The proportion of planktonic specimens increases from 0 percent in shallow marine environments to more than 90 percent in deep marine environments. Modern planktonic forams generally have globular chambers, often with spines. Some fossil planktonics, however, particularly in the Cretaceous, had a more flattened shape, sometimes with heavy keels running around the shell. This is simply the number of benthic species in a standard-sized sample. For example, assemblages characterized by high proportions of agglutinated taxa are found in intertidal marshes.
Assemblages dominated by porcelaneous species characterize shallow tropical environments.
This is the methodology that results in the most detailed interpretations. It involves the inference of palaeoenvironments based on the known environmental preferences of modern species or genera. Because it involves the exact identification of species, this approach is the most challenging, even for experts who have studied foraminifera for many years. These four approaches to paleoenvironmental interpretation have been used for several decades by oil company paleontologists. When an oil well is drilled, rock fragments are brought to the surface and among these fragments are often hundreds of specimens of foraminifera.