Modern cryptic microbialite/metazoan facies from Lizard Island (Great Barrier Reef, Australia) formation and concepts
Journal: Facies, 199329: 3 - 39
DOI: https://doi.org/10.1007/BF02536915
Persistent URL: http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/6859
Persistent URL: http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/6859
Reitner, Joachim, 1993: Modern cryptic microbialite/metazoan facies from Lizard Island (Great Barrier Reef, Australia) formation and concepts. In: Facies, Band 29: 3 - 39, DOI: 10.1007/BF02536915.
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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, serpuli$, thecidean brachiopods,
bryozoans, and coralline sponges. The observed benthic community
is very similar 10 thoseone bbserved in cryptic habitates
of Aptian and Albian reefs of northem Spain.
For longtime studies of the m~crobialite 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 Ilm/y). Only few calcifying microbes are participators
during microbialite formation. Calcifying acidic organic
macromolecules are mainly responsible for microbialite formation
by cementing detritical material. FelMn-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. The investigations began in 1990 with a pilot
study in fringing reefs of Lizard Island (Great
Barrier Reef) and reefs of the outer barrier for
comparison. Main goals are to study this environment
under normal conditions and for comparison
under controlled artificial conditions in
seawater running aquaria. Two reef caves were
selected for longtime research and all experiments
were carried out within these caves.
H.ZANKL(Marburg)hasrecentlyfoundnearly
similar microbialites in cryptic habitates of reefs
of St.Croix (US Virgin Islands, central Caribbean
realm) (ZANKL 1993).
Comparative fossil examples were studied
by NEUWEILER (1993) on middle Albian reefs of
northem Spain and KEupp et al. (this volume) for
Jurassic ones. Both studies refer to the presented
data.
Purpose of this study is to demonstrate the
growing procedure of a modem type of cryptic,
light independent microbialite, the interaction
with associated benthos, and its significance as a
key facies to understandfossil metazoan-micriticl
microbialitereefs. To understand these very complex
processes it is neecessary to review and
compile modem concepts of biomineralisation,
biofilms, and e.g. the alkalinity question. Therefore
mixing of own results and reviews is planned
and intended! Main goal of this study is creation of a working
hypothesis to understand the processes of
formation of micritic/microbial build ups ("mud
mounds"). Geochemically the observed microbiali tes are composed
of mainly high-Mg calcites and exhibit high positive ö13C
(+3 to +4) values.