Ostracods of the Cenomanian-Turonian transition in the Ksour and Amour Mountains (Saharan Atlas, Algeria): systematic and palaeobiogeographic implications

Introduction

The Cenomanian-Turonian transition was marked by palaeoceanographic and palaeoclimatic perturbations related to long-lasting carbon isotope anomalies and to an oceanic anoxic event (OAE2; Jenkyns, 1980Jenkyns, H.C. (1980). Cretaceous anoxic events: from continents to oceans. Journal Geological Society London, 137: 171-188. https://doi.org/10.1144/gsjgs.137.2.0171 , 1997Jenkyns, H.C. (1997). Mesozoic anoxic events and paleoclimate. Zentralblatt für Geologie und Paläontologie, 1: 943-949.; Schlanger et al., 1987Schlanger, S.O.; Arthur, M.A.; Jenkyns, H.C. & Scholle, P.A. (1987). The Cenomanian- Turonian oceanic anoxic event, I. Stratigraphy and distribution of organic-rich beds and the marine δ13C excursion. Geologival Society Special Publication, 26: 371-399. https://doi.org/10.1144/GSL.SP.1987.026.01.24 ; Jarvis et al., 1988Jarvis, I.; Carson, G.A.; Cooper, M.K.E.; Hart, M.B.; Leary, P.N.; Tocher, B.A.; Horne, D. & Rosenfeld, A. (1988). Microfossil assemblages and the Cenomanian-Turonian (late Cretaceous) oceanic anoxic event. Cretaceous Research, 9: 3-103. https://doi.org/10.1016/0195-6671(88)90003-1 ; Robaszynski, 1989Robaszynski, F. (1989). L’événement à l’échelle globale pendant la partie moyenne du Crétacé. Geobios Mémoire Spécial, 11: 311-319. https://doi.org/10.1016/S0016-6995(89)80067-1 ; Kaiho & Hasegawa, 1994Kaiho, K. & Hasegawa, T. (1994). End-Cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the northwestern Pacific Ocean. Palaeogeography, Palaeoclimatology, Palaeoecology, 111: 29-43. https://doi.org/10.1016/0031-0182(94)90346-8 ; Erbacher & Thurow, 1997Erbacher, J. & Thurow, J. (1997). Influence of oceanic anoxic events on the evolution of mid Cretaceous radiolaria in the North Atlantic and western Tethys. Marine Micropaleontology, 30: 139-158. https://doi.org/10.1016/S0377-8398(96)00023-0 ; Huber et al., 2002Huber, B.T.; Norris, R.D. & McLeod, K.G. (2002). Deep-sea paleotemperature record of extreme warmth during the Cretaceous. Geology, 30: 123-126. https://doi.org/10.1130/0091-7613(2002)030<0123:DSPROE>2.0.CO;2 ; Friedrich et al., 2006Friedrich, O.; Erbacher, J. & Mutterlose, J. (2006). Paleoenvironmental changes across the Cenomanian/Turonian Boundary Event (Oceanic Anoxic Event 2) as indicated by benthic foraminifera from the Demerara Rise (ODP Leg 207). Revue de Micropaléontologie, 49: 121-139. https://doi.org/10.1016/j.revmic.2006.04.003 ; Turgeon & Creaser, 2008Turgeon, S.C. & Creaser, R.A. (2008). Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode. Nature, 454: 323-326. https://doi.org/10.1038/nature07076 ; Voigt et al., 2008Voigt, S.; Erbacher, J.; Mutterlose, J.; Weiss, W.; Westerhold, T.; Wiese, F.; Wilmsen, M. & Wonik, T. (2008). The Cenomanian-Turonian of the Wunstorf section (North Germany): global stratigraphic reference section and new orbital time scale for Oceanic Anoxic Event 2. Newsletters on Stratigraphy, 43: 65-89. https://doi.org/10.1127/0078-0421/2008/0043-0065 ; Gebhardt et al., 2010Gebhardt, H.; Friedrich, O.; Schenk, B.; Fox, L.; Hart, M. & Wagreich, M. (2010). Paleoceanographic changes at the northern Tethyan margin during the Cenomanian-Turonian Oceanic Anoxic Event (OAE-2). Marine Micropaleontology, 77: 25-45. https://doi.org/10.1016/j.marmicro.2010.07.002 ; Monteiro et al., 2012Monteiro, F.M.; Pancost, R.D.; Ridwell, A. & Donnadieu, Y. (2012). Nutrients as the dominant control on the spread of anoxia and euxinia across the Cenomanian-Turonian oceanic anoxic event (OAE2): model-data comparison. Paleoceanography, 27 (4): PA4209. https://doi.org/10.1029/2012PA002351 ; Erba et al., 2013Erba, E.; Bottini, C. & Faucher, G. (2013). Cretaceous large igneous provinces: the effects of submarine volcanism on calcareous nannoplankton. Mineralogical Magazine, 77: 1044.; Elderbak et al., 2014Elderbak, K.; Leckie, R.M. & Tibert, N.E. (2014). Paleoenvironmental and paleoceanographic changes across the Cenomanian-Turonian Boundary Event (Oceanic Anoxic Event 2) as indicated by foraminiferal assemblages from the eastern margin of the Cretaceous Western Interior Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 413: 29-48. https://doi.org/10.1016/j.palaeo.2014.07.002 ; Reolid et al., 2016Reolid, M.; Sánchez-Quiñónez, C.A.; Alegret, L. & Molina, E. (2016). The biotic crisis across the Oceanic Anoxic Event 2: Palaeoenvironmental inferences based on foraminifera and geochemical proxies from the South Iberian Palaeomargin. Cretaceous Research, 60: 1-27. https://doi.org/10.1016/j.cretres.2015.10.011 ).

