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National Geologic Map Database
Geologic Unit: Pecatonica
Map showing publication footprint
  • Usage in publication:
    • "Pecatonica Formation"
  • Modifications:
    • Revised
    • Overview
  • AAPG geologic province:
    • Illinois basin
Publication:

Nelson, W.J., Devera, J.A., and Masters, J.M., 1996, Geology of the Jonesboro 15-minute quadrangle, southwestern Illinois; Jonesboro, Mill Creek, Ware, and McClure 7.5-minute quadrangle: Illinois Geological Survey Bulletin, no. 101, 57 p., See also Illinois Geol. Survey Geol. Quad. Map IGQ-14, scale 1:24,000, 1995


Summary:

Ordovician (Mohawkian) Pecatonica Formation was not consistently mapped in southeaster MO. For this reason, used in quotes as "Pecatonica Formation" as was done by Thompson (1991) who stated that the "Pecatonica" is nearly identical in lithology to the Plattin Formation. Tentatively identified in Humble No. 1 Pickel well, Mill Creek 7.5-min quad, IL, as a 93-ft interval of dark-colored micritic limestone; overlies sandy dolomite of Joachim and underlies thin oolitic limestone thought to be Brickeys Member of Plattin Limestone (M.L. Sargent, written commun., 1992). Other wells in and close to study area lack logs sufficiently detailed to differentiate "Pecatonica" from Plattin.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Pecatonica Formation
  • Modifications:
    • Revised
    • Overview
  • AAPG geologic province:
    • Ozark uplift
    • Illinois basin
Publication:

Nelson, W.J., 1996, Bedrock geology of the Paducah 1 degree x 2 degrees quadrangle, Illinois, Kentucky, and Missouri: Illinois Geological Survey Bulletin, no. 102, 40 p., (incl. geologic map, scale 1:100,000)


Summary:

In southeastern MO, Ordovician (Champlainian) Pecatonica Formation is nearly identical to Plattin Formation and probably was not mapped consistently from one 7.5-min quad to another. Thompson (1991) states that Pecatonica can be identified with certainty only at a few sites in MO and regards use of the name tentative and questionable. Accordingly, Pecatonica is combined with Plattin Formation, along with the thin Decorah Formation, on map accompanying report. Pecatonica consists of intercalated dolomite and limestone and thin shale interbeds. Carbonate rocks are light to medium brownish gray and micritic to finely granular or crystalline. Fossils include brachiopods, ostracods, and algae. Portions are burrowed ("fucoidal") and, in lower part, beds of brown laminated dolomite and dark gray laminated limestone alternate. Upper part contains chert. Medium gray shale occurs as thin partings and thin interbeds throughout formation. Reported to be 80 to 150 ft thick in most of study area. Amos (1985) indicated a maximum thickness of 290 ft in Altenburg quad, southeastern Perry Co., MO. Thompson (1991) states that Pecatonica is absent north of Perry Co. and reaches a maximum of 140 ft in Cape Girardeau and Scott Cos., southeastern MO. Amos and Thompson evidently have different perceptions about Pecatonica; further study is needed.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Pecatonica(?) Formation*
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Ozark uplift
    • Illinois basin
Publication:

Nelson, W.J., 1998, Bedrock geology of the Paducah 1 degree x 2 degrees CUSMAP quadrangle, Illinois, Kentucky, and Missouri, IN The Paducah CUSMAP quadrangle, resource and topographical investigations: U.S. Geological Survey Bulletin, 2150-B, p. B1-B36, (incl. geologic map, scale 1:250,000), A joint study conducted with Illinois, Indiana, Kentucky, and Missouri geol. surveys [http://ngmdb.usgs.gov/Prodesc/proddesc_19757.htm]


Summary:

Ordovician (Mohawkian) Pecatonica and Plattin Formations are lithologically similar units separable only in optimal exposures, such as roadcuts or quarry walls. Thompson (1991) stated that, for this reason, use of the name Pecatonica in Missouri had a "tentative and questionable future." Kolata and Noger (1991) reported Pecatonica and Plattin can be differentiated in subsurface by use of electric and gamma-ray logs. Some geologists who mapped 7.5-minute quadrangles in Missouri distinguished Pecatonica, but not consistently. For these reasons, used as Pecatonica(?) Formation and mapped undivided with Plattin Formation and Decorah Formation; Pecatonica(?) and Plattin are assigned to Platteville Group.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Pecatonica Formation*
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Illinois basin
    • Upper Mississippi embayment
Publication:

Harrison, R.W., 1999, Geologic map of the Thebes quadrangle, Missouri and Illinois: U.S. Geological Survey Geologic Quadrangle Map, GQ-1779, scale 1:24,000 [http://ngmdb.usgs.gov/Prodesc/proddesc_19294.htm]


Summary:

Middle Ordovician (Mohawkian) Pecatonica Formation mapped undivided with Plattin and Decorah Groups in subsurface of IL and MO.

Source: GNU records (USGS DDS-6; Reston GNULEX).


For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).