A taphonomic clock based on the coral grain size of beach sediments from the Yongle Atoll, South China Sea

Abstract

The grain size characteristics and aging of beach sediments from six islands of the Yongle Atoll, South China Sea, were measured to examine the taphonomic degradation of coral clasts in sediment reservoirs of reef environments. Seventy-one beach sediment samples were collected from 22 transects on 6 islands for sediment characteristic analyses, and 16 bulk sand samples and 28 coral samples were selected for 230Th dating. The mean grain size and ages of coral clasts showed a significant negative correlation (F25 = −0.721, p = 0.01). A grain size age model was established to explain the taphonomic degradation mechanism of coral clasts over time, and an empirical relationship between the mean grain size and 230Th ages was obtained from the Yongle Atoll. The mismatch of the taphonomic clock by grain size data was analyzed, and it was mainly caused by the influence of sorting processes and the intrinsic morphology of coral skeletons that occurred at the early stage of the breakdown process. The application of the model to a nearby atoll island showed that for coral sediments with homogeneous taphonomic conditions, the predicted age was well matched with the measured age. This work presents a general framework for understanding coral clast degradation trajectories with time in taphonomic environments, and it provides a feasible method to predict the coral age independent of other dating methods.