Microbes and
Reefs
Wood, Rachel A.1 (1)
The geological history of reef-building
was long thought to mirror the availability of large, calcified metazoans,
particularly those with modular organisations and inferred photosymbioses. It
is now apparent, however, that the formation of reefs is governed primarily by
physicochemical factors such as carbonate saturation state and Mg/Ca ratios. In
particular, modern oceanic saturation state (with respect to aragonite)
controls not only rates of carbonate production, but also species diversity of
reef-building corals, coral skeletal extension rates, and in some cases the
extent of microbialite and automicrite formation. Indeed, inferred
microbialites and automicrites are now accepted to have been a dominant
contributor to reef carbonate, from the inception of reef communities 3.6 Ga to
the present day. Such fabrics are notably important in mud-mounds, as
successive cavity encrustations during burial of surface reef frameworks, and
also in post-extinction reefs. Notwithstanding their clear importance, no
unequivocal criteria are yet available to either isolate and identify the
particular nature of microbial influence in any given ancient carbonate fabric,
or to place the diversity of fabrics within a consensus classification scheme.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California