Paleontological Contributions
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THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS June 8, 1984 Paper 109 CAMBRIAN AGNOSTIDA OF NORTH AMERICA AND GREENLAND PART I, PTYCHAGNOSTIDAE' R. A. ROBISON Department of Geology, University of Kansas Lawrence, Kansas 66045 Abstract—Representatives of the trilobite family Ptychagnostidae are described or further documented from open-shelf lithofacies in North America and Greenland. These include 21 species distributed among the genera Lejopyge, Onymagnostus, and Ptychagnostus. Seventeen of the 21 species have intercontinental distributions and are important for global biostratigraphy. New species from western North America include Lejopyge acantha, Lejopyge rigbyi, Ptychagnostus hintzei, and Ptychagnostus michaeli. A new geographic subspecies, Lejopyge laevigata rubyensis, also is described. Five successive interval-zones based on agnostoids are defined for the middle part of the Cambrian System. The base of each zone is defined by a biohorizon corresponding to the first appearance of a single species selected for its abundance and wide geographic distribution within the interval. In ascending order, the species and corresponding zone names are Ptychagnostus praecurrens, P. gibbus, P. atavus, P. punc- tuosus, and Lejopyge laevigata. The upper boundary of each zone is defined by the lower boundary of the one overlying it. Additional widespread agnostoid species are present in each zone. These together with the name species give each zone a distinctive character. As defined here, the Lejopyge laevigata Zone is stratigraphically equivalent to the uppermost Bolaspidella Zone and much of the Cedaria Zone as traditionally used in North America. An informal lower subzone probably has close temporal correlation with the Zone of Solenopleura brachymetopa as commonly used in Scandinavia, and an informal upper subzone probably correlates closely with the Zone of Lejopyge laevigata as used in Scandinavia. These correlations further support the idea that, in reference to the standard of northwestern Europe, much of the Cedaria Zone of North America is Middle rather than Late Cambrian in age. Also, the lower part of the Dresbachian Stage in North America is Middle Cambrian in age. I Manuscript received January 15, 1984. 2 The University of Kansas Paleontological Contributions—Paper 109 ABUNDANCE, WIDE geographic distribution, and documented similar Middle Cambrian ag- rapid evolution make agnostoid trilobites some nostoid successions elsewhere in the world. of the best indices for global correlation of Shergold (1981) has drawn attention to the Cambrian strata. The value of agnostoids for potential importance of agnostoids in Upper regional biostratigraphy was well demonstrated Cambrian biostratigraphy. by A. H. Westergard (1946) in his monograph This is the first of a planned series of papers on the Middle Cambrian agnostoids of Sweden. documenting the diverse Cambrian agnostoid Subsequent studies (e.g., Pokrovskaya, 1958; fauna of North America and Greenland. New Opik, 1961a, 1979; Robison, 1964, 1976, 1982; information about North American agnostoids Ergaliev, 1980; Egorova and others, 1982) have is based on several hundred collections of /Wellsville rMountains _JiVasatch Mountains Toana Range n nN ‘t . Deep Creek 1 --Mountains t UTAH I' , Dugway Range fi . _ ,-40° LAKE t Ruby Mountains i 1 L__L northern L.' •--_, I i Toiyabe Fish Springs Range 4 ,-- ,% 1 Drum Mountains 1 !`... Range northern f I ks 71. Egan Range I 7 I Eureka 4 northern 1 _, i'- mining district' Schell Creek 1 House Range Canyon Range Range 39° southern White Pine Range'. I Ft southern Snake Range southern Schell Creek Range southern Egan Ranges 38°-n .- 38° 0 < < > I 1— I D Z j 0 .kilometers 100 I \. Fig. I. Map of parts of Nevada and Utah showing outcrops of Cambrian rocks (black) in mountains or ranges mentioned in this paper (after Palmer, 1971). Robison—Cambrian Agnostida, Part I, Ptychagnostidae 3 Peary Land Cambrian fossils that I have assembled during Nyeboe Land nvggliT more than two decades. Most of these collec- tions are from thick, generally well-exposed 84/1/6, stud ylif area stratigraphic sections in the Great Basin of Nevada and Utah (Fig. 1). Other significant ( -r) GREENLAND information has come from about 50 collections <<` of Cambrian fossils from Peary Land in central North Greenland (Fig. 2). These were mostly "CD collected by John S. Peel of the Geological -7 -0 Survey of Greenland. The Survey generously \ -0 made them available for this study. A major purpose of this paper is to provide revised or new systematic descriptions for spe- cies of one agnostoid family, the