Deduction of the age of the Dali hominin fossil based on regional geomorphic-sedimentary evolution

Abstract

Dali hominin, an archaic type of early Homo sapiens, is of great significance to the understanding of the evolutionary processes of Homo sapiens in China. However, its age remains debatable. There developed a series of lacustrine and alluvial terraces both in the northeastern part of the Weihe Basin and in the stretch of the Luo River near the Dali hominin site, and the Dali hominin cranium fossil was yielded from the basal alluvium of T3 of the Luo River. The paper first adopted the loess-paleosol sequence dating method to determine the age of each terrace, in order to delineate the history of the regional paleolake regression-transgression cycles. Then, in combination with the characteristics of the geomorphic-sedimentary body bearing the Dali hominin fossil, the paper verified which paleolake regression-transgression cycle is represented by the fossil-bearing deposits. Last, based on grain-size and pollen evidences from this geomorphic -sedimentary body, the paper deduced the age of the cranium-bearing bed. The results show that there occurred several paleolake regressions and river down-cutting events when S14, L9, L6, S2, L2 and L1SS developed or accumulated respectively, and that the alluvium bearing the cranium fossil was deposited after the paleolake regression in the late stage of L6 deposition. This regression caused parts of the paleolake bed to emerge subaerially and the Luo River subsequently flowed over it, eroding the lacustrine sediment and depositing alluvium. The deposition of this alluvium was therefore probably synchronous with the development of S5, with a mean age of ∼550 ka. By comparison with Homo heidelbergensis at Mauer (Germany) in both the living paleoenvironment and the age, the paper found that both hominin may be penecontemporaneous.