Holocene Paleoenvironmental Reconstruction of Depositional Environments on the Sunda Shelf , Southwest South China Sea , using a Multidisciplinary Approach

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Michael R. Twarog (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: The last glacial maximum , ca. 21 , 000 years ago , caused a fall in eustatic sea level of ca. 120 m below present. The low-gradient , shallow Sunda Shelf , Southeast Asia was subaerially exposed during this sea-level lowstand and experienced rising sea level thereafter. Sea level rose to a +1.3--5 m highstand ca. 6 , 500 cal yr BP , and then fell to modern sea level. The objective of this research is to characterize environmental change on the Sunda Shelf in response to the post-glacial rising eustatic sea level. To address this objective , six gravity cores were collected along a transect crossing the paleo-Chao Phraya incised river valley complex between peninsular Malaysia and southern Vietnam. Thirteen AMS radiocarbon samples , 130 bulk sediment magnetic susceptibility samples (BMS) , 66 X-ray fluorescence spectrometry (XRF) samples , and 54 samples for the analysis of foraminiferal assemblages were used to characterize change in the depositional environments of the cored sediments. BMS , XRF , and foraminiferal analysis distinguish two main units. Unit 1 is found in the lower part of the cores and typically contains more terrestrial material than sediments further up-core as shown by higher BMS values , higher % Ti , % Al , % Fe , and lower indicators of marine influence , for example , lower % Ca , % planktonic foraminifera , and percentages of deeper water benthic foraminifera such as Heterolepa dutemplei. Unit 2 is characterized by a significant increase in % Ca , % Heterolepa dutemplei and % planktonic foraminifera ca. 6 , 500 cal yr BP. Unit 1 is consistent with shallower water depths and is part of a transgressive systems tract (TST , ca. 1 m thick) that terminates ca. 6 , 500 cal yr BP. Unit 2 represents the overlying highstand systems tract (HST , ca. 1 m thick) and is characterized by an increase in % planktonics , % Ca , and shifts in benthic foraminiferal assemblages , indicating deeper water conditions than the sediments below. This shift from a TST to a HST ca. 6500 cal yr BP is consistent with the Sunda Shelf sea-level record.

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Publication

Thesis

Language: English

Date: 2018

Keywords

sunda shelf, paleoenvironmental reconstruction, depositional environments

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