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Journal of Paleontology 92(3):442–458
Walker and Driese, 1991; Fig. 2, right hand column). However, Smoot and Southworth (2014) proposed an alternative model for correlation whereby the Weverton Formation represents the northward lateral equivalent of the Nebo Quartzite Member, the Harpers Formation represents the northward lateral equiva- lent of the Murray Shale Member, and the Antietam Formation is the northward lateral equivalent of just the Hesse Quartzite plus Helenmode members (see also Bloomer and Werner, 1955). Under that alternative model (Smoot and Southworth, 2014; Fig. 2, column second from right), localities north of Tennessee record a more obvious sedimentary expression of the two transgressive sequences within the upper Chilhowee Group. The upper part of the Antietam Formation (Helenmode
equivalent) contains trilobite fragments that have historically been identified as “Olenellus sp.” (Walcott, 1892, 1896, 1910; Bassler, 1919; Resser, 1938, pl. 2, fig. 23; Butts, 1940; Stose and Stose, 1944; Amsden, 1951). However, those specimens must undergo modern systematic revision before their bios- tratigraphic significance can be determined (MW and SJH, in preparation). The Helenmode Formation and its lateral equiva- lents also contain hyoliths and brachiopods (Neuman and Nelson, 1965; Hageman and Miller, 2016). The second transgression ultimately resulted in the develop-
ment of a carbonate bank that extended along the passive margin from present-day Alabama to Pennsylvania and the northern Appalachians (Landing, 2012). Development of the carbonate bank in the southern and central Appalachians is reflectedinthe conformable transition from the upper Chilhowee Group into the overlying Shady Dolomite and its lateral equivalents the Toms- town Dolomite, Jumbo Dolomite, and Murphy Marble (Fig. 2; Bloomer and Werner, 1955; Mack, 1980; Simpson and Eriksson, 1990; Tull et al., 2010). The carbonates have been well studied at localities such as Sleeping Giants, Alabama (Bearce and McKinney, 1977), and near Austinville, Virginia (Balsam, 1974; Pfeil and Read, 1980;Barnaby andRead, 1990;McMenamin et al., 2000). Locally, the carbonates contain a rich fauna of trilobites, archaeocyathids, brachiopods, Salterella Billings, 1861, hyoliths, and echinoderm plates (Resser, 1938; Butts, 1940; Yochelson, 1970; McMenamin et al., 2000; Tull et al., 2010). Faunas of the Shady and Tomstown dolomites indicate a mid-Dyeran age (McMenamin et al., 2000;MWunpublished observations).
Previous paleontological work on the Murray Shale
Biostratigraphic data from the subjacent and superjacent units (summarized above) constrain the Murray Shale to be of early Cambrian, and no younger than mid-Dyeran, age. According to the current working hypothesis of the Cambrian time scale (Peng et al., 2012), this indicates a numerical age somewhere between 541Ma and ~514 Ma. This is congruent with the coarse age constraint imposed by radiometric dating of glauconite grains from the unit (539±30 Ma; Walker and Driese, 1991). However, the uncertainty in age associated with these con- straints is large, at least in comparison to the high-resolution biostratigraphic framework that exists for the early Cambrian of the Cordilleran margin of Laurentia (e.g., Hollingsworth, 2011; Webster, 2011; Webster and Bohach, 2014). This section reviews previous paleontological discoveries within the Murray
Shale and discusses the extent to which those finds refine the age estimate for the unit.
Initial fossil discoveries.—Fossils from the Chilhowee Group were first found by Cooper Curtice during the geological resurvey of eastern Tennessee (noted by Walcott, 1891). The nature of Curtice’s fossils is nowhere mentioned, but they were apparently found “in the shales interbedded in the quartzite of Chilhowee Mountain” (Walcott, 1891, p. 302). Curtice’s dis- covery presumably occurred in 1885 (see Yochelson and Osborne, 1999), although the significance of the find might not have been immediately realized: Walcott (1889, table on p. 386) reported that fossils were unknown from the lower Cambrian of Tennessee. Nevertheless, in 1889, Walcott visited Chilhowee Mountain and discovered body fossils in the “banded shales at and near the summit of the [Chilhowee Group]” that allowed him to determine an early Cambrian age for the unit (Walcott, 1890, p. 536–537). Walcott (1890, p. 570, 583; 1891, p. 154) listed these fossils as a hyolith, the arthropod Isoxys chilho- weanus Walcott, 1890 (as Isoxys chilhoweana), an ostracod crustacean, and “an undetermined species of Olenellus.” In the associated table of fossil occurrences, Walcott (1890, table on p. 575) tentatively identified the trilobite as Olenellus thompsoni (Hall, 1859), and later referred to it as “a species of Olenellus closely allied to Olenellus thompsoni and O. asaphoides in that portion of the head preserved” (Walcott, 1891, p. 154; “O. asaphoides” is now Elliptocephala asaphoides Emmons, 1844). That faunal list—in part or in full—has been repeated many times in the literature by subsequent workers (e.g., Resser, 1933, 1938; Grabau, 1936; King et al., 1952; King and Ferguson, 1960; Neuman and Nelson, 1965), but very few of the fossils from Walcott’s collection have been illustrated. Two hyolith specimens were figured by Resser (1938, pl. 4, figs. 30, 31; USNM 18447, from lot USNM 26979). Two specimens
of Isoxys chilhoweanus were figured by Walcott (1890, pl. 80, figs. 10, 10a; also Williams et al., 1996, fig. 7.2) and nine specimens currently reside in the USNM (lots USNM 18444 and USNM 18445, including the holotype). The “ostracod crustacean” mentioned by Walcott (1891, p. 154) is the bra- doriid Indota tennesseensis (Resser, 1938), first named and illustrated as Indianites tennesseensis by Resser (1938, p. 107, pl. 3, fig. 47; holotype USNM94759; for subsequent taxonomic revisions see Siveter and Williams, 1997). The trilobite men- tioned by Walcott (1890, 1891) was never illustrated or descri- bed. This is unfortunate, because the historical identification of this trilobite as “Olenellus sp.” has been used to support a Dyeran age for the Murray Shale (e.g., Simpson and Sundberg, 1987), but such age assignment cannot be substantiated without modern systematic treatment of the taxon. The sole known specimen from Walcott’s original trilobite collection is illustrated for the first time herein (Fig. 4.8). This specimen does not represent a species of Olenellus, but instead a new species of a much older olenelline genus (described herein). Walcott’s fossils were collected from two areas on
Chilhowee Mountain—Little River Gap and near Montvale Springs (Walcott, 1890, p. 626; Fig. 3.1, 3.2)—but the exact locations of the fossil-bearing sites are unclear (see Appendix). The stratigraphic provenance of the fossils is also ambiguous. Walcott reported only that they were found “in the shale about
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