Written in the Hills
Geology of the Ozarks, part 4
The early Ordovician geologic history of the Ozarks. Rock strata of the early part
of Ordovician time occurs extensively in the Ozarks of both Missouri and Arkansas.
Consisting of thick beds of cherty dolomite, rocks of Lower Ordovician age make
up much of the scenic features of the Ozarks including many of its large springs, bluffs
and caves. Fossils in these rocks are featured including reefs made up of blue-green algae
(stromatolites) and fossil molluscan faunas associated with them, especially noteworthy
are the cephalopods. The red sandstone of the Roubidoux Formation is featured with
some of the fossils found both in the sandstone and in chert beds associated with it.
Lower Ordovician rock strata and associated fossils are so distinctive that it was once
proposed to have an Ozarkian Period between the Cambrian and Ordovician periods
of the geologic time scale. For various reasons this didn't catch on but it really makes
sense in many ways.