The southeast Missouri and Illinois-Kentucky districts are two of the most important mineral districts in the country in terms of variety of minerals produced, mineral output, and mineral potential. Both districts lie on faulted structural uplifts within the covered shield area of the Central States. Complex fault lineaments intersect in each district and are major structural controls. Two fault zones, the Ste. Genevieve and Cottage Grove, form connecting links between districts. The iron deposits of southeast Missouri are in rocks of Precambrian age; but the lead, zinc, barite, copper, cobalt, and pyrite deposits of southeast Missouri, and the fluorite, zinc, barite, lead deposits of Illinois-Kentucky, are all in the domed and faulted thin cover of Paleozoic rocks.

Four seismic reflection profiles from the Wabash Valley area of southeastern Illinois successfully imaged the Herald-Phillipstown fault. From the reflection profiles and geophysical well logs, it is interpreted that the Herald-Phillipstown fault is an inverted flower structure. Structural contour maps as well as maps of various reflector surfaces are prepared herein using two way travel time as well as depth. These maps show that the reflectors are undulating in character. The nature of faults of the inverted flower structure as observed on the seismic reflection profiles indicates that there has been a change in the stress regime from extensional to compressional. Structural cross sections were generated using geophysical well logs from drill holes located along these seismic lines to analyze the nature of these faults at shallower depths. From these cross sections numerous shallow faults were observed and many of them can be correlated with those observed on seismic records indicating upward migration of basement penetrating faults into shallow younger sediments. Many of these faults, including the Herald-Phillipstown fault show evidences of reactivation.