Stratigraphic distribution pattern of selected Paleogene calcareous nannofossil species in DSDP Hole 72-516F in the South Atlantic (Fig. 3)@en

The detailed study of an expanded Paleogene section with abundant, moderate to well preserved calcareous nannofossils from South Atlantic DSDP Site 516 has resulted in a precise correlation of most calcareous nannofossil markers with the magnetostratigraphy. Many nontraditional datums have also been documented and correlated to the magnetostratigraphy. Comparison of the results from Site 516 with those of previous studies from other areas enables a critical evaluation of the accuracy, synchroneity or diachroneity of the species events over geographically long distances. Of special significance is the correlation for the first time of the stratigraphic ranges of Chiasmolithus gigas and Rhabdosphaera gladius with the magnetostratigraphy. Other important results include the following: first occurrence (FO) of Cruciplacolithus primus, 66.3 Ma; FO Chiasmolithus danicus, 65.6-66.0 Ma; FO Prinsius martinii, 65.5-66.0 Ma; FO Heliolithus kleinpellii, 59.8-61.6 Ma (probably diachronous); last occurrence (LO) of Tribrachiatus orthostylus, 51.0-54.8 Ma (unreliable); FO Chiasrnolithus gigas, 47.4 Ma; FO Reticulofenestra umbilica, 44.6 Ma; LO Chiasmolithus gigas, 44.4-46.8 Ma (diachronous); LO Nannotetrina fulgens, 44.2 Ma; LO Chiasmolithus grandis, 40.0-41.6 Ma (probably diachronous); FO Chiasmolithus oamaruensis, 39.8-40.4 Ma (unreliable); FO Isthmolithus recurvus, 39.5 Ma; LO Reticulofenestra reticulata, 37.6 Ma; LO Discoaster saipanensis, 36.4 Ma; end acme of Ericsonia subdisticha, diachronous; FO and LO Sphenolithus distentus, unreliable; and LO Reticulofenestra bisecta, 24.0 Ma.针对南大西洋深海钻探计划（Deep Sea Drilling Project, DSDP）516站位产出的、保存中等至完好且富含化石的完整古近纪剖面展开详细研究后，已实现绝大多数钙质超微化石（calcareous nannofossils）标志层与磁地层学（magnetostratigraphy）的精准对比。本次研究还记录了诸多非传统地层基准面，并将其与磁地层学进行关联。将516站位的研究结果与其他区域既往研究成果对比，可批判性评估长地理尺度下各物种演化事件的准确性、同步性或穿时性。尤为重要的是，本研究首次实现了巨叉石藻（Chiasmolithus gigas）与剑形球石藻（Rhabdosphaera gladius）的地层延限与磁地层学的关联。其他重要研究结果如下：原始冠盘藻（Cruciplacolithus primus）的首现（first occurrence, FO）事件，对应年龄为66.3 Ma；丹麦叉石藻（Chiasmolithus danicus）首现，对应年龄为65.6~66.0 Ma；马丁氏普林藻（Prinsius martinii）首现，对应年龄为65.5~66.0 Ma；克莱佩尔太阳石藻（Heliolithus kleinpellii）首现，对应年龄为59.8~61.6 Ma（大概率为穿时事件）；直柱三臂藻（Tribrachiatus orthostylus）的末现（last occurrence, LO）事件，对应年龄为51.0~54.8 Ma（可信度较低）；巨叉石藻首现，对应年龄为47.4 Ma；脐状网球藻（Reticulofenestra umbilica）首现，对应年龄为44.6 Ma；巨叉石藻末现，对应年龄为44.4~46.8 Ma（穿时事件）；亮红纳米藻（Nannotetrina fulgens）末现，对应年龄为44.2 Ma；大叉石藻（Chiasmolithus grandis）末现，对应年龄为40.0~41.6 Ma（大概率为穿时事件）；奥马鲁叉石藻（Chiasmolithus oamaruensis）首现，对应年龄为39.8~40.4 Ma（可信度较低）；弯曲峡湾藻（Isthmolithus recurvus）首现，对应年龄为39.5 Ma；网状网球藻（Reticulofenestra reticulata）末现，对应年龄为37.6 Ma；塞班盘星藻（Discoaster saipanensis）末现，对应年龄为36.4 Ma；近距埃里克森藻（Ericsonia subdisticha）的演化峰期为穿时事件；近距斯芬藻（Sphenolithus distentus）的首现与末现事件可信度较低；二分网球藻（Reticulofenestra bisecta）末现，对应年龄为24.0 Ma。