Ordovician System

Type section and use of name in Indiana: The Dutchtown Limestone (McQueen, 1937, p. 12) was named for an exposure 1 mile (1.6 km) east of Dutchtown, Cape Girardeau County, Mo. The Dutchtown was traced through subsurface methods and designated with the surname Formation in Indiana by Droste, Abdulkareem, and Patton (1982).

Description: The Dutchtown Formation is composed generally of light-gray and brown, partly argillaceous dolomite and some interbeds of green shale. In southwestern Indiana the Dutchtown also contains sandy to argillaceous dolomite and some limestone. The rocks there are dark gray, dark brown, or black and are inter bedded with dark-brown shale. Everywhere in Indiana the uppermost Dutchtown rocks are light gray and brown, and it is in these light-colored rocks that the gradation from Dutchtown into the overlying Joachim Dolomite occurs. The Dutchtown overlies the Everton Dolomite or Shakopee Dolomite with unconformity (Droste and Shaver, 1983, fig. 2).

The thickness of the Dutchtown ranges from more than 150 feet (46 m) in southwestern Indiana to zero at its depositional or facies limits. Within the area where the Dutchtown is generally present, the unit is completely absent because of non deposition around and over high hills on the Knox erosion surface that were formed before Ancell deposition.

Correlation: The lower part of the Dutchtown of Indiana interfingers with that part of the St. Peter Sandstone that contains Chazyan conodonts of the same age as the Dutchtown of Missouri (Rex road, Droste, and Ethington, 1982), but uppermost Dutchtown rocks are earliest Blackriverian in age. The Dutchtown of Indiana is correlated with the Dutchtown Limestone of Missouri and Illinois, with the Wells Creek Formation of Ohio, and with the Wells Creek Dolomite of Kentucky. It has facies equivalency with the lower part of the St. Peter Sandstone of Indiana and Illinois and with the St. Peter Sandstone of Ohio and Kentucky.