Abstracts Category : Other

A multiproxy paleoenvironmental reconstruction of Late Quaternary marine sediments: Sunda Shelf, Southern South China Sea

by Bailey G Donovan

Two gravity cores were collected from 43 km and 90 km offshore of Kuala Terengganu (western Sunda Shelf, southern South China Sea) at ~60 m water depth to characterize late Quaternary paleoenvironments by using bulk sediment magnetic susceptibility (BMS), elemental analysis via X-ray fluorescence spectrometry (XRF), and foraminiferal analyses. Radiocarbon age estimates (using benthic foraminiferal carbonate material) indicated the nearshore core was Holocene (ca. 10,0006,000 cal years BP) in age while the offshore core was deposited prior to the last glacial maximum (ca. 45,000 cal years BP and possibly older) during marine isotope stage (MIS) 3 (ca. 60,000 30,000 yrs BP) within the late Pleistocene. Elemental and BMS data agree well within both cores, except Pleistocene sediments exhibit higher BMS (ca. 1x10-4 si) and higher calcium content (ca. 2%) than Holocene sediments. These data can be interpreted as representing stronger terrestrial influence during the deposition of Pleistocene sediments or a higher dissolution of calcium carbonate. BMS data, elemental data, and micropaleontological evidence, relative abundances of 64 benthic foraminiferal species, indicate that both cores were deposited in an inner shelf environment similar to the modern shelf environment at ca. 5060 m water depth. However, a higher ratio of planktonic foraminifera (Holocene: 01.3%, Pleistocene: 08.5%) suggests a greater influence of open marine waters in the Pleistocene sediments. The position of sea level during deposition of the late Pleistocene cored sediments is higher (ca. 6010 m depending on the data set) than eustatic published sea-level data for MIS 3. This incongruity could be caused by age inaccuracies from limitations of the radiocarbon dating technique, although this seems unlikely as the lower range of age estimates fall within the technique and the uppermost range falls on the border of the limitations of the technique. Other options for the incongruity include large margins of error for late Pleistocene sea-level reconstruction and vertical crustal movement post-deposition from isostatic adjustment or tectonic activity.