عنوان مقاله [English]
Southeastern Iran has experienced a complex history of geomorphological, hydrological and climatic conditions during the Quaternary period.Considering that Jazmourian Playa is located in one of the driest regions of Iran and the world and is very sensitive to climate and environmental changes.Therefore, it is a very important area for studying climate and environmental changes resulting from dry and wet cycles in the past. The history of sedimentation under the influence of climate and the identification of dry and wet periods during the Holocene in Jazmourian Playa is
the subject of the present study.
Jazmourian plateau between latitudes 58˚-40' to 59 ˚-14' and latitudes 27˚,10' to 27 ˚, 41' in southeastern Iran and west of Sistan and Baluchestan province and east of Kerman province. It is located at an altitude of about 360-500 meters above sea level . The catchment area is about 69,600 square kilometers, of which about 34,160 square kilometers are mountainous areas, 32,440 square kilometers are plains and foothills, and the remaining 3,000 kilometers are swamps and salt marshes.
For this study, intact sediment cores were used to reconstruct the Paleo climate. Five sedimentary cores with a maximum depth of 7 m and a total depth of about 30 m were collected and investigated from the sediments under of different areas of Jazmourian Playa using a hand-held core.Sedimentary facies were identified and distinguished based on sediment texture and composition, composition of destructive sediments and organic matter, color, presence of plant and shell residues, and other macroscopic components. According to sedimentological studies and changes in sedimentary facies, eight separable sedimentary facies belonging to river, playa, lake, delta and wind environments were identified.To estimate the time of climatic events in the region, the results of the survey of Vaezi et al. (2019) were used.
Results and Discussion
The stages of this research include data collection, published statistics, climatic data, telemetry surveys, field operations and coronation, laboratory operations, data processing and then interpretation and conclusion. In order to study the paleoclimate, changes in the sedimentary facies of the kernels based on macroscopic evidence (type of stratification surfaces, geometric form of sediments, sedimentary structures, fossil traces and contents, plant remains, color and changes) as well as sedimentation environment conditions, 5 intact sediment cores were harvested with a maximum depth of 7 m. The cores were prepared by a handy auger type. After determining the sedimentation status and type of sediments, studying the climate change and water level of the playa over time, the progress and regression of the coastline and the effect of these changes on the type of sediments and plant content of the playa, the harvesting position was such that Playa bed sediments should be allowed, maximum plaque sediment environments should be covered, at least one sample should be taken in each homogeneous unit. The location of the cores at the playa level was determined with appropriate distances and scattering so that climatic changes could be observed in them and the harvested cores could interpret various sedimentary environments in order to regenerate the climate in the region. Photographs were taken from the captured cores with a digital camera. The description of sediment cores and facies was carefully written and then sampling was done from inside the core collector for relevant analyzes according to the change of facies and type of sediments. As a result, eight major sedimentary facies were identified in the five studied brains . Facies were mostly clay, silt, sand, gravel and intermediate (combined) sediments with plant debris and evaporative sediments (gypsum and salt), which in most cases, alternation and interference in the mentioned sediments were seen frequently.
Sedimentological, paleoclimate and geographical studies of Jazmourian Playa have the following results: In the sediments of the studied cores, there are five sedimentary environments including wind, river, deltaic, lacustrine and layered sediments. Facies of windy environment are often dry brown colored sands with high sorting and medium grain. River environment (flood plain) with mud and silty sediments, usually hard, without organic matter and with gypsum and brown color, lake facies with gray to light green sediments (characteristic of regenerative environments) muddy and granular with organic matter, soft and juicy Thin laminae were identified with coarser (silty) sediment layers. Deltaic environments with very high frequency of granular and granular sediments due to many changes in the energy regime of rivers leading to the blue basin are dark gray to brown due to the seasonality of the rivers in the catchment. Playa environments are characterized by the presence of large amounts of evaporative minerals such as salt and gypsum, dark brown sediments. The rate of sedimentation rate in Jazmourian Playa is different in different parts. This rate is 0.1 mm per year in surface parts and 0.4 mm per year in deeper parts. It seems that during at least the last 25,000 years, Jazmourian Playa has often experienced playa conditions. Due to the changes in sedimentary facies along the harvested sedimentary cores, dry periods are often observed with the spread of windy sands in the playa bed and wet periods with alluvial facies, which sometimes extend to the center of the playa. Wetter conditions are evident in late Pleistocene than in the Holocene in harvested kernels. Holoceneconditions in Jazmourian Play were similar to today