Ptychag- nostidae. It is treated first because several of its species have been used by researchers around the world as zonal indices in Middle Cambrian rocks. Another purpose is to begin a global zonation based on agnostoids from the middle part of the Cambrian System. Fig. 2. Map of Henson Gletscher region, central North Faunas in terranes exotic that were accreted Greenland, indicating collecting localities (black dot, For- to North America after the Cambrian Period mation 2, Bronlund Fjord Group; black square, Formation are not included in this study. These are mainly TI, Tavsens Iskappe Group; black stars, Formation T2, the so-called "Atlantic province" faunas in Tavsens Iskappe Group). Margins of permanent i cc caps arc indicated by broken lines. such places as the Carolina slate belt (Secor and others, 1983) and the Avalonian terranes in LITHOFACIES AND BIOFACIES parts of New England and eastern Canada. The most diverse and best documented of these Similarities in patterns of lithofacies and faunas are in southeastern Newfoundland biofacies indicate that Greenland and most of (Hutchinson, 1962). North America were united in a single con- Acknowledgments. —I am indebted to several tinent during Cambrian time. Thick and friends who have generously contributed speci- widespread carbonate deposits support paleo- mens and information used in this study. Some magnetic evidence that the continent was in also have guided me to important localities and equatorial latitudes (e.g., Bambach and others, others have arranged for the loan of specimens 1980). Lithofacies show that the craton was from institutional collections. These include F. encircled by a broad marine shelf with shallow- J. Collier, W. H. Fritz, Lloyd Gunther, Metta water, carbonate platform deposits of variable Gunther, Val Gunther, L. F. Hintze, C. H. extent (Palmer, 1973; Robison, 1976). The Kindle, L. B. McCollum, M. B. McCollum, platform carbonates were flanked by lagoonal A. R. Palmer, J. S. Peel, R. L. Randolph, M. muds and nearshore sands on one side and by N. Rees, J. K. Rigby, A. J. Rowell, D. K. outer-shelf muds on the other side. Strickland, M. E. Taylor, and W. W. White. Two almost mutually exclusive biofacies are The manuscript has been improved by the common in Middle Cambrian rocks of North reviews of Virginia Ashlock, J. B. Jago, Rolf America. Evidently the faunas were separated Ludvigsen, and A. J. Rowell. Margery Rowell by salinity and temperature barriers on the translated much of the Russian literature that is shallow carbonate platforms. An inner, re- cited. The illustrations were prepared by R. B. stricted-shelf biofacies is found in limestone, Williams, photographs were printed by Eileen shale, and sandstone. Generally it is char- Williams, and manuscript was typed by Jane acterized by sparse, low-diversity, endemic, Priesner. The research was supported most polymeroid faunules. Agnostoids are almost recently by National Science Foundation grants unknown in this inner biofacies. An outer, EAR-8024066 and EAR-8218322. For all of open-shelf biofacies found mostly in limestone this help and support I am most grateful. and shale is characterized by common to abun- 4 The University of Kansas Paleontological Contributions—Paper 109 dant, high-diversity, mixed polymeroid and open-shelf biofacies are widely distributed agnostoid faunas. Fossils are usually most around the continent, but most lack interconti- abundant near the seaward margin of the car- nental distribution. Agnostoid taxa also are bonate lithofacies. Polymeroid genera in the widely distributed around the continent, but NEVADA UTAH _ northern s. Egan & central Deep Creek, Agnostoid Eureka northern Snake s. Schell Cr. House Fish Sp., & Zones mining Egan Schell Creek Range mtns. district Range Range ranges Range Drum 7 1 2 3 4 5 6 • CO Orr Formation 2 oc < Zi3 o a) 0 Q) C in 7) ...= ..= --o E o c D t 76 a) E 8 o o E E 's _o TD Q) u) E (21 ô a a) _a a IL Tts c a) _c E E ,._ a) ce .a. Weeks as a) '5 a co _J co ci. z) '5 u) Limestone a 8 CO z E -rE) o_ E" o) CO ca a ca -3 2 7 0 2 C C .6 (11 0 0 tt 7E1 L1J 0 E E 6 Is. men,. E A mem. Trippe u_ u_ Limestone Q) es Q) a) Il a_ c c co c o 75 6 0 0 o a) Secret c c Ta Marjum 0 ra 8 'i a) .?. Canyon E -_7.1 .c) _c Formation > c c) E u) 0o .—0 Z c Shale E a) co z u_ u) c 7'1 _< Q c E ca 0 E 0 a) a l.'2 'a CC >, Ts c c .c Q) IL CO co FL 2 112 8 a) < '8 3 CD 6'o O cs_ Q) atavus Geddes u) Wheeler Wheeler W Limestone Formation Formation _i 0 gibbus 0 .,= Swasey Swasey •a Limestone Limestone a) a) a) co c c c C C o o o E "V) 'j.). rn a) E '8 a) o o E E E Q)0 E -1' ai Z '5 zi Li a u_ c c c CI o O o o o ›, >, -o -o c c c as as ra as as ô '5 o o o -0 -0 a) a) o LI EL z z z Fig.