Stratigraphy of quaternary offshore sand and gravel deposits in the Hong Kong SAR, China

Abstract

The mining of Quaternary offshore sand and gravel deposits in the Hong Kong Special Administrative Region (SAR) down to a depth of about 60 m below the present sea level has yielded an estimated 350 million m3 to date. Three main types of deposits have been identified: (1) intertidal and near-shore subtidal deposits at the mouth of major streams formed by the reworking of pre-Holocene colluvial-alluvial fans; (2) alluvial deposits of last glacial and/or earlier glacial periods buried by Holocene and/or earlier interglacial marine deposits, and (3) last interglacial marine deposits reworked during the Holocene transgression. The first two types of deposits commonly occur in areas with or adjacent to granitic bedrock. These deposits were formed by the selective transport of deeply weathered granitic residual soils by fluvial processes. The third type of deposit includes calcareous shell remains, often showing signs of dissolution. Eustatic sea-level changes dating back to approximately 440,000 yr BP were responsible for the Quaternary succession. Palaeo-desiccated crusts formed by acid-sulphate soil development of the exposed interglacial marine deposits during glacial low sea-level stand(s) are found to be useful stratigraphic markers in assisting interpretation. © 2001 Elsevier Science Ltd and INQUA. All rights reserved.