This study examines the sedimentological and taphonomic controls on tropical, intertidal, foraminiferal assemblage development using a case site adjacent to Cocoa Creek, northern Queensland, Australia. The site is situated at the seaward margin of an extensive, coastal plain which has developed since a mid-Holocene sea-level highstand, and comprises several shoreparallel zones, including low-intertidal mudflat, mid- and high intertidal mangrove forest and . supra-tidal salt flat environments. Distinct mudflat and mangrove-associated facies units were identified within subsurface sediments which together indicated gradual shoreface progradation under relatively stable sea-level conditions. Calcareous species dominated living assemblages within low mangrove ~nd mudflat habitats, while upper mangrove standing crops were characterised by both agglutinated and calcareous species. The depth of infaunal populations was greatest within the upper mangrove (up to 50 cm) and shallowest within low mangrove sediments. At most stations >70% of the community was found beneath the upper 1 cm. A marked dichotomy occurred between the dead assemblages of mangrove and mudflat sediments. While mudflat dead assemblages were calcareous-dominated and occurred in high densities (up to 1,000s per cm\ dead assemblages within the mangrove were almost exclusively agglutinated, with comparatively low densities 300 per cm3 ). As well as the post-mortem loss of calcareous tests within the mangrove, a systematic seasonal decline in agglutinated dead test densities suggested this assemblage component was also highly susceptible to taphonomic loss. Detailed SEM examination of dead tests indicated that dissolution was the main taphonomic agent for calcareous tests, while organic cement loss and physical breakage caused the degradation of agglutinated tests. A conceptual model is proposed which describes foraminiferal assemblage development in terms of (1) assemblage r:naturation, and (2) burial trajectory. Seaward progradation at Cocoa Creek results in the overprinting of production and taphonomic regimes from higher-intertidal habitats onto those sediments formerly deposited within lower elevation settings. As. such, surface assemblages do not accurately reflect those assemblages which ,enter the longer-term fossil record.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:485322 |
| Date | January 2008 |
| Creators | Berkeley, Andrew |
| Publisher | Manchester Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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