Quaternary Journal of Iran

Abstract Abstract Damavand Volcano, as the highest volcano in Iran and the Middle East, is located approximately 50 km northeast of Tehran. The volcanic rocks of the Haraz Road region mainly consist of olivine basalt, trachyandesite, and basaltic trachyandesite, with the primary mineral phases including plagioclase, pyroxene, and olivine. Petrographic studies indicate the presence of textures such as hyalomicrophaneritic, glomeroporphyritic, and vesicular in these rocks. The occurrence of disequilibrium features, including sieve textures in plagioclase, oscillatory and reverse zoning, amphibole opacization, and xenolith fragments, suggests a lack of equilibrium between crystals and melt, indicative of magma evolution in an open thermodynamic system. Examination of these features reveals that magma mixing, together with fractional crystallization, played a key role in the evolution and formation of the region’s volcanic rocks. Lava evolution primarily occurred through crystallization at varying pressures, injection of hot magma with similar composition into magma chambers, and mixing with resident magma. Thermometric calculations of plagioclase indicate that crystallization occurred at pressures of approximately 2.5–18 kbar and temperatures ranging from 750 to 1200 °C. Keywords: Petrography, Plagioclase, Magma Mixing, Central Alborz, Haraz Road, Iran 1. Introduction Damavand Volcano, as the highest Quaternary volcanic edifice in Iran and the Middle East, represents a key location for understanding tectono-magmatic processes in the Central Alborz region. The structural framework of the Central Alborz exhibits a V-shaped configuration, where northwest–southeast trending faults and folds in the western part are separated from northeast–southwest structures in the eastern section. The region remains tectonically active, as indicated by seismicity, GPS-based crustal motion, and geodetic measurements, reflecting an incomplete isostatic equilibrium. This dynamic environment has facilitated magma ascent, influencing the emplacement and evolution of young volcanic products, particularly in Damavand. Volcanic products are predominantly trachyandesitic to trachytic lava flows accompanied by limited but significant pyroclastic and epiclastic deposits, mainly concentrated in the southern and southeastern sectors. Major faults in the area, including Mashaa, Ask, Bayjan, Nova, Sefidab, Shahandasht, and Vararud, play a crucial role in controlling magma migration and vent distribution. Previous geophysical studies estimate the crustal thickness beneath the Central Alborz to range from 35 km (gravity modeling) to 58 ± 2 km (seismic data), with some studies suggesting anomalously thick crust (~65–67 km) beneath Damavand, indicative of a deep magmatic root and complex crustal-mantle interactions. Understanding the petrography and geochemistry of key minerals such as plagioclase and amphibole provides insights into magmatic evolution, crystal fractionation, magma mixing, and thermodynamic conditions during crystallization. 2. Materials and Methods A total of 70 representative volcanic rock samples were systematically collected along the Haraz Road region. Thin sections were prepared from all samples and examined using a polarizing microscope to assess mineralogical composition, textures, and microstructures. The primary focus was on plagioclase and amphibole crystals, evaluating their zoning patterns, reaction rims, dissolution features, and textural relationships. Petrographic criteria for magma mixing, including oscillatory zoning, sieve textures, and xenocrystic inclusions, were identified. Amphiboles were studied for reaction rims, opacization, and evidence of chemical disequilibrium. Geochemical analyses were conducted to quantify major and trace elements, while thermobarometric calculations estimated crystallization temperatures and pressures of plagioclase and amphibole phases. Crystal size distribution (CSD) techniques were applied to quantify crystal populations and to interpret magmatic processes such as fractional crystallization, magma mixing, and multi-stage crystallization events. 3. Results and Discussion Petrographic observations indicate three dominant volcanic rock types: trachyandesitic-basaltic lavas, trachyandesites, and olivine basalts. Trachyandesitic-basaltic samples exhibit porphyritic to microlitic textures with plagioclase ranging from labradorite to anorthite, commonly displaying oscillatory and normal/reverse zoning. Alkali feldspars are generally sanidine with variable crystal shapes. Pyroxenes are mainly augite, occasionally showing twinning, and amphiboles display partial to severe alteration, including opacized margins. Olivine basalts show porphyritic and microlitic textures with olivine, augite, and minor plagioclase phenocrysts; mafic phases often partially replaced by opaque minerals. Textural evidence such as sieve textures, zoned plagioclase cores and rims, and reaction rims on amphiboles support the occurrence of open-system magma