A. Achab, C. V. Rubinstein, and R. A. Astini, Chitinozoans and acritarchs from the Ordovician peri-Gondwana volcanic arc of the Famatina System, northwestern Argentina, Review of Palaeobotany and Palynology, vol.139, issue.1-4, pp.129-149, 2006.
DOI : 10.1016/j.revpalbo.2005.07.004

R. Albani, G. Bagnoli, C. Ribecai, and E. Raevskaya, Late Cambrian acritarch Lusatia: Taxonomy, palaeogeography, and biostratigraphic implications, Acta Paleontologica Polonica, vol.52, pp.809-818, 2007.

M. H. Al-ruwaili, New Silurian acritarchs from the sub-surface of northwestern Saudi Arabia Stratigraphic Palynology of the Palaeozoic of Saudi Arabia. GeoArabia, Special Publication 1, Gulf Petrolink, pp.82-91, 2000.

D. I. Benn and D. J. Evans, Glaciers and Glaciation, 1998.

S. Beuf, B. Biju-duval, B. De-charpal, O. Rognon, P. Gariel et al., Les grès du Paléozoïque inférieur au Sahara: Sédimentation et discontinuités, évolution structurale d'un craton, pp.1-464, 1971.

G. Burmann, Diacrodien aus dem unteren Ordovizium, Paläontologische Abhandlungen, issue.2, pp.635-652, 1968.

G. K. Colbath, Organic-walled microphytoplankton from the Eden Shale (Upper Ordovician), Palaeontographica Abteilung B, vol.171, pp.1-38, 1979.

A. Combaz, Un microbios du Trémadocien dans un sondage d'Hassi-Messaoud, Série B, vol.104, pp.1-26, 1967.

F. H. Cramer, Some acritarchs from the San Pedro Formation (Gedinnien) of the Cantabric Mountains in Spain Bulletin de la Société belge de géologie, pp.33-38, 1964.

F. H. Cramer, Microplankton from three Palaeozoic formations in the Province of León, NW Spain, Leidse Geologische Mededelingen, vol.30, pp.253-361, 1964.

F. H. Cramer, Palynologic microfossils of the Middle Silurian Maplewood Shale in New York, pp.61-70, 1968.

F. H. Cramer, Distribution of selected Silurian acritarchs. Revista española de micropaleontología, Numero Extraordinario 1, 1?203, plates I?XXIII, 1970.

F. H. Cramer, M. Díez, and C. R. Del, Late Arenigian (Ordovician) Acritarchs from Cis-Saharan Morocco, Micropaleontology, vol.23, issue.3, pp.339-360, 1977.
DOI : 10.2307/1485220

A. Delabroye and M. Vecoli, The end-Ordovician glaciation and the Hirnantian Stage: A global review and questions about Late Ordovician event stratigraphy, Earth-Science Reviews, vol.98, issue.3-4, pp.269-282, 2010.
DOI : 10.1016/j.earscirev.2009.10.010

A. Delabroye, A. Munnecke, M. Vecoli, P. Copper, N. Tribovillard et al., Phytoplankton dynamics across the Ordovician/Silurian boundary at low palaeolatitudes: Correlations with carbon isotopic and glacial events, Palaeogeography, Palaeoclimatology, Palaeoecology, vol.312, issue.1-2, 2011.
DOI : 10.1016/j.palaeo.2011.09.011

J. Deunff, Sur la présence de microorganismes (Hystrichosphères) dans les schistes ordoviciens du Finistère, Comptes rendus des séances de l'Académie des sciences, pp.321-323, 1951.

J. Deunff, Veryhachium, genre nouveau d'hystrichosphères du Primaire, Compte rendus de la Société géologique de France, pp.305-307, 1954.
DOI : 10.1016/s0016-6995(77)80027-2

J. Deunff, Microorganismes planctoniques du primaire Armoricain. I.-Ordovicien du Veryhac'h (presqu'île de Crozon) Bulletin de la Société géologique et mineralogique de Bretagne, pp.1-41, 1958.

J. Deunff and W. R. Evitt, Tunisphaeridium, a new acritarch genus from the Silurian and Devonian, Geological Sciences, vol.12, pp.1-13, 1968.

M. Deynoux, J. Sougy, and R. Trompette, Lower Palaeozoic rocks of west Africa and the western part of central Africa Lower Palaeozoic of north-western and west?central Africa, pp.337-495, 1985.

