Landscape evolution in the northeastern Iranian Plateau reconstructed from Late Pleistocene to Holocene sediment archives – a project outline

The sediments of the great basins of Iran bear considerable potential for the reconstruction of pastgeomorphological processes and ecological changes (e.g. Sharifi et al., ۲۰۱۵, Büdel ۲۰۲۰). Recent studiesrevealed a rich landform inventory related to the Bajestan Playa in northeast Iran. In contrast to lakesediments, those from the playa bear poor amounts of biogenic environmental and climate proxyindicators, but anyway provide essential information for reconstructing past environmental and climaticconditions. The geomorphologic processes, which primarily shaped this landscape, take place on extentflood plains surrounding a central playa, which holds the local name ‘Kavir-e-Namak’ .A pediment withalluvial fans slopes towards the basins center. The bedrock is largely composed of Mesozoic sediments andPre-Neogene volcanic formations and is highly affected by tectonic activity in course of the movement ofthe Central-East Iranian Microcontinent (CEIM) (Pourlatifi ۱۹۹۸, Calzolari et al. ۲۰۱۶). Prevailing strong,dry winds from northeastern and southwestern directions and high temperatures today favor a hot arid tosemi-arid steppe climate. Aeolian and fluvial processes constantly alter the surface, and their combinedeffect results in a complex assemblage of alternating fluvial and aeolian sediment layers and landforms. Toincrease our knowledge of the basin's sedimentary history and local landscape evolution, detaileddeciphering of the different geomorphological activities is of paramount importance. In this context, thedetailed analysis of Quaternary relief features allows for a combined examination of multiple geologicalarchives and thus enables a synthesis from conclusions about the predominating environmental conditionsduring their formation. This way, even geological archives with limited coverage in space and time andonly sporadic appearance connect efficiently for an extensive paleo environmental reconstruction. Inpreliminary studies, first samples of different types of landforms from the central playa and the fluvialplain at Bajestan were described and samples were taken to laboratories in Germany and Iran. All sampleswere treated and analysed for grain-sizes, and mineralogical and elemental components using laser and xraydiffractometry, optical emission spectrometry and x-ray fluorescence spectroscopy. Morphoscopiccharacterisation was performed and thin sections were prepared for selected layers and describedaccording to the guidelines from Stoops (۲۰۰۳). The statistical evaluation of the granulometric signal wasperformed by a decomposition of multi-modal grain-size distributions, called end-member modellinganalysis, using the “EMMAgeo”-package for R (Dietze et al. ۲۰۱۹). One of the most important aspects forfuture analysis will be the precise determination of the time of deposition, as a correlation of the divergingsediment facies is very limited otherwise. Therefore, the chronostratigraphic classification of the archiveswill be a crucial part of the correlation and combination of their individual paleoenvironmental signals.The preliminary laboratory analysis and statistics refined the documentation of the complex genesis ofindividual landforms and allowed a first association with varying sedimentary environments. It alsoshowed that a complex combination of aeolian, fluvial and littoral processes seems to individuallycharacterise single sedimentary phases, which in a larger framework are formative for the local landscapehistory. In course of the applied project, effect and extent of the post-LGM lake level retreat within theBajestan Playa in the northeastern Iranian Bardeskan Basin will be determined. This will provide a base forthe reconstruction of regional and supraregional tendencies of late Pleistocene and Holoceneenvironmental change.

Keywords:

Basin geomorphology , Sediment archive , Playa , End-member modelling , Grain size distribution , Palaeoclimate , Drylands , Iran