Sediment facies and Late Holocene progradation of the Mekong River Delta in Bentre Province, southern Vietnam: an example of evolution from a tide-dominated to a tide- and wave-dominated delta

The Mekong River Delta, southern Vietnam, is a typical mixed tide and wave energy delta with a wide delta plain formed during the last 6 ka and is one of the largest deltas in the world, Three cores were taken from Bentre Province in the lower delta plain, with the objective to describe the sediment facies and to clarify the changes from fide-dominated to tide-wave-dominated delta of the Mekong River Delta during the Late Holocene. Three cores (BT1, BT2, and BT3) were obtained in 1997. Holocene sediments in BT1 and BT3, with thickness ranging from 10 to 20 m, were mainly composed of deltaic sediments unconformably overlying the Late Pleistocene sediments, The BT2 core, however, consisted of transgressive estuarine sediments covered by deltaic sediments infilling the paleo-Mekong River incised valley, which is more than 70 m deep and was formed during the last glacial period, The deltaic sediment facies and succession in the BT2 and BT3 cores taken from the outer delta plain, with beach ridges, were different from those of the BT1 core taken from the inland delta plain. The BT2 and BT3 cores provide a good example of tide- and wave-dominated delta sediments and were characterized by a coarsening-upward delta front facies covered by a fining-upward subtidal to intertidal flat facies, followed by a coarsening-upward foreshore/dune facies. These changes from the inland delta plain to the beach ridge delta plain were accompanied by changes in progradation rates and subaqueous delta topography caused by increased wave influence. (C) 2002 Elsevier Science B.V. All rights reserved.