Depositional sequences on a late Pleistocene–Holocene tropical siliciclastic shelf (Sunda Shelf, southeast Asia)

Abstract

This study describes, and reviews, the stratigraphic architecture of the world's largest but least known tropical siliciclastic shelf using the sequence-stratigraphic concept. The Sunda Shelf provides conditions particularly suited for reconstructing its depositional history due to a low gradient and extreme width, the presence of huge paleo-valley systems and abundant filled channels, tectonic stability during the Quaternary, and high sediment input due to a large catchment area. We investigated the subsurface along the most prominent paleo-valley by shallow-seismic surveying and 36 gravity cores controlled by 80 radiocarbon dates. The deposits during sea-level fall prior to the last glacial maximum lowstand and the subsequent deglacial rise correspond to four systems tracts: (a) wide, partly detached prograding deltaic clinoforms indicate forced regression related to a regressive systems tract; (b) sparse shoreline deposits and widespread soil formation refer to a lowstand systems tract; (c) rapidly backstepping coastline-related deposits form a confined transgressive systems tract without stacking patterns and are mainly restricted to the paleo-valley system; (d) a thin marine mud cover extends as a condensed section over the whole shelf area (the base of a highstand systems tract). The stratigraphic architecture on the central Sunda Shelf strata over the past 50,000 years is the result of the interplay of three major factors: (1) rapid sea-level changes, (2) locally pronounced physiography and (3) changes in sediment supply that determined the distribution and accumulation pattern.