Sedimentological study of the stratigraphy at the site of Homo erectus yunxianensis in the upper Hanjiang River valley, China

Geomorphological and sedimentological investigations were carried out in the upper Hanjiang River valley. The sediments in the profile at the site of Homo erectus yunxianensis were sampled systematically. Magnetic susceptibility, loss-on-ignition, particle size distribution and geochemical elements were analyzed in the laboratory. The results show that the medium sand and gravel beds in the lower part of the profile are fluvial deposits of the third terrace land of the Hanjiang River, the upper part is a blanket of aeolian loess and palaeosol deposited from dust storms and dust falls. According to stratigraphical correlation and palaeomagnetic dating, the carbonate nodules encasing the fossils of H. erectus yunxianensis and other mammalian faunas were formed during 800-785 ka. The palaeosol overlying on the fossil layer is defined as the S8 that was developed during the MIS-19, and the aeolian loess below the fossil layer is defined as L9 that was deposited during MIS-20. These loess and palaeosol are similar to those over the Chinese Loess Plateau and correlatable with those in the Luochuan loess profile. They are very different from the fluvial deposits in the Hanjiang River valley. These indicate that H. erectus yunxianensis lived at a climatic transition from glacial to interglacial. These results are very important in understanding the environment of H. erectus yunxianensis in the upper Hanjiang River valley.