Paleosols derived from loess and loess-like sediments in the Basin of Persepolis, Southern Iran

Abstract

In the Basin of Persepolis, late Quaternary basin fills consist of loess, loess-like sediments and fine- or coarse-textured alluvium. The loess and its derivatives are divided by various paleosols, which consist of well-developed fBw(t)-horizons, weakly developed fBwC- and fBwgC-horizons, as well as fAh-horizons. Strongly developed fBtk-horizons occur in stony alluvial fan deposits or superimpose residual loams of carbonate bedrock mixed with loess. The different types of paleosols result from various degrees of soil development as evidenced by micromorphological features such as the birefringence fabrics, and less clearly by pedochemical properties. Based on the stratigraphy and different degrees of soil development, various phases of soil formation and sediment deposition can be distinguished. Infrared optically stimulated luminescence (IRSL), thermoluminescence (TL) and radiocarbon dating methods are consistent with the stratigraphy and yielded, except for one sample, age estimates of less than about 30 ka. The strongly developed fBw(t) and fBtk horizons reflect soil-forming periods prior to the Last Glacial Maximum (LGM) and probably during Marine Isotope Stage 5 (MIS 5), with climatic conditions comparable to the present-day. The upper loess deposits likely formed under considerably cooler and drier climatic conditions during the LGM. However, poor bleaching of sediments prior to final deposition, as indicated by greater TL than IRSL dates, suggest fluvial reworking of these loesses. The weakly developed fAh, fBwC, and fBwgC horizons may indicate interstadial periods of MIS 3 and short phases of climate amelioration during the early Holocene. The formation of the modern soil probably did not start before 7–9 ka.