Well-preserved samples of upper Pliocene calcareous nannofossil ooze were subjected to elevated temperatures and pressures in order to simulate diagenetic effects. The samples were then studied and compared to an untreated control sample using both a light microscope and a scanning electron microscope. The order of alterations, progressing from the original sample to the sample exposed to highest temperatures and pressures, was observed to be (1) minor etching and overgrowth formation; (2) continued etching and secondary overgrowth formation, and the disaggregation of the elements of smaller coccoliths; and (3) dominant overgrowth on whole coccoliths with particularly massive overgrowth formation on the discoasters. Diversity of the nannofossil assemblage decreased under increasingly severe conditions.

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