Radiolarian chronology and fauna across the middle/late Eocene boundary at ODP Hole 171-1052A

Quantitative radiolarian assemblage analysis has been conducted on middle and upper Eocene sediments (Zones RP16 to RP18) from Ocean Drilling Program Site 1052 in order to establish the radiolarian magnetobiochronology and determine the nature of the faunal turnover across the middle/late Eocene boundary in the western North Atlantic Ocean. We recognize and calibrate forty-five radiolarian bioevents to the magneto- and cyclo-stratigraphy from Site 1052 to enhance the biochronologic resolution for the middle and late Eocene. Our data is compared to sites in the equatorial Pacific (Leg 199) to access the diachrony of biostratigraphic events. Eleven bioevents are good biostratigraphic markers for tropical/subtropical locations (south of 30°N). The primary markers (lowest occurrences of Cryptocarpium azyx and Calocyclas bandyca) which are tropical zonal boundary markers for Zones RP17 and RP18 provide robust biohorizons for correlation and age determination from the low to middle latitudes and between the Atlantic and Pacific Oceans. Some other radiolarian bioevents are highly diachronous (<1 million years) between oceanic basins. […]

对来自海洋钻探计划1052号站点的中上渐新统沉积物（RP16至RP18区）进行了定量放射虫群分析，旨在建立放射虫磁生物地时学，并确定西北大西洋中部/晚期渐新统界线处生物群演替的性质。我们识别并校准了45个放射虫生物事件，以Site 1052的磁性地层学和旋回地层学为基准，以提升中晚渐新统的生物地时分辨率。我们的数据与赤道太平洋地区的站点（Leg 199航次）进行比较，以评估生物地层事件的时间差异。其中11个生物事件是热带/亚热带地区（北纬30°以南）良好的生物地层标志。主要标志（Cryptocarpium azyx和Calocyclas bandyca的最低出现频率）作为RP17和RP18区的热带带界标志，为从低纬度到中纬度以及大西洋与太平洋之间的相关性和年代测定提供了坚实的生物地层界线。一些其他放射虫生物事件在不同海洋盆地间具有高度的时间差异（小于100万年）。