The Palynology of the Cambrian Nolichucky Shale at Thorn Hill, Tennessee, USA

Brian E. Pedder^1,2

¹Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK; ²Palaeontology Department, The natural History Museum, Cromwell Road, London SW7 5BD, UK

E-mail: brian.pedder@gmail.com

The Nolichucky Shale, as exposed at Thorn Hill in northeastern Tennessee, is a 179 m thick succession of predominantly shale subtidal with occasional carbonate/shale peritidal deposits. It constitutes part of the Tennessee Conasauga Group and represents near-shore deposition within a shallow carbonate-rimmed, intracratonic basin that was subject to transgressive/regressive cycles (Glumac & Walker 2000), that formed part of a passive continental margin along the eastern side of Laurentia. Trilobites from Thorn Hill and the adjacent Lee Valley section indicate a Guzhangian to Paibian age for the Nolichucky Shale, encompassing the uppermost Bolaspidella, Cedaria, Crepicaphalus and lowermost Aphelaspis faunal zones (Sundberg 1989; Derby 1965).

Fifty samples from the Nolichucky Shale were collected for palynological examination. In all fifty five acritarch species and morphotypes were recovered including at least twelve new species and four new genera. Various filaments and invertebrate spines, cuticular fragments and sclerites (including Wiwaxia sclerites) were also recovered. Of the acritarchs two species, Cerebrosphaera buickii and Apodastoides verobturatus are known only from the Precambrian and might be reworked, though their small sizes suggest otherwise. The new acritarch species include a Pirea-like morphotype with horns, a polarised acritarch with a complex excystment structure surrounded by processes and three anomalously large acanthomorphs measuring up to 155 µm. Two of the latter resemble the diapause egg cases of some extant crustacea; one resembles in both size and general morphology the egg case of the copepod Pontella meadii, whilst the other possesses a three-layered wall-ultrastructure similar to that observed in egg cases of extant Branchiopods. In fact, the size, surface ornament and wall ultrastructure, as well as the associated near-shore facies, together suggest they are more likely to be zooplankton egg cases than phytoplankton resting cysts.

References

Derby, J.R. (1965). Paleontology and stratigraphy of the Nolichucky Formation in southwest Virginia and northeast Tennessee. Ph.D. dissertation. Virginia Polytechnic Institute and State University, Blacksburg.

Glumac, B., and Walker, K.R., (2000). Carbonate deposition and sequence stratigraphy of the terminal Cambrian grand cycle in the southern Appalachians. Journal of Sedimentary Research, 70, 952-963.

Sundberg, F.A. (1989). Biostratigraphy of the lower Conasauga Group, a preliminary report. Appalachian Basin Industrial Associates Spring Program,1989, 15, 166-176