Geo-pic of the week: Chalk

 

Annona Fm (2)

Like the White Cliffs of Dover, England, the “White Cliffs of Arkansas” (pictured above) are composed of chalk.  Chalk is a marine sedimentary rock that forms of calcite-rich mud that accumulates in semi-deep marine environments.  The mud is composed of the accumulated skeletal remains of algal microorganisms called coccolithophores.  These algae grow and shed skeletal parts called coccoliths which they arrange around them, in life, in a structure called a coccosphere.  Below is a scanning electron microscopic image of some coccospheres (borrowed from news.algaeworld.org).

coccolithophores

Chalk in Arkansas is found in the Annona Formation, which formed in the late Cretaceous Period, and crops out in southwest Arkansas as well as parts of Texas.  In addition to being mined to make blackboard chalk, this resource is also used in brick, and cement manufacture. 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s