عنوان مقاله [English]
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.
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.
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.
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.