Quantitative analysis of Early Eocene radiolarian assemblages discovered in the sedimentary mélange (accretionary prism) of the Saga area,southern Tibet provides new information to constrain the timing of Tethys ...Quantitative analysis of Early Eocene radiolarian assemblages discovered in the sedimentary mélange (accretionary prism) of the Saga area,southern Tibet provides new information to constrain the timing of Tethys closure and the initial collision of India and Eurasia. The radiolarian species of Saga include Amphisphaera coronata (Ehrenberg),Buryella hannae Bak & Barwicz-Piskorz,Buryella clinata Foreman,Buryella tetradica Foreman,Calocycloma ampulla (Ehrenberg),Lamptonium fabaeforme constrictum Riedel and Sanfilippo,Lamptonium pennatum Foreman,Lithomespilus coronatus Squinabol and Lamptonium (?) colymbus Foreman. The adequate and reliable correlation of these radiolarians specimens indicates that the assemblage is of Early Eocene in age. The age and depositional envi-ronment of these radiolarians testify that deep ocean basins existed between India Plate and Asia Plate during the Early Eocene. The complete closure of Tethys must have taken place at least after the Early Eocene.展开更多
对湖北松滋黑档口早始新世洋溪组进一步采集和研究表明,该组下部黑色泥页岩乃是世界上罕见的早始新世猴鸟鱼化石库。不仅产有世界上最古老(距今5 500万年)的灵长类代表——阿喀琉斯基猴(Archicebus achilles Ni et al.,2013)、我国南方...对湖北松滋黑档口早始新世洋溪组进一步采集和研究表明,该组下部黑色泥页岩乃是世界上罕见的早始新世猴鸟鱼化石库。不仅产有世界上最古老(距今5 500万年)的灵长类代表——阿喀琉斯基猴(Archicebus achilles Ni et al.,2013)、我国南方已知鹤形目化石最早记录——黑档口松滋鸟(Songzia heidangkouensis Hou,1990)、尖爪松滋鸟(Songzia acutunguis Wang et al.,2012)以及高丰度且保存完美的湖北江汉鱼Jianghanichthys hubeisis(Lei,1987)化石群,而且又新发现鬣蜥类(Agamid)、蝉(cicada)、蜘蛛(spider)、白蚁(termite)、古植物以及江汉鱼以外的多种鱼类化石。这是继北美绿江组(Green River Formation)、德国梅瑟尔(Messel)化石库(Fossillagersttte)之后,世界上新近发现的第三个早始新世特异埋藏群,在产出时代上较前两者早700万年。生物地层、构造古地理、沉积相和生态与埋藏学的分析研究表明,该特异埋藏群形成于早始新世初期江汉盆地西缘松滋-当阳盆缘凹陷之中。温湿的气候、充足的陆缘供给为盆缘凹陷及相邻低山-湿地中生物群的繁衍创造了条件;继之鄂西山地抬升和江汉盆地向东收敛而诱发的湖平面上升、咸化、滞流和缺氧以及(或者)盆地中部继之喷溢的基性火山熔岩而散发的有害气体和火山粉尘,可能是导致该生物群集群死亡的主要原因;伴随湖底缺氧而出现大量厌氧细菌席和藻类,在吸食生物软体的同时,为沉入湖底生物群骨架的完好保存创造了必要的封闭条件。展开更多
A combined micropalaeontological and sedimentological investigation of the Early Eocene Naredi Formation (thickness varying between 20 m and 60 m) reveals a complete third-order cycle and six fourth-order sea level cy...A combined micropalaeontological and sedimentological investigation of the Early Eocene Naredi Formation (thickness varying between 20 m and 60 m) reveals a complete third-order cycle and six fourth-order sea level cycles. Within the third-order cycle the foraminiferal abundance and diversity gradually increase upwards and reach their maximum values at about 41 m thickness above the base of the formation and subsequently decrease upward and finally give way upward to an unfossiliferous zone at the topmost part. Within a fourth-order cycle foraminiferal abundance and diversity exhibit a similar increasing and decreasing pattern. Bounded between two unconformities the Naredi Formation represents a sequence. A highly fossiliferous Assilinabearing limestone interval represents the maximum flooding zone which separates the transgressive systems tract at the base from the highstand systems tract at the top.展开更多
