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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。
In the context of global oceanic anoxicity around the Cenomanian / Turonian boundary (ca.93Ma), a set of limestone-shale calcareous shale and mudstone shale with a few limestone lenses were developed in the southern Gangaba area Rich organic carbon deposition, foraminifera fossil preservation is good, rich in content, of which benthic foraminifera in the restoration of ancient water depth, the underlying dissolved oxygen concentration and paleocean productivity are important. Benthic foraminifera near the C / T boundary can be divided into three stages of evolution longitudinally. The main dominant genera include Dorothia, Anomalinoides, Lenticulina and Conobina. The planktonic / benthic ratios are between 50% and 80%, indicating the type Ⅳ2 habitat (the shelf-shelf boundary slope environment) with a depth of about 100-200m. Benthic foraminifera oxygen index (BFOI) between -6-25, the corresponding dissolved oxygen content of about 0.7-1.4ml / L, compared with other regions in the same period is low, is a weak oxidative environment. Both endophyte percentages and deep endophyte / exocrine ratios indicate higher levels of productivity near the C / T boundary. The short-term boom of marine productivity is likely to be the main reason for the aggravating seawater anoxic. The formation of long-term weak oxidative conditions is likely due to a lack of oxygen supply due to a series of environmental events during the same period.