Correlation of Gravity Anomalies with Precambrian Crystalline Basement, Bellefontaine Outlier, Ohio A Senior Thesis Submitted as Partial Fulfillment of the Requirements for the degree Bachelor of Science in Geological Sciences at The Ohio State University by Christian D. Steck The Ohio State University Winter, 1997 Dr. Hallan C. Noltimier Acknowledgments I would like to extend my sincere thanks to everyone who has supported me during this project. Special thanks go to my thesis advisor, Dr. Hallan Noltimier, for his continuous encouragement, sound advice, and helpful suggestions. He made this an extremely pleasurable endeavor. I would also like to thank Larry Wickstrom of the Ohio Division of Geological Survey for providing his geological expertise and the materials produced by the Cincinnati Arch Consortium. Jim MacDonald, also of the Survey, and Jeoong-Woo Kim of the Ohio State University were also very beneficial resources for their geologic and computer-related support. Many thanks go to my friends and family for their encouragement and assistance. All have been invaluable to the completion of this thesis. TABLE OF CONTENTS Acknowledgments ................................................................................................................................................ i List of Figures ...................................................................................................................................................... iii List of Tables ....................................................................................................................................................... iv INTRODUCTION ................................................................................................................................................ 1 REGIONAL GEOLOGY ..................................................................................................................................... 2 General Tectonic History ...................................................................................................................... 2 Precambrian Section .............................................................................................................................. 3 Granite-Rhyolite Province ...................................................................................................... 3 East Continent Rift Basin ....................................................................................................... 8 Grenville Front Tectonic Zone ............................................................................................... 9 Grenville Province .................................................................................................................. 9 Top of Precambrian unconfonnity ......................................................................................... 9 Top of Precambrian crystalline basement ............................................................................ 10 Paleozoic Section ................................................................................................................................. 10 BELLEFONTAINE OUTLIER ......................................................................................................................... 11 Introduction ......................................................................................................................................... 11 Stratigraphy ......................................................................................................................................... 11 Structure ............................................................................................................................................... 12 GRAVITY PROFILES ...................................................................................................................................... 13 Introduction ........................................................................................................................................ 13 Methods ............................................................................................................................................... 13 Sample Calculation .............................................................................................................................. 22 Results .................................................................................................................................................. 25 INTERPRETATION AND CONCLUSION ..................................................................................................... 36 References Cited ................................................................................................................................................. 39 Appendix: Gravity and Elevation Data ......................................................................................................... 40-5 1 LIST OF FIGURES Figure Page 1. State of Ohio showing county boundaries. the Bellefontaine Outlier (shaded). and the Study Area (box). modified from Wickstrom et a1 . (1 992)............................................................................................. 4 2 . State of Ohio showing the Study Area (box). the Bellefontaine Outlier (shaded). the Grenville Front. the Grenville Province. the Granite-Rhyolite Province. and the COCORP Seismic Line OH- 1. modified from Wickstrom et a1 . (1992).................................................................................................... 5 3 . Generalized stratigraphic column of the Bellefontaine Outlier. modified from Hull (1990) and Swinford and Slucher (1995)........................................................................................................................ 6 4 . Structure contour map of the Precambrian crystalline basement surface in western Ohio. modified from Wickstrom et a1 . (1992)....................................................................................................................... 7 5 . Structure contour map of the Precambrian crystalline basement surface in the Study Area. modified from Wickstrom et a1 . (1992)...................................................................................................... 14 6 . Topography of the Bellefontaine Outlier Study Area. modified from Weaver (1992)............................. 15 7 . Complete Bouguer Residual Anomaly in the Bellefontaine Outlier Study Area. modified from Weaver (1992)............................................................................................................................................ 16 8 . Station locations (510) in the Bellefontaine Outlier Study Area. modified from Weaver (1992) ............ 17 9 . Structure contour map of the Precambrian crystalline basement surface in the Study Area with profile locations. modified from Wickstrom et a1 . (1992)......................................................................... 18 10. Topography of the Bellefontaine Outlier Study Area with profile locations. modified from Weaver 11. Complete Bouguer Residual Anomaly map of the Bellefontaine Outlier Study Area with profile locations. modified from Weaver (1 992) ................................................................................................... 20 12. Complete Bouguer Residual Anomaly profile A-A' .................................................................................. 29 13. Complete Bouguer Residual Anomaly profile B-B' ................................................................................... 30 14. Complete Bouguer Residual Anomaly profile C-C' ................................................................................... 31 15. Complete Bouguer Residual Anomaly profile D-D' .................................................................................. 33 16. Complete Bouguer Residual Anomaly profile E-E' ................................................................................... 34 17. Complete Bouguer Residual Anomaly profile F-F' ................................................................................... 35 18. Locations of faults identified in this study................................................................................................. 37 LIST OF TABLES Table Page 1. All major units, thicknesses, and densities used for the throw calculations. These have the most significant influence on the gravity anomalies. Because the thickness of the Middle Run Fm. is highly variable within the Study Area, densities for the thickest and thinnest parts of the total overburden are given. For units above the Middle Run Fm., values are from Weaver (1992). Middle Run Fm. thicknesses are from Drahovzal et al. (1992). Density values for the Middle Run Fm. and the crystalline basement are from Telford et al. (1976). .............................................................. 23 2. Thickness and density of the overburden, change in density and distance across the faults, top-of- fault to bottom-of-fault ratios, calculated throws, throw differences, and location differences for the Bellefontaine Outlier Study Area. ........................................................................................................ 26 3. A 5% increase in the change-in-gravity to change-in-distance ratio across the faults. Results on average increase about 0.41% the ratio of zl/zO, the deepest to shallowest parts of the fault. ................. 27 INTRODUCTION Reaching a height