Isolation from clastic supply
The primary requirement for the formation of carbonate
platforms is an environment where the supply of
terrigenous clastic and volcaniclastic detritus is very
low and where there is a supply of calcium carbonate.
Clastic supply to shallow marine environments can be
limited by both tectonic and climatic factors. Most
terrigenous sediment is supplied to shallow seas by
rivers, and the pathways of fluvial systems are controlled
by the distribution of areas of uplift and subsidence
on the continents. On most continents the
bulk of the drainage is concentrated into a small
number of very large rivers that funnel sediment to
coastal deltas. Along coastlines distant from these
deltas the clastic supply is generally low, with only
relatively small river systems providing detritus. This
allows for quite extensive stretches of continent to be
areas that receive little or no terrigenous sandy or
muddy sediment. The climate of the continent adjacent
to the shelf also has an important effect. In desert regions the rainfall, and hence the run-off, is very
low, which means that there is little transport of
sediment to the sea by rivers.