In North Africa-Middle East, these both bioevent and isotopic event have widely been studied in Morocco (e.g. Gebhardt et al., 2004Gebhardt, H.; Kuhnt W. & Holbourn, A. (2004). Foraminiferal response to sea level change, organic flux and oxygen deficiency in the Cenomanian of the Tarfaya Basin, southern Morocco. Marine Micropaleontology, 53: 133-157. https://doi.org/10.1016/j.marmicro.2004.05.007 , 2010Gebhardt, H.; Friedrich, O.; Schenk, B.; Fox, L.; Hart, M. & Wagreich, M. (2010). Paleoceanographic changes at the northern Tethyan margin during the Cenomanian-Turonian Oceanic Anoxic Event (OAE-2). Marine Micropaleontology, 77: 25-45. https://doi.org/10.1016/j.marmicro.2010.07.002 ; Ettachfini & Andreu, 2004Ettachfini, M. & Andreu, B. (2004). Le Cénomanien et le Turonien de la Plate-forme Préafricaine du Maroc. Cretaceous Research, 25: 277-302. https://doi.org/10.1016/j.cretres.2004.01.001 ; Ettachfini et al., 2005Ettachfini, M.; Souhel, A.; Andreu, B. & Caron, M. (2005). La limite Cénomanien -Tutronien dans le Haut Atlas central, Maroc. Geobios, 38: 57-68. https://doi.org/10.1016/j.geobios.2003.07.003 ; Ettachfini, 2006Ettachfini, M. (2006). La transgression au passage du Cénomanien au Turonien sur le domaine atlasique marocain. Stratigraphie intégrée et relation avec l’évenement océanique global. PhD Thesis, University Chouaïb Doukkali, 299 p.; Jati et al., 2010Jati, M.; Grosheny, D.; Ferry, S.; Masrour, M.; Aoutem, M.; Içame, N.; Gauthier-Lafaye, F. & Desmares, D. (2010). The Cenomanian-Turonian boundary event onthe Moroccan Atlantic margin (Agadir basin): Stable isotope and sequence stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 296: 151-164. https://doi.org/10.1016/j.palaeo.2010.07.002 ; Lézin et al., 2012Lézin, C.; Andreu, B.; Ettachfini, M.; Walleez, M.-J.; Lebedel, V. & Meister, C. (2012). The upper Cenomanian-lower Turonian of the Preafrican Trough, Morocco. Sedimentary Geology, 245-246: 1-16. https://doi.org/10.1016/j.sedgeo.2011.12.003 ; Prauss, 2012Prauss, M.L. (2012). The Cenomanian/Turonian Boundary Event (CTBE) at Tarfaya, Morocco, northwest Africa: Eccentricity controlled water column stratification as major factor for total organic carbon (TOC) accumulation: Evidence from marine palynology. Cretaceous Research, 37: 246-260. https://doi.org/10.1016/j.cretres.2012.04.007 ; Andreu et al., 2013Andreu, B.; Lebedel, V.; Wallez, M.J.; Lézin, C. & Ettachfini, M. (2013). The upper Cenomanian lower Turonian carbonate platform of the Preafrican Trough, Morocco: Biostratigraphic, paleoecological and paleobiogeographical distribution of ostracods. Cretaceous Research, 45: 216-246. https://doi.org/10.1016/j.cretres.2013.04.005 ; Aquit et al., 2013Aquit, M.; Kuhnt, W.; Holbourn, A.; Chellai, E.H.; Stattegger, K.; Kluth, O. & Jabour, H. (2013). Late Cretaceous palleoenvironmental evolution of the Tarfaya Atlantic coastal Basin, SW Morocco. Cretaceous Research, 45: 288-305. https://doi.org/10.1016/j.cretres.2013.05.004 ; Wang et al., 2021Wang, J.P.; Bulot, L.G.; Taylor, K.G. & Redfern, J. (2021). Controls and timing of Cenomanian-Turonian organic enrichment and relationship to the OAE2 event in Morocco, North Africa. Marine and Petroleum Geology, 128, art. 105013. https://doi.org/10.1016/j.marpetgeo.2021.105013 ), in Algeria (e.g. Naili et al., 1995Naili, H.; Belhadj, Z.; Robaszynski, F. & Caron, M. (1995). Présence de roches mère à faciès Bahloul vers la limite Cénomanien-Turonien dans la région de Tébessa (Algérie orientale). Notes du Service Géologique Tunisie, 61: 19-32.; Harket & Delfaud, 2000Harket, M. & Delfaud, J. (2000). Genèse des séquences sédimentaires du Crétacé supérieur des Aurès (Algérie). Rôle de l’eustatisme, de la tectonique, de la subsidence : une mise au point. Comptes Rendus Academie Sciences de Paris, 330: 785-792. https://doi.org/10.1016/S1251-8050(00)00229-9 , Grosheny et al., 2008Grosheny, D.; Chikhi-Aouimeur, F.; Ferry, S.; Benkherouf-Kechid, F.; Jati, M.; Atrops, F. & Redjimi-Bourouiba, W. (2008). The Upper Cenomanian-Turonian (Upper Cretaceous) of the Saharan Atlas (Algeria). Bulletin Société Géologique France, 179: 593-603. https://doi.org/10.2113/gssgfbull.179.6.593 , 2013Grosheny, D.; Ferry, S.; Jati, M.; Ouaja, M.; Bensalah, M.; Atrops, F.; Chikhi-Aouimeur, F.; Benkherouf-Kechid, F.; Negra, H. & Aït Salem, H. (2013). The Cenomanian-Turonian boundary on the Saharan Platform (Tunisia and Algeria). Cretaceous Research, 42: 66-84. https://doi.org/10.1016/j.cretres.2013.01.004 ; Ruault-Djerrab et al., 2012Ruault-Djerrab, M.; Ferré, B.; Kechid-Benkherouf, F. & Djerrab, A. (2012). Etude micropaléontologique du Cénomano-Turonien dans la région de Tébessa (NE Algérie): implications paléoenvironnementales et recherche de l’empreinte de l’OAE2. Revue Paléobiologie, 31: 127-144., 2014Ruault-Djerrab, M.; Kechid-Benkherouf, F. & Djerrab, A. (2014). Données