martes, 20 de agosto de 2013

¿How ripple marks form under the influence of waves?

Ripple marks are sedimentary structures, and indicate agitation by water or wind. How does ripple marks form? Ripple cross-laminae forms when deposition takes place during migration of current or wave ripples. A series of cross-laminae are produced by superimposing migrating ripples. The ripples form lateral to one another, such that the crests of vertically succeeding laminae are out of phase and appear to be advancing upslope. This process results in cross-bedded units that have the general appearance of waves in outcrop sections cut normal to the wave crests. In sections with other orientations, the laminae may appear horizontal or trough-shaped, depending upon the orientation and the shape of the ripples. Ripple cross-laminae will always have a steeper dip downstream, and will always be perpendicular to paleoflow meaning the orientation of the ripples will be in a direction that is ninety degrees to the direction that current if flowing. Scientists suggest current drag, or the slowing of current velocity, during deposition is believed to be responsible for ripple cross-laminae.

I share with you a video recorded from a sand box which shows how exactly the ripple marks are formed under the influence of waves. I hope you enjoy it!

Miquel Mir Gual

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