Landscape changes, terraces and deposits of the river Pulvar (Fars, Iran): new perspectives and new chronology derived from OSL dating

International audienceThis work is implemented in the frame of an Iranian-French archaeological project focusing on the area of Pasargades, an Achaemenid capital founded in the middle of the 1st mill. BC, located in an intermountaneous flooding plain in the Zagros. The goal of the project is to understand the regional human occupation, consequently deeper study of the large-scale Holocene landscape dynamics is necessary. This project is implemented under the agreement of the of the Iranian Centre for Archaeological Research (ICAR) with the support the Pasargadae World Heritage Site Office, the Shahid Beheshti University, the French National Agency for Research (ANR), and the French Foreign Ministry.Critical results concerning landscape changes in mountain environment has been produced. Especially for the Holocene river dynamics, three main phases have been characterized corresponding to three alluvial terraces (T1 to T3) mapped and analyzed over the whole studied area.A large scale phase of alluvial deposits occured from the beginning of the Holocene until middle or even recent Holocene. It is characterized by a thick fine sediment layer visible throughout the region which fills plains and valleys. This deposit was cuted as terrace 15 meters up to the river (T1). The controlling factors of this accumulation appears to be climate and geological structure. Holocene climatic optimum (8000-5000 BP) increased the erosion of previous levels and especially sandy-marly quaternary deposits. This would explain both the high carbonate content and the fineness of the particles, because the quaternary deposits consist partly on the same type of sediment. Furthermore the increase of the precipitations and the vegetation covering could explain the strong cutting of the T1 terrace. An Achaemenid dam built over the T1 terrace gives a relative date to this phenomena (at least 500 BC). OSL dating (results to be received during the first 2019 semester) will precise this event.The thickness and granularity of the sediments in T1 are stricking, in such an environment. The steepness of the side slopes, the former Pleistocene deposits and the presence of intermountain plains downstream of the studied section (Tang-e-Bolaghi gorge) could have played a decisive role. The second terrace (T2) is linked to reactivation of the alluvial dynamic, with coarser deposit in a context that seems relatively wet. The obtained C14 dates refer to the Islamic period as also demonstrated by a ceramic sherd found in a sequence in the plain of Pasargades. Third terrace (T3) is less visible but still present as benches along the present river bed sides. It shows the sub-actual river dynamics, in elevation perhaps due to the excessive puncture of alluvium in the Pulvar bed

Geometry and development of the Jhajara thrust: An example of neotectonic activity in the Pinjaur Dun, NW Himalaya

Mountain fronts of orogenic belts are marked by dynamic landscape changes under the influence of contemporary tectonic activity. Longitudinal valleys (locally called as Duns) constitute important landforms associated with some segments of the Himalayan mountain front. A neotectonic feature – the Jhajara thrust, has been identified in the Pinjaur Dun of NW Himalaya on the basis of structural mapping and tectonic geomorphological analysis. Optically stimulated luminescence dating on quartz sand samples from the geomorphic surface constrains the last displacement associated with the Jhajara thrust to before $\sim 55.7 \pm 6 ka BP$

Luminescence and radiocarbon dates from alluvial sediments, Podhale, Central Europe — A methods comparison

Optically stimulated luminescence (OSL) and radiocarbon (14C) techniques were employed to investigate the absolute ages of alluvial sediments in Podhale in the West Carpathians, southern Poland. This is an approach to (i) testing the credibility of the above dating methods by their reciprocal age control and (ii) further implications to regional geochronology and to dating campaigns of alluvial sequences elsewhere. Nine geological sections comprised of mineral and organic material were selected for the study. Our age determinations range from 26.9 to 2.27 ka, and are in good geochronological order. OSL age estimates show good agreement with independent ages from radiocarbon dating. However, in three alluvial successions the discrepancy between the resulting ages is considerable. We attribute the difference to the partial bleaching, and organic material redeposition. We also report on an age reversal of sediments in a single geological section. This might have been resulted from the alluviation-erosion scheme of meandering rivers over a millennial time-scale, i.e. the dominance of channel migration, point bar deposition (lateral accretion), and crosswise erosion. Finally, new geochronological data are provided abolishing sediment age assumptions based on uncertain chronostratigraphical approaches

Pulvar River changes in the Pasargadae plain (Fars, Iran) during the Holocene and the consequences for water management in the first millennium BCE

International audienceLocated in the middle basin of the Pulvar river (Fars, Iran), Pasargadae was founded around 550 BCE in the early days of the Achaemenid Empire. Its territory is dotted with remains of imposing hydraulic facilities (dams, dikes, canals), some of which date to that very period. The purposes and functions of these structures, built to exploit surface water, located in today’s landscape (a deeply incised valley with temporary watercourses), raise questions and problems for which geomorphological studies provide major elements for consideration. Erosion of the Pleistocene glacis by the Pulvar and its tributaries caused several phases of alluvial deposition during the Holocene. They can be seen today in the Pasargadae region by examining the remains of three well-developed steplike terraces. These sedimentary units are primary archives for the reconstruction of river dynamics, and thus allow a better estimation of water availability. Since 2016, within the framework of a joint Iranian-French archaeological mission, several geo-archaeological campaigns have been carried out. Sediment analyses, C-14 dating and OSL dating of sediments collected in the alluvial formations, as well as in archaeological contexts, have been made to accurately reconstruct the variations over time in the Pulvar regime, as well as the past regional waterscape. From the beginning of the Holocene to the onset of the 1st millennium BCE, the Pulvarcatchment area was marked by an aggradation phase, which led to the valley being filled with alluvial deposits. This sedimentary unit provided vast areas of arable land where cultivation could be enhanced by irrigation. The creation of water inlets in the Pulvar and its tributaries was at that time facilitated by riverbeds less incised than present-day ones. Ancient hydraulic systems reflect these geomorphological conditions, since they were built to manage higher water levels, as well as stronger flows, when compared to irrigation facilities developed in modern time