CARBONATE PETROLOGY AND DEPOSITIONAL ENVIRONMENTS OF THE LITHOGRAPH CITY FORMATION (DEVONIAN) OF NORTHERN IOWA

The Lithograph City Formation was formed by a late Middle to early Late Devonian transgressive-regressive cycle within the Cedar Valley Group. It lies disconformably between the Coralville Formation and Shell Rock Formation or Sweetland Creek Shale. A north to south transect from the Mitchell County–Floyd County border to northern Black Hawk County reveals pronounced facies changes within the Lithograph City Formation. Northern exposures are dominated by vuggy, laminated, dolomitic and lithographic to sublithographic lithologies with low faunal diversity. These beds are interpreted as nearshore or tidal flat facies. To the south, the peritidal facies grade into shallow shelf deposits that are less dolomitic, more grain-supported with higher faunal diversity. Sections of the Lithograph City Formation in Black Hawk County contain spectacular stromatoporoid biostromes.

The Lithograph City Formation is an important source of aggregate for construction in northern Iowa. In the early part of the 20th Century, lithographic stone was quarried for use in lithographic printing. The lithographic stone is not micritic, but rather exceptionally homogeneous, fine, peloidal packstone.