Paleoenvironmental and Paleoclimatic Changes and their Reciprocal Effects on Ancient Settlements in Southern Iran, with a Focus on the Halil Rud Cultural Zone, from 4000 to 2900 Years Ago

Abstract
In the present study, multi-proxy climatic records—including palynological, sedimentological, and geochemical data—were employed to reconstruct palaeoenvironmental changes in the Halil Rud cultural zone from 4 to 2.9 ka BP, based on a 2.5-meter sediment core retrieved from a peat bog near the excavation site at Konar Sandal, located near Jiroft in southeastern Iran. The relatively low abundance of desert shrubs in the Konar Sandal sediment core indicates a humid/semi-humid climate from approximately 4 to 3.4 ka BP. Tepe Yahya shows occupation during this period (IVA, ca. 4.0-3.6 ka BP), followed by several centuries with no evidence of sedentary settlement in the region. A similar pattern is observed in the Lut Desert, Sistan, and Bard Sir Valley. However, in highland southwestern Iran, whereby the Kaftari period represents a peak in sedentary occupation in the Kur River Basin. Subsequently, in the later 4th millennium BP (Qaleh/Shogha-Teimuran periods, ca. 3.6-2.9 ka BP), there was a significant decline in population at the Kur River Basin. The high abundance of desert shrubs and the dominance of Amaranthaceae and Artemisia in the Konar Sandal sediment core signify dry environmental conditions alongside reduced agricultural activities in the Halil Rud cultural zone between 3.4 and 2.9 ka BP. This period, particularly around 3.2 ka BP, was characterized by severe droughts that coincided with a decline in settlements in the region. In southeastern Iran, occupation is currekntly not attested in Sistan, the western Lut, the Bard Sir Valley, or the Bam region before 2.8 ka BP. However, recent studies have recorded early Iron Age settlements (around 3.3-3 ka BP) at Tom-e Gavan and Konar Sandal North, partially filling the long settlement gap and aligning with the gradual rise in Cerealia-type pollen recorded in the Konar Sandal sediment core. The Kur River Basin witnessed a significant decline in settlement during the Qaleh/Shogha-Teimouran periods.
Keywords: Agro-pastoralism, Climate, Konar Sandal, Late Holocene Epoch, Peat.
 
Introduction
The Early Bronze Age, occurring in the 3rd millennium BCE, saw the emergence and prosperity of human societies in southeastern Iran. Notable settlements such as Konar Sandal, Shahr-i Sokhta, Tepe Yahya, Bampur, and Shahdad were integral to trade, agriculture, and cultural exchange. The community at Konar Sandal, situated by the Halil Rud, is particularly recognized for its unique ‘Jiroft’ artistic style, which features distinctive steatite engravings and clay pottery, alongside an early writing system. Investigations suggest that the Jiroft culture represented a socio-economically advanced agrarian society with far-reaching trade connections to other cultural centers. Nevertheless, around 4200 cal yr BP, the Halil Rud area and other Early Bronze Age civilizations, including the Akkadian Empire, the Old Kingdom of Ancient Egypt, and the Indus Valley Civilization, experienced a significant decline. This collapse is likely linked to a drought event around 4200 cal yr BP, which caused inadequate rainfall and subsequent desertification, severely impacting agricultural viability and leading to the abandonment of these settlements.
The main studies in Konar Sandal have focused on archaeological findings, geomorphology and bioarchaeology. However, the harsh environmental conditions combined with complex phytogeographic settings coupled with lack of suitable sedimentary archives and lack of multi-proxy high-resolution palaeo-environmental data hampers our understanding about the cultural dynamics in southeastern Iran.
Main questions of this study are: How did historical societies cope with aridity? What did they cultivate? What kind of natural vegetation was exploited and how this vegetation was impacted by human activities during wet or dry episodes? 
This research seeks to explore the historical patterns of regional climate variability, as well as paleoenvironmental and paleoclimatic transformations, and their interrelations with ancient settlements in southern Iran, particularly within the Halil Rud cultural zone, spanning the period from 4000 to 2900 years ago. The investigation centers on sediment cores obtained from a peat deposit adjacent to the excavation site at Konar Sandal. Variations in wetland water levels, surrounding flora, and other influencing factors are anticipated to be intricately linked to both natural climatic shifts and anthropogenic activities within these communities.
In order to meet these objectives, the study involve detailed analyses of:
Grain size and Magnetic susceptibility studies to trace landscape changes. Total organic carbon and nitrogen, along with the C/N ratio to trace organic matter source. Pollen analyses to determine the paleo-vegetation dominance and peatland water level.
 
