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Occurrence of marcasite in an organic-rich Holocene estuarine mud

Richard T. Bush A , Roger McGrath A and Leigh A. Sullivan A

Centre for Acid Sulfate Soil Research, School of Resource Science and Management, Southern Cross University, Lismore 2480, NSW, Australia.

Australian Journal of Soil Research 42(6) 617-621
Submitted: 16 May 2003  Accepted: 3 May 2004   Published: 17 September 2004


Substantial marcasite and pyrite were recently identified in the upper-most unoxidised Holocene clay–peat sediments at Bungawalbin Swamp, a coastal backswamp on the Richmond River floodplain, north-east New South Wales, Australia. Marcasite (FeS2), the mineral dimorph of pyrite, is considered a rare secondary mineral in estuarine sediments and its abundance at Bungawalbin Swamp is highly unusual. The morphology and distribution of marcasite in the sulfidic sedimentary profile was examined and compared with the palynological record. Marcasite, recognised by its distinctive platy morphology and disulfide composition, occurred exclusively within organic remnants in only the upper most 1 m of the sulfidic sediment layer. Pyrite occurred throughout the sulfidic profile. A dramatic change in the sedimentary conditions at Bungawalbin Swamp from a marine environment, characterised by the presence of avicenniaceae (i.e. mangrove), to a fresh–brackish environment correlates directly with the occurrence of marcasite. The occurrence of substantial marcasite may provide a valuable environmental proxy of fresh–brackish depositional swamp environments.

Additional keywords: iron sulfide, pyrite, acid sulfate soil, sulfidic.


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