CYCLIC SEDIMENTATION IN THE COON CREEK FORMATION AT THE TYPE SECTION, MCNAIRY COUNTY, TENNESSE

A grain size analysis waqs performed on a 25 ft. section of the Upper Cretaceous Coon Creek fm. at the Coon Creek Science Center in McNairy County, Tennesse. The Coon Creek fm. is a dark gray to greenish black,micaceous, glauconitic ,clayey fine sand that is well known for its fossil content. Clay mineralogy, glauconite,and fauna strongly suggest a relatively low energy nearshore environment. The Coon Creek is considered a regessive nearshore facies eqivalent to the offshore Selma fm. Grain size analysis indicates that the Coon Creek appears to be a positively skewed, moderately sorted, fine to very fine sand with silt and clay fractions ranging from 5 to 20 percent.Detailed analysis,however,Shows that the Coon Creek can be subdivided into alternating cyclic units.Fining upwards units alternate with coarsening upwards units. Coarsening upwards units relect periods of relatively high wave or current energy conditions while the fining upwards units were deposited under lower energy conditions. These alternating units may suggest cyclic changes in storm patterns.