Quaternary Journal of Iran

Analysis of Base-Level Changes and Geomorphological Evolution in the Qezel-Ozan- Shahroud Basin, Alborz Mountains, Iran

Document Type : Original Article

Author

Gholam Hassan Jafari

Associate Professor, Department of Geography, University of Zanjan, Zanjan, Iran

10.22034/irqua.2025.2057593.1043
Abstract
Abstract
This study investigates the base-level changes and geomorphological evolution of the Sefidrud drainage basin and its sub-basins, including Tarom, Zanjanrud, Mahneshan, and Bijar. The analysis of mechanisms transforming endorheic basins into exorheic systems reveals that factors such as head ward erosion, overspill, and tectonic activities play a fundamental role in shaping landforms and sedimentation patterns. Fluctuations in the Caspian Sea's base level, as a key factor, have caused significant erosion and river diversions. These phenomena, alongside local tectonic activities and climatic changes, have led to the formation of diverse landforms such as alluvial terraces, waterfalls, hoodoos, and badlands. The results demonstrate that head ward erosion and tensile forces were pivotal in shaping current landforms. Additionally, Quaternary climatic variations and base-level oscillations significantly influenced the basin's evolution. Further detailed studies on geomorphology and geology are essential for a comprehensive understanding of these processes.

Introduction
The Sefidrud drainage basin, located in the Alborz mountain range of northern Iran, has undergone significant geomorphological transformations due to tectonic activities and fluctuations in the Caspian Sea's base level. These changes have shaped diverse landforms and altered hydrological patterns. This paper aims to analyze the mechanisms driving the transformation of the Qezel-Ozan-Shahroud basin from an endorheic to an exorheic system, focusing on the interplay between tectonics, climate, and base-level changes.
The study area is divided into two zones:
1. Hydrological Basin: Defined by natural units, this includes sub-basins such as Shahroud, Taleqan, Tarom, Zanjanrud, Sohrain, Shorgol, Mahneshan, and Bijar.
2. Geomorphological Basin: A broader area encompassing adjacent basins (e.g., Urmia and Mesileh-Qom) to analyze surface levels and geomorphological phenomena.
The Tarom basin, located between 36.5°–37.5° N latitude and 48.5°–49.75° E longitude, is separated from the Talesh mountain range by the Tarom Mountains. Its elevation ranges from less than 250 m above sea level at the valley floor to over 2,800 m at surrounding peaks.
Materials and Methods
This research integrates field observations, GIS analyses, and geological data to provide a comprehensive understanding of base-level changes and their impacts on geomorphological processes. Data collection methods include:
1. Field Data:
• Identification and documentation of geomorphological landforms (e.g., hoodoos, badlands, waterfalls, alluvial terraces).
• Analysis of topographical changes along rivers to assess base-level fluctuations.
• Repeated field visits to evaluate long-term changes.
2. Documentary and Map Data:
• Digitization of lithological layers from 1:100,000 geological maps provided by the Geological Survey of Iran.
• Extraction of a 30×30 m DEM from the SRTM satellite via Earth Explorer to generate contour lines (10 m intervals) and drainage networks.
3. Scientific Literature Review:
• Examination of studies on the transformation of endorheic to exorheic basins (e.g., Douglas et al., 2009; Ballato et al., 2017).
4. Results and Discussion
Mechanisms of Basin Transformation: Four primary mechanisms drive the transformation of endorheic basins into exorheic systems:
1. Antecedent sedimentation.
2. Head ward erosion.
3. Overspill.
4. Tectonic valleys formed by tensile forces.
These mechanisms significantly alter hydrological patterns and geological structures. For instance, head ward erosion in the Tarom basin has led to the capture of drainage networks and the formation of deep canyons. Similarly, tectonic activities have divided the Zanjanrud basin into several tectonic blocks, with the Sultanieh fault creating subsidence zones.
Geomorphological Landforms: Fluctuations in the Caspian Sea's base level have resulted in diverse landforms, including:
• Alluvial terraces.
• Waterfalls.
• Hoodoos and badlands.
• Deep, narrow canyons.
In western Qezel-Ozan, unique "Martian-like" mounds have formed due to contrasting geological layer dips and lithological compositions of marls and sandstones.
Impact of Base-Level Changes: Base-level fluctuations have profoundly influenced geomorphological processes. For example, the diversion of the Ghal-e-Chay River has led to the formation of Lake Pari, which was later drained due to base-level lowering. Geomorphological evidence, such as slope gradients, sediment types, and channel morphology, supports these interpretations.
Role of Tectonics and Climate: Tectonic activities and climatic changes have played complementary roles in shaping the landscape. In the Mahneshan basin, large-scale structural changes have reoriented drainage patterns from NW-SE to nearly E-W. Similarly, Quaternary climatic oscillations during glacial and interglacial periods have caused significant variations in runoff and sedimentation.
Conclusion
The Sefidrud drainage basin has undergone profound geomorphological and hydrological transformations due to base-level changes, tectonic activities, and climatic variations. These processes have not only shaped unique landforms but also altered sedimentation patterns and drainage networks. This study highlights the importance of integrating field observations, GIS analyses, and scientific literature to understand complex geomorphological systems. Further research is needed to explore these dynamics in greater detail.
Keywords: Base-level changes, Head ward erosion, Tectonic activities, Alluvial terraces, Geomorphological landforms

Keywords

Base-level changes
Head ward erosion
Tectonic activities
Geomorphological landforms
Qezel-Ozan

Subjects

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Quaternary Journal of Iran
Volume 10, 1 , 2
September 2025
Pages 108-128

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