西藏岗巴地区Cenomanian-Turonian界线附近底栖有孔虫古环境指标及其古海洋学意义  

BENTHIC FORAMINIFERA AS PALEOENVIRONMENTAL INDICATORS AND THEIR PALEOCEANOGRAPHIC SIGNIFICANCE AROUND THE CENOMANIAN-TURONIAN BOUNDARY IN GAMBA,TIBET

作　　者：贾建忠[1] 万晓樵[1] 李国彪[1] 陈河淞[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《微体古生物学报》2010年第2期135-143,共9页Acta Micropalaeontologica Sinica

基　　金：科技部"973"项目(G2006CB701403);国家自然科学基金项目(40872016)

摘　　要：在Cenomanian/Turonian界线(ca.93Ma)前后全球性的大洋缺氧背景下,藏南岗巴地区发育一套以深灰绿色-灰黑色钙质页岩、泥页岩为主夹少量灰岩透镜体的富有机碳沉积,有孔虫化石保存较好,含量丰富,其中底栖有孔虫在恢复古水深、底层水溶解氧浓度和古海洋生产力等方面具重要意义。C/T界线附近底栖有孔虫纵向上大致可划分为3个演化阶段。主要优势属种包括Dorothia,Anomalinoides,Lenticulina,Conobina等,浮游/底栖比率在50%-80%之间,指示了水深约100-200m的Ⅳ2生境型(外陆棚-陆架边缘斜坡环境)。底栖有孔虫氧指数(BFOI)在-6--25之间,对应的溶解氧含量约为0.7-1.4ml/L,与同时期其它地区相比偏低,属弱氧化环境。内生种百分含量和深内生种/外生种比率均指示了C/T界线附近较高的生产力水平。短期的海洋生产力的勃发很可能是加剧海水缺氧的主要原因,而长期的弱氧化条件的形成很可能是同时期一系列环境事件所导致的氧气供应量不足所致。During the Cenomanian-Turonian boundary event（ca.93 Ma,OAE2）,several layers of the mid-Cretaceous carbon-rich sediments,containing abundant microfossils（especially foraminifera）,developed in Gamba,Southern Tibet.As a widely used paleoenvironmental proxy,benthic foraminifera have great significance in reconstructing the ancient water depth,bottom water oxygen concentration and the oceanic productivity.The benthic foraminifera across the C/T boundary can be divided into three evolution stages,and both the main advantage species（Dorothia,Anomalinoides,Lenticulina,Conobina etc.）and plankton/benthos ratios [P/（P＋B）are of 50%—80%] indicate that the habitat type is Ⅳ_2（outer shelf-shelf edge environment）with the water depth approximately 100—200 m.The benthic foraminiferal oxygen index（BFOI）ranges from-6 to-25,corresponding to the dissolved oxygen content of about 0.7—1.4 ml/L which belongs to suboxic condition.The benthic foraminiferal microhabitat（deep infauna/epifauna）shows a higher primary productivity in this area.Under the suboxic condition,a short-term blooming of primary producers may exacerbate the decrease of water oxygenation to form a more favorable conditions for organic matter accumulation and preservation,while the long-term conditions of a weak oxidation is likely to be caused by a series of environmental events around the C/T boundary.

关 键 词：底栖有孔虫 溶解氧含量 古海洋生产力 Cenomanian/Turonian界线 岗巴 西藏 

分 类 号：Q915[天文地球—古生物学与地层学]