控制流水波痕的外部地质作用

流水波痕可以广泛发育在不同的海、陆相环境中。对流水波痕的研究不能仅仅注意沉积作用方面，更要注意作用于流水波痕的外部条件。

Indicator of Outside Geologic Action:Ripple Marks

Ripple marks,a surface structure,occur in any area where there is water flowing (no matter what environment it is).Therefore,ripple marks do not indicate facies but directions of water flowing.Outside events such as floods and turbidity currents can form ripple marks of different types.In some gulleys over a flood land in the upper reaches of the Yellow River,modern subaerial ripple marks are discovered.The gulleys are about 200 m away from the flood land.Due to the actions of seasonal water flowing,there is a lush growth of grass at the outlets,and between the grass,appears a wide open area where there are a great number of modern asymmetric ripple marks.Substrate of the asymmetric ripple marks is grayish yellow subsilty soil overlain by purple and thin (about 0.5 cm thick)subsilty layer,which is closely related to the formation of the asymmetric ripple marks. The formation of such asymmetric ripple marks is based not only on open and flat areas but also on outside flood events.And as for those of continental basins,climatic conditions are always the leading factor for the sizes,scales and configurations of ripple marks.Ripple marks in deep-sea environments have various types,such as curved,linear,crescentic,tongue- and fork-like.These ripple marks often coexist with CD sequences of turbidity currents.The deep-sea ripples mainly develop from the foot of a slope to a continental rise,belonging to smooth landform.The ripple marks go in direct proportion to the thickness of turbidite and result from the dragging of low-density turbidity currents on the bed sand.In other words,the deep-sea ripples are controlled by the scales and intensities of the turbidity currents.And in land environments,the development of ripple marks is usually controlled by ancient climate.Wet climate often causes the levels of rivers and lakes to rise.And as a result of that,a lot of ripple marks are developed.