Stop 12: Ancient delta


Sedimentary structures:  Festoon crossbeds

 This is one of the classic sedimentary structures of the Berea Sandstone, called festoon (trough-shaped) cross bedding.  The outcrop shown here is on the south wall just upstream of the big waterfall. At first glance it appears that the Berea Sandstone was tilted about 30 degrees from the horizontal. This is not the case; just like the rock layers under it and over it, this massive bed is horizontal. If we were to cut through modern-day sediments of the Mississippi, Danube or Mekong deltas, we would see similar structures being formed in unconsolidated sand and silt at the mouth of a great river. What we see here is the same kind of delta, slowly growing toward the east as it fills the quiet marine waters of Ohio Bay some 350 million years ago.
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