K. J. Dorning, Silurian acritarchs from the type Wenlock and Ludlow of Shropshire, England, Review of Palaeobotany and Palynology, vol.34, issue.2, pp.175-203, 1981.
DOI : 10.1016/0034-6667(81)90037-3

C. Downie, Hystrichospheres from the Silurian Wenlock Shale of England, Palaeontology, vol.2, pp.56-71, 1959.

C. Downie, Hystrichospheres' (acritarchs) and spores of the Wenlock Shales (Silurian) of Wenlock, England. Palaeontology, vol.6, pp.625-652, 1963.

P. Dufka and O. Fatka, Chitinozoans and acritarchs from the Ordovician?Silurian boundary of the Prague Basin, Czech Republic. Special Papers in Palaeontology, vol.48, pp.17-28, 1993.

A. Eisenack, Neue Mikrofossilien des baltischen Silurs. III. und Neue Mikrofossilien des b??hmischen Silurs. I, Pal??ontologische Zeitschrift, vol.25, issue.1-2, pp.52-76, 1934.
DOI : 10.1007/BF03041667

A. Eisenack, Hystrichosphaerideen und verwandte Formen im baltischen Silur, Zeitschrift für Geschiebeforschung und Flachlandsgeologie, vol.14, issue.1, pp.1-30, 1938.

A. Eisenack, Hystrichosphären aus dem baltischen Gotlandium, Senckenbergiana Lethaea, vol.34, issue.46, pp.205-211, 1954.

A. Eisenack, Mitteilungen zur Biologie der Hystrichosphären und über neue Arten. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, vol.118, issue.2, pp.207-216, 1963.

A. Eisenack, Mikrofossilien eines Geschiebes der Borkholmer Stufe, baltisches Ordovizium, F 2, Mitteilungen aus dem Geologischen Staatsinstitut in Hamburg, pp.81-94, 1968.

A. Eisenack, F. H. Cramer, M. Díez, and C. R. Del, Katalog der fossilen Dinoflagellaten, Hystrichosphären und verwandten Mikröfossilien, Band III Acritarcha Teil. E. Schweizerbart'sche Verlagsbuchhandlung, vol.1, 1973.

D. J. Evans, E. R. Phillips, J. F. Hiemstra, and C. A. Auton, Subglacial till: Formation, sedimentary characteristics and classification, Earth-Science Reviews, vol.78, issue.1-2, pp.115-176, 2006.
DOI : 10.1016/j.earscirev.2006.04.001
URL : http://nora.nerc.ac.uk/7681/1/SubglacialTill.pdf

W. R. Evitt, A DISCUSSION AND PROPOSALS CONCERNING FOSSIL DINOFLAGELLATES, HYSTRICHOSPHERES, AND ACRITARCHS, II, Proceedings of the National Academy of Sciences, pp.1299-1313, 1963.
DOI : 10.1073/pnas.49.3.298

J. Ghienne, The Late Ordovician glacial record: state of the art, 2011.
URL : https://hal.archives-ouvertes.fr/hal-00749003

J. Ghienne, D. P. Le-heron, J. Moreau, M. Denis, and M. Deynoux, The Late Ordovician glacial sedimentary system of the North Gondwana platform Glacial sedimentary processes and products. International Association of Sedimentologists, pp.295-319, 2007.

D. O. Hemer, Diagnostic palynological fossils from Arabian formations American Institute of Mining and Metallurgical Engineers, Saudi Arabia Section, Second Regional Technical Symposium, Proceedings, pp.311-325, 1968.

P. J. Hill, K. J. Dorning, L. R. Cocks, N. H. Woodcock, R. B. Rickards et al., Appendix 1. Acritarchs The Llandovery Series of the type area, Bulletin of the British MuseumNatural History) Geology Series, vol.38, pp.174-176, 1984.

P. J. Hill and S. G. Molyneux, Biostratigraphy, palynofacies and provincialism of Late Ordovician?Early Silurian acritarchs from northeast Libya, 1988.

M. Jachowicz, Ordovician acritarch assemblages from central and northwestern Saudi Arabia, Review of Palaeobotany and Palynology, vol.89, issue.1-2, pp.19-25, 1995.
DOI : 10.1016/0034-6667(94)00039-M

S. R. Jacobson and A. Achab, Acritarch biostratigraphy of the Dicellograptus complanatus graptolite Zone from the Vaureal Formation (Ashgillian), Anticosti Island, pp.165-198, 1985.

