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Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p. ==Contributing author(s)== H. B. Willman and Elwood Atherton ==Name== ===Original description=== The Hunton Limestone Megagroup (Taff, 1902, p. 3; Swann and Willman, 1961, p. 478). ===Derivation=== Named for the former hamlet of Hunton, Coal County, Oklahoma. ===Other names=== ===History/background=== ==Type section== ===Type location=== ===Type author(s)=== ===Type status=== ==Reference section== ===Reference location=== ===Reference author(s)=== ===Reference status=== ==Stratigraphic relationships== The Hunton Limestone Megagroup comprises dominantly carbonate rocks of Silurian and Devonian age that in Illinois lie between the late Ordovician clastic rocks (Maquoketa Shale Group) and the late Devonian clastic rocks (New Albany Shale Group) at the base of the overlying Knobs Megagroup (fig. 14). In local areas, siltstone and shale in the base of the Silurian System are not included in the megagroup, whereas limestone in the uppermost Ordovician strata is included. At the top of the Hunton, shale of Middle Devonian age, locally present, is excluded, but basal Upper Devonian limestone is included. <center> <gallery caption="" widths=250px heights=250px perrow=4> Figure_14.jpg|alt=Stratigraphic diagram showing the Hunton Limestone Megagroup between underlying Ordovician clastic rocks and overlying Devonian clastic units in Illinois (Figure 14)|{{file:Figure_14.jpg}} </gallery> </center> ==Extent and thickness== Hunton strata occur throughout most of Illinois, but are absent in the central northern region and in small areas in western and southern Illinois where Ordovician and older rocks are exposed. The megagroup thickens from those areas to over 1800 feet in the southeastern part of the state (fig. S-13). <center> <gallery caption="" widths=250px heights=250px perrow=4> Figure_S-13.jpg|alt=Map of Illinois showing distribution and thickness of the Hunton Limestone Megagroup, increasing to more than 1800 feet in southeastern Illinois (Figure S-13)|{{file:Figure_S-13.jpg}} </gallery> </center> ==Lithology== The Hunton Limestone Megagroup varies from being almost entirely dolomite in northern Illinois to limestone in southern Illinois. It contains some thin or local noncarbonate units—particularly Devonian chert units in the extreme southwestern part of Illinois, some shaly strata in the Silurian Moccasin Springs Formation, and the patchy Dutch Creek Sandstone at the base of the Middle Devonian Series. <br> The Hunton Megagroup includes within it the sub-Kaskaskia unconformity, along which in some areas Middle Devonian strata completely truncate Lower Devonian and Silurian strata, leaving only Middle Devonian strata in the Hunton Megagroup. In other areas, the sub-Absaroka unconformity, at the base of the Pennsylvanian System, truncates all the Devonian strata, so that the megagroup consists entirely of Silurian carbonates. In a few places the sub-Absaroka unconformity cuts out the Hunton entirely. In a small area in northwestern Schuyler County, the Upper Devonian New Albany Shale Group truncates the Hunton Megagroup and rests on the Ordovician Maquoketa Shale Group. ==Core(s)== ==Photograph(s)== ==Contacts== ==Well log characteristics== ==Fossils== ==Age and correlation== ==Environments of deposition== ==Economic importance== ==Remarks== ==References== SWANN, D. H., and H. B. WILLMAN, 1961, Megagroups in Illinois: American Association of Petroleum Geologists Bulletin, v. 45, p. 471-483; Illinois State Geological Survey Reprint 1961-N.<br> TAFF, J. A., 1902, Atoka Quadrangle: USGS Geological Atlas Folio 79, 8 p. {{Codes |membercode=5890 |geo_unit=-- }}

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