琼东南盆地深水区WN A井渐新世-中新世孢粉地层学及古气候

Oligocene-Miocene Palynostratigraphy and Paleoclimate of Well WN-A from Deep Water Area,Southeast Hainan Basin

琼东南盆地深水区是21世纪南海北部大陆架地区天然气勘探的重点区带之一.为了划分该盆地WN A井的地层时代及探明其沉积物所记录的古气候条件,笔者对该井分布于3261.25~5079.00m井段共计108份岩屑样品进行了孢粉分析.研究结果显示,该井孢粉化石种类较丰富且分布连续,由下至上可划分为4个孢粉组合:Pinuspollenites Polypodiaceoisporites Juglanspollenites Quercoidites E Quercoidites D组合、Pinuspollenites Juglanspollenites Polypodiaceoisporites Dicolpopollis kockelii组合、Quercoidites E Polypodiaceoisporites Pinuspollenites Polypodiisporites组合和Pinuspollenites Polypodiaceoisporites Randiapollisreticulatus Quercoidites E组合.其中:4425.00~5079.00m井段孢粉组合的优势组分是Pinuspollenites、Juglanspollenites和Quercoidites D,指示热带、亚热带针叶、常绿、落叶阔叶混交林,气候较温凉;3261.25~4425.00m井段孢粉组合中Quercoidites E占优势,指示热带、亚热带常绿、落叶阔叶混交林,气候温暖湿润.WN A井孢粉组合记录了一次明显的由温凉转为温暖的气候变化,与全球渐新世—中新世的气候变化可以对比,其发生位置,即4425.00m可以作为WN A井渐新统和中新统的界线.

The deep water area of southeast Hainan basin has become one of the most important natural gas exploration areas in the northern continental shelf of the South China Sea.A total of 108 samples were collected from the depth of 3261.25-5079.00 m in Well WN-A for spores and pollen analyses in order to determine the stratigraphic age and reconstruct the paleoclimate conditions.The results show that the fossils are rich in species and distributed continuously,and can be divided into four sporopollen zones including Pinuspollenites-Polypodiaceoisporites-Juglanspollenites-Quercoidites E-Quercoidites D,Pinuspollenites-Juglanspollenites-Polypodiaceoisporites-Dicolpopollis kockelii,Quercoidites E-Polypodiaceoisporites-Pinuspollenites-Polypodiisporites,and Pinuspollenites-Polypodiaceoisporites-Randiapollis reticulatus-Quercoidites E from the bottom to the top of WN-A well.The sporopollen at 4425.00-5079.00 m is dominated by Pinuspollenites,Juglanspollenites and pollen from deciduous Quercus,indicating tropic-subtropical cool conditions,and developing evergreen broadleaved,deciduous broadleaved,and coniferous mixed forest,however,the sporopollen at 3261.25-4425.00 m,is dominated by pollen from evergreen Quercus,suggesting tropic-subtropical warm climate conditions,and developing evergreen broadleaved and deciduous broadleaved mixed forest.This big climate change from relatively cool to relatively warm is comparable to the global climate change of Oligocene to Miocene.The depth of recorded climate change,i.e.4425.00 m should be the boundary between Oligocene and Miocene.