چکیده:
عصر هولوسن علیرغم کوتاه بودن، شرایط پایداری را از نظر اقلیمی پشت سر نگذاشته است. وجود چنین شرایطی در حوزه عملکرد سامانههای شکلزای حوضهها، جنس و عمق رسوبات بهویژه در نوار و جلگههای ساحلی مانند جلگه خوزستان تأثیر زیادی داشته است. بنابراین پژوهش حاضر با هدف تعیین شواهد رسوبی ناشی از تغییرات اقلیمی هولوسن در پایاب رودخانه کرخه انجام شده است. در این پژوهش با استفاده از یک دستگاه ماشین حفاری دورانی، نمونهگیریها به صورت مغزهگیری پیوسته تا عمق 10 متری انجام شد. پس از آن، نمونهها برای انجام آزمایشهای دانهبندی، بافت، مورفوسکوپی و XRD به آزمایشگاه ارسال شدند. آزمایشهای دانهبندی و بافت خاک با استفاده از روش الک خشک - الک تر و آزمایشهای مورفوسکوپی، با تهیه مقاطع نازک و میکروسکوپ بینوکولر و پولاریزان انجام شد. نتایج نشان داد، علیرغم ثابت بودن نوع کانیها در اعماق مختلف، روند تغییرات اندازه ذرات رسوبی در توالی عمودی از ریزدانه به درشتدانه میباشد و بافت خاک نیز از سیلتی لومی به لومی شنی تغییر میکند. این روند نشان از وجود دو محیط رسوبگذاری متفاوت است. علاوه بر تفاوت در اندازه ذرات، ویژگیهای مورفوسکوپی در عمق 6 تا 10 متری مانند کرویت، گردشدگی و میزان بالای زاویهدار بودن ذرات رسوبی به همراه افزایش تیرگی و جورشدگی بالای آنها، شواهد یک محیط رسوبی بادی را در گذشته نشان دادند. بر اساس شواهد دانهبندی و مورفوسکوپی موجود میتوان نتیجه گرفت، دو محیط رسوبی آبی و بادی به ترتیب در عمق یک تا 6 متر و 6 تا 10 متری در محل پژوهش قابل تشخیص هستند.
Extended Abstract Introduction The most prominent features in the Southwest of Khuzestan province are variety of sedimentary environments. There are usually many questions about the type and origin of sedimentary condition. The study of the morphoscopic and Granulometric evidence is one way to answer these questions. These methods are frequently used to identify the sedimentary condition (Blott & Pye, 2001). Therefore, the present study aimed to determine sedimentary conditions of Karkheh river delta at the upper Holocene. The Holocene Era has not had stable climate conditions and the sea level rise about 6,000 years ago. At this time, Persian Gulf expanded to near Ahwaz and the Hawizeh lagoon (Kennett & Kennett, 2006, 74). During middle Holocene (5500 years ago), coastline started retreating. The Karun Delta has developed and displacements as well as diversion paths are emerging along the Karkheh river bed (Heyvaert and Baeteman, 2007, 167). The development of the Karkheh River Delta has caused changes in particle size and sedimentary conditions (Iranmanesh et al., 2015). However, there is still no conclusive evidence of the sedimentary conditions. This study specifically seeks to respond to the paleo sedimentary conditions using morphoscopic and Granulometric evidence in southwest of Khuzestan province. Methods and materials The study is based on remote sensing, soil laboratory as well as the soil primary data collected from abandoned channel in Karkheh River. The abandoned channel (Jofeir River) was selected on the basis of nearby karkheh river which has been identified in the beginning through the Landsat data. Field operations on the abandoned Jofeir River were undertaken to completing the required research information such as GPS points and sediment core samples. The six samples were collected from 1-10 m depths. Sediment core collection have been performed by a Drilling Machine and digging a Bore to depth of ten meters from mentioned region. After that, the core samples were transferred to the ground surface and they were placed in special boxes, in depth order. Soil laboratory operation included Granulometric, soil texture, soil bulk density, XRD and morphoscopic tests. Granulometric and soil physical experiments were performed using dry and wet sieve, desiccator and morphoscopic experiments using thin sections, binocular and polarizing microscopy. Grain and texture size analysis was performed using Gradistat and American Hydraulic Properties Calculator. KEView software was used to