Figure F15. Eocene–Oligocene transitional interval, Hole U1356A. Oligocene and Miocene nonprotoperidinioid dinocysts comprise the oceanic oligotrophic genera Impagidinium and Batiacasphaera, as well as Operculodinium. Chemical index of alteration (CIA; see “Geochemistry and microbiology”) exhibits a large decline coeval with the onset of protoperidinioid-dominated dinocyst assemblages.
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