There are a number of features of shallow marine
carbonate environments that are distinctive when
compared with the terrigenous clastic depositional
settings considered in Chapter 14. First, they are largely
composed of sedimentary material that has
formed in situ (in place), mainly by biological processes:
they are therefore not affected by external processes influencing the supply of detritus, except
where increased terrigenous clastic supply reduces
carbonate productivity, i.e. the rate of formation of
calcium carbonate by biological processes. Second,
the grain size of the material deposited is largely
determined by the biological processes that generate
the material, not by the strength of wave or current
action, although these processes may result in breakup
of clasts during reworking. Third, the biologicalenvironment, principally in places where reef formation
strongly controls the distribution of energy
regimes. Finally, the production of carbonate material
by organisms is rapid in geological terms, and occurs
at rates that can commonly keep pace with changes
in water depth due to tectonic subsidence or eustatic
sea-level rises: this has important consequences for
the formation of depositional sequences (Chapter 23).
processes can determine the characteristics of the