Tag Archives: Eocene

Geo-pic of the week: Sand and clay of the Wilcox Group

wilcox sand canyon pit enhanced

This rather handsome outcrop of the Wilcox group consists of alternating layers of sand and clay of the Eocene Epoch which lasted from about 56-34 million years ago.   The Wilcox Group is a non-marine unit mostly composed of sand with lesser clay, silt, gravel, and lignite (low-grade coal).  

This geologic unit is part of a larger sequence of loosely-consolidated sedimentary rocks exposed in south central Arkansas, south of Pulaski county.  These rocks are the northern extent of the West Gulf Coastal Plain, a physiographic province that stretches from central Arkansas, south, to the Gulf of Mexico.

Advertisements

Geopic of the week: Arkansas Bauxite

 

bauxite enhanced

Pictured is a piece of bauxite, a sedimentary rock for which the central Arkansas town of Bauxite is named.  It’s also the principal ore of aluminum.  At times in the past century, Arkansas bauxite was the source of as much as 90% of the aluminum produced in the US.

Bauxite is a chemical sedimentary rock that formed in Arkansas from weathering of igneous rock.  During the Eocene (55 – 34 million years ago), North America was nearer the equator, and the tropical climate concentrated aluminum in rocks exposed south of Little Rock.

Following WW2, production of aluminum from Arkansas bauxite declined due to availability of rich international ores.  Mining of bauxite for aluminum ceased altogether in the state in 1981, though there is still a significant quantity of reserves.

 

To see more views of Arkansas Bauxite, click here