GeoPic of the Week: Checkerboard Point on Lake Ouachita

Checkerboard Point on Lake Ouachita

      Checkerboard Point on Lake Ouachita

The sandstone at this location shows a well-defined joint system that has allowed the rock to erode and resemble a checkerboard pattern.  A joint is a fracture or parting in the rock without displacement.  Joints are present in most rock formations and provide a record of the stress and strain the rock has undergone.  When two or more joints intersect it is called a joint system.  The joint system at this location consists of a primary joint set in the N/S direction with a secondary joint set in the E/W direction.  The primary joint set formed at right angles to the compression event that formed the Ouachita Mountains.  This joint system is present in the Blakely Sandstone and can be seen on an island west of Lake Ouachita State Park.  For more information on a geologic float on Lake Ouachita, check out this teacher workshop guidebook at http://www.geology.ar.gov/pdf/EWS-04.pdf.

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