Geoheritage significance of three contiguous Holocene wetlands 161, 162, & 163 in the Becher Wetland Suite, south-western Australia

Semeniuk, Christine1, Semeniuk, Vic1,2

1V & C Semeniuk Research Group, , , 2Notre Dame University, Fremantle, Australia

The Becher Wetland Suite comprises a series of wetland basins located in inter-dune depressions on a Holocene prograded beach-ridge plain.  With progradation, the wetlands formed by the regional water table naturally rising into the inter-dune depressions.  As beach-ridge progradation is westerly, the inter-dune depressions (becoming wetland basins) generally young towards the west, with the oldest basins some 4500 years old, and the youngest < 900 years old.  Through the Becher region, the insertion of wetlands on the prograded beach-ridge plain, through generally younging westwards, in detail, is staggered because of the uneven topography of the depressions along their length.  For instance, wetlands 161, 162, & 163, the subject of this paper, all occur along an inter-dune depressions located on the 4500-year beach-ridge isochron (the oldest part of the beach-ridge plain) and, as such, ideally should be the same age and show the same history. However, they have a staggered history, with wetland 161 commencing accretion some 4350 years ago, wetland 162 commencing 4110 years ago, and wetland 163 commencing 2920 years ago.  All three basins filled with calcilutite.  However, with different ages and longevity of accretional history, and subject to differing small-scale temporal climate changes (in the order o 100 years of less) they exhibit different sedimentary history in terms of thickness of calcilutite, the relationship of calcilutite to underlying sand, diagenetic effects (such as dissolution of underlying carbonate sand, dissolution of Chara and sponge spicules, and patchy cementation of calcilutite), and the responses to fire.  This sequence of wetlands illustrates the complexities of wetland basin sedimentation.   As such, the contiguous wetlands 161, 162, & 163 are a system of international geoheritage significance.


Biography

Christine Semeniuk is a Director of VCSRG, a Research & Development Corporation.    Graduated from the University of Sydney in 1969, she was awarded a PhD from Murdoch University in 2003. Christine arrived in Western Australia 50 years ago, undertaking research into wetlands of Western Australia, and has over 30 peer-reviewed publications in wetland science and geoheritage, including the geoheritage values of wetlands of the Swan Coastal Plain. Christine is a founding member of the NGO the Wetlands Research Association inaugurated in 1999.

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