Geology of the SURREY PE^FI'SSION AL PA-PEA, 1.042- done in heJmlf ofM®ti@ tics and Space Geology of the Decaturville Impact Structure, Missouri By T. W. OFFIELD and H. A. POHN GEOLOGICAL SURVEY PROFESSIONAL PAPER 1042 Work done in behalf of National Aeronautics and Space Administration A detailed description of stratigraphy, style of deformation, and shock features at the Decaturville structure. Origin of the structure by impact is indicated UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Offield, Terry W. Geology of the Decaturville impact structure, Missouri. (Geological Survey Professional Paper 1042) Bibliography: p. 46 Supt. of Docs, no.: I 19.16:1042 1. Cryptoexplosion structures Missouri Decaturville region. 2. Geology Missouri Decaturville region. I. Pohn, Howard A., joint author. II. Title. III. Series: United States Geological Survey Professional Paper 1042. QE613.5.U5035 551.8 77-608119 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-03166-3 CONTENTS Page Page Abstract ............................................................................................. 1 Regional paleogeographic implications .............................................. 10 Introduction ....................................................................................... 1 Structure ............................................................................................ H Previous work .................................................................................... 2 Deformation outside the structure .............................................. H Acknowledgments .............................................................................. 4 Ring-fault boundary ................................................................... 13 Stratigraphy ....................................................................................... 4 Depressed zone ........................................................................... 15 Precambrian rocks ...................................................................... 6 Exotic blocks in the depressed zone ........................................... 16 Cambrian System ....................................................................... 6 Central uplift .............................................................................. 17 Lamotte Sandstone ............................................................. 6 Geophysical data ............................................................................... 22 Bonneterre Dolomite ........................................................... 6 Shock-related deformation features ................................................... 26 Davis Formation ................................................................. 7 Monolithologic breccias ............................................................. 26 Derby and Doe Run Dolomites .......................................... 7 Mixed breccias ........................................................................... 27 Potosi Dolomite .................................................................. 7 Shatter cones .............................................................................. 29 Eminence Dolomite ............................................................. 7 Planar elements in quartz ........................................................... 30 Ordovician System ..................................................................... 7 Asterism in dolomite .................................................................. 34 Gasconade Dolomite ........................................................... 7 Kink bands in mica .................................................................... 34 Gunter Sandstone Member .......................................... 7 Shock-envelope configuration .................................................... 34 Upper part ................................................................... 8 Roubidoux Dolomite .......................................................... 8 Age of structure and depth of erosion ............................................... 35 Jefferson City Dolomite ...................................................... 8 Origin of the structure ....................................................................... 37 Kimmswick Limestone ........................................................ 9 Endogenetic origin ...................................................................... 37 Noix(?) Oolite ...................................................................... 10 Exogenetic origin ........................................................................ 39 Leemon Formation ............................................................. 10 Interpreted crater profile and postcrater disruption ................... 41 Silurian System .......................................................................... 10 Implications for other astroblemes .................................................... 43 Bainbridge Limestone .......................................................... 10 References cited ................................................................................. 46 ILLUSTRATIONS Page PLATE 1. Geologic map of Decaturville structure, Missouri.............................................................................................. In pocket 2. Block diagrams showing structural detail, Decaturville impact structure, Missouri ........................................... In pocket FIGURE 1. Index map of southern Missouri, showing location of Decaturville structure, outline of area shown in figure 2, and features mentioned in text ........................................................................................................................................................ 2 2. Frame 1073-16224 by Landsat, showing Decaturville region ............................................................................................. 3 3. High-altitude aerial photograph showing circular patterns of Decaturville structure ......................................................... 4 4. Column showing lithologies and estimated thicknesses of formations present in Decaturville structure ........................... 5 5. Structure contour map on the base of upper part of the Gasconade Dolomite ................................................................. 12 6. Map of isopleths showing vertical displacements relative to prestructure configuration .................................................... 14 7. Photograph showing drill hole numbers and locations at center of structure, and diagrams of sections cut in drill holes around pegmatite locality and sulfide pit ................................................................................................................................ 20 8. Pegmatite area showing juxtaposition of blocks of different formations at center of structure ......................................... 22 9. Sulfide pit showing juxtaposition of blocks of different formations and mixed breccia .................................................... 22 10. Aeromagnetic map, Decaturville region ............................................................................................................................. 23 11. Gravity map, Decaturville region ....................................................................................................................................... 24 12. Gravity map, central area of Decaturville structure ........................................................................................................... 25 IV CONTENTS FIGURE 13-18. Photographs: Pa§e 13. Monolithologic breccia, Eminence Dolomite ............................................................................................................ 26 14. Core samples of mixed breccia .................................................................................................................................. 27 15. Core samples of mixed breccia showing alined grains in flow laminae and fragments drawn out or shaped by flowage ............................................................................................................................................................... 27 16. Mixed breccia at sulfide pit in center of structure ................................................................................................... 28 17. Sandstone from Lamotte Sandstone emplaced between block of Potosi Dolomite and mixed breccia in sulfide pit 28 18. Shatter-coned Derby and Doe Run Dolomites ......................................................................................................... 29 19. Stereographic projection of shatter-cone striations ............................................................................................................ 30 20. Photomicrograph showing rhombohedral fractures in quartz grain of sandstone .............................................................. 31 21. Photomicrograph of decorated planar features in quartz grains from mixed breccia, spaced 9-60/zm and oriented parallel to {OOOU ............................................................................................................................................................... 31 22. Photomicrograph of mixed