Macro- versus microfauna: resolution potential of bivalves, gastropods, foraminifera and ostracods in reconstructing the Holocene palaeoenvironmental evolution of the Pearl River delta, China

Sedimentological, taphonomic, and palaeoecological analyses of a core from the central Pearl River delta plain allow a detailed reconstruction of the Holocene sedimentological and biological evolution. The marine ingression of the postglacial sea-level rise reached the core site 9,600 years ago and quickly established brackish conditions. Subsequent to a minor regression, water depths and salinity levels peaked between 7,500 and 6,800 years ago. The eventual cessation of the postglacial sea-level rise led to progradation of the delta front and the establishment of fluvial conditions around 4,200 years BP. Subsequent episodic and short-lived marine ingressions can be attributed to shifting delta lobes. While the reconstructed model parallels already established global and regional sea-level curves, the dataset allows further conclusions. The highly fossiliferous core yields abundant bivalves, gastropods, foraminifera and ostracods. Although these fossil groups recur throughout the core, their resolution potentials for palaeoenvironmental reconstructions differ substantially. Bivalves and foraminifera are extremely abundant. However, their very low species richness and high tolerance to environmental fluctuations only allow the reconstruction of the major steps of delta evolution. Gastropods are more diverse (22 taxa) but occur only sporadically, which diminishes their resolution potential. Another problem is the insufficient knowledge on these mm-scale brackish-water molluscs. In the present study, ostracods exhibit the highest resolution potential, which is mainly due to their high abundance and diversity (32 taxa). Although many of the recorded ostracod species are euryoecious with regard to environmental factors such as salinity, substrate, or water depth, the use of palaeocommunity analyses allows the most detailed palaeoenvironmental reconstruction. While the study of molluscs involves considerably less preparation time than that of microfossils, only ostracods reflect all environmental changes present in the studied core.