南大洋深水沉积物波举例研究
RESEARCH OF DEEP-WATER SEDIMENT WAVES IN THE SOUTHERN OCEAN
-
摘要: 深水细粒底流型沉积物波多分布于陆坡、洋盆等深水洋底。以大澳大利亚湾上部陆坡和康拉德隆起西南坡的波状底形为例,解释了南大洋深水沉积物波的形态特征、分布特点和形成发育机理。以大澳大利亚湾的沉积物波为代表的钙质细粒底流型沉积物波波高约40 m,波长1~2 km,直线型脊线长10 km,平行于等深线,主要由苔藓虫软泥组成,间冰期陆架上苔藓虫丰富,冰期移至陆架外缘和陆坡上部,在流速约16 cm/s的高密度出流作用下于陆坡上部发育成泥质沉积物波。康拉德隆起西南坡的硅质细粒底流型沉积物波由硅藻软泥组成,绕南极流锋面的上升流使得此处的生产力高,硅藻类微体生物丰富,在流速约6 cm/s的底流作用下发育大量沉积物波。2种细粒底流型沉积物波的向陆侧翼的沉积率大于向海侧翼,披覆形成后爬不同相爬升层理,显示沉积物波向上游坡迁移。Abstract: Fine-grained sediment waves formed by deep-water bottom current usually occur on continental slopes or ocean basins. This paper takes some examples from the wavy bedforms occurred at the upper slope of the Great Australian Bight and the southwestern slope of the Conrad Rise. The morphology, distribution pattern and formation mechanisms are discussed. The fine-grained calcareous sediment waves near the shelf-slope break of the Great Australian Bight are oriented parallel to contours in a strip along the shelf-slope break. They are up to 40 m high, 1~2 km wide and 10 km long composed of cool water carbonate oozes. Bryozoans were abundant during the interglacial period, and then moved to the edge of shelf and the upper slope, forming sediment waves under the action of bottom current with a velocity of about 16cm/s. There are some sediment waves developed at the southwestern slope of the Conrad Rise. They are composed of diatom ooze. This is probably due to the high diatom productivity caused by vigorous upwelling of nutrients in the Antarctic Circumpolar Current. Diatoms were abundant for the formation of sediment waves under the action of bottom current, with a velocity about 6 cm/s. The sedimentation rate of the landward flank is higher than the rate on the seaward flank, thus the sediment waves show a pattern of landward migration.