Magnetic susceptibility study of Late Quaternary inner continental shelf sediments in the Hong Kong SAR, China

Abstract

Four cores of inner continental shelf sediment from the Hong Kong Special Administrative Region (SAR) have been measured for magnetic susceptibility. In all the cores, the upper part of Marine Isotope Stage (MIS) 1 down to about 3 m below seabed show abruptly elevated but highly variable levels of magnetic susceptibility attributable mainly to shipping contamination over the past 160 years. The uncontaminated lower MIS 1 deposits show a consistently low magnetic susceptibility above a sharp increase at the Holocene-Pleistocene boundary. This increase is accounted for by the presence of eroded palaeosol fragments enriched in iron oxides and hydroxides. Acid-sulphate soil development during MIS 2-4 on the sub-aerially exposed inner continental shelf covered by MIS 5 deposits is responsible for the formation of palaeosols. The timing is therefore the opposite of palaeosols within terrestrial loess sequences in that they were formed during the Last Glacial Period. Seventeen uncorrected conventional and accelerator mass spectrometry (AMS) radiocarbon dates of mud and shell samples from the cores indicated that the palaeosols were formed before about 9130 yr BP to 19,430 yr BP. © 2003 Elsevier Ltd and INQUA. All rights reserved.