Morphogenesis characteristics of the Lut Desert based on sedimentary granulometry

Extended Abstract

Introduction

The Lut Desert is one of the most prominent and significant desert regions located in southeastern Iran. Due to its unique climatic and geological conditions, it has attracted considerable attention in geomorphological and geological studies. This desert is known as one of the hottest and driest places on Earth, with extremely high temperatures and very low precipitation rates. Such harsh climatic conditions have led to the formation of distinctive landforms and surface features, which are the focus of many scientific investigations. Studying the surface sediments and geomorphology of the Lut Desert can provide valuable insights into erosional and depositional processes in arid and semi-arid environments. The Lut Desert lies within the Lut structural block in eastern Iran and plays a crucial role in understanding the geomorphological evolution of Iran’s desert regions. This area has been subjected to various tectonic systems, leading to the formation of igneous and metamorphic structures. Given that current tectonic activity in the region is minimal, aeolian (wind-driven) erosion and deposition have become the primary factors shaping the landscape. Detailed investigation of surface sediments and particle morphology offers a deeper understanding of the origins and processes behind sediment deposition. The Lut Desert experiences a hot and arid climate with annual precipitation rarely exceeding a few millimeters. Summer temperatures often surpass 50 degrees Celsius. Dominant winds in the region, especially the “120-day wind” blowing from the northwest to southeast, play a central role in transporting fine sand and dust particles. These winds contribute significantly to the erosion and formation of diverse geomorphological features such as yardangs (wind-carved ridges), sand dunes (barchans), and gravel plains.

Methodology

In this study, samples were collected from 19 different locations across the Lut Desert to represent its geomorphological diversity. Samples were prepared in the laboratory using wet sieving methods for particle size analysis. Using a shaker and standard sieves, particle size distributions were determined. For a more detailed analysis, particle morphoscopy was conducted using stereomicroscopy and electron microscopy to examine particle shape and surface texture. Statistical analysis was carried out with SPSS software to calculate parameters such as mean particle size, sorting, elongation, and skewness. These analyses helped distinguish between wind-driven (Aeolian) and water-driven (fluvial) sediments.

Results and Discussion

Particle size analysis showed that surface sediments of the Lut Desert include a wide range of grain sizes from coarse sand to fine silts and sandy silts. Generally, sediments showed moderate to poor sorting and a negative skewness, indicating a dominance of wind-derived sediments. Morphoscopic studies revealed many particles possess rough, angular surfaces consistent with short-distance aeolian transport and mechanical abrasion by wind. Some particles appeared semi-translucent and slightly rounded, suggesting secondary processes such as limited fluvial reworking. The evidence from the data indicates that aeolian erosion and deposition are the dominant processes shaping the surface of the Lut Desert. Prevailing winds transport sand particles from eastern sand seas towards western yardang fields. Although limited signs of fluvial activity were observed in some localities, their influence is considerably less than that of wind processes. This is especially evident in areas covered by hamada (Rocky desert pavements) and stone pavements, where wind is the main shaping agent. Mineralogical composition and particle morphology indicate that the source materials are primarily igneous and sedimentary rocks from adjacent regions, transported and deposited by wind over varying distances. The findings of this study contribute to a better understanding of erosional and depositional processes in desert environments and can be useful for environmental management, predicting geomorphological changes, and climatic studies. Furthermore, understanding aeolian sediment characteristics aids in evaluating surface mineral resources and environmental studies. Knowledge of these processes is also vital for addressing dust storm phenomena and their impacts on nearby human settlements and agriculture.

Conclusions

According to the results of the studies, the most important surface features in the Yalan Sand include star-shaped dunes, wind holes or wind basins, irrigation holes, sand blades, longitudinal and saif hills, barkhans and kaluts. The erosion rate in the Lut Desert is very high due to the high wind speed, so that the trunks of Gaz and Taq trees are up to 120 cm outside the sediments.

Based on the grain size analysis and statistical analysis of sedimentological parameters, the collected sediments indicate three types of sedimentary environments and two types of processes. Aeolian, playan and alluvial environments have been created by the activity of two types of wind and water processes. Based on the mineralogical and morphoscopy results, the dominant minerals in the sandy sediments of the Lut Desert and Yalan Sand include quartz, feldspar, calcite and clay minerals. In the Rigi Plain and the Kalut Zone, the simultaneous presence of particles with different roundness, opaque and transparent particles, as well as sediments with low mineralogical maturity in the aeolian sand samples indicates that sediment was supplied from multiple sources, with different intervals and processes in the past. The sources of aeolian sand outside the Kalut area include large alluvial fan deposits in the northern, northwestern, and western parts of the Lut Block, which are mostly igneous particles and alluvial fan deposits that are igneous, metamorphic, and sedimentary in the order of abundance. Given that the cobbles have lower chemical and mechanical resistance, it is not possible to make a definitive statement about the transport factors by studying the grain surface effects, so quartz grains are used to study the grain surface effects. In the coarser fractions, small rocks are more abundant, but in the medium fractions, quartz, detrital carbonate, feldspar, and heavy minerals are more abundant, and wind-blown quartz is more abundant in the finer fractions.



Keywords: Geomorphological features, Sedimentology, Sedimentary environments, Aeolian deposits, Lut Desert