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

摘要

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.