Resumen de Coastal laterite profiles at Po Chue Tam, Lantau Island, Hong Kong: the origin and implication
Seven lithostratigraphic units were identified from a 180-m-long, up to 6-m-high coastal cliff exposure at Po Chue Tam, Lantau Island, Hong Kong. They include older slope wash, debris-flow deposits, raised beach deposits, slope debris, stream-flood gravels, hyperconcentrated flood gravels and younger slope wash. Laterite profiles had developed in the older slope wash and the debris-flow deposits. The profile in the former includes, from bottom to top, slightly weathered but ferruginized bedrock, a mottled pebble/cobble zone and a vesicular laterite horizon. In contrast, the profile in the latter consists of only debris-flow deposits that contain detrital laterite fragments and underlying slightly weathered bedrock. The deposits have been cemented and indurated.
There are no genetic links between the main zones in the laterite profiles. This is evidenced by the sharp bed contact, the absence of a leaching zone in the bedrock, and the general constraint of the main zones by stratigraphic sequences. The present study highlights that both relative accumulation of iron from pedogenic weathering and absolute accumulation of iron from a lateral source through groundwater and/or surface water occur concomitantly and superimpose upon each other. This leads to the development of a polygenetic laterite profile rather than a single, monogenetic profile.
Caution should be exercised to ascertain the origin of laterite before attempting to explore the paleoclimatic imprints or reconstruct landscape evolution. Laterites of both pedogenic and groundwater origins can represent paleosurfaces that required prolonged subaerial exposure, quiescent tectonism and climatic stability.
