Early Silurian Graptolites From Southeastern Alaska and Their Correlation With Graptolitic Sequences in North America and the Arctic GEOLOGICAL SURVEY PROFESSIONAL PAPER 653 Early Silurian Graptolites From Southeastern Alaska and Their Correlation With Graptolitic Sequences in North America and the Arctic By MICHAEL CHURKIN, JR., and CLAIRE CARTER GEOLOGICAL SURVEY PROFESSIONAL PAPER 653 Descriptions and illustrations of $9 species of Graptoloidea and correlation of the assemblages with other graptolitic successions in North America, the Soviet Arctic, and Great Britain UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress Catalog-card No. 78-605140 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $1 (paper cover) CONTENTS Page Page Abstract-_ _________________________________________ 1 Standard graptolite zones for the Lower Silurian___-_._- 6 Introduction-______________________________________ 1 Lower Silurian graptolites in western North America-___ 6 Acknowledgments. ____ __--_-_________-____-__-______ 1 Systematic descriptions._____________________________ 13 Graptolites of the Descon Formation, southeastern Alaska__ _____________________________________ 2 Class Graptolithina.____________________________ 13 Description of the Descon Formation.________..___ 2 Order Graptoloidea_-___________---___-__-_- 13 Graywacke sandstone and banded mudstone___ 2 Family Diplograptidae__________________ 13 Conglomerate and sedimentary breccia. _______ 3 Family Dimorphograptidae______________ 33 Black chert and siliceous shale________________ 3 Family Monograptidae__________________ 34 Quartzo-feldspathic arenite.__________________ 3 Volcanic rocks,_____________________________ 3 References cited.___________________________________ 46 Stratigraphic relations to other units and age___--_- 3 Index ____.._______-__ __-_______-__-___---__-__--- 49 ILLUSTRATIONS [Plates 1-4 follow index] PLATE 1, Climacograptus, Pseudoclimacograptus, and Diplograptus. 2. Diplograptus, Glyptograptus, and Orthograptus. 3. Orthograptus, Petalograptus, Dimorphograptus, Akidograptus, and Monograptus. 4. Monograptus and Rastrites. Page FIGUBE 1. Geologic map of Prince of Wales Island area_________________--____-_--_-------_----_------_-------- 4 2. Index map showing Silurian graptolite localities_______________--_-_-----------_--------------------- 7 3. Correlation diagram showing graptolitic sequences-_____-__-_--___---__-_---------------------------- 9 4-5. Columnar sections showing graptolite localities: 4. Esquibel Island.________________-_________________-_------_-------_----------------------- 11 5. San Fernando Island.__________________________-_______-_-__--_---___--------------------- 12 6-19. Camera lucida drawings of: 6. Climacograptus. ________________-________________-_____-___-___-_-_-__-------------------- 13 7. Climacograptus- ________________-_______-____-__-_--__---_----_--------------------------- 17 8. Climacograptus and Pseudoclimacograptus. ______________________-_-__-__-----_----_--_------- 18 9. Diplograptus. __________________________________--___----___--_-_--__--------------------- 21 10. Glyptograptus and Diplograptus... _____________--__---_-----__-------_--_------------------- 22 11. Glyptograptus _______________________________________----_____--_--__-_-_----------------- 25 12. Glyptograptus and OrtAogrrapfus______---__--_----------------------------------------------- 26 13. ^.Orthograptus, Petalograptus, Dimorphograptus, and Akidograptus. ________-__------------------- 31 14. Dimorphograptus and Monograptus... ____________________-_______-._____------------_-------- 35 15. Monograptus... _______________________________________-______--------------------_------- 36 16. Monograptus_______________________________________-_--_______-___----------_----------- 38 17. Monograptus..- ________________________________________________-______----_--__----------- 40 18. Monograptus... _______________________________________________-____-_--_----------------- 41 19. Rastrites............ ___________ ______ _ _____________________.._-_-._--.-_--.---- 45 TABLES Page TABLE 1. Partial list of graptolites from northeastern Nevada showing British ranges and associations on single talus slabs--_-________________________________________________--_-___----_----------------------- 1 2. Silurian graptolite faunas from Prince of Wales Island area, Alaska__-____-_-__------------------------ 10 3. Lower Silurian graptolites of Alaska and Nevada showing a comparison of their zonal ranges to the same or similar species in Canada, Great Britain, and the Soviet Arctic.