GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 194-15
Presentation Time: 9:00 AM-6:30 PM


GIBSON, Michael, Dept. of Agriculture, Geosciences, Natural Resources, University of Tennessee at Martin, 256 Brehm Hall, University of Tennessee at Martin, Martin, TN 38238

The Ross Formation (Lower Devonian, West Tennessee), which Yale paleontologist Carl O. Dunbar made famous as the "happy hunting ground" of fossils, crops out in a north‑south belt in the western valley of the Tennessee River. The Ross is subdivided into three members: the lowermost Rockhouse Limestone Member (bioclastic limestone interbedded with thin shale beds), which grades laterally into the Ross Limestone Member (dark, thin-bedded cherty limestone), and the overlying Birdsong Shale Member (thin, shaly, bioclastic limestone interbedded within thicker fossiliferous terrigenous shale). All members were deposited on a storm-dominated level-bottom muddy shelf setting below wave base. The Ross Formation contains an abundant, diverse, sclerobiont-rich, shelly macrofauna dominated by bryozoans, brachiopods and pelmatozoan echinoderms. The Birdsong can be subdivided into an upper bryozoan‑ and echinoderm‑rich portion and a lower bryozoan‑ and echinoderm‑poor portion, both sclerobiont-rich. Herein is reported an occurrence from an isolated float block of the exoskeleton of a conulariid; unfortunately, not assignable with confidence to a specific member. Dunbar reported the only previous conulariids from the Ross Limetone Member, listed as “very rare” and much further south, 100 years ago, in his original dissertation work, of which no specimens remain in his Yale collection. The incompletely preserved portion of the exoskeleton is eight cm long and bedding plane compacted. This exoskeleton is missing the attachment stalk, adapical cone apex, and the oral aperture, but shows well-preserved ridges and interridges. Several small portions have eroded through to expose an external mold of the buried opposite surface. Also present are portions of both corner grooves, one midline with a well-developed keel, and a distinctly reticulate ornamentation. Reconstructed, the specimen would be a minimum of 15cm long. It tentatively assigned as Conularia huntiana Hall predominantly based upon this ornamentation. This specimen was collected from the Rockhouse or Birdsong members, further North and not from the Ross Limestone Member reported by Dunbar, thus extending the stratigraphic and geographic range of conulariid scyphozoans in the Ross Formation, as well as being the only pelagic member of the cnidarians from the Ross.