Depositional Framework and Regional Correlation of Pre-Carboniferous Metacarbonate Rocks of the Snowden Mountain Area, Central Brooks Range, Northern Alaska U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1545 Cover: Massive carbonate rocks chiefly of the Mathews River unit, Chandalar D-6 quadrangle, central Brooks Range, northern Alaska. The image is a digital enhancement of the photograph (fig. 4) on page 7. Design and layout by Sunne Rinkus, 1994. Depositional Framework and Regional Correlation of Pre-Carboniferous Metacarbonate Rocks of the Snowden Mountain Area, Central Brooks Range, Northern Alaska By J.A. Dumoulin and Anita G. Harris U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1545 Lithofacies, conodont biostratigraphy and biofacies, and depositional environments of pre-Carboniferous metacarbonate rocks, correlation with other sequences across northern Alaska, and paleogeographic and paleotectonic implications UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994 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. Published in the Eastern Region, Reston, Va. Manuscript approved for publication August 17, 1993. Library of Congress Cataloging in Publication Data Dumoulin, Julie A. Depositional framework and regional correlation of pre-Carboniferous metacarbonate rocks of the Snowden Mountain area, central Brooks Range, northern Alaska / by J.A. Dumoulin and Anita G. Harris. p. cm.—(U.S. Geological Survey professional paper ; 1545) "Lithofacies, conodont biostratigraphy and biofacies, and depositional environments of pre-Carboniferous metacarbonate rocks, correlation with other sequences across northern Alaska, and paleogeographic and paleotectonic implications." Includes bibliographical references. Supt. of Docs. no. : I 19.16:1545 1. Rocks, Carbonate—Alaska—Snowden Mountain Region. 2. Conodonts— Alaska—Snowden Mountain Region. 3. Stratigraphic correlation. I. Harris, Anita G. II. Title. III. Series. QE471.15.C3D86 1994 552'.58-dc20 93-21361 CIP CONTENTS Abstract........................................................................................... 1 Acknowledgments .............................................................................. 1 Introduction...................................................................................... 2 Geologic Setting ................................................................................ 2 Previous Work .................................................................................. 3 Stratigraphic Nomenclature ................................................................... 3 Methods.......................................................................................... 6 Metacarbonate Succession—Cambrian (and older?) to Middle Devonian Metasedimentary Rocks .............................................................. 6 Cambrian Rocks .......................................................................... 6 Lithologies........................................................................... 7 Age and Biofacies .................................................................. 7 Distribution.......................................................................... 8 Depositional Environment......................................................... 8 Middle Ordovician Rocks................................................................. 8 Lithologies........................................................................... 10 Age and Biofacies .................................................................. 14 Distribution.......................................................................... 14 Depositional Environment......................................................... 14 Upper Ordovician and Silurian Rocks ................................................ 16 Lithologies........................................................................... 17 Age and Biofacies .................................................................. 20 Distribution.......................................................................... 21 Depositional Environment......................................................... 21 Lower and (or) Middle Devonian Rocks ............................................. 22 Metacarbonate Rocks of Uncertain Age .............................................. 23 Wiehl Mountain Area.............................................................. 23 Dillon Mountain Area.............................................................. 24 Snowden Mountain Massif........................................................ 25 Table Mountain Area .............................................................. 25 Summary of the Metacarbonate Succession in the Snowden Mountain Area................................................................................ 26 Devonian Metaclastic Rocks.................................................................. 28 Beaucoup Formation ..................................................................... 28 Carbonate Lithologies.............................................................. 28 Age and Biofacies .................................................................. 30 Distribution.......................................................................... 30 Depositional Environment......................................................... 30 Hunt Fork Shale .......................................................................... 31 Carbonate Lithologies.............................................................. 31 Age and Biofacies.................................................................. 31 Distribution.......................................................................... 31 Depositional Environment......................................................... 32 Nutirwik Creek Unit ..................................................................... 33 Carbonate Lithologies.............................................................. 33 Age and Biofacies .................................................................. 34 Distribution.......................................................................... 34 Depositional Environment......................................................... 34 Summary of Devonian Metaclastic Rocks in the Snowden Mountain Area................................................................................ 34 m IV CONTENTS Regional Relationships......................................................................... 35 Pre-Carboniferous Metacarbonate Successions ...................................... 35 Eastern Baird Mountains Metacarbonate Succession ......................... 37 Proterozoic and (or) Cambrian Rocks..................................... 37 Lower and Middle Ordovician Rocks..................................... 39 Upper Ordovician to Devonian(?) Rocks................................. 40 Comparison of the Snowden Mountain and Eastern Baird Mountains Metacarbonate Successions .............................................. 40 Other Pre-Carboniferous (Meta)sedimentary Successions ................... 42 Western Baird Mountains ................................................... 42 York Mountains............................................................... 44 Shublik and Sadlerochit Mountains........................................ 47 Doonerak Window............................................................ 47 Devonian Siliciclastic Units............................................................. 48 Devonian Siliciclastic Units in the Baird Mountains ......................... 48 Nakolik River Unit........................................................... 48 Unit ftqs ...................................................................... 48 Hunt Fork Shale .............................................................. 49 Comparison of Snowden Mountain and Baird Mountains Devonian Siliciclastic Units .......................................................... 49 Discussion.................................................................................. 50 Comparative Microfacies Analysis .............................................. 51 Paleobiogeography.................................................................. 53 Conclusions...................................................................................... 57 References Cited................................................................................ 57 Appendix......................................................................................... 62 PLATES [Plates follow appendix] 1. Ordovician conodonts from the Snowden Creek unit. 2. Late Ordovician and Silurian conodonts from the Mathews River unit. 3. Latest Givetian and Frasnian conodonts from the Beaucoup Formation, Hunt Fork Shale, and Nutirwik Creek unit. FIGURES 1. Index map showing location of Snowden Mountain study area, northern Alaska ................................. 2 2. Map showing generalized distribution of geologic units in the Snowden Mountain area ........................ 4 3. Index map showing geographic names and location of measured sections and lithologic and fossil collections ......................................................................................................................