New progress in the geochronology of hominin relics in loess strata of the Chinese Loess Plateau

Many hominin sites have been found since 1920 in the Chinese Loess Plateau and its adjacent areas, such as Nihewan, Shuidonggou, Dingcun, Dali, Kehe, Xihoudu, east Qinling Mts. and Lantian. Recently two very important investigations of hominin occupation in the Chinese Loess Plateau have caused a huge impact in the world. The Homo erectus cranium from Gongwangling, Lantian County, Shaanxi Province of China is the oldest fossil hominin specimen in North China. It was found in 1964 in a layer below the Jaramillo subchron and was initially attributed to loess L15 in the Chinese loess-paleosol sequence, with an estimated age of ca. 1.15 Ma (millions of years ago). Here, we demonstrate that there is a stratigraphical hiatus in the Gongwangling section immediately below loess L15, and the cranium in fact lies in paleosol (S) S22 or S23, the age of which is ca. 1.54 similar to 1.65 Ma. High-resolution paleomagnetic investigations at two sections at Gongwangling and one at Jiacun, 10 km to the north, indicate that the fossil layer at Gongwangling and a similar fossil horizon at Jiacun were deposited immediately before a short normal magnetozone above the Olduvai subchron, which is attributed to the Gilsa excursion and dated elsewhere to ca. 1.62 Ma. Our investigations thus demonstrate that the Gongwangling cranium is slightly older than ca. 1.62 Ma, probably ca. 1.63 Ma, and significantly older than previously supposed. This re-dating now makes Gongwangling the second oldest site outside Africa (after Dmanisi in Georgia) with cranial remains, and causes substantial re-adjustment in the early fossil hominin record in Eurasia. At the same time, the earliest hominin evidence outside Africa came from our newly found 2.12-million-year old stone tools, which were found at Shangchen, a paleolithic locality, in Lantian County in the southern margin of the Chinese Loess Plateau. The loess-paleosol sequence and magnetostratigraphy were established by using different methods, including marker layers, sedimentology, mineralogy, geochemistry, paleomagnetism and rock magnetism. The stone artefacts (including cores, flakes, scrapers, points, borers, hammerstones and picks) from the Shangchen locality were found in a successive loess-paleosol section, and 17 stone artefact horizons of early Pleistocene strata (1.26-2.12 Ma) were used to establish the chronological framework of the loess-paleosol-paleolithic culture sequence during the early Pleistocene. The artefact-bearing layers were dated by linking the geomagnetic polarity variations changes in the earth's magnetic field. The oldest artefacts (2.12 Ma) found within L28 layer between the Olduvai subchron and the Reunion excursion are ca. 270 thousand years older than the 1.85-million-year old skeletal remains and stone tools from Dmanisi, Georgia, which were previously the earliest evidence of hominin outside Africa. Because no skeletal remains were found with the stone tools from Shangchen, we do not know who made them, but it is likely to be an early form of our own genus Homo. Moreover, the length of our artefact sequence with17 stone cultural horizons (probably with a high average occupation of similar to 50 ka) found in the same locality - is very rare world-wide, and indicates a repeated - but not necessarily continuous - hominin occupation of the Chinese Loess Plateau for almost a million years between 1.26 and 2.12 Ma. Most occupations occurred in the paleosol layers (11 layers of total 17 layers) which indicate a kind of warm-wet climate. This breakthrough expands the "Loess lithic industry" and the "Loessic Geoarchaeological Belt" direction of research on the internationally-leading Chinese loess-paleosol sequence, and prompts reconsideration on the pattern of early human's origin, migration and dispersal.