SEDIMENT FACIES AND EVIDENCE OF MIDDLE HOLOCENE TRANSGRESSION IN THE VL1 CORE, MEKONG RIVER DELTA

Abstract

A detailed description of sediment facies, diatom and 'Cages of a new 42 m long core (VLI) is one of the basic data to study Holocene sedimentation in the Mekong River Delta. This core is divided into seven sediment facies on the basis of sedimentary properties, diatom assemblages, and '*C ages. These facies show changes from transgression to regression in relation to the late Pleistocene-Holocene sea-level changes. The Postglacial transgression caused by a sea-level rise led to formation of open bay muddy sediments. This muddy facies, around 10 m thick, is characterized by abundant marine planktonic diatoms. This facies indicates the maximum Holocene marine influence was around 5,000 cal yr BP at the VLI site. The regressive succession is composed of deltaic sediments from prodelta, delta front, sub- to inter-tidal flat and floodplain in ascending order. Cages indicate that prodelta and delta front passed the core site at approximately 4,000 to 3,600 cal yr BP. The accumulation rates were closely related to the sediment facies: low rate for prodeita facies, high rate for delta-front facies.