Loess-soil sequence at Toshan (Northern Iran): Insights into late Pleistocene climate change

The knowledge of palaeoclimate in Iran is still limited. However, insight into the timing and the dynamics of Quaternary climate change in Iran might offer valuable information to improve the global palaeoclimate record. The loess-soil sequence of Toshan provides the first high-resolution record of late Pleistocene climate dynamics in Iran and complements the hitherto known sections at Neka, Now Deh and Agh Band to establish a pedostratigraphic record of the north-eastern Caspian Lowland. Our spectroscopic and grain-size analysis are combined to propose (i) a pedostratigraphical scheme for the sequence at Toshan, (ii) describe and estimate the degree of soil development of selected stratigraphical units, (iii) infer palaeoclimatic information, and provide (iv) a correlation with previous loess-palaeosol records of N-Iran as based on pedostratigraphic assumptions. The section at Toshan hosts a strongly developed reddish-brown argillic palaeosol (Bt) as well as eight moderately to weakly developed brownish palaeosol horizons lacking clay illuviation features (Bw/Bwk). These remnants of fossil soils are separated by finely textured loess and horizons that host characteristics of both loess and mineral subsoils (CB/CBk), giving evidence for syngenetic soil formation. The stratigraphical succession of palaeosols, loess and syngenetically altered sediments, covering the last ca. 130 ka, gives evidence for recurrent climate changes as well as fluctuations between dominance of soil formation or dust accumulation in relation to changes in moisture regime. The formation of Bt and Bw/Bwk-horizons is related to relatively humid and warm conditions likely corresponding with interglacial and interstadial climate.