Chronology of Holocene Cheniers and Oyster Reefs on the Coast of Bohai Bay, China

Abstract

Cheniers and oyster reefs are two essential components of Holocene strata on the coast of Bohai Bay, China. The existing nonconventional14C dates, often with unsuitable sample positions, less-tested samples, and unreasonable data comparisons, limit the refined analysis of the local chronostratigraphy. On the basis of a number of pretreatment routines, including geological investigations, X-ray diffraction analysis (XRD), δ13C measurement of shells, selection of appropriate shell species (Umboniumsp. and Terebridae) for14C dating, and determination of the local mean δ13C value (−2.68‰ PDB) for the common shells, a set of samples was radiocarbon-dated by Accelerator Mass Spectrometry (AMS). These new ages, obtained from the lower part of cheniers, enable us to estimate the initiation of the cheniers, and confirm that the existing nonconventional dates are often questionable due to unsuitable sample positions. Another two AMS ages, dated for two different microgrowth layers, precipitated in a varying water body, of the sameCrassostrea gigasshell are statistically identical within 2σ error. This implies that the different water masses in the coastal environment would be rapidly in balance with the contemporaneous atmospheric CO2. Both MARINE93 and INTERCAL93 were used for calibration of radiocarbon dates. These amended the time frame of the local Holocene history.