Holocene settlement shifts and palaeoenvironments on the Central Iranian Plateau: Investigating linked systems

Abstract

For thousands of years, humans have inhabited locations that are highly vulnerable to the impacts of climate change, earthquakes, and floods. In order to investigate the extent to which Holocene environmental changes may have impacted on cultural evolution, we present new geologic, geomorphic, and chronologic data from the Qazvin Plain in northwest Iran that provides a backdrop of natural environmental changes for the simultaneous cultural dynamics observed on the Central Iranian Plateau. Well-resolved archaeological data from the neighbouring settlements of Zagheh (7170-6300 yr BP), Ghabristan (6215-4950 yr BP) and Sagzabad (4050-2350 yr BP) indicate that Holocene occupation of the Hajiarab alluvial fan was interrupted by a 900 year settlement hiatus. Multiproxy climate data from nearby lakes in northwest Iran suggest a transition from arid early-Holocene conditions to more humid middle-Holocene conditions from c. 7550 to 6750 yr BP, coinciding with the settlement of Zagheh, and a peak in aridity at c. 4550 yr BP during the settlement hiatus. Palaeoseismic investigations indicate that large active fault systems in close proximity to the tell sites incurred a series of large (M W ~7.1) earthquakes with return periods of ~500-1000 years during human occupation of the tells. Mapping and optically stimulated luminescence (OSL) chronology of the alluvial sequences reveals changes in depositional style from coarse-grained unconfined sheet flow deposits to proximal channel flow and distally prograding alluvial deposits sometime after c. 8830 yr BP, possibly reflecting an increase in moisture following the early-Holocene arid phase. The coincidence of major climate changes, earthquake activity, and varying sedimentation styles with changing patterns of human occupation on the Hajiarab fan indicate links between environmental and anthropogenic systems. However, temporal coincidence does not necessitate a fundamental causative dependency.

New evidence for large earthquakes on the Central Iran plateau: palaeoseismology of the Anar fault

“…These two extreme hypotheses raise the problem of the abandonment age of the alluvial fan at the precise location where the trench was excavated. Interestingly, this rate is comparable to the late Pleistocene-Holocene aggradation rates derived from alluvial sediments in similar deposition settings at southwestern Nebraska, Negev desert and Central Iran plateau (Daniels et al 2003;Guralnik et al 2011;Schmidt et al 2011). 1, see also figs 4a and 7 in Le Dortz et al 2009) at 0.8 m below the surface of another fan on the riser of a ≈4.5-m incised dry stream, suggests that its surface was abandoned some 9-10 ka ago at this site whereas the fan surface at the trench site cannot be older than 6.6 ka.…”

Evidence of resilience to past climate change in Southwest Asia: Early farming communities and the 9.2 and 8.2 ka events

“…Firstly, more information is needed on local climate and environment. For example, the assertions that settlement on the Iranian Plateau was delayed due to unfavourable conditions (Schmidt et al, 2011), while settlement in the Fars region may have increased or changed during the 8.2 ka event (Nishiaki, 2010;Weeks, 2013), need to be checked against data from local climate records. Secondly, more site-specific detailed studies focusing on the ecological bases and strategies, like conducted for Sabi Abyad, are needed.…”

“…Interestingly, the start of the occupation on the Iranian Plateau occurred from ca 8000 cal BP (long-lived samples) or 7500 cal BP (short-lived samples) (Fig. 5K) and may therefore be concurrent with increasing precipitation and humidity (Schmidt et al, 2011). This is an intriguing possibility, but more precisely dated local climate records and more archaeological 14 C-dates on short-lived samples are needed to assess this.…”

Modern impacts on an ancient landscape, the piedmont plain in southwest Turkmenistan

“…The OSL dates from the lowest part approximate the onset of this loess deposition between 3.1 ± 0.6 and 3.4 ± 0.1 ka (samples Turk OSL 1 and LUM 1, respectively). Comparative active loess depositions are reported from the Iranian plains and might point to more arid conditions . However, interpretation is difficult, because different reasons might cause the deposition of the loess layer, which here is up to several meters thick.…”

“…Comparative active loess depositions are reported from the Iranian plains and might point to more arid conditions. 43,57 However, interpretation is difficult, because different reasons might cause the deposition of the loess layer, which here is up to several meters thick. Reasons might be: (1) less vegetation or changing wind directions in the potential source areas, leading to intensified deflation, (2) more vegetation in the sink area, leading to more deposition, (3) the fluvial redeposition of loess, which is readily available in the lower Kopet Dag range, and (4) the alteration of vegetation or fluvial patterns by humans.…”