INTEGRATED SEDIMENTOLOGICAL, GEOPHYSICAL
AND GEOTECHNICAL STUDY OF INNER SHELF
SEDIMENTS IN HONG KONG
Wing Yan Mok, Lung Sang Chan and Wyss WS Yim
University of Hong Kong, Hong Kong SAR)
(Department of Earth Sciences,
The physical properties of inner continental shelf sediments can be used to
provide a record of sequence stratigraphy. Previous work on an offshore borehole
located in the West Lamma Channel, Hong Kong, has revealed a sedimentary
sequence dating back to ca. 0.5 Ma with five interglacial-glacial cycles consistent
with the Vostok ice core in Antarctica. In the present study, two new vibrocores
located adjacent to the site of previously rotary borehole found to show five marine
transgressive units were examined for their sedimentological, geotechnical and
geophysical properties. The results obtained include (1) In-situ cone penetration test
(CPT); (2) laboratory measurements of p-wave velocity, magnetic susceptibility,
moisture content, density and sedimentological core logging; and (3) automated
measurements of properties and collection of digital images using the GEOTEK
multi-sensor core logging system with GEOSCAN.
The properties of the sea-floor sediments were found to be related to both the
depositional and post-depositional processes. Five marine units (M1 to M5) and three
terrestrial units (T2 to T4) can be recognized. The Holocene M1 unit has never been
sub-aerially exposed, the clayey silt is soft and saturated, shells and shell fragments
are preserved and properties including moisture content, porosity, magnetic
susceptibility, impedance and density differ from the pre-Holocene M2 to M5 units.
Variable properties were found reflecting the more desiccated upper part in
comparison to the less desiccated lower part because of subaerial exposure of the M2
to M5 units during glacial period(s). The T2 to T4 units mainly comprising of sand
and gravel are different from the M2 to M5 units in their higher cone resistance,
density, and p-wave velocity and their lower friction ratio, moisture content, porosity
and impedance.
The application of fast and non-destructive measurements of physical properties
of sediment cores shows great potential for supporting offshore ground investigation
in Hong Kong.