paléoenvironnementales sur le Vraconnien/Cénomanien de la région de Tébessa (Atlas Saharien, nord-est Algérie). Caractérisation de l’OAE2. Annales de Paléontologie, 100: 343-359. https://doi.org/10.1016/j.annpal.2014.03.002 , Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ), in Tunisia (e.g. Accarie et al., 2000Accarie, H.; Robaszynski, F.; Amédro, F.; Caron, M. & Zagrarni, M.F. (2000). Stratigraphie événementielle au passage Cénomanien-Turonien dans le secteur occidental de la plate-forme de Tunisie centrale (Formation Bahloul, région de Kalaat Senan). Annales des Mines et de la Géologie Tunis, 40: 63-80.; Amédro et al., 2005Amédro, A.; Accarie, H. & Robaszynski, F. (2005). Position de la limite Cénomanien-Turonien dans la Formation Bahloul de Tunisie centrale: apports intégrés des ammonites et des isotopes du carbone (δ¹³C). Eclogae Geologicae Helvetiae, 98: 151-167. https://doi.org/10.1007/s00015-005-1158-5 ; Caron et al., 2006Caron, M.; Dall’ Agnolo, S.; Accarie, H.; Barrera, E.; Kauffman, E.G.; Amédro, F. & Robaszynski, F. (2006). High-resolution stratigraphy of the Cenomanian-Turonian boundary interval at Pueblo (USA) and Wadi Bahloul (Tunisia): stable isotope and bio-events correlation. Geobios, 39: 171-200. https://doi.org/10.1016/j.geobios.2004.11.004 ; Zagrarni et al., 2008Zagrarni, M.F.; Negra, M.H. & Amine Hanini, A. (2008). Cenomanian-Turonian facies and sequence stratigraphy, Bahloul Formation, Tunisia. Sedimentary Geology, 204: 18-35. https://doi.org/10.1016/j.sedgeo.2007.12.007 ; Robaszynski et al., 2010Robaszynski, F.; Zagrararni, M.F.; Caron, M. & Amedro, F. (2010). The global bio-event at the Cenomanian-Turonien transition in the reduced Bahloul Formation of Bou Ghanem (central Tunisia). Cretaceous Research, 31: 1-15. https://doi.org/10.1016/j.cretres.2009.07.002 ; Negra et al., 2011Negra, M.H.; Zagrarni, M.F.; Hanini, A. & Strasser, A. (2011). The filament event near the Cenomanian-Turonian boundary in Tunisia: filament origin and environmental signification. Bulletin de la Société Géologique de France, 182: 507-519. https://doi.org/10.2113/gssgfbull.182.6.507 , Grosheny et al., 2013Grosheny, D.; Ferry, S.; Jati, M.; Ouaja, M.; Bensalah, M.; Atrops, F.; Chikhi-Aouimeur, F.; Benkherouf-Kechid, F.; Negra, H. & Aït Salem, H. (2013). The Cenomanian-Turonian boundary on the Saharan Platform (Tunisia and Algeria). Cretaceous Research, 42: 66-84. https://doi.org/10.1016/j.cretres.2013.01.004 ; Zaghbib-Turki & Soua, 2013Zaghbib-Turki, D. & Soua., M. (2013). High resolution biostratigraphy of the Cenomanian-Turonian interval (OAE2) based on planktonic foraminiferal bioevents in North-Central Tunisia. Journal of African Earth Sciences, 78: 97-108. https://doi.org/10.1016/j.jafrearsci.2012.09.014 ; Reolid et al., 2015Reolid, M.; Sánchez-Quiñónez, C.A.; Alegret, L. & Molina, E. (2015). Palaeoenvironmental turnover across the Cenomanian-Turonian transition in Oued Bahloul, Tunisia: foraminifera and geochemical proxies. Palaeogeography, Palaeoclimatology, Palaeoecology, 417: 491-510. https://doi.org/10.1016/j.palaeo.2014.10.011 ; Aguado et al., 2016Aguado, R.; Reolid, M. & Molina, E. (2016). Response of calcareous nannoplankton to the Late Cretaceous Oceanic Anoxic Event 2 at Oued Bahloul (central Tunisia). Palaeogeography, Palaeoclimatology, Palaeoecology, 459: 289-305. https://doi.org/10.1016/j.palaeo.2016.07.016 ; Touir et al., 2017Touir, J.; Mechi, C. & Ali, H.H. (2017). Changes in carbonate sedimentation and faunal assemblages in the Tunisian carbonate platform around the Cenomanian-Turonian boundary. Journal of African Earth Sciences, 129: 527-541. https://doi.org/10.1016/j.jafrearsci.2017.01.025 ), in Egypt (e.g. Lüning et al., 1998Lüning, S.; Marzouk, A.M.; Morsi, A.M. & Kuss, J. (1998). Sequence stratigraphy of the Upper Cretaceous of central-east Sinai, Egypt. Cretaceous Research, 19: 153-196. https://doi.org/10.1006/cres.1997.0104 ; Aly et al., 2001Aly, M.F. & Abdel-Gawad, G.I. (2001). Upper Cenomaniane Lower Turonian ammonites from north and central Sinai, Egypt. El-Minia Science Bulletin, 13: 17-60.; Bauer et al., 2002Bauer, J.; Kuss, J. & Steuber, T. (2002). Platform environments, microfacies and systems tracts of the Upper Cenomanian - Lower Santonian of Sinai, Egypt. 