Shelf-margin architecture and deposition variability across the mid-Pleistocene climate transition, northeastern South China Sea

Abstract The shelf-margin prism of the Upper Pliocene to Pleistocene in the northeastern South China Sea has recorded significant signatures of glacio-eustatic cycles and paleo-climatic conditions. Integrated analysis of 3D seismic, well-logging, and borehole dating data in the study area provided a detailed depiction of the high-resolution sequence architecture and depositional evolution as they responded to the glacio-eustatic cycles and climate changes. The shelf-margin section of the Upper Pliocene to Pleistocene is comprised of a composite sequence bounded by a regional unconformity, which can be further divided into five sequences confined by subordinate unconformities. The two lower sequences (S1-S2) with similar and simple internal structures, are displayed as having roughly equal thicknesses (ca. 50 m) and gently seaward-dipping foresets. In contrast, the upper three sequences (S3-S5) are characterized by the development of high (200–600 m) and steep (2–5°) shelf-margin clinoforms, which can be further divided into fifteen clinothems. The sequences generally embody four systems tracts, showing different stratal stacking patterns, and the linking contemporaneous depositional systems including fluvial channels, deltaic and slope fan systems are documented. Based on the chronostratigraphic framework, comparisons have been made between the sequence cycles and the global oxygen isotopic records. The results suggest that the formation of different order sequences may have been in response to the glacio-eustatic cycles paced by the Milankovitch orbital cyclicity. The abrupt changes in the sequence and depositional architectures between S1-S2 and S3-S5 are assumed to be related to the significant increases in the amplitudes and durations of the glacio-eustatic fluctuations across the mid-Pleistocene climate transition (MPT). Intensively variable climatic conditions with strengthened monsoons during and after the MPT could have potentially led to an abundant sediment supply, which may have enhanced the development of shelf to shelf-edge delta systems with the large-scale prograding clinoforms.