Discussion
The results reveal that the Konar Sandal peatland ecosystem evolved from a shallow marsh around 4000–3900 cal yr BP to a water-rich wetland between 3800 and 3400 cal yr BP, dominated by Sparganium/Typha and Poaceae. The presence of Riparian trees (e.g., Salix and Tamarix) in the pollen record suggests that climatic conditions were sufficiently humid to support adequate water discharge in the Halil River and/or the expansion of human-made canals and channels. However, given the low pollen production capacity of Tamarix, its pollen presence likely indicates abundant riparian forests. Changes in vegetation composition and the abundance of Cerealia-type pollen suggest agricultural activities between 3900 and 3700 years ago. Studies indicate that wet to semi-wet conditions were also recorded in various regional lakes during this period.
The present study reveals that, despite minimal signs of agricultural activity between 4000 and 3200 cal yr BP, there were two probable periods of extensive agricultural activity between 3900 and 3700 cal yr BP.
Between approximately 3400 and 2900 cal yr BP, the Jiroft region experienced severe droughts, indicated by the abundance of desert shrubs and the dominance of Artemisia and Calligonum pollen. The wetland underwent oxidation (decomposition) due to desiccation. Overall, organic matter content was very low during this period. Oxidation facilitated the degradation of organic matter and the formation of amorphous peat, which is common in the region. The water table of the peatland declined during this time, indicating drought conditions. Limited water resources may have hindered tree growth, as evidenced by the disappearance of riparian trees and the emergence of Prosopis. These climatic changes align with findings from other studies in the Middle East. With the onset of the Iron Age (3400–2900 cal yr BP), the region experienced severe aridity and water scarcity, leading to population decline and settlement abandonment. Unfavorable climatic conditions had a profound impact on the lifestyle of the region’s inhabitants, potentially prompting a shift from agriculture to pastoralism. The driest conditions in the Iranian Plateau occurred around 3200 cal yr BP, coinciding with the decline of late Bronze Age settlements in ancient Mesopotamia and the eastern Mediterranean.
 
Conclusion 
The unique combination of phytogeographic, climatic, and archaeological characteristics has made the Halil River cultural basin an ideal location for studying paleoclimatic changes and human-environment interactions. Results obtained from various climatic proxies (sedimentological, geochemical, and palynological) indicate that the region experienced environmental changes between 4000 and 2900 years ago, driven by both natural and anthropogenic pressures. During the late Holocene, the region was characterized by a Saharo-Sindian pseudo-savannah flora vegetation cover. However, the landscape transitioned from scattered shrub forests to open and degraded shrublands. 
The Konar Sandal peatland evolved from a shallow marsh around 4000–3900 cal yr BP to a water-rich wetland between 3800 and 3400 cal yr BP. Cerealia-type pollen between 3900 and 3700 cal yr BP indicates agricultural activity, supported by wet to semi-wet conditions in regional lakes. However, minimal agricultural signs are noted between 4000 and 3200 cal yr BP, with two probable periods of extensive activity around 3900–3700 cal yr BP.
Severe droughts between 3400 and 2900 cal yr BP in Jiroft are evidenced by desert shrubs and Artemisia/Calligonum pollen. The wetland dried, causing organic matter oxidation and amorphous peat formation. Declining water tables and the disappearance of riparian trees, replaced by Prosopis, reflect drought conditions. These changes align with broader Middle Eastern aridity during the Iron Age, causing population decline, settlement abandonment, and a potential shift from agriculture to pastoralism. The driest period around 3200 cal yr BP coincided with the collapse of late Bronze Age settlements in Mesopotamia and the eastern Mediterranean, highlighting the widespread impact of climatic changes on ancient civilizations.
The findings of this study highlight the relationship between environmental changes and human lifestyles in the Halil River cultural basin. The Konar Sandal sediment core analysis reveals significant human intervention in wetland hydrology since ancient times. Human activities such as cereal cultivation, burning, and vegetation clearance are traceable throughout the study period. Specifically, drought had a major impact on agricultural-pastoral communities. However, complete abandonment of settlements is unlikely, as pollen from plants such as Plantaginaceae and Polygonum aviculare-type persists during dry periods, particularly between 3400 and 2900 cal yr BP. It appears that pastoralism expanded around 3600 cal yr BP. The identified pollen during this period is likely associated with livestock trampling and grazing. Thus, harsh climatic conditions may explain the development of a nomadic pastoralist lifestyle, which has deep historical roots in the region.