Silurian phytoplankton of the type Ludlow area
by Gary Mullins, Richard Aldridge and David Siveter
Holotype
Baltisphaeridium aff. polytrichium (Valensi, 1947) in Stockmans & Willière 1963, pl. 3, figs 24–25; subsurface Llandovery Series, Belgium [designated by Lister 1970, p. 73].
Diagnosis (Lister 1970, p. 73)
"Vesicle hollow, subspherical to elongate polygonal; vesicle wall unilayered, thin; numerous slender, solid, flexuous processes about 40% of vesicle diameter in length; distally the processes most often taper to a point but occasionally branch. Excystment by cryptosuture."
Description of specimens from the Ludlow type area (after Mullins 2001)
"Vesicle laevigate, spherical to ellipsoidal, extremely thin-walled. A dense arrangement of solid, wiry, flexuous processes, with slightly expanded bases, covers the vesicle surface. Excystment by a large, unornamented rupture."
Dimensions (type material)
Vesicle width = 25.8 x 24.4 µm, Process length = 4.8–8 µm, Diameter of the process bases = 0.3–1 µm.
Dimensions (in the type Ludlow area)
Vesicle width = 22–37 µm, Process length = 8–14 µm, Process number > 35.
Occurrence in the type Ludlow area
Most common over the Much Wenlock Limestone–Lower Elton formation boundary (Pitch Coppice Quarry & Goggin Road) with a single occurrence in the Middle Elton Formation (Goggin Road).
Reported occurrence elsewhere
Upper Llandovery Series–Emsian Stage, Belgium (Stockmans & Willière 1963; Martin 1966, 1969; Vanguestaine 1979); Formigoso, San Pedro and Furada formations, Llandovery Series–lower Gedinnian Stage, Spain (Cramer & Díez 1968, Cramer 1970a); subsurface middle–upper Silurian, Libya and Saudi Arabia (Cramer 1970a); Red Mountain, Ross Brook, Rose Hill, Rochester and Power Glen formations, Neahga Formation, Crab Orchard Group, Maplewood Shale, Plum Creek Clay, St. Clair Limestone, Illion Shale and Medina Group, Llandovery–lower Ludlow series, USA; Power Glen and Neahga formations, Llandovery–Wenlock series, Nova Scotia and Ontario; Florida borehole material (Cramer 1968, 1969a, 1969b, 1970a & b; Loeblich 1970; Cramer & Díez 1972; Thusu 1973a, 1973b; Miller & Eames 1982); Llandovery–Prídolí series, Welsh Borderland (Lister 1970, Lister & Downie 1974, Hill 1974, Hill & Dorning 1984); Silurian, Siberia (Sheshegova 1984); lower Silurian, Norway (Smelror 1987); Slite Group–Sundre Formation, Wenlock–?Prídolí series, Gotland (Le Hérissé 1989).
Reported stratigraphical range (worldwide)
Llandovery Series (Silurian) to the Emsian Stage (Devonian).
References
CRAMER, F. H. 1968. Considérations paléogéographiques à propos d’une association de microplanctontes de la série gothlandienne de Birmingham (Alabama, USA.). Bulletin de la Société géologique de France, 7e sér., 10, 126–131.
CRAMER, F. H. 1969a. Possible implications for Silurian paleogeography from phytoplancton assemblages of the Rose Hill and Tuscarora formations of Pennsylvania. Journal of Paleontology, 43, (2), 485–91, pl. 1.
CRAMER, F. H. 1969b. Consideraciones sobre la palinología y las paleolatitudes silúricas a proposito del microplancton silúrico de las Montañas Cantábricas del Noroeste de España. Comunicacoes dos Servicos geologicos de Portugal, 53, 67–94, pls 1–11.
CRAMER, F. H. 1970a. Distribution of selected Silurian acritarchs. An account of the palynostratigraphy and paleogeography of selected Silurian acritarch taxa. Revista Española de Micropaleontologia, numero extraordinerio, pp. 203, pls 1–23.
CRAMER, F. H. 1970b. Acritarchs and chitinozoans from the Silurian Ross Brook Formation, Nova Scotia. Journal of Geology, 78, 745–749.
CRAMER, F. H. & DÍEZ, M. del C. R. 1968. Consideraciones taxonómicas sobre las acritarcas del Silúrico Medio y Superior del Norte de España. Instituto Geológico y Minero de España, Boletín, 79, (6), 541–574, pls 1–21.
CRAMER, F. H. & DÍEZ, M. del C. R. 1972. North American Silurian palynofacies and their spatial arrangement: Acritarchs. Palaeontographica, Abt. B, 138, (5–6), 107–180, pls 31–36.
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HILL, P. J. 1974. Stratigraphic palynology of acritarchs from the type area of the Llandovery and the Welsh Borderland. Review of Palaeobotany and Palynology, 18, (1–2), 11–23.
HILL, P. J. & DORNING, K, J. 1984. The Llandovery Series of the type area. Appendix I. Acritarchs. In: COCKS, L. R. M., WOODCOCK, N. H., RICKARDS, R. B., TEMPLE, J. T. & LANE, P. D. The Llandovery Series of the type area. Bulletin of the British Museum of Natural History (Geology), 38, (3), 174–176.
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LISTER, T. R. & DOWNIE, C. 1974. The stratigraphic distribution of the acritarchs in the Ludlow succession at Ludlow. Review of Palaeobotany and Palynology, 18, 25–27.
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VALENSI, L. 1947. Note preliminaire à une étude des microfossiles des silex jurassiques de la région de Poitiers. Comptes rendu des séances de l'Académie des sciences, Paris, 225, 816–818.
VANGUESTAINE, M. 1979. Remaniements d'Acritarches dans le siegenien et l'Emsien (Devonien inferiur) du Synclinorium de Dinant (Belgique). Annales de la Société Géologique de Belgique, 101, 243–267, pls 1–4. [Cover date 1978, Issue date 1979].
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