Age and source of coastal loess in Shandong Peninsula, Bohai Sea, China: Implications for dust aggradation in respond to sea-level change

Abstract

Coastal loess is a unique and intriguing eolian sediment on Earth, but understanding its formation time, provenance, composition and the geomorphic processes that resulted in its accumulation is very limited compared to its inland counterpart. In this paper, we focused on a loess section at Xiazhupan (XZP) Village, Penglai City in Shandong Peninsula, the only known coastal loess bluffs preserved in China. The coastal loess here not only has characteristics that are common to loess terrains such as being composed of predominantly silt-sized particles and the tendency to stand in vertical exposures, but it also reportedly preserves planktonic foraminifera, sizable pebbles and volcanic glass. In addition to its peculiar near-shore locality, these features make it more unusual compared to other loess deposits. Systematic optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL and pIRIR) and radiocarbon dating reveal it was deposited mostly during 60–20 ka, Marine Isotope Stage (MIS) 4-2, which correlates to the deposition of the Malan loess (L1) in the Chinese Loess Plateau. High-resolution grain size data indicate that the coastal loess is relatively coarse-grained, suggesting a source terrain that is at least partially proximal. Given its proximal source and the geochronological evidence, this coastal loess was sourced from the exposed continental shelf during the sea-level lowstand of the last glacial period, and this hypothesis is further supported by a core collected from the Bohai Sea in which silt was present and would have been subaerially exposed during MIS 4-2. In addition, this source area of exposed continental shelf is comparable to coastal loess in Europe. The coastal loess in Shandong can be regarded as a special type of desert or dryland loess, rather than glacial loess. Finally, future sea level rise will likely increase the erosion potential of these vulnerable coastal loess bluffs, making it urgent to study this special landform.