S. Jardiné, A. Combaz, L. Magloire, G. Peniguel, and G. Vachey, Distribution stratigraphique des acritarches dans le pal??ozo??que du sahara alg??rien, Distribution stratigraphique des acritarches dans le Paléozoïque du Sahara algérien, pp.99-129, 1974.
DOI : 10.1016/0034-6667(74)90012-8

N. G. Johnson, Early silurian palynomorphs from the tuscarora formation in central Pennsylvania and their paleobotanical and geological significance, Review of Palaeobotany and Palynology, vol.45, issue.3-4, pp.307-360, 1985.
DOI : 10.1016/0034-6667(85)90006-5

V. V. Kiryanov, Akritarkhi silura Volyno-Podolii, Akademiya Nauk Ukrainskoi SSR, pp.1-116, 1978.

G. Kjellström, Ordovician microplankton (baltisphaerids) from the Grötlingbo Borehole No. 1 in Gotland, Sweden. Avhandlingar och Uppsatser Sveriges Geologiska Undersökning Serie C Nr 655, Årsbok, vol.65, issue.1, pp.1-75, 1971.

L. Hérissé and A. , Characteristics of the acritarch recovery in the early Silurian of Saudi Arabia Stratigraphic Palynology of the Palaeozoic of Saudi Arabia. GeoArabia, Special Publication 1, Gulf Petrolink, pp.57-81, 2000.

L. Hérissé, A. A1-tayyar, H. Van-der-eem, and H. , Stratigraphic and paleogeographical significance of Silurian acritarchs from Saudi Arabia, Review of Palaeobotany and Palynology, vol.89, issue.1-2, pp.49-74, 1995.
DOI : 10.1016/0034-6667(95)00041-U

L. Hérissé, A. Al-ruwaili, M. Miller, M. Vecoli, and M. , Environmental changes reflected by palynomorphs in the early Middle Ordovician Hanadir Member of the Qasim Formation, Saudi Arabia, pp.3-16, 2007.

L. Hérissé, A. Paris, F. Steemans, and P. , Late Ordovician?earliest Silurian palynomorphs from northern Chad and correlation with contemporaneous deposits of southeastern Libya, Bulletin of Geosciences, vol.88, pp.483-504, 2013.

L. Heron, D. P. Craig, and J. , First-order reconstructions of a Late Ordovician Saharan ice sheet, Journal of the Geological Society, vol.165, issue.1, pp.19-29, 2008.
DOI : 10.1144/0016-76492007-002

L. Heron, D. P. Craig, J. Etienne, and J. L. , Ancient glaciations and hydrocarbon accumulations in North Africa and the Middle East, Earth-Science Reviews, vol.93, issue.3-4, pp.47-76, 2009.
DOI : 10.1016/j.earscirev.2009.02.001

T. R. Lister, The acritarchs and chitinozoa from the Wenlock and Ludlow Series of the Ludlow and Millichope areas, Shropshire. Part 1. Monograph of the, pp.1-100, 1970.

A. R. Loeblich and . Jr, Morphology, ultrastructure and distribution of Paleozoic acritarchs, Proceedings of the North American Paleontological Convention, pp.705-788, 1969.

F. Martin, Late Ordovician and Early Silurian acritarchs A global analysis of the Ordovician?Silurian Boundary, Bulletin of the British MuseumNatural History) Geology Series, vol.43, pp.299-309, 1988.

F. Martin, ACRITARCHSA REVIEW, Biological Reviews, vol.121, issue.1, pp.475-538, 1993.
DOI : 10.1016/0301-9268(92)90004-8

F. Martin, Systematic revision of the acritarch Ferromia pellita and its bearing on Lower Ordovician stratigraphy, Review of Palaeobotany and Palynology, vol.93, issue.1-4, pp.23-34, 1996.
DOI : 10.1016/0034-6667(95)00118-2

M. Masiak, T. Podhala?ska, and M. Stempie?-sa?ek, Ordovician?Silurian boundary in the Bardo Syncline, Holy Cross Mountains, Poland ? new data on fossil assemblages and sedimentary succession, Geological Quarterly, vol.47, pp.311-330, 2003.

H. A. Mcclure, Early paleozoic glaciation in Arabia, Palaeogeography, Palaeoclimatology, Palaeoecology, vol.25, issue.4, pp.315-326, 1978.
DOI : 10.1016/0031-0182(78)90047-0

H. A. Mcclure, Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the early palaeozoic of Northwest Arabia, Review of Palaeobotany and Palynology, vol.56, issue.1-2, pp.41-60, 1988.
DOI : 10.1016/0034-6667(88)90073-5

J. Mcneill, F. R. Barrie, W. R. Buck, V. Demoulin, W. Greuter et al., International Code of Nomenclature for algae, fungi, and plants (Melbourne Code), Regnum Vegetabile, vol.154, 2012.

M. Senalp, M. H. Al-ruwaili, and M. A. Miller, New evidence on the stratigraphy of the Ordovician-Silurian boundary in Saudi Arabia. 5 th Middle East Geoscience Conference, pp.298-299, 2002.

