Abstract: The estuary bay of the Pearl River Delta is influenced by a complex interplay of waves, tides, and river flows, resulting in a unique sedimentary environment rich in modern biological relics. These relics serve as highly sensitive indicators of environmental changes during deposition. High-precision identification of the biological relics' composition within this estuary bay, coupled with the establishment of a relationship model between their distribution characteristics and the sedimentary environment, enriches our ichnological understanding of modern estuary systems. Utilizing sedimentological and ichnological methods, this study examined the biological relics in the Pearl River Delta estuary through a multi-faceted approach, including salinity, particle size, turbidity analysis, X-ray computed tomography, and computer reconstruction of core samples. Detailed analysis was conducted on the characteristics of biological relics across various microenvironments within the study area.(1) The primary trace-makers identified include species such as Brachyura, Perinereis, Periophthalmus, Paguridae, and Mactridae. The surface traces comprise primarily crawling and foot traces, as well as drag marks, foraging paths, excavation marks, bird footprints, and sand silkworm feces, with the most abundant traces found within the sediment layers. The burrows exhibit shapes such as I-shaped, Y-shaped, and U-shaped.(2) The spatial distribution of biological relics in the Pearl River Delta estuary reveals an imbalance, with higher diversity and abundance observed in tidal flats compared to other microenvironments.(3) Benthic trace-making organisms occupy different spatial positions within the sediment bottom layer. Small crabs, mudskippers, and clams inhabit the shallow layer, while larger crabs and Perinereis aibuhitensis are found in the middle layer. The deep layer is predominantly occupied by Perinereis aibuhitensis, indicating its extensive utilization of the ecological space and the intensity of its disturbance. This study provides empirical observation data for modern sedimentology and ichnology in the Pearl River Delta estuary, laying a solid foundation for the reconstruction of ancient ichnology and environments, and enhancing our accurate understanding of ancient estuary environments.

Key words: modern biological relics, estuary, biological sedimentary structure, pearl River Delta, sedimentary model