A comment on Lai et al. (2014) concerning the origin of the Shell Bar section from the Qaidam Basin, NE Tibetan Plateau: lake formation versus river channel deposit, and 14C versus OSL dates

Abstract

Without understanding the true meaning of why it is called Shell Bar, and ignoring the unreliability of OSL dating and the data of Fan (2009), Lai et al. (J Paleolimnol 51:197–210, 2014) concluded that the upper part of the Shell Bar section from Qaidam Basin, which they call the SB section, was formed during MIS5 (~113–99 ka). This is at odds with Zhang et al. (Quat Sci 27:427–436, 2007a, Radiocarbon 50:255–265, 2008b) who argued that the whole 260-cm section accumulated between ~39.7 and ~17.5 14C ka BP. Using grain-size data and ostracod assemblages, they further asserted that the elevated sediments of the Shell Bar were stream deposits (Mischke et al. in J Paleolimnol 51:179–195, 2014) and support their conclusion using a nearby section they call the SSB section. This section, we believe, is old, fluvial–alluvial and shallow-water sediments, interbedded with eolian deposits, and its cliff-like appearance can be attributed to backward erosion processes during a high-water stand. All the OSL measurements used to date the section were produced at one laboratory, and the results are at odds with their conclusions. It is impossible for Lai et al. (J Paleolimnol 51:197–210, 2014) to ignore the AMS 14C dates and rely fully on their OSL ages, which are not constrained or verified by other dating techniques. For the sedimentation and geomorphologic processes to be fully understood, we must have a solid understanding of the paleoclimatic and paleoenvironmental changes, and paleolake evolution, reconstructed using lake deposits, geomorphologic features, microfossil and macrofossils, pollen and other environmental variables.