Coralline algal nodules off Fraser Island, eastern Australia |
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Authors: | Dr Michelle Lund Dr Peter J Davies Dr Juan C Braga |
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Institution: | (1) Imperial Oil Resources, 3535 Research Rd. N.W., T2L, 2K8 Calgary, Alberta, Canada;(2) School of Geosciences, Division of Geology and Geophysics University of Sydney, 2006 Sydney, N.S.W., Australia;(3) Departamento de Estratigrafía y Palcontología, Universidad de Granada, Campus Fuentenueva s/n, 18002 Granada, Spain |
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Abstract: | Summary Calcareous red algal nodules growing on mobile substrates have been sampled from 28 to 117m off Fraser Island in southern
Queensland, eastern Australia. This is a subtropical, transitional area between the tropical Great Barrier Reef to the north
and temperate, cooler waters to the south. Red algal nodules are the most common components in bioclastic gravels that extend
from about 50 to 110 m and locally cover 40–50% of the seafloor. Variations in the overall character and floristic composition
of the nodules with depth can be observed. Algal nodules comprise algal covered pebbles/cobbles and rhodoliths in depths shallower
than 60 m whereas only rhodoliths occur in deeper settings. No changes in nodule shape occur but shallower algal nodules have
larger mean size with higher standard deviation than the deeper ones (39.2 vs. 30.5 mm and 20.5 vs. 6.3 mm s.d.). Living and
subrecent red algae in nodules shallower than 60 m are mainly Melobesioideae and peyssonneliaceans with minor Lithophylloideae
and Mastophoroideae. Most plants belong to a few species of the generaPhymatolithon andLithothamnion. Below 68 m, rhodoliths are dominated by the family Sporolithaceae, melobesioids and peyssonneliaceans.Sporolithon is the main component below 80 m. Algal growth forms are mostly smooth encrusting to warty with no depth variation. Maximum
plant thickness, however, decreases with increasing depth. Thallus thickness in the deeper water samples is more than three
times smaller than in those from shallower waters. These data are important for understanding the paleoenvironmental context
of deposition of the abundant coralline algal limestones with similar algal nodules found in the geological record. |
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Keywords: | Red Algae Rhodoliths Eastern Australia Recent |
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