Important primary producers. Important index fossil for Mesozoic to Recent . They are important primary producers in the modern oceans. Generally, a high abundance of diatoms means nutrient-rich waters, such as in upwelling zones . When diatoms are extremely abundant, enough of their skeletons settle on the seafloor to form siliceous ooze .
Siliceous oozes can eventually recrystallize to form the rock chert .
Economically important as abrasives, filtering agent, etc. Their abundant accumulation in deep-sea sediment began in the Cretaceous . Important in biostratigraphy. They occur where forams don't. The best known and most widespread chalks are of Cretaceous age, such as those exposed as cliffs on both sides of the English Channel.