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U.S. Geological Survey, Earth Science Information Center 101 Twelfth Ave., Box 12 STENNIS SPACE CENTER, Mississippi-Bldg. 3101 Fairbanks, AK 99701 Table Mountain Quartzite and Moose Formation (new names) and Associated Rocks of the Middle Proterozoic Belt Supergroup, Highland Mountains, Southwestern Montana By J. Michael O'Neill BELT SUPERGROUP IN THE HIGHLAND MOUNTAINS AND PROBABLE EQUIVALENT ROCKS IN THE PIONEER AND ANACONDA RANGES, SOUTHWESTERN MONTANA J. Michael O'Neill and Robert C. Pearson, Editors U.S. GEOLOGICAL SURVEY BULLETIN 2121-A 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 O'Neill, J. Michael. Table Mountain Quartzite and Moose Formation (new names) and associated rocks of the middle Proterozoic Belt Supergroup, Highland Mountains, southwestern Montana / by J. Michael O'Neill. p. cm. (U.S. Geological Survey bulletin ; 2121) (Belt supergroup in the High­ land Mountains and probable equivalent rocks in the Pioneer and Anaconda ranges, south­ western Montana; A) Includes bibliographical references. Supt. of Docs, no.: I 19.3:2121-A 1. Geology, Stratigraphic Proterozoic. 2. Geology Montana Highland Mountains. 3. Table Mountain Quartzite (Mont.) 4. Moose Formation (Mont.) I. Title. II. Series. III. Series: Belt supergroup in the Highland Mountains and proba­ ble equivalent rocks in the Pioneer and Anaconda ranges, southwestern Montana ; A. QE75.B9 no. 2121-A [QE653.5] 557.3 s dc20 95-3772 [551.7'15] CIP CONTENTS Abstract.......................................................................................................................... Al Introduction.................................................................................................................... 1 Middle Proterozoic Regional Geologic Setting ..................................................... 2 Previous Work........................................................................................................ 3 Stratigraphic Nomenclature........................................................................................... 3 Lower Belt Rocks................................................................................................... 3 Lahood Formation.......................................................................................... 3 Lithologic Description........................................................................... 5 Facies...................................................................................................... 6 Moose Formation........................................................................................... 6 Type Locality and Type Section............................................................ 8 Contacts with Adjacent Units................................................................. 10 Facies...................................................................................................... 10 Table Mountain Quartzite.............................................................................. 12 Type Locality and Type Section ............................................................ 12 Contacts with Adjacent Units................................................................. 14 Facies...................................................................................................... 14 Newland Formation........................................................................................ 14 Lithologic Description........................................................................... 15 Contacts with Adjacent Units................................................................. 15 Facies...................................................................................................... 15 Ravalli Group......................................................................................................... 16 Greyson Shale................................................................................................ 16 Lithologic Description and Facies ......................................................... 16 Spokane Formation........................................................................................ 17 Lithologic Description........................................................................... 17 Contacts with Adjacent Units................................................................. 18 Facies...................................................................................................... 19 Empire Formation.......................................................................................... 19 Lithologic Description ........................................................................... 19 Middle Belt Carbonate Rocks................................................................................ 19 Helena Formation........................................................................................... 19 Lithologic Description........................................................................... 19 Contacts with Adjacent Units................................................................. 20 Facies...................................................................................................... 20 Missoula Group...................................................................................................... 21 Lithologic Description and Facies ................................................................. 21 Contacts with Adjacent Units......................................................................... 22 Middle Cambrian Rocks ........................................................................................ 22 Tectonics and Sedimentation......................................................................................... 22 References Cited............................................................................................................ 25 FIGURES 1. Index map showing location of study area, extent of Belt Supergroup rocks, and location of Helena embayment of the Belt Basin .................................................................................................................................. A2 2. Map and cross