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The OAE2 has been associated to climatic and palaeoceanographic changes including a sea-level transgression (Hallam, 1992Hallam, A. (1992). Phanerozoic sea level changes. Columbia Press, New York, 266 p.), a perturbation of the carbon cycle (e.g. Kuypers et al., 2002Kuypers, M.M.M.; Pancost, R.D.; Nijenhuis, I.A. & Sinninghe-Damste, J.S. (2002). Enhanced productivity led to increased organic carbon burial in the euxinic North Atlantic Basin during the late Cenomanian oceanic anoxic event. Paleoceanography, 17: 1051. https://doi.org/10.1029/2000PA000569 ; Erba, 2004Erba, E. (2004). Calcareous nannofossils and Mesozoic oceanic anoxic events. Marine Micropaleontology, 52: 85-106. https://doi.org/10.1016/j.marmicro.2004.04.007 ; Pogge von Strandmann et al., 2013Pogge von Strandmann, P.A.E.; Jenkyns, H.C. & Woodfine, R.G. (2013). Lithium isotope evidence for enhanced weathering during Oceanic Anoxic Event 2. Nature Geosciences, 6: 668-672 https://doi.org/10.1038/ngeo1875 ), a greenhouse warming (e.g. Huber et al., 2002Huber, B.T.; Norris, R.D. & McLeod, K.G. (2002). Deep-sea paleotemperature record of extreme warmth during the Cretaceous. Geology, 30: 123-126. https://doi.org/10.1130/0091-7613(2002)030<0123:DSPROE>2.0.CO;2 ; Norris et al., 2002Norris, R.D.; Bice, K.L.; Magno, E.A. & Wilson, P.A. (2002). Jiggling the tropical thermostat in the Cretaceous hothouse. Geology, 30: 299-302. https://doi.org/10.1130/0091-7613(2002)030<0299:JTTTIT>2.0.CO;2 ; Pogge von Strandmann et al., 2013Pogge von Strandmann, P.A.E.; Jenkyns, H.C. & Woodfine, R.G. (2013). Lithium isotope evidence for enhanced weathering during Oceanic Anoxic Event 2. Nature Geosciences, 6: 668-672 https://doi.org/10.1038/ngeo1875 ), and a probable massive magmatic episode (e.g. Kuroda et al., 2007Kuroda, J.; Ogawa, N.O.; Tanimizu, M.; Coffin, M.T.; Tokuyama, H.; Kitazato, H. & Ohkouchi, N. (2007). Contemporaneous massive subaerial volcanism and late Cretaceous Oceanic Anoxic Event 2. Earth Planetary Science Letters, 256: 211-223. https://doi.org/10.1016/j.epsl.2007.01.027 ; Turgeon & Creaser, 2008Turgeon, S.C. & Creaser, R.A. (2008). Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode. Nature, 454: 323-326. https://doi.org/10.1038/nature07076 ; Erba et al., 2013Erba, E.; Bottini, C. & Faucher, G. (2013). Cretaceous large igneous provinces: the effects of submarine volcanism on calcareous nannoplankton. Mineralogical Magazine, 77: 1044.). The impact of this event on fossil assemblages have been focused on different groups of organisms such as cephalopods (e.g. Monnet, 2009Monnet, C. (2009). The Cenomanian-Turonian boundary mass extinction (Late Cretaceous): New insights from ammonoid biodiversity patterns of Europe, Tunisia and the Western Interior (North America). Palaeogeography, Palaeoclimatology, Palaeoecology, 282: 88-104. https://doi.org/10.1016/j.palaeo.2009.08.014 ; Nagm et al., 2017Nagm, E.; Farouk, S. & Ahmed, F. (2017). The Cenomanian-Turonian boundary in Jordan: Ammonite biostratigraphy and faunal turnover. Geobios, 50: 37-47. https://doi.org/10.1016/j.geobios.2016.11.002 ; Kostak et al., 2018Kostak, M.; Cech, S.; Ulicny, D.; Sklenar, J.; Ekrt, B. & Mazuch, M. (2018). Ammonites, inoceramids and stable carbon isotopes of the Cenomanian-Turonian OAE2 interval in central Europe: Pecinov quarry, Bohemian Cretaceous Basin (Czech Republic). Cretaceous Research, 87: 150-173. https://doi.org/10.1016/j.cretres.2017.04.013 ), bivalves (e.g. Takahashi, 2005Takahashi, A. (2005). Responses of inoceramid bivalves to environmental disturbances across the Cenomanian/Turonian boundary in the Yezo forearc basin, Hokkaido, Japan. Cretaceous Research, 26: 567-580. https://doi.org/10.1016/j.cretres.2005.02.006 ; Negra et al., 2011Negra, M.H.; Zagrarni, M.F.; Hanini, A. & Strasser, A. (2011). The filament event near the Cenomanian-Turonian boundary in Tunisia: filament origin and environmental signification. Bulletin de la Société Géologique de France, 182: 507-519. https://doi.org/10.2113/gssgfbull.182.6.507 ; Posenato et al., 2020Posenato, R.; Frijia, G.; Morsilli, M.; Moro, A.; Del Viscio, G. & Mezfa, A. (2020). Paleoecology and proliferation of the bivalve Chondrodonta joannae (Choffat) in the upper Cenomanian (Upper Cretaceous) Adriatic Carbonate Platform of Istria (Croatia). Palaeogeography, Palaeoclimatology, Palaeoecology, 548: 109703. https://doi.org/10.1016/j.palaeo.2020.109703 ), foraminifera (e.g. Gebhardt et al., 2004Gebhardt, H.; Kuhnt W. & Holbourn, A. (2004). Foraminiferal response to sea level change, organic flux and oxygen deficiency in the Cenomanian of the Tarfaya Basin, southern Morocco. Marine Micropaleontology, 53: 133-157. https://doi.org/10.1016/j.marmicro.2004.05.007 ; Caron et al., 2006Caron, M.; Dall’ Agnolo, S.; Accarie, H.; Barrera, E.; Kauffman, E.G.; Amédro, F. & Robaszynski, F. (2006). High-resolution stratigraphy of the Cenomanian-Turonian boundary interval at Pueblo (USA) and Wadi Bahloul (Tunisia): stable isotope and bio-events correlation. Geobios, 39: 171-200. https://doi.org/10.1016/j.geobios.2004.11.004 ; Friedrich et al., 2006Friedrich, O.; Erbacher, J. & Mutterlose, J. (2006). Paleoenvironmental changes across the Cenomanian/Turonian Boundary Event (Oceanic Anoxic Event 2) as indicated by benthic foraminifera from the Demerara Rise (ODP Leg 207). Revue de Micropaléontologie, 49: 121-139. https://doi.org/10.1016/j.revmic.2006.04.003 ; Ismail et al., 2009Ismail, A.A.; Hussein-Kamel, Y.F.; Boukhary, M. & Ghandour, A.A. (2009). Late Cenomanian-Early Turonian foraminifera from Eastern Desert, Egypt. Micropaleontology, 55: 396-412. https://doi.org/10.47894/mpal.55.4.05 ; Elderbak et al., 2014Elderbak, K.; Leckie, R.M. & Tibert, N.E. (2014). Paleoenvironmental and paleoceanographic changes across the Cenomanian-Turonian Boundary Event (Oceanic Anoxic Event 2) as indicated by foraminiferal assemblages from the eastern margin of the Cretaceous Western Interior Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 413: 29-48. https://doi.org/10.1016/j.palaeo.2014.07.002 ; Reolid et al., 2015Reolid, M.; Sánchez-Quiñónez, C.A.; Alegret, L. & Molina, E. (2015). Palaeoenvironmental turnover across the Cenomanian-Turonian transition in Oued Bahloul, Tunisia: foraminifera and geochemical proxies. Palaeogeography, Palaeoclimatology, Palaeoecology, 417: 491-510. https://doi.org/10.1016/j.palaeo.2014.10.011 , 2016Reolid, M.; Sánchez-Quiñónez, C.A.; Alegret, L. & Molina, E. (2016). The biotic crisis across the Oceanic Anoxic Event 2: Palaeoenvironmental inferences based on foraminifera and geochemical proxies from the South Iberian Palaeomargin. Cretaceous Research, 60: 1-27. https://doi.org/10.1016/j.cretres.2015.10.011 ; Bryant & Belanger, 2023Bryant, R. & Belanger, C.L. (2023). Spatian heterogeneity in benthic foraminiferal assemblages tracks regional impacts of paleoenvironmental change across Cretaceous OAE2. Paleobiology, 1-23, https://doi.org/10.1017/pab.2022.47 ) and nannoplankton (e.g. Wan et al., 2003Wan, X., Wignall, P.B. & Zhao, W. (2003). The Cenomanian-Turonian extinction and oceanic anoxic event: evidence from southern Tibet. Palaeogeography, Palaeoclimatology, Palaeoecology, 199: 283-298. https://doi.org/10.1016/S0031-0182(03)00543-1 ; Hardas & Mutterlose, 2007Hardas, P. & Mutterlose, J. (2007). Calcareous nannofossil assemblages of Oceanic Anoxic Event 2 in the equatorial Atlantic: Evidence of a eutrophication event. Marine Micropaleontology, 66: 52-69. https://doi.org/10.1016/j.marmicro.2007.07.007 ; Erba et al., 2013Erba, E.; Bottini, C. & Faucher, G. (2013). Cretaceous large igneous provinces: the effects of submarine volcanism on calcareous nannoplankton. Mineralogical Magazine, 77: 1044.; Aguado et al., 2016Aguado, R.; Reolid, M. & Molina, E. (2016). Response of calcareous nannoplankton to the Late Cretaceous Oceanic Anoxic Event 2 at Oued Bahloul (central Tunisia). Palaeogeography, Palaeoclimatology, Palaeoecology, 459: 289-305. https://doi.org/10.1016/j.palaeo.2016.07.016 ; Farouk et al., 2022Farouk, S.; Jain, S.; Shabaan, M.; Ahmad, F.; Salhi, I.; Elamri, Z.; El-Kahtany, K.; Zaky, A.S. & Abu Sham, A. (2022). High resolution upper Cenomanian to Turonian paleoenvironmental changes: Inferences from calcareous nannofossils at the Oued Ettalla section (Central Tunisia). Marine Micropaleontology, 175: 102151. https://doi.org/10.1016/j.marmicro.2022.102151 ). However, recent studies on ostracod assemblages from Cenomanian-Turonian transition are comparatively scarcer (Horne et al., 2011Horne, D.J.; Brandao, S.N. & Slipper, I.J. (2011). The Platycopid signal deciphered: responses of ostracod taxa to environmental change during the Cenomanian-Turonian boundary event (Late cretaceous) in SE England. Palaeogeography, Palaeoclimatology, Palaeoecology, 308: 304-312. https://doi.org/10.1016/j.palaeo.2011.05.034 ; Andreu et al., 2013Andreu, B.; Lebedel, V.; Wallez, M.J.; Lézin, C. & Ettachfini, M. (2013). The upper Cenomanian lower Turonian carbonate platform of the Preafrican Trough, Morocco: Biostratigraphic, paleoecological and paleobiogeographical distribution of ostracods. Cretaceous Research, 45: 216-246. https://doi.org/10.1016/j.cretres.2013.04.005 ; Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ; Khalil, 2020Khalil, M.M. (2020). Biostratigraphy and paleobiogeographic implications of the Cenomanian-Early Turonian ostracods of Egypt. Annales de Paléontologie, 106: 102408. https://doi.org/10.1016/j.annpal.2020.102408 ; Shahin & Elbaz, 2013bShahin, A. & Elbaz, S.M. (2013b). Cenomanian-Early Turonian Ostracoda of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 ; Mebarki et al., 2016Mebarki, K.; Sauvagnat, J.; Benyoucef, M.; Zaoui, D.; Benachour, H-B.; Mohammed, A.; Mahboubi, M. & Bensalah, M. (2016). Cenomanian-Turonian ostracodes fron the Western Saharan Atlas and the Guir Basin (SE Algeria): systematic, biostratigraphy and paleobiogeography. Revue de Paleobiologie, 35: 249-277.; Tchenar et al., 2020Tchenar, S.; Ferré, B.; Adaci, M.; Zaoui, D.; Benyoucef, M.; Bensalah, M. & Kentri, T. (2020). Incidences de l’Évènement Anoxique Océanique II sur l’évolution des ostracodes des dépôts cénomano-turoniens du bassin du Tinrhert (SE Algérie). Carnets de Géologie, 20 (08): 145. https://doi.org/10.4267/2042/70792 ).