analysis of morphoscopic properties of Sedimentary particles such as roundness, sphericity, and form. Results and discussion Physical and Granulometric: The results showed; Sedimentary sequence and features can be divided into two main parts: one from the surface to the depth of 4 meters and another one from depth of 4 meters to depth of 10 meters. The first part includes fine particles of silt loam texture and second part includes coarse particles of sandy loam texture. Morphoscopic: The results showed that 77% of the particles in the depth of 1 to 2 meters had high sphericity. The ratio of spherite in the sedimentary sequence decreases with depth and reaches about 30% at 9 to 10 m depth. Roundness of sedimentary particles in the Jofeir area showed that the proportion of sedimentation in the sedimentary sequence increased with depth. As in the depth of 1-2 meters, about 70% of the particles are semi angular and angular, but at a depth of 9-10 meters more than 90% of the particles are very angular. XRD analysis: The samples were mostly mixed phases composed of various minerals including quartz. The absorption frequencies of the peaks in the spectra of each depth in wave number unit are reported. By comparing the observed frequencies, the minerals such as quartz, feldspar, kaolinite, calcite and Vermiculite have been identified. Conclusion Research conducted by Kennett & Kennet (2006) found that environmental conditions such as climate and sea level of the Persian Gulf were not constant. Obviously, changes in environmental conditions have a direct impact on the type of sediments and their physical, chemical, mineralogical and morphoscopic properties. Therefore, the present study has investigated the granulometric, mineralogy and morphoscopic properties of sedimentary particles deposited in Karkheh flood plain in Jofeir region. Particles size distribution varies in the vertical sequence, from fine-grained to coarse-grained. Soil texture also changes from silty loam to sandy loam. So, these trend indicate the difference between two depositional environmental. These depositional environments affect not only the granulometric, but also the morphoscopic. The high angularity of the sedimentary particles at depths of 6 to 10 m relative to the depths of 1 to 6 m, together with the increase in darkness and high particle sorting at the same depth, reflects the conditions of the paleo-aeolian environment. Keywords: Khuzestan Plain, Sphericity, roundness, Sedimentary Environment, Morphoscopy.
خلاصه ماشینی:
نتايج نشان داد، عليرغم ثابت بودن نوع کانيها در اعماق مختلف ، روند تغييرات اندازه ذرات رسوبي در توالي عمودي از ريزدانه به درشت دانه ميباشد و بافت خاک نيز از سيلتي لومي به لومي شني تغيير مي کند.
علاوه بر تفاوت در اندازه ذرات ، ويژگيهاي مورفوسکوپي در عمق ٦ تا ١٠ متري مانند کرويت ، گردشدگي و ميزان بالاي زاويه دار بودن ذرات رسوبي به همراه افزايش تيرگي و جورشدگي بالاي آن ها، شواهد يک محيط رسوبي بادي را در گذشته نشان دادند.
توسعه دلتاي رودخانه کرخه باعث تغييراتي در دانه بندي ذرات شده است و توالي رسوبي را در محيط هاي رودخانه اي و درياچه اي تحت تأثير قرار داده است ، (ايران منش و همکاران ، ۱۳۹۴، ۱۳۴).
اين تحقيق به طور مشخص به دنبال پاسخگويي به شرايط ديرينه منشأ و انتقال رسوبات با استفاده از روش هاي مورفوسکوپي و دانه بندي ذرات رسوبي در جنوب غرب استان خوزستان است .
Blott and Pye کوچک(S نتايج نتايج آزمايش هاي دانه بندي و فيزيکي ميانگين اندازه قطر ذرات ، براي منطقه جفير ۲/۱۳ در مقياس في است .
بنابراين پژوهش پيش رو به بررسي ويژگي دانه بندي و مورفوسکوپي ذرات رسوبي نهشته شده در دشت سيلابي کرخه در منطقه جفير پرداخته است .
Particle shape: a review and new methods of characterization and classification.
A procedure for particle size separation of soils for X-ray diffraction analysis.
C. , 1953, a new roundness scale for sedimentary particles: Journal of Sedimentary Petrology, 23: pp.
, 1932, Volume, shape, and roundness of rock particles.