Calcareous nannofossils in ODP Sites 135-840 and 135-841

Ocean Drilling Program Leg 135 drilled at two sites on the Tonga Ridge. Calcareous nannofossils recovered at Site 840 on the Tonga Ridge date the sedimentary sequence as late Pleistocene or Holocene (CN15) through late Miocene (CN9) in age. A hiatus occurs in the mid Pliocene. Site 841 in the Tonga Trench yielded a sedimentary sequence with nannofossils from middle Pleistocene Subzone CN14b through the middle or late Eocene Subzones CP14a-CP15b overlying a rhyolitic volcanic basement. Part of the Eocene interval contains the shallow-water nannofossil taxa Braarudosphaera, Micrantholithus, and Pemma. A major unconformity separates lower Oligocene Zone CP 16 from lower middle Miocene Zone CN4 strata.

大洋钻探计划（Ocean Drilling Program）第135航次在汤加海岭的两个站位实施钻探作业。汤加海岭840站位发现的钙质超微化石（calcareous nannofossils）限定了该站位沉积序列的年代范围为更新世晚期或全新世（CN15）至中新世晚期（CN9），上新世中期存在沉积间断。汤加海沟841站位获取的沉积序列所含超微化石的年代跨度为更新世亚带CN14b中期至始新世中晚期（CP14a-CP15b亚带），该沉积序列上覆于流纹质火山基底之上；该站位始新世部分层段含有Braarudosphaera、Micrantholithus及Pemma等浅水超微化石分类群，且发育一处重大不整合面，将渐新世下部CP16带与中中新世下部CN4地层分隔开来。