Written in the Hills
Geology of the Ozarks, part 3a Cambrian bioturbation
These Cambrian age rocks (Davis Formation) show extensive occurrences of fossil worm burrows
(also known as trace fossils) formed in what was originally sea floor sediment. Such trace fossils are
almost entirely absent from sedimentary rocks older than the Cambrian Period. Such abundant"worm"
tracks or bioturbation accompanies the first appearance of animals with hard parts and which marks
what is known as the Cambrian radiation event, the first appearance of undoubted animal life. Similar
beds occur in the Grand Canyon's Bright Angle Shale as well as elsewhere over the globe in rocks
somewhat older than half a billion years.