processes, including repeated injections of hotter, more mafic magma into evolving magma chambers. Oscillatory zoning in plagioclase is attributed to variations in pressure, temperature, water content, and diffusion kinetics within the magma chamber. Sieve textures and dissolution features in plagioclase and olivine indicate magma mixing and transient disequilibrium during crystallization. Amphibole breakdown, formation of reaction rims, and opacization reflect sensitivity to temperature, pressure, and volatile content, consistent with observations in analogous volcanic systems. Thermobarometric results suggest plagioclase crystallization occurred at pressures of ~2.5–18 kbar and temperatures of ~750–1200 °C. CSD analyses reveal crystal population heterogeneity, confirming fractional crystallization, magma mixing, and polyphase growth events. The combined petrographic, textural, and geochemical evidence indicates that magma mixing and partial crystallization played critical roles in the evolution of Haraz Road volcanic rocks. 4. Conclusion The volcanic rocks of Haraz Road, Central Alborz, record complex magmatic processes characterized by magma mixing, oscillatory zoning in plagioclase, dissolution features, and amphibole reaction rims. The interplay between repeated injections of hotter mafic magma, fractional crystallization, and variations in pressure, temperature, and water content controlled mineral textures and chemical compositions. Thermobarometric results confirm crystallization of plagioclase at 2.5–18 kbar and 750–1200 °C, consistent with open-system magmatic evolution. Crystal size distribution analyses support the occurrence of polyphase growth, magma mixing, and fractional crystallization. Collectively, petrographic and geochemical evidence highlights the dynamic magmatic environment of the Central Alborz and provides insights into crustal processes controlling volcanic activity in Damavand.

Abstract Barzok Cave of Kashan is one of the active karst formations west of central Iran. This karst formation is located in parts of shale and limestones of the Shemshak formation (Jurassic) and mainly in Cretaceous limestones (Coniacian to Santonian). The systems affecting the Barzok cave karst network are considered based on the combined processes of tectonic forces, reverse fault activity, and chemical dissolution. Barzok Cave has various forms of special stones in the cave, including stalagmites, stalactites, flowstones, draperies, rim stones, popcorn, and stars. The initial stage of the formation of this karst cave began with reverse fault activity, and compressional forces extending northeast-southwest caused the displacement of Cretaceous limestone layers along the fault plane. Erosion regimes have caused the formation of numerous joints and cracks, all of which follow the aforementioned fault movements, and in these limestones, have increased the porosity and secondary permeability of the rock mass. Then, chemical dissolution by carbonic acid and organic acids caused the formation of karst deposits on the limestone masses and the emergence of the Barzok Cave karst network.
Introductions
Despite extensive research on caving, the role of hydrogeochemistry in cave development in interaction with an active tectonic substrate is not well understood. According to the definition, any empty natural space in the rock that can be suitable for human entry is called a cave. It should be noted that the above definition is a little different from what hydrologists have about caves. The karst formations of Barzok Cave are mainly developed in upper Cretaceous limestones (Coniacian to Santonian) and limestone and shale layers of the Shemshak Formation of the Jurassic age. The Barzok Karst Cave is affected by phenomena of tectonic origin, fault movements, and chemical dissolution, and erosional regimes over a relatively long period have caused the deposition of karst forms in this cave.
Despite the historical and geological importance of Barzok Cave, no significant study has been conducted on it due to its difficult access, very narrow and long entrances, and dangerous traffic routes. This research deals with the role of tectonic and hydrochemical factors and the relationship of sedimentary deposits inside the cave on the emergence and development of its morphology.
Materials and Methods
The research method was based on field visits, including the study of rock and strata units in the area, topographic features, linear structures, including joints and fault systems, and collecting rock samples to prepare thin sections, laboratory studies, and remote sensing studies.
Geographical location of Barzok Cave
The Barzok region of Kashan is located in the west of the Central Iran zone, 45 kilometers southwest of Kashan and on the Kashan-Golpaygan Road.
The karst formation of Barzok Cave was formed based on faulting events, with the displacement of Coniacian-Santonian limestone layers and limestone and shale layers of the Shemshak Formation of Jurassic age, followed by chemical dissolution.