The purpose of this present work is to study the ostracods of the Cenomanian-Turonian transition in the Ksour and Amour Mountains (Saharan Atlas, Algeria). It is a systematic and palaeobiogeographic study that allowed us to highlight a global biological event corresponding to the explosion of smooth-shaped ostracods, represented mainly by the Family Cytherellidae (Barroso-Barcenilla et al., 2011Barroso-Barcenilla, F.; Pascual, A.; Peyrot, D. & Rodríguez-Lazaro, J. (2011). Integrated biostratigraphy and chemostratigraphy of the upper Cenomanian and lower Turonian succession in Puentedey, Iberian Trough, Spain. Proceedings of Geologists’ Association, 122: 67-81. https://doi.org/10.1016/j.pgeola.2010.11.002 ; Shahin & Elbaz, 2013bShahin, A. & Elbaz, S.M. (2013b). Cenomanian-Early Turonian Ostracoda of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 ; Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ). The biogeographic analysis is carried out to test for the presence of potential similarities between the ostracod assemblages of the Atlasic Basin and other basins of the northern palaeomargin of Gondwana outcropping in the North Africa and the Middle East (Fig. 1).

Geological Setting

The Ksour Mountains (Western Saharan Atlas) and Amour Mountains (Central Saharan Atlas) are part of a vast mountainous area, the Atlas Cordillera, stretching for almost 2000 km from Agadir in Morocco to Gabes in Tunisia. It includes from west to east: the Moroccan High Atlas, the Saharan Atlas, the Aurès and finally the Tunisian Atlas (Fig. 2A). This cordillera presents a general NE-SW orientation. In Algeria, the Saharan Atlas is represented by a structural alignment extending over more than 1000 km, from the Algerian-Moroccan borders in the west to the western limit of the Aurès Mountains in the east. It is composed of the Ksour Mountains, Amour Mountains and the Ouled Naïl Mountains (Fig. 2B). The Zibane and the Aurès follow these clusters. A total of three sections have been studied from Ksour Mountains (Rhoundjaïa, M’Daouer and Chellala Dahrania) and other from Amour Mountains (El Kohol).

Material and Methods

The chronological interval studied in the different sections, the Whiteinella archaeocretacea Zone that contains the Cenomanian-Turonian boundary (see Caron et al., 2006Caron, M.; Dall’ Agnolo, S.; Accarie, H.; Barrera, E.; Kauffman, E.G.; Amédro, F. & Robaszynski, F. (2006). High-resolution stratigraphy of the Cenomanian-Turonian boundary interval at Pueblo (USA) and Wadi Bahloul (Tunisia): stable isotope and bio-events correlation. Geobios, 39: 171-200. https://doi.org/10.1016/j.geobios.2004.11.004 ; Reolid et al., 2015Reolid, M.; Sánchez-Quiñónez, C.A.; Alegret, L. & Molina, E. (2015). Palaeoenvironmental turnover across the Cenomanian-Turonian transition in Oued Bahloul, Tunisia: foraminifera and geochemical proxies. Palaeogeography, Palaeoclimatology, Palaeoecology, 417: 491-510. https://doi.org/10.1016/j.palaeo.2014.10.011 ), consists mainly of limestone beds and some marlstone levels. A total of 107 samples have been analyzed (35 from Rhoundjaïa, 18 from M’Daouer, 20 from Chellala Dahrania, and 34 from El Kohol). Most of the samples were from limestones and prepared for thin sections and analysis of microfacies, where as a total of 30 marl samples (500 g/sample) were washed under a gentle jet of water over a set of standard stainless-steel sieves (250 µm, 125 µm and 63 µm) and sorted for examining ostracods and foraminifera. The identification and systematic classification of ostracods is based mainly on the work of Bassoullet & Damotte (1969)Bassoullet, J.P. & Damotte, R. (1969). Quelques ostracodes nouveaux du Cénomanien-Turonien de l’Atlas saharien occidental (Algérie). Revue de Micropaléontologie, 3: 130-144., Andreu et al. (2013)Andreu, B.; Lebedel, V.; Wallez, M.J.; Lézin, C. & Ettachfini, M. (2013). The upper Cenomanian lower Turonian carbonate platform of the Preafrican Trough, Morocco: Biostratigraphic, paleoecological and paleobiogeographical distribution of ostracods. Cretaceous Research, 45: 216-246. https://doi.org/10.1016/j.cretres.2013.04.005 and Benadla (2019)Benadla, M. (2019). Le passage Cénomanien-Turonien dans l’Atlas Saharien algérien: Sédimentologie, Biostratigraphie et Géochimie. PhD Thesis, University of Tlemcen, 184 p.. The most systematically and biostratigraphically representative species were selected and gold-coated for analyzing under a scanning electron microscope Merlin Carl Zeiss SEM at the University of Jaén (Centro de Instrumentación Científico-Técnica).

