西太平洋782A钻孔新生代的有孔虫

CENOZOIC FORAMINIFERA FROM THE BOREHOLE 782A IN THE WESTERN PACIFIC OCEAN

大洋钻探工程” 1 2 5航次的 782 A钻孔位于西太平洋菲律宾海东北部 ,井深 4 76.8m。基底为安山岩 ,上覆盖层为中始新统—更新统的沉积层 ,其中保存有低丰度的有孔虫。自下而上可划分出 8个浮游有孔虫带。由于出现 Catapsydrax dissimilis,C.stainforthi为 N5 、N6 带的带化石 ,表明本钻孔存在早中新世的地层。同时由于缺失浮游有孔虫带 P1 5 — P1 6 下部 ,N3上部—N4,N7—N1 1 带的带化石 ,说明在中始新世与晚始新世之间、晚渐新世与早中新世之间、早中新世与中中新世之间存在 3个沉积间断。钻孔中的有孔虫标志本区当时处于温暖亚热带环境。根据不同时期温度的变化 ,可划分出 5个阶段 ,包括 3个偏暖时期和 2个温凉时期。

Site 782A (ODP,Leg125)lies on the eastern margin of the Izu Bonin forearc basin,about halfway between the active volcanic arc and the Izu Bonin trench in the western Pacific Ocean.The borehole 782A,476 8 m deep,was fully cored and described.A simple subdivision is made into two lithologic units:one sedimentary and the other volcanic basement.Stratigraphic age of the sediments is Pleistocene to Middle Eocene.The generally low abundance of planktonic foraminifera was observed in the pre Quaternary cores.The results of foraminiferal study from the borehole 782A indicate the sedimentary sequence between the Quaternary (zone P 22 ) and the late Middle Eocene (zone P 14 ),there are 8 zones that might be divided based on the zonation of Bolli's et al.Among these zones,the Catapsydrax dissimilis (zone N 5) and Catapsydrax stainforthi (zone N 6) were found in sample 125 782A 35X～31X,showing the existence of Lower Miocene.The absences of zones P 15 —lower P 16 ,upper N 3-N 4,N 7-N 11 ,show the hiatuses between Late Eocene/Middle Eocene,Early Miocene/Late Oligocene,Middle Miocene/Early Miocene.Temperate to warm subtropical planktonic foraminifera forms dominate the whole of the sedimentary sequence.The five stages of temperature changes in this area can be identified based on the foraminiferal abundance,diversity,ratios of planktonic and benthonic foraminifera.They are:Ⅰ.late Middle Eocene to Early Miocene,Ⅱ.middle Middle Miocene to early Late Miocene,Ⅲ.middle Late Miocene to early Early Pliocene,Ⅳ.middle Early Pliocene to middle Middle Pliocene,Ⅴ.late Middle Pliocene to Pleistocene.Among them,Ⅰ,Ⅲ,Ⅴ stages are relatively warm and Ⅱ and Ⅳ ones are relatively temperate.