Discussion and Results
In general, the karst formation of Barzok Cave was formed based on tectonic and fault activity during different geological times and the dissolution of limestone layers in atmospheric waters with significant acidity. This cave was formed in limestone rocks of Jurassic age in the Shemshak Formation and Upper Cretaceous from the Coniacian to Santonian. Considering that the primary factor of the emergence of the Barzok Karst Cave was reverse fault activities, it is possible to show the role of the dissimilarity of the Coniacian to Santonian limestone layers and Jurassic limestones in the formation of this cave, considering the shape that indicates a similar process.
Numerous tectonic forces during different geological times, predominantly in a northwest-to-southeast trend with an azimuth of N268 ͦ, have been very effective in creating the cave.
The deposits inside the cave are divided into two main groups: destructive and chemical. Stalagmite, Stalactite, Flowstone, Drapery, Rimstone, Popcorn or Coralloids, Stars, and Helictite are the major chemical deposits of Barzok Cave, which have different ages. The mechanism of these limestones is that empty spaces are formed inside the limestones due to the dripping of water into the cave. Barzok Cave is one of the active caves. Examining the cave rocks can also help determine past climate. Various forms of dissolution and sedimentation change with different colors and shapes in the form of cauliflower and crystallized sedimentary rocks have been shown in the Barzok Cave.
Chemical dissolution by carbonic acid and organic acids has caused the formation of karst deposits on limestone masses and the emergence of the karst network of Barzok Cave.
Conclusion
The karst formation of Barzok Cave, in the northwest of central Iran, was formed based on tectonic, faulting and dissolution activities of limestone layers in atmospheric waters with significant acidity. The role of temperature is also significant in the development of this karst. Considering the proximity of this cave to numerous travertine formations of the Oligocene-Miocene Qom Formation and the fact that the region was affected by Eocene volcanic activity and the presence of temperature changes of karst waters and relatively severe climatic and temperature changes during the periods of the emergence and development of the cave, it can be concluded that the expansion of this cave occurred in numerous and irregular periods and the diversity of karst features formed in this cave can also confirm this issue. The compressive force required for the rupture of the reverse fault and the displacement of the layers can be attributed to tectonic forces and recent orogenic phases. Given the relatively high purity of Coniacian-Santonian limestones and the crystallization of these limestones, the starting point of chemical dissolution can be considered to be the points of morphological-crystalline disturbance and their discontinuity boundaries. The logarithmic constant K can indicate the difference in the occurrence of various karst phenomena in Barzok Cave.

Abstract Introduction
Following the heavy rainfall in late 2018 and Nowruz 2019, numerous landslides have occurred in mountainous areas and slopes prone to instability in many parts of the country. The average rainfall in Iran is 250 mm. In this study, by examining the landslides that occurred in the last days of 2018 and early 2019 after floods in some provinces of the country, and using groundwater level data collected from boreholes drilled in the area of the landslides, and comparing the results obtained from stability analyses conducted in stabilizing the landslides that occurred, the effect of groundwater level changes on the occurrence of landslides and comparing the location of the landslides with the country's landslide hazard zoning map were investigated. The number of landslides caused by rising groundwater levels has also been statistically examined and determined.

Materials and methods
The research method in this study is based on library surveys and studies and field observations. In this regard, information related to the geological, tectonic and landslide conditions that occurred in the village area is examined in a library manner, and then the effects of rising groundwater levels and the occurrence of landslides are investigated, and by comparing the changes in groundwater levels and the conditions of each landslide, the effect of rising groundwater levels will be expressed. Next, a statistical study of the effect of rising groundwater levels and the percentage of landslides caused by rising groundwater levels will be conducted, and the location of landslides will be compared with the landslide zoning map of the country.
