PRESERVATION OF IN-SITU, ARBORESCENT VEGETATION AND FLUVIAL BAR CONSTRUCTION IN THE BURDEKIN RIVER OF NORTH QUEENSLAND, AUSTRALIA

In sub-humid parts of north Queensland, NE Australia, certain types of trees are well adapted to living in river bed habitats. The bed of th e tropical, variable-discharge, upper Burdekin River hosts a community dominated by the paperbark Melaleucu argentea. Trees grow preferentia lly in flow-parallel, linear groves, and engineer their own environmen t by deflecting currents, building sand and gravel bars and stabilisin g banks. This is the first study to document in-channel bar developmen t resulting from vegetation growth, rather than the reverse which has been inferred by previous workers. In the Burdekin River study site, i ndividual Melaleuca range from seedlings to mature trees over 100 year s old. These trees survive regular, partial to total submergence and i mpact damage during wet season runoff events (often reaching over 20,0 00 m(3) s(-1) at peak discharge) partly by adopting structural and gro wth modifications. These modifications include a reclined, downstream- trailing habit, multiple-stemmed form, modified crown with weeping fol iage, development of thick, spongy bark, root regeneration and group s trategies, notably development of flow-parallel, linear groves. Follow ing death, in situ remains of trees are preserved within the mainly co arse sand to gravel channel fill, either as reclined stems/trunks stri pped of branches and foliage or as more upright trunks snapped at a he ight of typically 1-2 m above base, both with roots. The morphological adapations and styles of preservation of in situ vegetation within th e Burdekin River are considered distinctive of variable-discharge rive rs, and may be useful in the identification of facies formed in such e nvironments in the rock record, particularly when associated with bar development. (C) 1997 Elsevier Science B.V.