__________-_-----_------------------- ^ ill EARLY SILURIAN GRAPTOLITES FROM SOUTHEASTERN ALASKA AND THEIR CORRELATION WITH GRAPTOLITIG SEQUENCES IN NORTH AMERICA AND THE ARCTIC By MICHAEL CHURKIN, JR., and CLAIRE CARTER ABSTRACT Dimorphograptus (proximally uniserial and distally A succession of graptolite faunas across the Ordovician-Silurian biserial) together with the first monograptids were not boundary has been discovered in North America. The earliest reported in Ruedemann's (1947) cataloging of Nor^h Silurian graptolite zones, characterized by the association of American graptolites. the biserial graptolites Climacograptus, Glyptograptus, and Orthograptus, established much earlier in the Ordovician More recently, Ross, (1962) described several lower together with the first Silurian monograptids, Akidograptus and Silurian species from Illinois, but they are fragmentary Dimorphograptus are described for the first time in North and poorly preserved. Another lower, but not lowest, America. These new collections of Lower Silurian graptolites Silurian graptolite collection that has beautifully are from dark shales in southeastern Alaska and Nevada. The preserved specimens was recently made from talus in occurrence of Silurian graptolites in western North America is reviewed, and the Alaskan graptolite faunas are correlated a mine dump in Nevada (Kerr, 1962; Churkin and Kay, with other graptolitic successions in North America and the 1967). These graptolites are illustrated for the first Soviet Arctic. The Alaskan graptolite species and zonal succession time in this paper. are remarkably similar to that in the Birkhill Shales of Scotland, The senior author in the company of G. D. Eberleni the type section for the standard Lower Silurian graptolite and M. A. Lanphere made several discoveries of con­ zones. From Alaska, graptolite assemblages equivalent to the zones of Akidograptus acuminatus, Monograptus cyphus, and siderably older Silurian graptolite faunas in south­ Monograptus grcgarius are recognized and illustrated. In addition, eastern Alaska during the 1964 field season. Subse­ the following new graptolite species are established: Climaco­ quently in 1965, new lower Silurian graptolite localities graptus indivisus esquibelensis, C. innotatus obesus, C. tnedius were found by Eberleiii, A. T. Ovenshine, and Churkin. brevicaudatus, C. stenotelus, C. rectangularis abbreviatus, Diplo- The most important of these localities was revisited graptus mucroterminatus, D. elongatus, Glyptograptus tamariscus magnus, G. lanphcrei, G. laciniosits, G. gnomus, G. kayi, Ortho­ by Churkin in 1968, and the highest Ordovician grapto­ graptus eberleini, 0. insectiformis minutus, Dimorphograptus lites were found just below the previously known lowest physophora alaskensis, Monograptus calamistratus, M. budding- Silurian faunas, thus establishing the Ordovician- toni, M. noyesensis, M. kerri, M. hamatus, Rastrites orbitus. Silurian boundary. The earliest Silurian graptolite zones are present in some of these localities the first INTRODUCTION record of their occurrence in North America. The Graptolite faunas, especially from black shale se­ purpose of this paper is to describe this new material, quences bordering North America, show a remarkable briefly review the occurrence of Lower Silurian grapto­ similarity in species and faunal succession to the British lites in western North America and the Soviet Arctic, graptolites made famous first by Charles Lapworth, correlate the Alaskan graptolites within these areas, then by Elles and Wood (1901-18). In Australia and show the differences in associations of certain (Thomas, 1960), Asia (Sun, 1933; Hsii, 1934; Obut, critical graptolite species that most likely reflect 1959, 1960), and North Africa (Waterlot, 1945), where changes in their stratigraphic range from one region good graptolite sections are known, the similarity in to another. species and succession of faunas above the initially The biostratigraphic section is by Michael Churkin, somewhat provincial Lower Ordovician faunas is again and the systematic descriptions are largely by Claire remarkable. Despite the cosmopolitan character of Carter, who also did all of the camera lucida drawings graptolites, the lowest Silurian graptolite zones are of the graptolites. relatively unknown outside of Great Britain. The lowest Silurian graptolite zones characterized by the ACKNOWLEDGMENTS association of biserial genera such as the long- The authors are indebted to the collecting zeal of established Ordovician Climacograptus, Glyptograptus, G. D. Eberlein, A. T. Ovenshine, M. A. Lanphere, and and Orthograptus and the appearance of the new Charles Carter, without whose help this report would 1 EARLY SILURIAN GRAPTOLITES FROM