Results and discussion
Of the landslides studied in this study, 23 occurred in the Kopeh Dagh and Alborz areas. These landslides include landslides that occurred in the villages of Kashkak, Khak Pirzan, Azdaran, Qarnaveh Alia, Imam Abdullah, Belmjarak, Kafcherin, Nargeslu Alia, Goli, Arab, Qale Shaban, Sarani, Azarsei, Khanghah, Arka, CP, Estakhar Sar, Mamshi, Panu, Qale Qafeh Bala, Hossein Abad Kalposh, Narab, Kamerpasht, and Domanli in the provinces of North Khorasan, Golestan, Mazandaran, Semnan, East, and West Azerbaijan. Of the landslides studied in this study, 30 occurred in the Zagros region. These landslides include landslides that occurred in the villages of Surin, Tefin, Kish Gole Bid, Qaleh Rostam, Chal Pareh, Mobah, Abidak, Kafcherin, Garmavele Olia, Dowlat Abad, Ganjali Payin, Taleghan, Dartoot, Rah Sefid, Gol Haidar, Barfian, Deh Haidar, Manarjan, Melle Khan, Cheragh Abad, Psil, Kazem Abad, Bivand Sofli, Zarvor, Golbaghi, Cheshme Godar, Darre Sheikh Ali, Dam Bagh, Khoyeh, and Halul in the provinces of Lorestan, Kermanshah, Chaharmahal and Bakhtiari, Ilam, and Hamadan. Of the 53 landslides investigated, based on the results of excavations and borehole logs, groundwater levels were observed in boreholes drilled in the landslide area in 25 landslides, and groundwater levels were not observed in 28 drilled boreholes. According to the conducted investigations and field observations and the results of geotechnical excavations and geophysical surveys conducted in the area of the studied landslides, the type of movement in landslides has been divided into four categories: rotational, translational, rotational-translational and mudflow. Of the 53 landslides studied, 7 landslides had translational movement, 24 landslides had rotational movement, 17 landslides had rotational-translational movement and 5 landslides were mudflows.


Conclusion
Landslides occurred in the last days of 2018 and early 2019 after flooding in many provinces of the country, including North Khorasan, Golestan, Semnan, Mazandaran, Gilan, Hamedan, Lorestan, Kurdistan, Kermanshah, East and West Azerbaijan, and Zanjan. Due to the large number of landslides in rural areas of the country, the perspective of moving to another place and escaping from landslides has changed and the environment of stabilizing the landslides and in situ construction has been replaced. According to field observations during landslide occurrences and observations of groundwater levels in drilled boreholes, in 28 cases of landslides, due to intense and long-duration rainfall, instantaneous saturation of the soil mass was formed and led to landslide occurrences, in 5 cases these slope movements occurred as mudflows. In 25 cases of landslides where water level was observed in boreholes drilled at the site of the landslide mass, the rise in groundwater level (caused by intense and long-duration rainfall and its penetration into the mass) caused slope instability and landslide occurrences. It was also found that a large number of these landslides were located in the medium-risk zone, indicating that landslide activity was stimulated by rising groundwater levels.

Abstract Introduction: The Quaternary period, particularly the Holocene epoch, has witnessed significant climatic oscillations that have profoundly influenced environmental conditions, geomorphic processes, and human civilizations across the globe. The concept of climate, defined as the long-term average of temperature and precipitation, has been continuously fluctuating throughout Earth's history, with inseparable connections to biological and cultural responses. The rise and fall of ancient civilizations have been directly linked to climatic transformations, as changing environmental conditions shaped settlement patterns, agricultural practices, and migration routes of early human societies. Closed basin systems, such as playas and seasonal lakes, serve as exceptional natural archives for reconstructing paleoenvironmental and paleoclimatic conditions due to their high sensitivity to the balance between evaporation and precipitation. These sedimentary environments record physical, chemical, and biological signatures that reflect past climatic conditions, making them invaluable for understanding long-term environmental changes. The southeastern region of Iran, influenced by both the Indian Ocean summer monsoon and mid-latitude westerly winds, has experienced a complex history of climatic and hydrological variations during the late Quaternary. Among these critical sites, the Kaji Namakzar playa, located in the northern part of Nehbandan in South Khorasan Province (eastern Iran), represents a significant yet understudied sedimentary archive. This playa, situated in an arid to semi-arid region with mean annual precipitation below 150 mm and characterized by high evaporation rates exceeding 3000 mm per year, provides an