Tag Archives: crinoid

Geopic of the week: Fossiliferous limestone


This is a picture of weathered fossiliferous limestone of the Pitkin Formation.  It was taken in a quarry near Batesville Arkansas.  The picture displays fossil remains of two common aquatic animals that lived in the shallow sea covering northern Arkansas between 360 – 320 million years ago. 

The screw-shaped remains are parts of bryzoans; they are commonly referred to as Archimedes screws.  The nut-shaped fossils- which also resemble rolls of smarties candies- are the remains of crinoids, commonly called sea-lilies, which have living relatives in the ocean today.  Both animals lived by attaching themselves to the sea floor and filtering food, such as plankton, from the ocean water.

GeoPic of the Week: Skeletal Limestone — Happy Halloween!

Crinoidal Imo Face

Skeletal limestone – Happy Halloween!

Limestone varies in color from shades of gray to white and red.  This limestone gets its red color from iron oxide in the rock and contrasts nicely with the white crinoids.  Crinoids are a group of marine invertebrates sometimes referred to as “sea lilies”.  The animal was attached to the ocean floor by a main stem or stalk with long arms flowing outward from a central head on top of the stem.  These animals were abundant in the Mississippian Period in Arkansas.  It is unusual to find a complete crinoid fossil; however, pieces of the stalk (commonly called stem or column) are abundantly preserved in the rocks in northern Arkansas.  This limestone is fossiliferous or since it contains the skeletons of animals can be referred to as a skeletal limestone.  This adjective is especially fitting for the rock considering how it has weathered to resemble a skeleton face and the fact that it is Halloween week.  Happy Halloween!