Mid-Holocene mangrove succession and its response to sea-level change in the upper Mekong River delta, Cambodia

Abstract

Middle Holocene vegetation and mangrove successions are clearly evident in the palynological records of two cores from the upper Mekong River delta in Cambodia. Spanning from ~9.4 to 6.3calkaBP, the cores mainly record a transgressive sequence from floodplain freshwater marsh to tidal flat, which was overlain by mangrove. Corresponding to the decelerated sea-level rise at ~8.3calkaBP, pioneer mangrove species Sonneratia alba and Sonneratia caseolaris appeared in the sediments, and then was replaced by regressive mangrove succession containing upward-increasing abundances of Rhizophora apiculata and Bruguiera spp. High salinity- and flooding-tolerant community S. alba was developed at the western core site PSG at ~8.2calkaBP, and the eastern core site PK at ~7.5calkaBP. The time difference of S. alba appearance between the two sites might be resulted from the complexity of sedimentary environment, where a higher sediment supply was provided to the western floodplain than to the eastern floodplain. After 7.5calkaBP, aggradational stacking of intertidal sediments, of which the thickness is larger than the present maximum tidal range, may have resulted from continuous sea-level rise during 7.5–7.0calkaBP.