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"Calcareous algae and stromatolites" is shorthand for a wider array
of organisms and fabrics that also includes calcified
cyanobacteria, plus thrombolites and other microbial carbonates.
Composition is the link: these are all important components of CaC0
sediments, from 3 Archaean to present and from the ocean floor to
streams and lakes. It is hardly possible to examine limestones of
any age without en- countering them. Simultaneously they are
fossils, sediments, and en- vironmental indicators. It is the range
of significance, coupled with the breadth of their distribution in
time and space, which compels their study. Modern calcareous marine
algae mainly include reds (corallines, squamariaceans, and the
nemalialean Galaxaura) and greens (dasy- cladaleans, udoteaceans,
halimedaceans). Blue-greens, of course, are cyanobacteria and not
algae, and significantly, although they are largely responsible for
Recent tidal flat stromatolites, they are not calcified in the same
way that pre-Cenozoic marine blue-greens are. It is in the
freshwater environment of calcareous streams and lakes that we find
modern calcified cyanobacteria, and they are commonly associated
with the only major group of non-marine calcareous algae, the
charophytes. However, in the past, and especially in the Palaeozoic
and Mesozoic, things look radically different. Mingling with the
ancestors of the modern flora are distinct, and often problematic,
organisms.
The Cambrian radiation was the explosive evolution of marine
life that started 550,000,000 years ago. It ranks as one of the
most important episodes in Earth history. This key event in the
history of life on our planet changed the marine biosphere and its
sedimentary environment forever, requiring a complex interplay of
wide-ranging biologic and nonbiologic processes.
"The Ecology of the Cambrian Radiation" offers a comprehensive
and surprising picture of the Earth at that ancient time. The book
contains contributions from thirty-three authors hailing from ten
countries and will be of interest to paleontologists, geologists,
biologists, and other researchers interested in the global
Earth-life system.
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