HOLOCENE EVOLUTION OF COASTAL WETLANDS IN WET-TROPICAL NORTHEASTERN AUSTRALIA

Pollen in sediments drilled from the Innisfail coastal plain, northeas t Queensland, Australia, was examined to reconstruct the evolution of Holocene wetlands in a wet-tropical environment. In contrast to monsoo nal Australia, stable environmental conditions created by year-round r ainfall and low tidal range caused abrupt, unidirectional transitions in wetland zonation as marine influence changed. This has enabled a de tailed reconstruction of the marine transgression and subsequent progr adation. Mangroves colonized in response to marine transgression at c. 7400 BP, as riverine mangroves of low salt tolerance migrated up the Mulgrave River. These were replaced around 7000 BP by extensive Rhizop hora-dominated mangroves, coinciding with the development of a Rhizoph ora-dominated community in Wyvuri embayment. Mangroves reached their g reatest extent as sea-level rise slowed towards 6000 BP, with a stills tand indicated by a brief return to terrestrial conditions at one site . High freshwater input depressed salt intrusion in the upper reaches of the Mulgrave estuary and prevented the development of hypersalinity in the upper tidal zone. Drainage conditions then controlled whether mangroves were succeeded by freshwater swamp or swamp-forest.