Structure of the Reelfoot-Rough Creek Rift System, Fluorspar Area Fault Complex, and Hicks Dome, Southern Illinois and Western Kentucky— New Constraints from Regional Seismic Reflection Data U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-Q MISSOURI - ^^*- » ~: ^ ARKANSAS Cover. Gray, shaded-relief map of magnetic anomaly data. Map area includes parts of Missouri, Illinois, Indiana, Kentucky, Tennessee, and Arkansas. Illumination is from the west. Figure is from Geophysical setting of the Reelfoot rift and relations between rift structures and the New Madrid seismic zone, by Thomas G. Hildenbrand and John D. Hendricks (chapter E in this series). Structure of the Reelfoot-Rough Creek Rift System, Fluorspar Area Fault Complex, and Hicks Dome, Southern Illinois and Western Kentucky— New Constraints from Regional Seismic Reflection Data By Christopher J. Potter, Martin B. Goldhaber, Paul C. Heigold, and James A. Drahovzal INVESTIGATIONS OF THE NEW MADRID SEISMIC ZONE Edited by Kaye M. Shedlock and Arch C. Johnston U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1538-Q UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging-in-Publication Data Structure of the Reelfoot-Rough Creek rift system, Fluorspar area fault complex, and Hicks dome, southern Illinois and western Kentucky : New constraints from regional seismic reflection data / by Christopher J. Potter....[et al.]. p. cm.—(Investigations of the New Madrid seismic zone ; Q) (U.S. Geological Survey professional paper ; 1538) Includes bibliographical references. Supt.ofDocs.no. : I 19.16: 1538Q 1. Geology, Structural—Illinois. 2. Geology, Structural—Kentucky. 3. Geology, Stratigraphic—Cambrian. 4. Seismic reflection method. I. Potter, Christopher J. II. Series. III. Series : U.S. Geological Survey professional paper ; 1538. QE535.2.UGI59 1995 vol. Q [QE627.5.13] 551.2'2'09778985—dc20 [551.8'09773] 95-3057 CIP CONTENTS Abstract........................................................................................................................... Ql Introduction.................................................................................................................... 2 Geologic Setting............................................................................................................. 2 Data Acquisition and Processing.................................................................................... 4 Correlation of Reflections with Regional Stratigraphy.................................................. 4 Velocity Assumptions..................................................................................................... 5 Interpretation of the Seismic Profile............................................................................... 6 Stephens Well and Vicinity.................................................................................... 6 Tabb Fault System.................................................................................................. 6 Fluorspar Area Fault Complex............................................................................... 7 Ohio River-Rock Creek Graben Area.................................................................... 10 Discussion....................................................................................................................... 13 Reelfoot-Rough Creek Rift.................................................................................... 13 Fluorspar Area Fault Complex............................................................................... 16 Hicks Dome............................................................................................................ 16 Conclusions.................................................................................................................... 17 References Cited............................................................................................................. 18 PLATE [Plate is in pocket] 1. Interpretive line drawing of seismic reflection profile, southern Illinois and western Kentucky FIGURES 1. Regional geologic setting and location of seismic line, southern Illinois and western Kentucky................................ Q3 2. Seismic reflection data near the Tabb fault zone, western Kentucky............................................................................ 5 3. Detail, seismic reflection data in the Tabb fault zone, western Kentucky .................................................................... 7 4. Seismic reflection data, Griffith Bluff graben, western Kentucky................................................................................ 8 5. Seismic reflection data, Mexico graben, western Kentucky......................................................................................... 9 6. Seismic reflection data, Hicks dome, southern Illinois................................................................................................. 11 7. Map showing regional variation in Cambrian rift structure, U.S. Midcontinent.......................................................... 15 III STRUCTURE OF THE REELFOOT-ROUGH CREEK RIFT SYSTEM, FLUORSPAR AREA FAULT COMPLEX, AND HICKS DOME, SOUTHERN ILLINOIS AND WESTERN KENTUCKY- NEW CONSTRAINTS FROM REGIONAL SEISMIC REFLECTION DATA By Christopher J. Potter,1 Martin B. Goldhaber,2 Paul C. Heigold,3 and James A. Drahovzal4 ABSTRACT Because the New Madrid seismic zone coincides spa­ 0.76 s (2.1 km) near the Ohio River and is thickest against tially with a segment of the Cambrian Reelfoot rift (RFR), basement-cutting normal faults in the area of intersection of regional studies of subsurface Cambrian rift structures may the Tabb and Pennyrile fault systems in western Kentucky, provide important insights into the structural fabric of the where it occupies 1.13 s (3.1 km). Near the southeast margin New Madrid seismic zone. High-quality seismic reflection of the rift, the Cambrian syn-rift sequence thins markedly to data examined in this study show that, north of the New the southeast across steep basement-cutting normal faults in Madrid seismic zone within the major dogleg bend in the rift the Tabb-Pennyrile zone; these northwest-dipping faults system in southern Illinois and western Kentucky, the geom­ appear to have been the dominant faults in this part of the etry of the Cambrian rift system is that of a half-graben that Cambrian rift. Post-Mississippian reverse displacements are thickens to the southeast. This contrasts with the northward- also evident in the Tabb-Pennyrile fault zone. thickening half-graben observed to the east, in the Rough Comparison of these seismic reflection data with other Creek graben in Kentucky, and with the more symmetric published reflection data in the Cambrian rift system reveals graben to the south, in the seismogenic part of the RFR. several major along-strike changes in the cross-sectional The 83-km segment of seismic reflection data examined geometry of the rift, similar to other rift systems. We propose here is oriented northwest-southeast within the major bend in that the localization of New Madrid seismicity within a dis­ the Cambrian rift, in southeastern Illinois and western Ken­ crete segment of the Reelfoot rift is inherited from Cambrian tucky. The margins of the 110-km-wide rift (as determined rift structure; the zone of seismicity appears bounded on the north and south by Cambrian accommodation zones that by aeromagnetic data) lie beyond the ends of the seismic line. linked segments with differing rift geometry. The data show that, near Hicks dome (southeastern Illinois), Lower and Middle Cambrian syn-rift sedimentary rocks The seismic data also provide new information on the occupy about 0.4 s two-way travel time on the seismic reflec­ late Paleozoic development of Hicks dome (southeastern tion section (corresponding to a thickness of about 1.1 km). Illinois) and the surrounding Fluorspar area fault complex This stratigraphic interval thickens to the southeast within (FAFC) in southeastern Illinois and western Kentucky. Near the rift. The syn-rift sedimentary sequence occupies about Hicks dome (a center of carbonatitic intrusions), strong Mis- sissippian reflections are relatively continuous, whereas the Cambrian-Ordovician section is greatly disrupted. This dis­ 1 U.S. Geological Survey, Mail Stop 939, P.O. Box 25046, Denver ruption is probably related to the combination of intrusive Federal Center, Denver, CO 80225. and explosive processes that formed the dome. The entire 2 U.S. Geological Survey, Mail Stop 973, P.O. Box 25046, Denver section of Paleozoic rocks and the top of the Precambrian Federal Center, Denver, CO 80225. 3 Illinois State Geological Survey, Champaign, IL 61820 [now at Ar- basement are domed, demonstrating that the uplift originated gonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439]. in the basement rather than within the sedimentary section. 4 Kentucky Geological Survey, 228 Mining and Mineral Resources, Southeast of Hicks dome in western Kentucky, a series of University of Kentucky, Lexington, KY 40506. grabens and horsts in the FAFC document a late Paleozoic Ql Q2 INVESTIGATIONS OF THE NEW