Continuing from the Late Devonian, shallow, epicontinental
seas covered most of the state. The black shales characteristic of the Woodford
and Chattanooga Shale quickly gave way to limestone and chert deposition in
the early part of the Mississippian (from 363-323 million years ago). These
Mississippian limestones (i.e., Boone Formation of the Ozarks; Sycamore Limestone
of the Arbuckle Mountains; and the Osage Limestone in the subsurface of northern
Oklahoma) attain a thickness between 200-600 feet on the shallow shelf areas,
and as much as 5000 feet in the deeper parts of the Anadarko basin to the
west. These limestones also represent the last widespread carbonate producing
epeiric sea in North America. These quiet marine conditions that would produce
thick sequences of limestone would never be duplicated again.
By the Late Mississippian, crustal instability and mountain building events
(orogenesis) started to affect the types of sediments being deposited. This
is characterized by extensive sandstone and shale formation into the rapidly
subsiding sedimentary basins in southern Oklahoma. Predominant units include
the Delaware Creek and Goddard shales in the Ardmore and Anadarko basins,
and interbedded sandstones and shales of the Stanley Group in the Ouachita
Basin. These basinal sediments may reach 10,000 feet in thickness (Johnson,
1996).
The lower Mississippian carbonates host a wide variety of fossil brachiopods,
crinoids, blastoids, and bryozoans. These formations also host beautiful mineral
deposits of galena (lead sulfide), sphalerite (zinc sulfide), and pyrite (iron
sulfide) in the Tri-state mining district (Johnson, 1996).
To glimpse what Oklahoma may have looked like during this time click on Paleogeography of the Mississippian.
Reference: Johnson, K. S. 1996. Geology of Oklahoma, p. 1-9. In, K. S. Johnson and N. H. Suneson (eds.), Rockhounding and Earth-Science Activities in Oklahoma. Oklahoma Geological Survey Special Publication 96-5.