Media Anticline

Location

T9N, R4 and 5W, Henderson County (D-2)

References

Bell and Workman 1928, Electric Power Research Institute (EPRI) 1982

Description

Bell and Workman (1928) defined an anticline near the town of Media by mapping the base of the Burlington Limestone (Mississippian) from outcrop and well data. Their map shows the anticline trending west-northwest and having two areas of closure separated by a saddle. Maximum closure is about 60 feet (18 m), and total relief on the structure is 80 to 110 feet (24-34 m) on the base of the Burlington. Bell and Workman reported oil and gas in wells and natural seeps along the anticline; they recommended the area for further prospecting.

From 1973 to 1974, Northern Illinois Gas Company extensively drilled the Media Anticline and conducted seismic and gravity surveys to evaluate the structure as a gas storage reservoir. Their findings were summarized by EPRI (1982) and logs of their test holes are on file at the ISGS. These data permit interpretation of the time and manner of origin of the Media Anticline.

A structure map of the top of the Galena (Trenton) Group (fig. 51) reveals considerably greater relief on that horizon than at the base of the Burlington. The anticline has a steep north flank on the Galena; the Galena drops 300 feet (90 m) within a horizontal distance of about 3,000 feet (900 m). Closure is at least 90 feet (27 m). The highest point on the Galena is located about 1 mile (1.6 km) northwest of the highest point on the Burlington, as shown by Bell and Workman (1928). The reduction in relief is due to thinning of the New Albany Shale (Upper Devonian and Kinderhookian) across the crest of the fold (figs. 51, 52). The New Albany is reduced from about 250 feet (75 m) in thickness north of the anticline to less than 40 feet (12 m) on the crest. Other mappable intervals between top of Galena and base of Burlington do not change in thickness appreciably across the anticline. Thus, the major uplift of the Media Anticline can be dated to the Late Devonian Epoch and/or the Kinderhookian Epoch, with additional lesser movement after deposition of the Burlington.

Northern Illinois Gas Company drilled numerous test holes to the Cambrian Galesville Sandstone; several wells reached the Mt. Simon Sandstone. A structure map of the top of the Galesville (EPRI 1982) shows a configuration similar to that on the Galena, and its maximum relief is about 400 feet (120 m). Seismic and gravity surveys indicate a steeply dipping fault with the north side downthrown roughly 150 feet (45 m) just north of the steepest dips on the north limb of the anticline. The fault offsets Cambrian rocks but dies out upward into the Ordovician. The Media Anticline is thus one of the clearest examples in Illinois of a fold controlled by faulting at depth.

Regional mapping of structure on the Galena Group (Bristol and Buschbach 1973) shows that the Media Anticline lies along a structural ridge that extends southeastward into central McDonough County. Westward, the Media Anticline may line up with the Burlington Anticline in Iowa. The Burlington Anticline is one of several northwest-trending anticlines that have been mapped in southeastern Iowa. Harris and Parker (1964) showed that the lower Valmeyeran Series (Burlington, Keokuk, and Warsaw Formations) thins markedly across the crests of all of these anticlines, thickens into the intervening synclines, and thus provides additional evidence for structural movements during Mississippian sedimentation.

See also MISSISSIPPI RIVER ARCH.

Figure(s)

Figure 52   Cross section of the Media Anticline, Henderson County. Wells are designated by ISGS county number. See figure 51 for location.