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 6.3 cal ka BP, 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 ~ 8.3 cal ka BP, 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 ~ 8.2 cal ka BP, and the eastern core site PK at ~ 7.5 cal ka BP. 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 7.5 cal ka BP, 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 7.5–7.0 cal ka BP.

Rapid flooding of the southern Vietnam shelf during the early to mid‐Holocene

“…), and was therefore used for linking the South Vietnam shelf and the Cambodian lowlands. The final flooding stage occurred between 8 and 7 ka BP and has been consistently recorded by coastal peat and saltmarsh deposits of the Cambodian lowlands (Tamura et al ., ; Li et al ., ).…”

Early to mid‐Holocene rapid sea‐level rise and coastal response on the southern Yangtze delta plain, China

“…3 m 100 a −1 . This result is similar to that in the Mekong River delta (Tamura et al ., ; Li et al ., ), also a far‐field area from the ice sheets, but much greater than documented in near‐field regions; these include a sea‐level rise of 1.2 m during 8.4–8.0 cal ka BP from North America (Törnqvist et al ., ) and 3.0 ± 1.2 m during 8.5–8.3 cal ka BP from Europe (Hijma and Cohen, ).…”

“…A high‐resolution pollen analysis revised this to a ca. 3‐m sea‐level rise and delta initiation at 8.2 cal ka BP (Li et al ., ). These results seem to support findings from the Rhine‐Meuse delta (Hijma and Cohen, ).…”

Mangrove Sedimentation and Response to Relative Sea-Level Rise

“…The final stages are recorded in the Mekong River Delta by basal transgressive sediments overlying Pleistocene basement, culminating in a period of abrupt SLR approximately 8,200 years ago. At the apex of the modern delta, a vertical sequence of mangrove sediments in southern Cambodia indicates the persistence of mangrove forests during this period (Tamura et al 2009, Li et al 2012. Since then, the delta has gradually built more than 200 km southward to form the modern coast.…”