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Genesis of microbialites as contemporaneous framework components of deglacial reefs, Tahiti (IODP 310) ARTICLE in FACIES · JULY 2009 Impact Factor: 1.45 · DOI: 10.1007/s10347-009-0207-3
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Facies (2010) 56:337–352 DOI 10.1007/s10347-009-0207-3
O R I G I N A L A R T I CL E
Genesis of microbialites as contemporaneous framework components of deglacial coral reefs, Tahiti (IODP 310) H. Westphal · K. Heindel · M. Brandano · J. Peckmann
Received: 25 August 2009 / Accepted: 31 October 2009 / Published online: 11 December 2009 © Springer-Verlag 2009
Abstract Deglacial reefs from Tahiti (IODP 310) feature a co-occurrence of zooxanthellate corals with microbialites that compose up to 80 vol% of the reef framework. The notion that microbialites tend to form in more nutrient-rich environments has previously led to the concept that such encrustations are considerably younger than the coral framework, and that they have formed in deeper storeys of the reef ediWce, or that they represent severe disturbances of the reef ecosystem. As indicated by their repetitive interbedding with coralline red algae, the microbialites of this reef succession of Tahiti, however, formed immediately after coral growth under photic conditions. Clearly, the deglacial reef microbialites present in the IODP 310 cores did not follow disturbances such as drowning or suVocation by terrestrial material, and are not “disaster forms”. Given that the corals and the microbialites developed in close spatial proximity, highly elevated nutrient levels caused by Xuvial or groundwater transport from the volcanic hinterland are an unlikely cause for the exceptionally voluminous development of microbialites. That voluminous deglacial reef microbialites generally are restricted to volcanic islands, however, implies that moderately, and possibly episodically elevated nutrient levels favored this type of microbialite formation.
H. Westphal (&) · K. Heindel · J. Peckmann MARUM, Center for Marine Environmental Sciences, Universität Bremen, Leobener Straße, 28359 Bremen, Germany e-mail:
[email protected] M. Brandano Dipartimento di Scienze della Terra, Università di Roma “La Sapienza”, Ple Aldo Moro, 5, 00185 Rome, Italy
Keywords Tahiti · IODP 310 · Microbialites · Reef development · Nutrients
Introduction Whereas modern stromatolites have been studied for decades (e.g., Black 1933; Logan 1961; Dravis 1983; Reid et al. 1995), only later did modern microbialites in coral reefs become the subject of scientiWc study (Land and Moore 1980; Montaggioni and Camoin 1993; Webb and Jell 1997). Despite the increase in knowledge of the structure and diversity of microbialites and the ecological conditions favoring their occurrence, the biological processes and the exact mechanisms of formation are still far from being fully understood (Arp et al. 2008). Microbialites are organosedimentary deposits that are layered, massive, domal or dendritic, and have precipitated as a result of microbiological activity or trapping and binding of detrital sediment; the term microbialite describes the lithiWed product. The role of microbes in the formation of microbial crusts is still under debate and is certainly quite variable for diVerent microbiological communities and precipitates (e.g., Babel 2004; Jenkins et al. 2008; SanzMontero et al. 2008). In particular, the ecological conditions leading to the formation of microbialites encrusting shallowwater tropical coral reefs is still enigmatic, given that such corals prosper under euphotic, oligotrophic conditions, whereas microbialite formation is thought to be favored by elevated trophic levels (Hallock and Schlager 1986; Brachert and Dullo 1991; Dupraz and Strasser 2002). One reason for the slow progress in understanding reefal microbialites is the scarcity of modern analogs (cf. Camoin et al. 1999). In Earth history, microbialites commonly overgrow or succeed framework builders and thus have been interpreted
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to represent shifts in ecological conditions (e.g., Whalen et al. 2002; Adachi et al. 2007). The notion that elevated trophic conditions favor microbialite development was suggested by several lines of evidence. For example, in Devonian strata, oligotrophic taxa (stromatoporoids) are replaced by mesotrophic taxa (tabulate and rugose corals) that are accompanied by microbialites (Whalen et al. 2002). However, coeval growth of corals and microbialites has also been described, e.g., from Jurassic (Olivier et al. 2004; Dupraz and Strasser 2002) and Miocene coral reefs (up to 80 vol% microbialites in the coral framework; Riding et al. 1991). Modern tropical shallow-water reefs usually feature only minor, mostly cryptic microbialite crusts (Reitner et al. 1995; Webb and Jell 1997; Webb et al. 1998). In contrast, numerous Pleistocene to Early Holocene deglacial reefs are encrusted by large volumes of microbialites. In such postglacial reefs, microbialites were Wrst reported from Tahiti (
