美国阿巴拉契亚山脉芬卡苏地区奥陶纪海底水道中的内潮汐沉积  

Internal-tide Deposits in an Ordovician Submarine Channel, Fincastle, Appalachians, USA

作　　者：高振中[1] K.A.Eriksson 

机构地区：[1]江汉石油学院地质系 [2]美国弗吉尼亚州大学地质系

出　　处：《沉积学报》1993年第1期12-22,共11页Acta Sedimentologica Sinica

摘　　要：本文论述了在世界范围内首次鉴别出的新的沉积类型——内潮汐沉积,发现于美国弗吉尼亚州芬卡苏地区奥陶纪深水海底水道充填沉积中。已识别出两种相:①双向交错纹理极细砂岩相,以发育分别向古水道上方和下方倾斜的双向交错纹理为特征,被归因于内潮汐作用沉积的产物。②单向交错层和交错纹理中至细砂岩相,发育向古水道上方倾斜的低角度板状交错层和交错纹理,被解释为叠加有内波的内潮汐沉积物。据沉积相层序分析,内潮汐沉积形成于海平面上升、粗屑重力流受到抑制的时期。Current- meter data collected over the past 20 years has revealed the existence of currents flowing alternatively up and down most submarine canyons and other submarine valleys. These currents are attributed to internal weaves that are subsurface waves between layers of different density or within layers where vertical density gradients are present. An important kind of internal wave is that which has a period equal to the semidiurnal or diurnal tide and referred to as an internal tied. Velocities of bidirectional deep-water currents range from 20-50 cm / sec. Such currents can move sediment up to fine sand and form a lot of ripples at depths of several thousand meters. Nevertheless, internal-tied deposits have not been recognized in the ancient rock record. Recently, the authors identified evidence for internal tides in an upped Middle Ordovician deep-water, submarine channel-fill deposit in Fincastle area, Virginia Appalachians, USA. During late Middle Ordovician time, the Fincastle area was located on the southeastern slope of a foreland basin. There was a series of submarine channels that were oriented southeast-northwest in the paleoslope. The channel-fill deposits are dominantly various kind of gravity flow deposits, showing an up- ward fining and thinning trend. The internal-tide deposits cap the up-fining sequence. Flute casts on the bottom turbidite beds and ripple cross laminations defining the C- division of Bouma sequences yield paleocurrent directions towards NW325-330. A calculated paleowater depth are more than 204m. Two internal-tide facies are recoginzed. 1. Bidirectionnal, cross-laminated, very fine-grained sandstone facies. This facies is composed mainly of very fine-grained, sublithic wackes and locally siltstones. Interbed-ded with this facies are dark shales and thin turbidite beds. This facies is characterized by well-developed, bidirectional ripple cross laminations that display high-frequency alternations of paleocurret azimuths, the paleocurrent direct

关 键 词：奥陶纪 海底 水道 潮汐 沉积 

分 类 号：P736.211[天文地球—海洋地质]