松辽盆地西部斜坡区LD17井明水组孢粉组合及其地质意义

PALYNOLOGICAL ASSEMBLAGES FROM THE MINGSHUI FORMATION OF WELL LD17,WESTERN SONGLIAO BASIN,NORTHEAST CHINA AND THEIR GEOLOGICAL IMPLICATIONS

松科1井位于松辽盆地,是中国大陆第一口以白垩纪陆相地层为研究对象的全取心科学探井,其生物地层、磁性地层等证据显示白垩纪/古近纪界线可能位于明水组二段上部。为了进一步确定松辽盆地白垩纪/古近纪界线位置和晚白垩世末期气候-环境变化,本研究选择位于松辽盆地西部斜坡区的LD17井,对明水组的孢粉类化石开展了分析。自下而上识别出三个组合:Taxodiaceaepollenites-Wodehouseia-Aquilapollenites组合、Schizaeoisporites-Pinuspollenites-Callistopollenites组合和Pinuspollenites-Ulmipollenites-Tricolpollenites组合。组合1、2的时代为Maastrichtian,而组合3面貌可能更接近于早古新世,白垩纪/古近纪界线可能位于组合3底部,即明二段中部。同时,对含孢粉化石丰富的明一段进行定量分析,孢粉植被主要为针、阔混生林和灌丛,总体反映了一种半湿润的亚热带气候。根据特征孢粉类型推断明一段中部沉积期,即Maastrichtian早期可能发生了一次极冷极湿事件,与当时全球白垩纪变冷事件同步。

Biostratigraphy,magnetostratigraphy and other evidences from Well SK1 suggest that the Cretaceous/Paleogene（K/Pg）boundary lies in the upper part of the Member 2of the Mingshui Formation in the Songliao Basin,Northeast China.In order to determine the inferred position of the K/Pg boundary,the sporepollen fossils of the Mingshui Formation from Well LD17,which is located in west slope of the Songliao Basin,are analyzed in this study.Three zonations are identified in ascending order：Taxodiaceaepollenites-Wodehouseia-Aquilapollenites,Schizaeoisporites-Pinuspollenites-Callistopollenites and Pinuspollenites-Ulmipollenites-Tricolpollenites zones.It is deduced that the age of the Zone 1and Zone 2is Maastrichtian,while Zone 3might be of the Early Paleocene.Hence,it is likely that the K/Pg boundary is within the bottom of the Zone 3,i.e.the middle part of the Mingshui Formation.The Member 1of the Mingshui Formation is rich in sporepollen fossils,which is quantitatively analysed.The result indicates a subhumid subtropical paleoclimate condition,with vegetation of theropencedrymion and shrub.A cooling and wetting event might happen in the middle part of the Member 1of the Mingshui Formation（early Maastrichtian）,consistent with the contemporaneous global cooling.