Latest Oligocene through early middle Miocene diatom biostratigraphy of the eastern tropical Pacific

Study of DSDP Sites 71, 77, and 495 has allowed the development of a refined diatom biostratigraphy for the latest Oligocene through early middle Miocene of the eastern tropical Pacific which is well correlated to the low-latitude zonations for planktonic foraminifers, coccoliths, and radiolarians. Six zones and 7 subzones are proposed, and correlation with high-latitude diatoms zonations for the North Pacific, the Norwegian Sea, and the Southern Ocean is suggested by the discovery of selected diatoms in these tropical sediments which were previously thought to be restricted to high latitudes. Six new species and one new variety of diatoms which are stratigraphically useful are proposed : Actinocyclus hajosiae, n. sp., A. radionovae, n. sp., Coscinodiscus blysmos, n. sp., C. praenodulifer, n. sp., Craspedodiscus rydei, n. sp., Thalassiosira bukryi, n. sp., and Coscinodiscus lewisianus var. robustus n. var.深海钻探计划（Deep Sea Drilling Project，DSDP）71、77及495站位的研究，成功构建了东热带太平洋渐新世最晚期至中中新世早期的高精度硅藻生物地层学（diatom biostratigraphy）框架，该序列可与浮游有孔虫（planktonic foraminifers）、颗石藻（coccoliths）及放射虫（radiolarians）的低纬度生物地层分带（low-latitude biostratigraphic zonations）实现良好对比。本研究共划定6个硅藻带与7个硅藻亚带；通过在该热带沉积物中发现此前被认为仅局限于高纬度区域的特定硅藻类群，本研究提出可将该序列与北太平洋、挪威海（Norwegian Sea）及南大洋（Southern Ocean）的高纬度硅藻生物地层分带进行关联。本研究还建立了7个具备地层学应用价值的硅藻新类群，包含6个新种（new species，n. sp.）及1个新变种（new variety，n. var.）：Actinocyclus hajosiae, n. sp.、A. radionovae, n. sp.、Coscinodiscus blysmos, n. sp.、C. praenodulifer, n. sp.、Craspedodiscus rydei, n. sp.、Thalassiosira bukryi, n. sp. 以及Coscinodiscus lewisianus var. robustus n. var.