HOLOCENE PALEOENVIRONMENTAL RECONSTRUCTION OF THE SUNDA SHELF, OFF NORTHEASTERN PENINSULAR MALAYSIA

Abstract

In order to understand Holocene paleoenvironmental evolution of the western Sunda Shelf (southern South China Sea), two gravity cores TER15-GC10A and TER15-GC9A were collected (2015) 33 and 37 km offshore of Kuala Terengganu (KT), Peninsular Malaysia at ca. 60 m water depth. The cores were sampled every 1 cm and analyzed for three paleoenvironmental proxies; 1) bulk sediment magnetic susceptibility (BMS); 2) elemental analysis by x-ray fluorescence (XRF) spectrometry, and 3) foraminiferal content. Radiocarbon age estimates indicate that cores have a maximum age of ca. 8,400 cal. yr BP. BMS values decrease up-core (1.95 x 10-4-1.04 x 10-4 SI). XRF data also indicate a decrease up-core for Al (12.82%-17.05%), Fe (5.45%-3.65%), and Ti (0.78%-0.61%) with an inverse relationship to the concentration of Ca (3.29%-7.77%). This is interpreted to reflect a decrease in amount of terrestrial material supplied to the shelf over the last ca. 8,400 years, a dilution of detrital material by the local productivity of marine carbonates, and/or a stabilization of sea level. Cluster analysis indicates four groups of benthic foraminifera within the two cores. Within all four clusters Textularia sp. A, Heterolepa dutemplei, Asterorotalia milletti, and Hanzawaia nipponica were the most abundant species. Within three of the four groups, Textularia sp. A was the most abundant. Benthic foraminiferal assemblages, along with the presence of planktonic foraminifera suggest an open inner-shelf marine environment. Within the two cores, three paleoenvironmental episodes were recognized. The first episode occurred from ca. 8,400 cal. yr BP to ca. 6,500 cal. yr BP and was characterized by relatively high terrigenous input. At the beginning of this episode, sea level was at about -5 m rising to a maximum height of around +5 m by the mid-Holocene highstand (6,500 BP). The second episode (6,500 cal. yr BP-4,000 cal. yr BP) was transitional, from the relatively high influence of terrigenous material to a third episode, which ranged from 4,000 cal. yr BP-1,000 cal. yr BP, and was characterized by lower terrigenous influence and higher marine influence. During this episode, sea-level fell to its current position.