Modern cryptic microbialite/metazoan facies from Lizard Island (Great Barrier Reef,Australia) formation and concepts |
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Authors: | DozDr Joachim Reitner |
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Institution: | 1. Freie Universit?t Berlin Institut für Pal?ontologie, Malteserstr. 74-100, Haus D, D-12249, Berlin, Germany
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Abstract: | Summary From shallow water caves of fringing reefs related to continental islands of the Lizard Island Section thrombolitic micritic
microbialites were observed. The microbialites exhibit always a light decreasing facies succession. The succession starts
with a coralgal community and ends with light independent microbial biofilms and benthos (coralline sponges). The sessile
mineralized benthos community is constructed of crustose foraminifera, serpulids, thecidean brachiopods, bryozoans, and coralline
sponges. The observed benthic community is very similar to those one observed in cryptic habitates of Aptian and Albian reefs
of northern Spain.
For longtime studies of the microbialite formation and growth rates of coralline sponges the specimens were stained in vivo,
within their natural habitat with histochemical fluorochromes and nonfluorescent agents. Main results are a very slow growth
of the microbialite and associated sponges (50–100 μm/y). Only few calcifying microbes are participators during microbialite
formation. Calcifying acidic organic macromolecules are mainly responsible for microbialite formation by cementing detritical
material. Fe/Mn-bacterial biofilms are responsible for strong corrosion of the microbialite. Beside the corrosive activity
of the Fe/Mn-bacterial biofilms boring sponges (Aka, Cliona) are the main destructors.
Geochemically the observed microbialites are composed of mainly high-Mg calcites and exhibit high positive δ13C (+3 to +4) values. |
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Keywords: | Origin of Microbial Carbonates Reef Caves Peloid Formation Biofilms Sponges Great barrier Reef Recent |
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