TY  - JOUR
A1  - Reitner, Joachim
T1  - Modern cryptic microbialite/metazoan facies from Lizard Island (Great Barrier Reef, Australia) formation and concepts
Y1  - 1993
VL  - 29
SP  - 3
EP  - 39
JF  - Facies
DO  - 10.1007/BF02536915
DO  - 10.23689/fidgeo-2546
N2  - 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.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/6859
ER  -