In this work, the application of quantitative biogeography is used to compare the studied ostracod assemblages with those from different basins belonging to different palaeobiogeographic provinces. Therefore, the basins included in the palaeobiogeographic analysis are located in Morocco (Agadir Basin, Central High Atlas, Middle Atlas and Preafrican Basin) (Andreu, 2002Andreu, B. (2002). Cretaceous ostracode biochronology of Morocco. Eclogae Geologicae Helvetiae, 95: 133-152.; Ettachfini & Andreu, 2004Ettachfini, M. & Andreu, B. (2004). Le Cénomanien et le Turonien de la Plate-forme Préafricaine du Maroc. Cretaceous Research, 25: 277-302. https://doi.org/10.1016/j.cretres.2004.01.001 ; Ettachfini et al., 2005Ettachfini, M.; Souhel, A.; Andreu, B. & Caron, M. (2005). La limite Cénomanien -Tutronien dans le Haut Atlas central, Maroc. Geobios, 38: 57-68. https://doi.org/10.1016/j.geobios.2003.07.003 ; Jati et al., 2010Jati, M.; Grosheny, D.; Ferry, S.; Masrour, M.; Aoutem, M.; Içame, N.; Gauthier-Lafaye, F. & Desmares, D. (2010). The Cenomanian-Turonian boundary event onthe Moroccan Atlantic margin (Agadir basin): Stable isotope and sequence stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 296: 151-164. https://doi.org/10.1016/j.palaeo.2010.07.002 ), Algeria (Ksour, Amour and Tébessa sub-basins) (Benadla, 2019Benadla, M. (2019). Le passage Cénomanien-Turonien dans l’Atlas Saharien algérien: Sédimentologie, Biostratigraphie et Géochimie. PhD Thesis, University of Tlemcen, 184 p.; Ruault-Djerrab et al, 2012Ruault-Djerrab, M.; Ferré, B.; Kechid-Benkherouf, F. & Djerrab, A. (2012). Etude micropaléontologique du Cénomano-Turonien dans la région de Tébessa (NE Algérie): implications paléoenvironnementales et recherche de l’empreinte de l’OAE2. Revue Paléobiologie, 31: 127-144.), Tunisia (Central Tunisia) (Salmouna et al., 2014Salmouna, D.J.; Chaabani, F.; Dhahri, F.; Mzoughi, M.; Salmouna, A. & Zijlstra, H.B. (2014). Lithostratigraphic analysis of the Turonien-Coniacian Bireno and Douleb carbonate Members in Jebels Berda and Chemsi, Gafsa basin, central-southern Atlas of Tunisia. Journal of African Earth Sciences, 100: 733-754. https://doi.org/10.1016/j.jafrearsci.2014.07.025 ), Egypt (East and central Sinai) (El-Nady et al., 2008El-Nady, H.; Abu-Zied, R. & Ayyad, S. (2008). Cenomanian Maastrichtian ostracods from Gabal Arif El-Naga anticline, Eastern Sinai, Egypt. Revue de Paléobiologie, 27: 533-573.; Shahin & Elbaz, 2013aShahin, A. & Elbaz, S. (2013a). Cenomanian-Early Turonian of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie, 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 ), Jordan (Central Jordan) (Morsi & Wendler, 2010Morsi, A.M. & Wendler, J.E. (2010). Biostratigraphy, palaeoecology and palaeogeography of the Middle Cenomanian-Early Turonian Levant Platform in Central Jordan based on ostracods. Geological Society Special Publication, 341: 187-201. https://doi.org/10.1144/SP341.9 ), Lebanon (Damotte & Saint-Marc, 1972Damotte, R. & Saint-Marc, P. (1972). Contribution a la connaissance des ostracodes Crétacé du Liban. Revista Española de Micropaleontología, 4: 273-296.) and finally western Oman (Athersuch, 1988Athersuch, J. (1988). The Biostratigraphy of Cretaceous Ostracods from Oman. Developments in Palaeontology and Stratigraphy, 11: 1187-1206. https://doi.org/10.1016/S0920-5446(08)70249-8 ). This biogeographical quantification is based on two types of data processing:

Lithostratigraphy

As indicated before, the studied ostracod assemblages come from four sections (Fig. 3): Rhoundjaïa and M’Daouer (western Ksour Mountains), Chellala Dahrania (eastern Ksour Mountains) and El Kohol (Amour Mountains).

Rhoundjaïa section

 ⌅

Located at 60 km west of locality of Aïn Séfra, the Rhoundjaïa section (32º44’45.00’’N, 0º14’24.58’’W) was studied on the south-western end of a SSW-NNE syncline (Fig. 3B). This section is of particular interest for the study of the Cenomanian-Turonian transition (Bassoullet & Damotte, 1969Bassoullet, J.P. & Damotte, R. (1969). Quelques ostracodes nouveaux du Cénomanien-Turonien de l’Atlas saharien occidental (Algérie). Revue de Micropaléontologie, 3: 130-144.; Galmier, 1972Galmier, D. (1972). Photogéologique de la région d’Aïn Séfra (Algérie). Bulletin Service Géologique Algérie, 42: 1-177.; Bassoullet, 1973Bassoullet, J.P. (1973). Contribution à l’étude stratigraphique du Mésozoïque de l’Atlas saharien occidental (Algérie). PhD Thesis, Univ. Pierre et Marie Curie Paris, 477 p.; Marok et al., 2009Marok, A.; Sebane, A. & Bensalah, M. (2009). Les événements anoxiques du Mésozoïque dans quelques bassins nord algériens: Résultats préliminaires. Conférences sur l’Exploration dans le Nord de l’Algérie: Perspectives et Défis, Alger, 27-28. ; Mebarki et al., 2016Mebarki, K.; Sauvagnat, J.; Benyoucef, M.; Zaoui, D.; Benachour, H-B.; Mohammed, A.; Mahboubi, M. & Bensalah, M. (2016). Cenomanian-Turonian ostracodes fron the Western Saharan Atlas and the Guir Basin (SE Algeria): systematic, biostratigraphy and paleobiogeography. Revue de Paleobiologie, 35: 249-277.; Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ). Lithostratigraphically, the two geomorphologically detectable bars (Fig. 4A) correspond to the Rhoundjaïa Formation (58.15 m) which can be subdivided into three members (Fig. 5A):

• Lower Member (24.25 m) overlyes the M’Daouer Formation composed by gypsum-rich claystones, limestones and dolostones, and this lower member is mainly composed of bioclastic bioturbated limestones (wackestones to packstones of ostracods and planktic foraminifera) with common Thalassinoides and Planolites. Locally it is recorded mudstone with planktic foraminifera (Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ). In the Lower Member are recorded Dicarinella sp., Rotalipora sp., Muricohedbergella delrioensis, M. planispira, Planoheterohelix moremani, Helvetoglobotruncana praehelvetica and Guembelitria cretacea. The genus Rotalipora is restricted to the lowermost part of the section (samples Rh-4 and Rh-5) and Guembelitria is recorded in the top of the Lower Member (from sample Rh-14) (Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ).

• Middle Member (30 m) is an alternation of whitish bioclastic limestones (wackestones to packstones with foraminifera, filaments and echinoderms) and marls with some lumpy levels rich in sea urchins (Holaster subglobosus, Mecaster pseudofournelli, Hemiaster syriacus and Prionocidaris granulostriata), ammonites (Vascoceras gamai and Vascoceras sp.) and gastropods (Tylostoma sp.). Locally, there are dense accumulations of serpulids. The bioturbated carbonate levels correspond to biomicrites. Towards the top, this alternation is followed by limestones with flint nodules and bioturbated limestones with Thalassinoides. Planktic foraminiferal assemblage is dominated by Planoheterohelix moremani, P. reussi, Guembelitria cretacea and G. cenomana. The species of the genus Muricohedbergella are recorded in the lower part of this member.

• Upper Member (10.60 m) is constituted by massive beds of slightly bioclastic (wackestones to packstones of foraminifera, ostracods and filaments) and highly bioturbated limestone (Thalassinoides). Planktic foraminifera are scarce and only Planoheterohelix moremani is recorded.

