Abundance of stratigraphically important planktic foraminifera and biohorizons of ODP Site 186-1150 and Hole 186-1151A@en

The planktonic foraminiferal biostratigraphy of Sites 1150 and 1151 drilled in the Japan Trench region during Ocean Drilling Program Leg 186 has been examined. At these drill sites, more than 1100 m of sediment, reaching to the middle Miocene, were obtained with good core recovery. Although planktonic foraminiferal records of the two sites are discontinuous, probably because of carbonate dissolution beneath the carbonate compensation depth, 16 stratigraphically important taxa of planktonic foraminifers were detected. Eight biohorizons were recognized in same stratigraphic order between these two sites. With respect to the diatom data, these eight planktonic foraminiferal biohorizons are possibly synchronous for correlating marine strata from the upper Miocene to Pleistocene in the Japan Trench region. The last occurrence of Neogloboquadrina asanoi falls within Olduvai Subchron. Therefore, the Pliocene/Pleistocene boundary of both sites is situated a little above this biohorizon.本研究针对大洋钻探计划（Ocean Drilling Program）第186航次于日本海沟区域钻取的1150号与1151号钻孔的浮游有孔虫生物地层学（planktonic foraminiferal biostratigraphy）开展了系统分析。上述两个钻孔获取了累计厚度超1100米的沉积物岩芯，岩芯回收率良好，沉积层位延伸至中中新统。尽管两处钻孔的浮游有孔虫记录存在不连续性，推测其成因是碳酸盐补偿深度（carbonate compensation depth）之下的碳酸盐溶蚀作用，但研究仍检出16个具有地层学重要意义的浮游有孔虫类群。两处钻孔均识别出8个遵循相同地层顺序的生物地层面。结合硅藻数据，这8个浮游有孔虫生物地层面可作为日本海沟区域晚中新世至更新世海相地层对比的潜在等时界面。阿佐野新抱球虫（Neogloboquadrina asanoi）的末现面（last occurrence）落入奥杜威亚时（Olduvai Subchron）范围内，因此两处钻孔的上新世/更新世界线均略高于该生物地层面。