J. J. Sepkoski, Patterns of Phanerozoic Extinction: a Perspective from Global Data Bases, Global Events and Event Stratigraphy in the Phanerozoic, 1996.
DOI : 10.1007/978-3-642-79634-0_4

T. Servais, R. Brocke, and O. Fatka, Variability in the Ordovician acritarch Dicrodiacrodium, Palaeontology, vol.39, pp.389-405, 1996.

P. R. Sharland, R. Archer, D. M. Casey, R. B. Davies, S. H. Hall et al., Arabian Plate Sequence Stratigraphy. GeoArabia Special Publication 2, Gulf PetroLink, 2001.

P. M. Sheehan, The Late Ordovician Mass Extinction, Annual Review of Earth and Planetary Sciences, vol.29, issue.1, pp.331-364, 2001.
DOI : 10.1146/annurev.earth.29.1.331

P. K. Strother, Acritarchs Palynology: Principles and Applications, pp.81-106, 1996.

H. Tappan, The Paleobiology of Plant Protists, p.1028, 1980.

H. Tappan, A. R. Loeblich, and . Jr, Surface Sculpture of the Wall in Lower Paleozoic Acritarchs, Micropaleontology, vol.17, issue.4, pp.385-410, 1971.
DOI : 10.2307/1484870

B. V. Timofeev, O novoi gruppe iskopaemykh spor. [On a new group of fossil spores, Ezhegodnik Vsesoyuznogo Paleontologicheskogo Obshchestva, pp.280-284, 1957.

B. V. Timofeev, Drevneishaya flora Pribaltiki i ee stratigraficheskoe znachenie, 1959.

I. Plate, Scale bar = 10 µm for Figs. 1?5; 20 µm for Figs, pp.6-7

. Actinotodissus-sp, 503.1 ft, slide 64089, LPB 13223

. Veryhachium-lairdii-deflandre-ex-loeblich, 488.3 ft, slide 64143, LPB 13221, pp.24-27, 1970.

. Striatotheca-aff, . Monorugulata-yin, and . Leiming, ft, slide 64076, LPB 13229, 1998.

I. Plate, Scale bar = 10 µm for Figs. 1?8; 20 µm for Figs, pp.9-11

. Sol, 3 ft, slide 64143, LPB 13221, pp.0-1

. Pirea-sp, 488.3 ft, slide 64143, LPB 13221

I. Plate, Scale bar = 10 µm for Figs. 1-6, 8?9

. Comasphaeridium-sp, 488.3 ft, slide 64143, LPB 13221

C. Leprotolypa, 535.2 ft, slide 64076, LPB 13229, 1979.

. Comasphaeridium-sp, 528.3 ft, slide 64191, LPB 13227

L. Actipilion, 3 ft, slide 64143, 1970.

. Veryhachium and . Martin, 488.3 ft, slide 64143, LPB 13221, pp.0-4, 1969.

. Veryhachium-sp, 488.3 ft, slide 64143, LPB 13221

. Dictyotidium-sp, 503.1 ft, slide 64089, LPB 13223

. Helosphaeridium-sp, 3 ft, slide 64191

. Falavia-magniretifera-gen, et sp. nov., Holotype, 488.3 ft, slide 64143, LPB 13221

. Falavia-magniretifera-gen, et sp. nov., Paratype, 503.1 ft, slide 64089, LPB 13223

V. Plate, Scale bar = 10 µm for Figs. 1?6; approximately 5.6 µm for Fig

. Oppilatala-sp, 503.1 ft, slide 64089, LPB 13223, pp.0-3

. Oppilatala-sp, 503.1 ft, slide 64089, LPB 13223, Q50/0-3; inset showing details of ornament and striations at base of process

V. Plate, Scale bar = 10 µm for Figs µm for Fig. 1; approximately 5.6 µm for Figs, pp.3-4

J. Dactylofusa, 3 ft, slide 64191, LPB 13227, W49/0; box indicates area of Fig, 1974.

J. Dactylofusa, 3 ft, slide 64143, LPB 13221, S43/3-T43/1; detail of Fig, 1974.

J. Dactylofusa, 3 ft, slide 64143, LPB 13221, S43/3-T43/1; boxes indicate areas of Figs, 1974.

V. Safirotheca, 535.2 ft, slide 64076, LPB 13229, pp.0-1, 1989.

I. Plate, Scale bar = 10 µm for Figs. 1?4, 6; 15 µm for Fig

. Ordovicidium-sp, 535.2 ft, slide 64186, LPB 13229

. Inflatarium-trilobatum-gen, et sp. nov., Holotype, 518.5 ft, slide 64036, LPB 13226