Late holocene depositional environments and coastal evolution of the Mekong River Delta, Southern Vietnam

The Mekong River Delta in Southern Vietnam is a tide-dominated delta and ha s been formed by the Mekong River system. The sediments are dominantly fine grained and were deposited in the receiving basin with slight inclination of pre-existing deposits in the South China Sea and Gulf of Thailand. Around 6000 to 5000 yr BP maximum Holocene transgression occurred and seawa ves surrounded uplands of the Late Pleistocene terrace, basement rock and w eathered land in the northern parts of the delta. Double notches were under cut by seawaves on the limestone hill in Hatien at about 4.5 and 2.5 m abov e present sea level. Marine deposits prevailed throughout the delta. During the highstand and regressions of relative sea level over the last 4550 yr BP, delta progradation has produced a great flat-plain of 62,520 km(2). Thi s extremely fast progradation could be due to: (a) very high sediment suppl y depositing in the slight inclination of the receiving basin; (b) neotecto nic movements and relative sea-level changes; (c) widespread mangrove fores ts playing an important role to enhance sediment accumulation. Former mangr ove marshy deposits were significantly developed in the Plain of Reeds and Longxuyen Quadrangle. Mangrove marshes have also been developing well in th e Camau Peninsula and present coastlines. Moreover, regressions over the la st 4550 yr BP have produced many distinct sets of relict beach ridges which are useful in distinguishing the former coastlines and evolutionary histor y of the delta. (C) 2000 Elsevier Science Ltd. All rights reserved.