Marine Geology | 2021
Depositional environments and sequence stratigraphy of post-last glacial maximum incised valley-fill, Malay Basin, northern Sunda Shelf
Abstract
Abstract The alternating submergence and subaerial exposure of the low-gradient, shallow Sunda Shelf of southeast Asia during Quaternary interglacial-glacial cycles played an important role in ocean circulation and monsoonal climate through the interchange of Indian Ocean and Pacific Ocean waters. The Quaternary stratigraphic development of this margin is, however, poorly understood. This study uses a multi-proxy approach (AMS radiocarbon, bulk sediment magnetic susceptibility, X-ray fluorescence spectrometry, and foraminiferal assemblage data) to characterize environmental change and late Pleistocene to Holocene sequence stratigraphic architecture in 16 cores from the northern Sunda Shelf off the east coast of Peninsular Malaysia. Five chronostratigraphic units are recognized. Unit 1 is an inner shelf deposit dating from a late Pleistocene sea-level highstand (the highstand systems tract of the pre-LGM base-level cycle). Units 2–4 represent different paleoenvironmenal components of the transgressive systems tract (TST) of the most recent base-level cycle. Unit 2 is a late Pleistocene shallow open embayment deposit that formed during the post-LGM inundation of the paleo-Chao Phraya River valley as sea level rose. Unit 3 is composed of late Pleistocene to early Holocene paralic peat and organic-rich mud and is capped by a transgressive ravinement surface. Unit 4 is a shallow shelf unit deposited during the early Holocene transgression on the Sunda Shelf prior to ca. 6500\u202fcal\u202fyr BP (the onset of the regional Holocene sea-level highstand). Unit 5 represents the mid-Holocene to recent highstand systems tract (HST) deposited from ca. 6500\u202fcal\u202fyr BP to present. The incised paleovalleys of the paleo-Chao Phraya River and its tributaries provide more accommodation space for sediment accumulation than the surrounding shelf. However, the thinness of the Holocene sedimentary record, 2–3\u202fm in the incised valleys compared to