Abstract

High-resolution seismic reflection profiles and continuously sampled boreholes have been used to investigate the Quaternary offshore sequence that overlies weathered bedrock in Hong Kong. Four formations have been recognized: the lowermost Chek Lap Kok Formation comprises dominantly fluvial sand and mud, much of which probably accumulated prior to 130 000 years BP, during sea-level lowstands of Middle Pleistocene (Oxygen Isotope Stage 6) age and earlier. The upper surface of the Chek Lap Kok Formation is defined by a fluvial/tidal entrenchment surface that is overlain by transgressive, fine-grained, marine sediments of the Sham Wat Formation. These were deposited during the Eemian interglacial (Stage 5c) at a time when sea level was similar to that of today. In southeastern Hong Kong waters, a late Weichselian (Stage 5c) ravinement surface is overlain by submerged shoreface sands, succeeded by a back-stepping wedge of marine sediments that comprise the Waglan Formation. Fluvial/tidal entrenchment of the top of this formation occurred prior to the deposition of the uppermost dominantly marine Hang Hau Formation, deposited during the Late Weichselian to Holocene transgression, the main phase of which is represented by a ravinement surface.

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