Abstract
AbstractThe 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 chilhoweensisn. 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 “Olenellussp.” from within the unit as reported by workers more than a century ago.Buenellus chilhoweensisn. sp. represents only the second known species ofBuenellus, 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
Highlights
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 paleocontinent (Thomas, 1977, 2014; Mack, 1980; Bond et al, 1984; Simpson and Sundberg, 1987; Simpson and Eriksson, 1989, 1990)
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
We demonstrate that Buenellus chilhoweensis n. sp. is the oldest known trilobite from the Iapetan margin of Laurentia, and we discuss the significance of the trilobite in terms of the much-needed biostratigraphic constraint it provides on the timing of events during the early evolution of that margin
Summary
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 paleocontinent (Thomas, 1977, 2014; Mack, 1980; Bond et al, 1984; Simpson and Sundberg, 1987; Simpson and Eriksson, 1989, 1990). Stose and Stose (1944) expressed doubt as to whether the collections mentioned by Keith (1895) came from the Murray Shale Their skepticism stemmed from ambiguities over the mapping in the Little River Gap and from the fact that all other Chilhowee Group fossils had otherwise been reported only from the uppermost beds marking the transition into the Shady Dolomite (see references above). 520) acknowledged that the fossil collection from the crest of Chilhowee Mountain above Montvale Springs mentioned by Keith (1895) was almost certainly from the Murray Shale and represented the stratigraphically oldest occurrence of trilobites and brachiopods in the southern Appalachians. We do not claim precise ageequivalence of the upper Murray Shale and lower Buen Formation within the Montezuman Stage ( such equivalence is possible), and we stress that our provisional age assignment for the Murray Shale (Fig. 2.2) is a working hypothesis that should be tested with additional data
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