ideal setting for investigating Holocene climatic variability. Despite the importance of understanding past climate dynamics in this region, comprehensive geochemical studies on the sedimentary sequences of the Kaji Namakzar playa have been notably absent. This research aims to address this knowledge gap by conducting detailed geochemical analysis of sediment cores from the Kaji Namakzar playa to reconstruct Holocene climatic and environmental conditions, identify periods of aridity and humidity, determine sedimentary facies and depositional environments, and establish the chronostratigraphic framework of the basin. Methodology: The study area, Kaji Namakzar playa, is located in South Khorasan Province, approximately 70 km north of Nehbandan and 120 km south of Birjand, between 31°45'34" to 32°29'56" North latitude and 59°32'37" to 60°12'52" East longitude. The playa exhibits typical geomorphic zonation from the margin to the center, including alluvial fans, clay flats, wet zones, salt crusts, and seasonal lakes. The geological setting comprises Flysch deposits (extensive in the northern region of the Sahlabad plain), an ophiolitic mélange complex including peridotite, gabbro, diabase dikes, pillow basalts, and sedimentary rocks such as pelagic limestone, radiolarite, and shale from the Late Cretaceous. The area is characterized by faulted, crushed, and folded structures dominated by thrust and strike-slip faults with a northwest-southeast trend, creating a pull-apart basin. Three undisturbed sediment cores (Kj-1, Kj-2, and Kj-3) with depths ranging from 691 to 880 cm were extracted from the playa bed using a manual hand auger, with precise locations recorded by GPS. The cores were described in detail based on sedimentary structures, bedding characteristics, color, texture, evaporite crystal types, relative hardness, and presence of plant and animal remains. A total of 168 sediment samples were collected from the three cores for geochemical analysis at the Geological Survey and Mineral Explorations of Iran laboratory. Elemental analysis was performed using ICP-OES (Varian 735-ES) for trace elements and XRF (MAGIC-PRO) for major elements expressed as oxides (wt%) and trace elements (ppm). Approximately 10% of samples were analyzed as duplicates for quality control. Geochemical data processing included the calculation of elemental ratios (Mn/Al, K/Al, V/Cr, Ti/K, Fe/Ca, Fe/Al, Ti/Al, Mn/Ca, Ca/Sr) that serve as paleoenvironmental proxies based on established relationships between element behavior and climatic conditions. Additionally, sedimentological analysis identified seven primary sedimentary facies through detailed core description. Results: The sediment cores revealed three distinct lithostratigraphic sequences reflecting the basin's depositional history. Core Kj-1 (860 cm) exhibited a complex stratigraphy with the upper section (0-200 cm) dominated by clay and silty mud with alternating sandy mud and sand layers, containing plant remains and organic matter indicating low-energy conditions with high biological productivity. The middle section (200-600 cm) comprised mixtures of sand, silty clay, and clayey sand with halite crystals indicating arid and saline conditions. The lower section (600-850 cm) consisted of thick evaporite layers and mud suggesting significant arid episodes. Core Kj-2 (880 cm) showed more uniform sequences dominated by mud and clayey sand with brown to gray alternations, suggesting a more stable depositional environment with less variation in energy conditions. Core Kj-3 (691 cm) displayed similar patterns to Kj-2 but with greater diversity in the upper 150 cm including sand, mud, clay, and clay nodules. Seven sedimentary facies were identified: Clay (Cl), Silty Clay (ClS), Mud (MU), Silty Clay (SiC), Sand (Sa), Muddy Sand (MS), and Evaporite facies. These facies indicate deposition under fluvial-lacustrine, playa, and alluvial fan environments. Geochemical analysis revealed significant elemental variations. In Core Kj-1, maximum concentrations were dominated by Ti (17 samples) and Sr (4 samples), while K consistently showed minimum values. Al concentrations ranged from 3.19% to 6.66%, Ca from 3.29% to 9.34%, and Sr exhibited dramatic spikes at 220-229 cm (6878 ppm) and 270-275 cm (3189 ppm) indicating intense evaporative events. Cr reached 388 ppm at 625-634 cm, while Ti peaked at 3042 ppm at 840-850 cm. In Core Kj-2, Al ranged from 4.84% to 8.05%, Ca from 2.80% to 9.51%, and an extreme anomaly at 750-760 cm showed Ca at 9.51% and Sr at 5227 ppm with simultaneous minimal values of other major elements. Core Kj-3 exhibited Al values between 4.99% and 8.13%, and Fe ranging from 3.11% to 5.99% with maximum at 240-250 cm. Elemental ratios showed significant fluctuations: Mn/Al ranged 73.43-236.89, V/Cr 0.18-1.07, Ti/K 1265-2458, and Ti/Al 417-592 across all cores. The Mn/Ca ratio varied from 