Acritarchs and prasinophytes from the Lower Devonian (Lochkovian) Ross Formation, Tennessee, USA: stratigraphic and paleogeographic distribution

Abstract

A diverse and abundant organic-walled microphytoplankton assemblage is reported from two measured sections of the Lower Devonian (Lochkovian) Ross Formation in Benton and Decatur counties, Tennessee, USA. The palynoflora comprises 24 genera and 34 species of acritarchs, including one new genus and species (Caulissoma gordonii); and five genera and 11 species of prasinophyte phycomata (excluding Leiosphaeridia and Tasmanites). Other components include chitinozoans, miospores, and scolecodonts. This is the first Early Devonian acritarch/prasinophyte assemblage to be described from Tennessee, and it is assigned a Lochkovian age based on marine invertebrate faunas, stratigraphic relationships, and the palynomorph assemblage. A high degree of similarity (67% commonality) exists between this palynoflora and that from the stratigraphic and age-equivalent Haragan and Bois d’Arc formations of Oklahoma. Appreciable numbers of the microphytoplankton taxa identified herein are common to the Haragan and Bois d’Arc formations and are, moreover, restricted to the Lochkovian and endemic to Laurentia. Additionally, a number of species are widely distributed and confined to the Early Devonian, and three species, Demorhethium lappaceum, Riculasphaera fissa, and Thysanoprobolus polykion – all cosmopolitan – are constrained to the Lochkovian. With increasing knowledge of Early Devonian palynofloras, the apparent degree of provincialism is progressively declining as seemingly endemic taxa are reported from more regions in both hemispheres. The Ross Formation sediments were deposited in a low-energy, offshore, normal marine environment, punctuated by intermittent episodes of shallow-water current and storm deposition.

Keywords:

• acritarchs
• prasinophyte phycomata
• Lower Devonian (Lochkovian)
• Ross Formation
• Tennessee USA

Acknowledgements

Sincere appreciation is extended to Professor Jonathan Aitchison, Head of The University of Queensland’s School of Earth and Environmental Sciences (UQ, SEES), as well as staff members for their assistance during Reed Wicander’s UQ Adjunct Professor appointment and collaboration with Geoffrey Playford. We thank Derek Hoy and Vikram Vakil (UQ, SEES) for drafting Figures 2 (VV), 3 (DH), and 5 (VV). We also thank Dr Rainer Brocke, Senckenberg Research Institute and Natural History Museum, Frankfurt, Germany, and an anonymous reviewer for their critical review of the manuscript and their helpful suggestions for its improvement.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Reed Wicander

REED WICANDER is a professor emeritus of geology at Central Michigan University, USA, where he taught for 39 years. He is currently an adjunct professor in the School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia. He earned his BS degree in geology from San Diego State University in 1969 and his PhD degree from the University of California, Los Angeles, in 1972 under the guidance of Dr Helen Tappan Loeblich and Dr Alfred R. Loeblich, Jr. His palynologic research focuses on Paleozoic acritarchs and prasinophytes, and he has published more than 50 peer-reviewed research papers during his career. He has also published numerous editions of both physical and historical geology textbooks with his long-time faculty colleague, Dr Stewart Monroe.

Geoffrey Playford

GEOFFREY PLAYFORD is a graduate of the Universities of Western Australia (BSc Hons I, DSc) and Cambridge (PhD) and is currently a professor emeritus in the School of Earth and Environmental Sciences, The University of Queensland (UQ). While an honors student at The University of Western Australia (UWA), he was introduced to palynology by the inspirational Dr Basil Balme, then newly appointed to the university. His PhD research at Cambridge – supervised by Dr Norman Hughes – was undertaken during the tenure of a Robert & Maude Gledden Research Fellowship awarded by UWA. Subsequently, during tenure of a National Research Council of Canada Postdoctoral Fellowship, he worked with Dr Peter Hacquebard and Sedley Barss at the Geological Survey of Canada (Ottawa), followed by a lectureship appointment at UQ. During periods of sabbatical leave from UQ, he has conducted collaborative research, notably with the late Dr Francine Martin (Belgium); the late Dr Colin McGregor (Canada); Prof. Reed Wicander and Merrell Miller (USA); the late Prof. Marco Tongiorgi (Italy); Drs Felipe González and Carmen Moreno (Spain); and, in Brazil, with Drs Rodolfo Dino and José Henrique Gonçalves de Melo, at the Petrobras Research Centre in Rio de Janeiro and the State University of Rio de Janeiro (UERJ). He has published extensively on a diverse range of Paleozoic–Cenozoic palynomorphs, with main emphasis on their stratigraphic applications.