How do foraminiferan shells contribute to limestone rocks?

Foraminiferans contribute to the formation of limestone and chalk through the accumulation of their protective shells, known as tests.1

These unicellular organisms inhabit marine environments, and upon their death, their empty calcareous tests sink to the ocean floor. Over time, these remains accumulate to form foraminiferal ooze, which covers approximately 30 percent of the ocean floor. Through the process of lithification, these loose carbonate sediments are transformed into limestone.12

In addition to forming deep-sea deposits, foraminiferan remains are often found mixed with other skeletal debris and ooliths in shallow-water marine environments. While these organisms are essential to the creation of many limestone types, it is important to note that if the limestone later undergoes dolomitization, the original fossilized textures and details of the foraminiferan shells may be obscured or destroyed.34