Sundaland is the currently partially drowned continental landmass that encompasses Borneo, Sumatra, Java, and the Malay Peninsula. It has episodically been reclaimed by the sea during successive Quaternary glaciations, and is commonly thought to be vertically stable. Combining geomorphological observations with numerical simulations of coral reef growth and shallow seismic stratigraphy, we show that the Sunda shelf is subsiding, and that the intermittent regime of transgressions only prevailed over the past 400,000 yr. Prior to that time, Sundaland was permanently exposed. We relate these drowning events to transient dynamic topography in the Indo-Australian subduction zone. Because the Sunda shelf is very shallow, these new data provide important insights into Pleistocene paleogeography, with implications on the interactions between the solid Earth and climate, oceanography, and dispersal of species, including hominids.
-Rising sea levels since the Last Glacial Maximum (LGM), some ~20,000 years ago, has drowned the Sunda Shelf and generated the complex coastal morphology as seen today. The pattern of drowning of the shelf will be utilized to assess likely timing of shoreline displacements and the duration of shelf exposure during the postglacial sea level rise. From existing sea level records around Sunda Shelf region, "sea level curve" was assembled to reconstruct the shelf drowning events. A five stage drowning model is proposed, including 1) maximum exposure of the shelf at approximately 20,500 years Before Present (y.B.P.), when sea level had fallen to about -118 m below present sea level (bpl.), 2) melt water pulse (MWP) 1A at ~14,000 y.B.P. when sea level rose to about -80 m bpl., 3) melt water pulse (MWP) 1B at ~11,500 y.B.P., when sea level was predicted around -50 m bpl., 4) Early-Holocene at ~9,700 y.B.P, when sea level was predicted at about-30 m bpl, and 5) sea level high stand at ~4,000 y.B.P., when sea level jumped to approx. +5 m above present sea level (apl.). This study shows that the sea level fluctuated by more than 120 m at various times during LGM and Holocene. Also confirmed that sea level curve of Sunda Shelf seems to fit well when combined with sea level curve from Barbados, although the comparison remains controversial until now due to the considerable distinction of tectonic and hydro-isostatic settings.
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