Late Quaternary pluvial episodes in a dryland of central Iran: insights from a radiocarbon chronology of pedogenic carbonates

Although geomorphic and pedogenic proxies have proved the occurrence of pluvial episodes in arid regions of central Iran during the late Quaternary, precise timing of  such events have remained unclear and have been under debate for long time. Pedogenic carbonates can provide insight into the timing of soil leaching and pluvial periods. Therefore, the aim of this study was to establish an accurate chronology based on pedogenic carbonates and using radiocarbon to understand the regional and global temporal correlations of pluvial events in eastern Isfahan (central Iran). For this purpose, two palaeosols having non-calcareous gravels on the summit of alluvial landforms were selected. Macromorphology of the carbonates was checked in the field and submicroscopy was studied by scanning electron microscopy. Radiocarbon analysis was performed using accelerated mass spectroscopy (AMS) at ETH Zurich and the ages were calibrated using OxCal 4.4 software. In addition, the d¹³C values for both the soil matrix and pedogenic carbonates was measured using mass spectroscopy. The pedogenic carbonates occurred predominantly as gravel coating in the Bk and as fine nodules in Btk horizon. Submicroscopic analyses of the carbonates showed the abundance of micritic and microsparic rhombohedral crystals of calcite without signals of recrystallization or overprinting. The d¹³C  values indicated that the upper ~50cm of the pedons were influenced by calcareous dust input. Radiocarbon dating of deep carbonates revealed the existence of at least four phases of considerable leaching and, thus, humid conditions: around 42.2–39.5, 39.3–36.2, 31,6–29.2 and 26.9–26.0 ka BP, i.e., during marine isotope stage (MIS) 3a and 3b. These ages correlated well with regional paleoclimatic proxies in the Levant and NE Syria suggesting the impact of the Mediterranean cyclones and westerlies and the increase in precipitation in the region. The global correlation of our ages with Greenland ice core records demonstrated that wet periods in central Iran were in agreement with periods of low oxygen isotope values (stadial periods) in Greenland suggesting a climatic teleconnection between North Atlantic and western Asia.