Clay Mineralogical Record and Its Paleoenvironmental Significance during Marine Isotope Stage 3 on the Sunda Shelf, Southern South China Sea

Variation in source of terrigenous sediments on the Sunda Shelf in the southern South China Sea during the sea-level lowstand is of great significance to reconstruct the evolution of the land-sea configuration. Varying provenances response to sea-level fluctuations within Marine Isotope Stage 3 (MIS 3) was investigated by high-resolution clay mineralogy of Core 18282-2 recovered from the outer Sunda Shelf. The results indicate that clay mineral compositions on the outer shelf show relatively high contents of smectite (29%-44%), moderate contents of kaolinite (21%-27%), illite (19%-27%), and chlorite (14%-20%). The provenance analysis based on clay mineralogy suggests a mixture of individual clay mineral from various sources surrounding the southern South China Sea. Smectite originated mainly from Sumatra and middle Thailand. Kaolinite derived mainly from the Malay Peninsula, Sumatra, and western Borneo. Illite and chlorite were mainly contributed by the Mekong River. During 44.5-36.0 cal ka BP, the sea-level was below -80 m for most of the time, the vast paleo-river systems developed on the emerged shelf, namely the North Sunda River, the paleo-Chao Phraya River, and the paleo-Mekong River. Terrigenous sediments from the surrounding provenances were transported through these major ancient drainage systems directly to the outer shelf at that time. Variations in the smectite/(illite + chlorite) ratios correspond well to the sea-level fluctuations with relatively higher ratios developed during the sea-level lowering periods, implying that the sedimentary environmental evolution during the MIS 3 on the outer Sunda Shelf was dominantly controlled by the sea-level change. Modification of the land-sea configuration resulted from sea-level fluctuations, especially the migration of paleo-coastlines, could significantly affect the transport distance between the paleo-river mouths and the study area, resulting in variations in relative contributions of the surrounding provenances to the outer Sunda Shelf. © 2021, Editorial Department of Earth Science. All right reserved.