Stratification

The most common of all sedimentary structures is simple layering that results as sediment builds up in even, parallel bands. This layering is known as stratification. The layers can be of almost any thickness—typically layers that are less than about one centimeter thick are called laminae, while layers thicker than about a centimeter are called beds.

To the left of the silver part of the pen is a good example of parallel stratification.  This image shows planar laminae passing upward to cross-stratified laminae.  The significance of this change relates to a change in flow speed at the time of deposition: during the main phase of deposition, flow speeds were relatively rapid, producing parallel planar laminae; as the flow waned, speeds slowed, and ripples formed along the top of this bed.