Tag Archives: Imo Formation

Geopic of the week: Lepidodendron

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Pictured here is not an alligator or lizard skin fossil, for which these are commonly mistaken.  It’s an impression of the trunk of a now extinct tree-sized plant, known as a Lepidodendron.  It was collected from a stream bed in north Arkansas.  The diamond-shaped patterns are sockets where leaves once attached to the trunk.  The holes that are just visible within the “diamonds”, are pores through which the plant inhaled carbon dioxide.

Lepidodendron were common in Arkansas during the Carboniferous period (359-299 million years ago).  The Carboniferous (or coal-bearing) period is known for lush vegetation.  Many of the earth’s important coal deposits were formed from the remains of the rich forests that dominated the land during that time.

For more views of Lepidodendrons click here

GeoPic of the Week: Soft Sediment Deformation

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Soft sediment deformation in silty shale of the Imo Formation near the Middle Fork of the Little Red River near Shirley, Arkansas. Features like that pictured here result from sediment being exposed to pressure prior to being completely lithified. Many factors can contribute to soft-sediment deformation including uneven settling, slumping, and escape during compaction of water trapped in the sediment.