26.67 to 212.44, clearly distinguishing wet and dry periods. The K/Al ratio remained relatively constant (0.22-0.34), suggesting mineralogically consistent clay composition throughout the depositional history. The V/Cr ratio indicated alternating oxic and anoxic conditions, with higher values suggesting increased water depth and enhanced inputs from the catchment. Sedimentation rates derived from stratigraphic correlations indicate higher rates during the early Holocene (up to 5900 years BP) with progressive decrease over time, closely linked to facies variations. Conclusion: The integrated geochemical and sedimentological investigation of the Kaji Namakzar playa sediment cores reveals a complex history of climatic and environmental fluctuations during the Holocene in eastern Iran. The three sediment cores collectively demonstrate distinct climatic phases alternating between humid and arid conditions. Wet periods, characterized by elevated concentrations of Al, Fe, V, Ti, K, and Cr, correspond to enhanced chemical weathering, increased fluvial input, and higher erosion rates within the catchment basin due to intensified precipitation. These humid phases are clearly indicated by increased elemental ratios including Ti/K, Ti/Al, and K/Al, reflecting enhanced detrital input. Conversely, arid intervals are characterized by reduced terrigenous sediment influx, dominance of evaporitic processes, and formation of carbonate and evaporite minerals, as evidenced by elevated Ca and Sr concentrations. The dramatic Sr spikes at 220-229 cm (6878 ppm) and 750-760 cm (5227 ppm) in different cores represent two distinct and intense evaporative events, possibly indicating periods of extreme aridity when the lake completely desiccated. The relatively constant Ti/Al ratios suggest stable provenance of terrigenous materials throughout much of the depositional history, while variations in Fe/Ca and Ca/Sr ratios reflect diagenetic processes and changes in the chemical composition of the basin. The Mn/Al and Mn/Ca ratios effectively distinguish oxic versus anoxic conditions, with higher values indicating oxidizing environments suitable for manganese precipitation. The V/Cr ratio demonstrates the transition between seasonal (oxic) and permanent (anoxic) lake conditions. The sediment cores show that the depositional environment evolved from a relatively deep, stable lake (indicated by green and dark gray clay-rich layers in the lower sections) to a seasonal playa with high salinity (evidenced by halite crystals and evaporite layers in the upper sections). Core Kj-2 and Kj-3, located in deeper and more stable parts of the basin, show greater lithological uniformity with limited organic matter and the absence of halite crystals, suggesting they were less influenced by water level fluctuations and evaporative conditions. The identified sedimentary facies (clay, silty clay, mud, sand, muddy sand, and evaporite facies) confirm the transition from alluvial fan and fluvial environments at depth to playa and lacustrine conditions upward in the sequence. The presence of mud cracks, carbonate nodules, halite crystals, plant remains, and diverse color variations (black, gray, brown, red, green, olive) within the stratigraphic columns provides additional evidence for alternating wet and dry conditions, oxidation-reduction changes, and periodic exposure of sediments to atmospheric conditions. This research significantly enhances our understanding of how sensitive arid and semi-arid environments in eastern Iran have responded to past climatic changes, providing a high-resolution sediment archive that can serve as an analog for predicting future ecosystem responses to ongoing climate change. The findings underscore the vulnerability of playa systems to climatic perturbations and highlight the importance of paleoenvironmental studies for sustainable environmental management in water-scarce regions.

Abstract Introduction: The Earth's surface is directly influenced by climate and environmental conditions, resulting in the preservation of diverse information during soil formation and transformation processes. Paleosols, like modern soils, exhibit characteristics that reflect the environmental conditions prevailing during their formation, making them powerful tools for reconstructing past environmental conditions. In recent years, paleosols have become recognized as reliable indicators enabling scientists to reconstruct environmental and climatic changes. The Quaternary period, characterized by alternating cold glacial and warm interglacial cycles, represents one of the most significant periods of climatic fluctuation in Earth's history. These changes are well-preserved in various archives including marine sediments, lacustrine deposits, and continental loess-paleosol sequences. Loess-paleosol sequences, in particular, are considered invaluable archives for