摘要
我国淤泥质海岸由微型和小型层序构成。微型层序主要是潮汐作用形成的,小型层序由粗、细粒单层构成,其中粗粒单层形成于风暴时期,细粒单层形成于平静天气。小型层序系完整的风暴层序。在游泥质海岸层序中风暴沉积的厚度超过非风暴沉积,且排列有序。低潮坪沉积物粗,向陆向海变细,从而构成中间粗、两端细的淤泥质海岸典型垂直层序。随着条件和因素的变化,典型垂直层序可以产生若干变异,识别出三种变异层序。
Two different scale dipositional micro-and small sequences are distinguished to de essential components of the sequences of low-energy coast. Micro-sequences, with the thickness of mm scale, are mainly formed by tides, and can be distinguished as mud laminae and sand laminae. Small sequences are composed of micro-sequences and are generally several to 20cm thick. According to the relative ratio of mud and sand laminaes inside, the small sequences can also be classified as fine (muddy) small-sequences and coarse (sandy) ones which are belived to be formed under fair weather and storm weather respectively, and can also be regarded as normal and event sequences respectively. Grain size and sand contents in both normal and event layers increase from low tidal level both seaward (downward) to subtidal zone and upward (landward) to upper inlertidal flat. Near the lower water level the sand contents in the normal layers can be higher then that of the event layers in the upper tidal flat, and the sands are also coarser. The differences in sand contents and the grain size between adjacent normal and event deposites are obvious. The seaward changes from the lower tidal flat to the wave base are similar to the landward changes that occured from the lower tidal flat to the upper tidal flat.
Comparision among the present, subrecent and ancient sections in many areas demonstrated that the basic sequences of the low-energy coast of China is a sequence that fines from lower tidal flat both upward to the upper tidal deposits and downward to the wave base deposits. In the tidal flat where the tidal channels are developed, the tidal sequence fines only upward with a obvions erosional surface at the bottom and with underlying mud deposits, which is similar to the classic sequence described by Klein (1977) .In the areas where river mouth sand bars and tidal sand ridges are developed, the sequence also fines only upwards but with underlying sand deposits. Adjacent coastal rocky hills or man-made dams can make the slope of the upper tidal flat or supertidal steepen, which subsequently cause the sediments coarser at the top of the low-energy coast sequence. Shell layers can sometimes be found in the coarsened upper tidal deposits. Such sequence had been detected in the Yangtze Delta and the Paleozoic tidal deposits in western Zhejiang Province.
出处
《沉积学报》
CAS
CSCD
北大核心
1992年第4期119-128,共10页
Acta Sedimentologica Sinica
基金
教委基金资助的课题
