LAUSR

Abstract Chronological analysis is the basic premise for paleoenvironmental research on lake sediment cores. It mainly employs bulk organic matter as a mixed dating material, although terrestrial plant remains are believed to provide reliable radiocarbon (14C) ages. 14C reservoir effects (REs) are generally problematic in establishing a final chronology and are usually recorded in aquatic macrophytes by the incorporation of dissolved inorganic carbon in high-altitude lakes of the Tibetan Plateau. We present a typical case of a 5.48 m-long core sampled from Chibuzhang Co, a lake in north Tibet, China, which contained two obvious obstacles: high REs and age reversals. The 14C RE was recently as much as ∼3500 years in the upper part according to total organic carbon (TOC) 14C ages and related dating from 210Pbex activity. It notably changed during the climatic transition to the Holocene due to carbonate input from catchment erosion and glacial meltwater, resulting in reversed 14C ages in the lower section of the core. 14C-dead carbon (or old carbon) dissolved in lake water was incorporated in the dating materials, as inferred from the 14C ages of plant samples. By combining data on grain size and carbonate content changes, two sedimentary units were identified with a boundary at 390 cm depth. These were used to estimate individual sediment accumulation rates (SARs) for the final age-depth models, instead of using a constant RE-corrected chronology. Our results provide an environmental history of ∼12.7 kyr in a long sediment core, based on an optimized SAR model of conventional 14C ages, which is supported by related lacustrine records and Bacon models. Use of separate 14C SAR analyses can solve the problem of age inversion in sediment cores, as sedimentological chronology analysis.