reconstructing Pleistocene-Holocene climate variability. Loess deposits, which cover approximately 10% of the Earth's land surface, consist primarily of fine-grained wind-transported sediments that accumulated during cold, dry glacial periods. These deposits frequently appear as alternating sequences with paleosols that developed during warmer, more humid interglacial and interstadial periods. The loess-paleosol sequences of northern Iran, particularly in the Golestan Province along the southern Caspian Sea coast, represent a critical part of the Eurasian loess belt extending from northwestern Europe to Central Asia and China. These sequences, reaching thicknesses of up to 30 meters along the Alborz Mountains and approximately 60 meters in the northern Iranian loess plateau, provide exceptional archives for Quaternary studies. Approximately 17% (3,200 km²) of the Golestan region is covered by loess deposits. These sediments not only provide detailed information on past climatic changes but also serve as a crucial link between Central Asian and European archives. Soil structural changes can be investigated using various proxies influenced by climate, with soil micromorphology being one of the most precise approaches. In recent decades, micromorphology has gained significant importance in paleoclimate and geological studies as an effective tool for elucidating pedogenic processes and reconstructing past environmental conditions. This science focuses on microscopic examination of pedological features, providing valuable genetic information about soil structure including the analysis of relationships between mineral components, particles, and voids, and their changes over time. The MISECA index (Micromorphological Soil Development Index), originally developed by Khormali et al. (2003) for evaluating argillic horizon development in calcareous soils of arid and semi-arid regions, serves as a semi-quantitative tool for assessing soil development degree. This index incorporates micromorphological criteria including microstructure, b-fabric, clay coatings, decarbonated zones, iron and manganese oxides, and mineral weathering degree, with scores ranging from 0 to 24. The Sa'adabad 3 loess-paleosol sequence, located in the northern slopes of the Alborz Mountains near Gorgan, represents a particularly promising archive for investigating Pleistocene-Holocene climatic fluctuations. This study aims to reconstruct paleoclimatic and paleoenvironmental conditions of the Sa'adabad 3 sequence using integrated micromorphological analysis and the MISECA development index, and to evaluate the applicability of these methods for estimating paleoprecipitation in this region.
Methodology: The study area, Sa'adabad 3, is located on the northern slopes of the Alborz Mountains in Golestan Province, near Gorgan city, at coordinates 54°22'30" E longitude and 36°49'23" N latitude. The region has a mean annual precipitation of 620 mm and is classified as temperate and semi-humid, with xeric and thermic soil moisture and temperature regimes. The sequence, approximately 12 meters thick, comprises 28 distinct horizons. Following field reconnaissance, the Sa'adabad 3 sequence was selected as the most complete loess-paleosol sequence in the region. Scaffolding was installed for precise sample collection from accurate heights. Soil horizons were classified according to the USDA Soil Taxonomy (Soil Survey Staff, 2014) and WRB (2006) systems. Undisturbed samples were collected from each horizon for thin section preparation. For micromorphological sample preparation, undisturbed soil samples were air-dried and impregnated with polyester resin. A mixture of 60% polyester resin with 40% acetone as thinner was used, with 20 drops of stearic acid as catalyst and 10 drops of cobalt hardener added. Impregnation was performed in multiple stages using a vacuum pump in a desiccator to remove trapped air. After hardening, samples were cut into 1 cm-thick slabs, with one surface ground and polished flat. Polished surfaces were mounted on frosted glass slides using a mixture of resin, hardener, and catalyst. Mounted samples were cut to approximately 2 mm thickness using a cutting machine, then ground to 70-100 μm thickness, and finally polished to approximately 30 μm thickness following Murphy's methodology. Micromorphological descriptions were conducted using a polarizing microscope under plane-polarized light (PPL) and cross-polarized light (XPL), following the methodologies of Bullock et al. (1985), Stoops (2003), and Stoops et al. (2018). The MISECA index was calculated by assigning weights to micromorphological parameters including b-fabric, frequency of clay coatings, decarbonated zones, microstructure, iron and manganese oxides, and mineral weathering degree. The cumulative score determined the soil development degree, with higher scores indicating more developed soils.
