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How did coccolithophores and foraminifera change deep-sea sediments during the Jurassic?

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Jurassic paleogeography — Jurassic Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Jurassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

During the Jurassic Period, the evolution and rapid radiation of coccolithophores and foraminifera fundamentally transformed deep-sea sedimentation. Before these skeletonized planktonic organisms appeared, carbonate deposition was primarily restricted to shallow-water, nearshore environments.1

As these organisms evolved, their calcareous tests (shells) began to settle on the ocean floor upon their death, leading to the accumulation of pelagic calcareous oozes in the deep sea. This development significantly altered the geochemistry of the oceans and the nature of the deep-sea floor, as these biogenic deposits became a major contributor to deep-sea sediments. The accumulation of these sediments is dependent on the presence of such calcium-secreting plankton, which did not exist prior to the Mesozoic Era. Consequently, the advent of these groups shifted the primary location of carbonate accumulation from shallow shelves to the deep-sea abyssal plains, provided the depth remained above the carbonate compensation depth.21