Planktonic foraminifera are widely used for biostratigraphy of pelagic sequences, but a major complication is diachronism — the same species' first and last appearances occur at different times in different regions — because planktonic foraminifera are latitudinally provincialized: their distribution is controlled by sea-surface temperature and water-mass boundaries, so speciation, migration, and extinction events do not occur simultaneously across all latitudes/oceans.
Planktonic foraminifera live in surface waters and are strongly controlled by sea-surface temperature, which varies systematically with latitude. This creates latitudinal provinces (tropical, subtropical, transitional,...
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