北海盆地维京地堑新近纪下切谷发育主控因素及其内部充填特征

Controlling factors of incised valley development in the Neogene and its characteristics of internal filling in Viking Graben,North Sea Basin

下切谷是陆地上一种常见的侵蚀地貌,古今均十分发育,但是不同盆地、不同时代发育的下切谷,无论是在沉积充填特征还是平面展布形态等多个方面都大相径庭。为此,作者依据曼宁公式进行理论推导,再结合分析北海盆地维京地堑发育的典型下切谷实例以及前人进行的相关水槽实验结果总结认为:地形坡度、基准面下降速率及幅度与下切谷所侵蚀地层的岩性是影响下切谷发育模式的最主要因素。这些因素共同控制了:(1)下切谷的弯度指数及宽深比,(2)下切谷平面上发育密度及其规模,(3)与下切谷伴生的陆棚三角洲、陆棚边缘三角洲沉积厚度及展布范围。海侵过程中下切谷的沉积充填类型及岩性,受平均基准面上升速率及沉积物供应量的共同控制,根据沉积充填类型及岩性的不同可将其划分为富砂型陆棚三角洲充填及富泥型河口湾充填两类。

Incised valley is a common erosional landform, which is well-developed in ancient rock records and modern depositional settings. However, various sedimentary filling characteristic and planar morphology of incised valley have been reported in different basins and of different ages. Based on theoreti- cal derivation according to Manning formula, the typical incised valley examples of the Viking Graben in North Sea Basin and previous relevant flume experiment results, it is concluded that the slope gradient,rate and amplitude of base level descending and lithology of underlying formation are the main controls on the pattern of incised valley development. These factors control： （1） sinuosity index and width to depth ratio of the incised valley; （2） Planar developing density and scale of the incised valley; （3） thickness and spatial distribution of shelf delta and shelf margin delta associated with the incised valley. During transgression, sedimentary filling and lithology variation of incised valley are mainly controlled by the mean rate of sea-level rising and sediment supply. Based on differences in sedimentary filling and litholo- gy, filling-type of the incised valley can be classified as sand-rich shelf delta and mud-rich estuary.