Journal of Paleontology, 92(3), 2018, p. 442–458 Copyright © 2018, The Paleontological Society. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/ licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.155


Buenellus chilhoweensis n. sp. from the Murray Shale (lower Cambrian Chilhowee Group) of Tennessee, the oldest known trilobite from the Iapetan margin of Laurentia


Mark Webster,1 and Steven J. Hageman2


1Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 ⟨mwebster@geosci.uchicago.edu⟩ 2Department of Geology, Appalachian State University, Boone, North Carolina 28608, USA ⟨hagemansj@appstate.edu⟩


Abstract.—The Ediacaran to lower Cambrian Chilhowee Group of the southern and central Appalachians records the rift-to-drift transition of the newly formed Iapetan margin of Laurentia. Body fossils are rare within the Chilhowee Group, and correlations are based almost exclusively on lithological similarities. A critical review of previous work highlights the relatively weak biostratigraphic and radiometric age constraints on the various units within the succession. Herein, we document a newly discovered fossil-bearing locality within the Murray Shale (upper Chilhowee Group) on Chilhowee Mountain, eastern Tennessee, and formally describe a nevadioid trilobite, Buenellus chilhoweensis n. sp., from that site. This trilobite indicates that the Murray Shale is of Montezuman age (provisional Cambrian Stage 3), which is older than the Dyeran (provisional late Stage 3 to early Stage 4) age suggested by the historical (mis)identification of “Olenellus sp.” from within the unit as reported by workers more than a century ago. Buenellus chilhoweensis n. sp. represents only the second known species of Buenellus, and demonstrates that the genus occupied both the Innuitian and Iapetan margins of Laurentia during the Montezuman. It is the oldest known trilobite from the Iapetan margin, and proves that the hitherto apparent absence of trilobites from that margin during the Montezuman was an artifact of inadequate sampling rather than a paleobiogeographic curiosity. The species offers a valuable biostratigraphic calibration point within a rock succession that has otherwise proven recalcitrant to refined dating.


UUID: http://zoobank.org/30af790b-e7b1-44c3-b1d5-55cdf579bde2 Introduction


The Neoproterozoic to lower Cambrian Chilhowee Group is exposed in the western Blue Ridge and the Valley and Ridge provinces of the broader Appalachian Mountains from Alabama to Pennsylvania (Figs. 1, 2), and provides a record of the early evolution of the Iapetan margin of the Laurentian paleoconti- nent (Thomas, 1977, 2014; Mack, 1980; Bond et al., 1984; Simpson and Sundberg, 1987; Simpson and Eriksson, 1989, 1990). The Chilhowee Group has received much study in terms of sedimentology, facies analysis, and basin analysis (e.g., King and Ferguson, 1960; Whisonant, 1974; Mack, 1980; Cudzil and Driese, 1987; Simpson and Eriksson, 1989, 1990; Walker et al., 1994; Hageman and Miller, 2016), and has been used in con- tinental- and global-scale correlations of the Cambrian and of the Precambrian-Cambrian boundary (e.g., Walcott, 1891; Resser, 1933; Howell et al., 1944; Wood, 1969). However, metazoan body fossils—including trilobites, which form the primary basis for the biostratigraphic zonation and correlation of lower Cambrian Laurentian strata (e.g., Fritz, 1972; Palmer, 1998; Hollingsworth, 2011; Webster, 2011; Webster and Bohach, 2014; Webster and Landing, 2016)—are rare within the Chilhowee Group. Consequently, correlations are based almost exclusively on lithological similarities (e.g., Palmer, 1971;


Mack, 1980), and ages of the rock units and the timing of geologic events associated with the rift-to-drift transition along the continental margin are relatively poorly constrained. The discovery of biostratigraphically useful fossils within the Chilhowee Group is therefore important. Lower Cambrian trilobites have been previously reported


from two stratigraphic intervals within the Chilhowee Group. The stratigraphically lower occurrence was reported from the Murray Shale on Chilhowee Mountain, Blount County, eastern Tennessee (Figs. 1, 2; Walcott, 1890, 1891; Keith, 1895); that unit is the focus of the present paper. The stratigraphically higher occurrence was reported from the upper part of the Antietam Formation at several localities in Virginia, Maryland, and Pennsylvania (Fig. 2.2, white circles; Walcott, 1892, 1896, 1910; Bassler, 1919; Resser, 1938; Butts, 1940; Stose and Stose, 1944; Amsden, 1951); those younger trilobites will be the focus of a separate study. All trilobites from the Chilhowee Group were initially identified as “Olenellus sp.” (Walcott, 1890, 1891, 1896, 1910; Resser, 1938), and later workers have uncritically accep- ted that generic identification. Historically, the genus name Olenellus Hall in Billings, 1861 was applied so broadly that its stratigraphic range spanned the entire Dyeran Stage and even down into the preceding Montezuman Stage (provisional Cambrian Stages 4 and 3, both in part; Peng et al., 2012)


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