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Abundant well-preserved radiolarians were recovered from Ocean Drilling Program Leg 171B Hole 1051A, western North Atlantic, and range from upper middle Eocene radiolarian Zone RP16 through lower Palaeocene Zone RP6. This mid-latitude fauna contrasts with tropical faunas in lacking many tropical zonal markers and in its high proportion of diachronous first and last occurrences. The sequence from Hole 1051A contains the lower Eocene-middle Eocene and Palaeocene-Eocene (P-E) boundaries, and the only known record of a well-preserved Late Palaeocene Thermal Maximum (LPTM) radiolarian assemblage. There is no gross change observed in the composition of the fauna, only a minor increase in the number of first and last occurrences across the LPTM interval and P-E boundary. Calcareous evidence indicates two hiatuses, each 1–2 Ma long, one in the lowermost middle Eocene sequence and a second in the upper Palaeocene sequence. Presence of the middle Eocene hiatus is corroborated by an abnormally large radiolarian turnover. Twenty-six events are documented and show that most of radiolarian Zone RP10 and a substantial part of Zone RP9 are missing. Seven new species are described: Spongatractus klausi, Calocyclas aphradia, Lychnocanoma (?) parma, Sethocyrtis austellus, Sethocyrtis chrysallis, Thyrsocyrtis (Pentalacorys) krooni and Thyrsocyrtis (Thyrsocyrtis) norrisi.

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