Results: Micromorphological analysis of the Sa'adabad 3 sequence revealed distinct pedological features across the loess and paleosol horizons. Microstructure analysis showed massive microstructure in CBk, BCk, CBkk, and BCkg horizons, while weak to strong angular and subangular blocky microstructures dominated the paleosol horizons (Btkgss2, BAk1, BAtkg1, Bk1, Btk, Btkgss1). The transition from massive to well-developed blocky microstructure reflects increasing pedogenic development under more humid conditions. Void analysis identified channels, chambers, vughs, and planar voids (planes) in the sequence. Paleosols exhibited abundant channels, chambers, and planes indicating intense biological activity (roots and fauna), while loess horizons were dominated by channels and vughs. The b-fabric was predominantly crystallitic (calcitic) throughout most horizons, with speckled b-fabric occurring in some argillic horizons, and a combination of both types observed in certain horizons. Coarse fragments were dominated by subangular to angular quartz grains. Clay coatings (clay cutans) were observed as orange-colored features around voids and within the soil matrix, predominantly in argillic horizons (Btkgss, Btkg, Btk, BAtkg), indicating active clay translocation (lessivage) under humid conditions. Carbonate pedofeatures included nodules, concretions, coatings and hypocoatings, needle-fiber calcite, micrite, and sparitic calcite. Needle-fiber calcite indicated suitable moisture conditions and decomposable organic matter in paleosols. Calcitic crystallitic b-fabric resulted from carbonate leaching and reprecipitation in lower horizons. Decarbonated zones were observed, indicating carbonate dissolution and translocation. Micritic and sparitic calcites represented different precipitation rates and time scales. Iron and manganese pedofeatures included coatings, hypocoatings, quasi-coatings, and nodules, formed under alternating oxidation-reduction conditions associated with periodic wetting and drying. Biological remains included mollusk shell fragments (more abundant in loess horizons indicating cold, dry conditions) and faunal excrements (indicating suitable environmental conditions for biological activity). The MISECA index classified soil horizons into well-developed, moderately developed, and weakly developed categories. Horizons Btkgss (2350-2250 cm), Btkg (2195-2250 cm), Btk3 (1390-1440 cm), BAtkg (1882-1970 cm), Btkg (1600-1670 cm), and Btk (1390-1520 cm) were classified as well-developed soils. Decarbonated zones, iron and manganese oxides, and clay coatings had the greatest influence on the index and soil development. Based on the MISECA index and correlation with precipitation graphs established by Khormali et al. (2012), Taheri et al. (2016), and Shahriari et al. (2018), annual precipitation estimates for the Sa'adabad 3 region were derived. The most developed horizons (Btkgss1 and Btk1) indicated estimated annual precipitation of approximately 741 mm, while the least developed horizon (BCkg) indicated 470 mm. In horizons Bkkm and CBk, where simultaneous soil distribution and loess particle deposition occurred, precipitation decreased to approximately 370 mm.
Conclusion: Integration of micromorphological features and the MISECA development index for the Sa'adabad 3 sequence provides robust evidence for multiple-stage climatic fluctuations during the Pleistocene-Holocene period in northern Iran. The observed variations in horizon development degree, pedofeature types, and patterns of mineral accumulation or depletion indicate significant climatic oscillations during paleosol formation. The MISECA index demonstrates a strong positive correlation with mean annual precipitation, enabling quantitative estimation of past rainfall conditions. Horizons with low index values, characterized by weak structure, primary carbonate accumulations, and limited evidence of clay translocation, represent weakly developed soils formed under semi-arid climatic conditions with low weathering intensity and short pedogenesis duration. Conversely, horizons with higher index values, exhibiting evidence of active deep leaching, chemical weathering, and advanced soil structure development, indicate more advanced pedogenesis under semi-humid to humid conditions. The presence of argillic horizons with clay coatings (clay cutans), angular to subangular blocky structure, and weak reaction to hydrochloric acid indicates active clay translocation (lessivage) and gradual carbonate removal from upper horizons through water infiltration. These features typically develop under conditions of sufficient moisture, denser vegetation cover, and longer pedogenesis duration, indicating relatively stable humid climatic conditions during interglacial periods. The occurrence of needle-fiber calcite in paleosols provides further evidence for suitable moisture conditions and decomposable organic matter, consistent with warmer and more humid climates. Iron and manganese pedofeatures, including coatings and nodules, indicate alternating oxidation-reduction conditions associated with periodic water saturation and drainage, reflecting climate variability. Mollusk shell fragments in loess horizons indicate cold, dry glacial conditions, while faunal excrements in paleosols reflect favorable environmental conditions for biological activity. The estimated precipitation values (370-741 mm) derived from the MISECA index demonstrate that the Sa'adabad 3 region experienced progressive climatic shifts from semi-arid to semi-humid and ultimately to humid conditions during paleosol formation. These climatic changes likely occurred in response to periodic fluctuations in precipitation, temperature, and vegetation expansion or retreat during Quaternary interglacial and post-glacial periods, providing the necessary conditions for advanced genetic and structural soil evolution. This research confirms that integrated micromorphological analysis and the MISECA index are powerful and reliable tools for paleoclimate reconstruction in loess-paleosol sequences, with significant implications for understanding regional climate dynamics and their impact on landscape evolution in northern Iran. The findings contribute to the broader understanding of Quaternary climate variability in the Eurasian loess belt and highlight the importance of northern Iranian loess-paleosol sequences as exceptional archives for paleoenvironmental research.