیمی، کانی شناسی و تفسیر محیطی افق های وزیکولار در خاک های منطقۀ سگزی، شرق اصفهان (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
افق های وزیکولار در سطح لندفرم های مناطق خشک معمول هستند و نقش مهمی در ویژگی های چرخه هیدرولوژی و فرایندهای پدوژنیک در این مناطق دارند. بر این اساس هدف پژوهش حاضر، بررسی ویژگی های فیزیکی، شیمیایی، ژئوشیمیایی و کانی شناسی افق های وزیکولار در سطوح مختلف ارتفاعی سه لندفرم در ناحیه شرق اصفهان در اطراف پلایای سگزی است. لندفرم های مطالعه شده شامل یک سطح قدیمی باقی مانده در امتداد رودخانه زاینده رود (RP)، یک پدیمنت در شهرک صنعتی جی (JP) و یک مخروط افکنه در نزدیکی زفره (ZA) هستند. برای انجام پژوهش، هفت نمونه از افق های وزیکولار شامل دو نمونه در RP و دو نمونه در JP و سه نمونه در ZA در سطوح ارتفاعی مختلف برداشت شد. ضخامت افق های وزیکولار مطالعه شده در دامنه 3- 6 سانتی متر متغیر بود. همه نمونه ها توزیع دونمایی در بخش شن و سیلت داشتند که نشان دهنده مشارکت دست کم دو فرایند در انتقال ذرات در تشکیل این افق ها بود. کوارتز و کلسیت در همه نمونه ها غالب بودند، ولی ازنظر وجود میکا و کانی های فیبری تفاوت داشتند. مقایسه ویژگی های ژئوشیمیایی افق های وزیکولار با سنگ های همراه نشان دهنده غنی شدن SO 3 و CaO نسبت به ماده مادری متناظر آنها بود که با افزودن املاح محلول، کربنات ها و به ویژه گچ به سطح لندفرم ها توسط فعالیت های بادرفتی ارتباط داشت. نسبت Zr/Al 2 O 3 با افزایش مقدار سیلت، روند افزایشی داشت که منبع بادرفتی ذرات سیلت را ثابت می کند. وجود افق های وزیکولار توسعه یافته در سطوح لندفرم های منطقه نشان دهنده فرایندهای طولانی مدت فرسایش بادی و رسوب گذاری غبار در این منطقه است که این فرایند طبیعی به واسطه فعالیت های انسانی در سال های اخیر تشدید شده است.Geochemistry, Mineralogy, and Environmental Interpretation of Vesicular Horizons in the Soils of the Segzi Region, Eastern Isfahan
Extended Introduction Vesicular horizons are common on the surface of landforms in arid regions and play an important role in the hydrological properties and pedogenic processes in these areas. Vesicular pores are a characteristic feature of vesicular horizons and include separate pores with spherical to elliptical shapes and dimensions of micrometers to millimeters in diameter (Dietze et al., 2012). The eastern region of Isfahan located in the eastern part of the Zayandehroud River basin is affected by environmental disasters due to severe environmental drought, destructive human activities, and desertification processes. Although vesicular horizons are frequent in the soils and landforms of the eastern region of Isfahan (Bayat et al., 2018), there is no information about the geochemical and mineralogical properties of these horizons. The aim of the present study was to investigate the physical, chemical, geochemical, and mineralogical properties of vesicular horizons at different elevation levels of three landforms in the eastern region of Isfahan. Materials and Methods The study area is located in the center of Iran, east of Isfahan and around Segzi Playa. According to the meteorological stations of the region, the mean annual precipitation and temperature are about 107 mm and roughly 15 ˚C, respectively. Groundwater in piedmonts and plateaus of the region is deep and there are no signs of groundwater activity in the studied soils and landforms. The studied landforms include a remnant paleosurface across the Zayandehroud River (RP), a pediment in Jey industrial city (JP), and an alluvial fan near the Zefreh (ZA). Seven samples of vesicular horizons were taken from vesicular horizons in RP (at altitudes of 1542 and 1552 m), ZA (altitudes of 1623, 1764, and 1901 m), and JP (at altitudes of 1542 and 1557 m) landforms. The samples were described according to Schoenberger (2012) and analyzed regarding standard methods (Soukup et al., 2008; Soil Survey Staff, 2014). Results and Discussion The thickness of the studied vesicular horizons varied in the range of 3-6 cm, and on the alluvial fan, the thickness of the horizon increases with increasing the elevation. The chemical properties of the studied samples indicated very low electrical conductivity and organic carbon content and were similar to vesicular horizons in the Mojave Desert of California (McFadden et al., 1998). The particle size distribution indicated the predominance of sand particles in all samples and all samples were characterized by a bimodal distribution of particle sizes suggesting the contribution of at least two mechanisms in the transfer of particles to the studied vesicular horizons (Karimi et al., 2017; Sweeney et al., 2013). Mineralogical analysis of the samples showed the predominance of quartz and calcite in all samples and varied concerning the presence of mica and fibrous minerals. It seems that quartz is inherited from the parent material while calcite and mica minerals originated from the parent material and were also added by the wind. Fibrous minerals were probably of autogenic origin. The geochemical properties of the samples were consistent with the mineralogical results and showed the abundance of SiO 2 and CaO in all samples. Among the trace elements, the highest abundance is observed in the strontium, which is due to the association of this element with carbonates (Ding et al., 2019). A comparison of geochemical properties of vesicular horizons with associated rocks showed the enrichment of SO 3 and CaO relative to corresponding parent material indicating the addition of soluble ions, carbonates, and especially gypsum to the surface of the studied landforms. The Zr/Al ratio showed an increasing trend with increasing the silt content which proved the aeolian source of the silt particles as previous studies have shown a very strong correlation between aeolian sediments and the element zirconium (e.g., Waroszewski et al., 2018). Conclusions Increasing the amount of silt and the ratio of fine-grained particles to sand with increasing the elevation indicated the role of aeolian processes in adding fine-grained particles to the surfaces of different landforms of eastern Isfahan. Mineralogical and geochemical evidence also confirms the effect of dust on the formation of these horizons, so that the addition of mica minerals along with silt particles has occurred at higher altitudes. The geochemical study of vesicular horizons and application of Zr/Al ratios show that the composition of past and current dust in eastern Isfahan was the origin of dust for different landforms of the region is the same. Finally, the existence of developed vesicular horizons in the surfaces of the landforms of the region demonstrates long-term processes of wind erosion and dust influx into the soils. These natural processes are probably intensified by anthropogenic activities in recent years. Keywords: Aeolian Processes, Dust Addition, Alluvial Fan, Bulk Mineralogy. References - Anderson, K., Wells, S., & Graham, R. (2002). Pedogenesis of vesicular horizons, Cima volcanic field, Mojave Desert, California. 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