基金the National Natural Science Foundation of China (Grant No.40672086)the National Key Basic Research Program of China (Grant No.2006CB701400)
文摘Quantitative analysis of Early Eocene radiolarian assemblages discovered in the sedimentary mélange (accretionary prism) of the Saga area,southern Tibet provides new information to constrain the timing of Tethys closure and the initial collision of India and Eurasia. The radiolarian species of Saga include Amphisphaera coronata (Ehrenberg),Buryella hannae Bak & Barwicz-Piskorz,Buryella clinata Foreman,Buryella tetradica Foreman,Calocycloma ampulla (Ehrenberg),Lamptonium fabaeforme constrictum Riedel and Sanfilippo,Lamptonium pennatum Foreman,Lithomespilus coronatus Squinabol and Lamptonium (?) colymbus Foreman. The adequate and reliable correlation of these radiolarians specimens indicates that the assemblage is of Early Eocene in age. The age and depositional envi-ronment of these radiolarians testify that deep ocean basins existed between India Plate and Asia Plate during the Early Eocene. The complete closure of Tethys must have taken place at least after the Early Eocene.
文摘对湖北松滋黑档口早始新世洋溪组进一步采集和研究表明,该组下部黑色泥页岩乃是世界上罕见的早始新世猴鸟鱼化石库。不仅产有世界上最古老(距今5 500万年)的灵长类代表——阿喀琉斯基猴(Archicebus achilles Ni et al.,2013)、我国南方已知鹤形目化石最早记录——黑档口松滋鸟(Songzia heidangkouensis Hou,1990)、尖爪松滋鸟(Songzia acutunguis Wang et al.,2012)以及高丰度且保存完美的湖北江汉鱼Jianghanichthys hubeisis(Lei,1987)化石群,而且又新发现鬣蜥类(Agamid)、蝉(cicada)、蜘蛛(spider)、白蚁(termite)、古植物以及江汉鱼以外的多种鱼类化石。这是继北美绿江组(Green River Formation)、德国梅瑟尔(Messel)化石库(Fossillagersttte)之后,世界上新近发现的第三个早始新世特异埋藏群,在产出时代上较前两者早700万年。生物地层、构造古地理、沉积相和生态与埋藏学的分析研究表明,该特异埋藏群形成于早始新世初期江汉盆地西缘松滋-当阳盆缘凹陷之中。温湿的气候、充足的陆缘供给为盆缘凹陷及相邻低山-湿地中生物群的繁衍创造了条件;继之鄂西山地抬升和江汉盆地向东收敛而诱发的湖平面上升、咸化、滞流和缺氧以及(或者)盆地中部继之喷溢的基性火山熔岩而散发的有害气体和火山粉尘,可能是导致该生物群集群死亡的主要原因;伴随湖底缺氧而出现大量厌氧细菌席和藻类,在吸食生物软体的同时,为沉入湖底生物群骨架的完好保存创造了必要的封闭条件。
基金financial support (project No. SR/S4/ESe281/2007)
文摘A combined micropalaeontological and sedimentological investigation of the Early Eocene Naredi Formation (thickness varying between 20 m and 60 m) reveals a complete third-order cycle and six fourth-order sea level cycles. Within the third-order cycle the foraminiferal abundance and diversity gradually increase upwards and reach their maximum values at about 41 m thickness above the base of the formation and subsequently decrease upward and finally give way upward to an unfossiliferous zone at the topmost part. Within a fourth-order cycle foraminiferal abundance and diversity exhibit a similar increasing and decreasing pattern. Bounded between two unconformities the Naredi Formation represents a sequence. A highly fossiliferous Assilinabearing limestone interval represents the maximum flooding zone which separates the transgressive systems tract at the base from the highstand systems tract at the top.