Figure 4.  Outcrop view of studied sections. A. Rhoundjaïa section, B. M’Daouer section, C. Chellala Dahrania section, and D. El Kohol section.

Figure 5.  Stratigraphic columns of the Rhoundjaïa, M’Daouer, Chellala Dahrania and El Kohol (A to D).

In this section, the age of the Rhoundjaïa Formation is based on the palaeontological record. Thus, the few ammonites (Vascoceras gamai and Vascoceras sp.) collected in levels Rh-15’, Rh-18’, Rh-26’ and Rh-29 indicate the upper Cenomanian. On the other hand, the ammonites collected in the bed Rh-31 and correlated with the M’Daouer sections give a lower Turonian age.

The last occurrence of Rotalipora at the top of bed Rh-5 would indicate the upper boundary of the Rotalipora cushmani Zone (Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ). The beginning of the Whiteinella archaeocretacea Zone is signalled in the Rhoundjaïa section by the absence of R. cushmani and the record of Helvetoglobotrunana praehelvetica in bed Rh-6. According to the Robaszynski & Caron (1995)Robaszynski, F. & Caron, M. (1995). Foraminifères planctoniquesdu Crétacé: Commentaire de la zonation Europe-Méditerranée. Bulletin de la Société Géologique France, 166: 681-692. the base of the W. archaeocretacea Zone is defined by the last occurrence of R. cushmani. The record of Helvetoglobotruncana praehelvetica has been reported from the base of the W. archaeocretacea Zone (Wan et al., 2003Wan, X., Wignall, P.B. & Zhao, W. (2003). The Cenomanian-Turonian extinction and oceanic anoxic event: evidence from southern Tibet. Palaeogeography, Palaeoclimatology, Palaeoecology, 199: 283-298. https://doi.org/10.1016/S0031-0182(03)00543-1 ).

Systematic palaeontology of ostracoda

The ostracod assemblages of the studied sections are characterised by the dominance of Family Cytherellidae (mainly genus Cytherella), followed by components of the families Paracyprididae (exclusively genus Paracypris) and Trachyleberididae (mainly genus Cythereis). Less common are components of families Bythocypridae and Macrocyprididae. The microfauna studied yielded 15 species, seven of which are left to open nomenclature. These taxonomic categories of ostracods belong to seven genera. In this systematics work, we adopted the classification of the European Register of Marine Species http://erms.biol.soton.ac.uk, and Integrated Taxonomic Information System http://www.itis.usda.gov. The systematic established by Horne et al. (2002)Horne, D.J.; Cohen, A. & Martens, K. (2002). Taxonomy, morphology and biology of Quaternary and living Ostracoda. In: Holmes, J.A., Chivas, A.R. (Eds.), The Ostracoda: Applications in Quaternary Research. AGU Geophysical Monograph Series, 131: 5-36. https://doi.org/10.1029/131GM02 was also used to bring more precision to our work. Note that L, H, and W, represent measurements of length, height, and width respectively.

Material: More than 200 specimens.

Dimensions: L: 0.08-0.62 mm; H: 0.06-0.40 mm; W: 0.02-0.28 mm.

Locality: Rhoundjaïa, M’Daouer, Chellala Dahrania and El Kohol.

Description: Form of genus Cytherella, ovoidal to subquadrangular in lateral view. The species is charaterized by an oval outline. Right valve larger, overlapping left valve along entire periphery. Posterior and anterior margin are rounded. Valve surface is smooth.

Age: Upper Cenomanian-lower Turonian.

Stratigraphic and geographic distribution: Cytherella gr. ovata is known from the lower Cenomanian of Egypt (El-Nady et al., 2008El-Nady, H.; Abu-Zied, R. & Ayyad, S. (2008). Cenomanian Maastrichtian ostracods from Gabal Arif El-Naga anticline, Eastern Sinai, Egypt. Revue de Paléobiologie, 27: 533-573.), upper Cenomanian-Turonian of the Western Saharan Atlas (Bassoullet & Damotte, 1969Bassoullet, J.P. & Damotte, R. (1969). Quelques ostracodes nouveaux du Cénomanien-Turonien de l’Atlas saharien occidental (Algérie). Revue de Micropaléontologie, 3: 130-144.) and Tinrhert Basin of eastern Algeria (Tchenar et al., 2020Tchenar, S.; Ferré, B.; Adaci, M.; Zaoui, D.; Benyoucef, M.; Bensalah, M. & Kentri, T. (2020). Incidences de l’Évènement Anoxique Océanique II sur l’évolution des ostracodes des dépôts cénomano-turoniens du bassin du Tinrhert (SE Algérie). Carnets de Géologie, 20 (08): 145. https://doi.org/10.4267/2042/70792 ), France (Babinot, 1980Babinot, J.F. (1980). Les ostracodes du Crétacé supérieur de Provence: systématique, biostratigraphie, paléoécologie, paléogéographie. Travaux du Laboratoire de Géologie Historique et Paléontologie, 10: 1-624.; Jolet et al., 2001Jolet, P.; Philip, J.; Cecca, F.; Thomel, G.; López, G.; Tronchetti, G. & Babinot, J.F. (2001). Integrated platform/basin biostratigraphy of the Upper Cenomanian-Lower Turonian in Provence (SE France). Geobios, 34: 225-238. https://doi.org/10.1016/S0016-6995(01)80063-2 ; Andreu & Bilotte, 2006Andreu, B. & Bilotte, M. (2006). Ostracodes du Cenomanien supérieur et du Turpnien de la zone sous-pyrénéenne orientale (Corbières méridionales, SE France). Systématique, biostratigrahie, paléoécologie et paléobiogéographie. Revue de Micropaléontologie, 49: 55-73. https://doi.org/10.1016/j.revmic.2005.12.001 ) and Egypt (Shahin, 1991Shahin, A. (1991). Cenomanian-Turonian ostracods from Gebel Nezzazat, southwestern Sinai, Egypt, with observations on δ13C values and the Cenomanian/Turonian boundary. Journal of Micropalaeontology, 10: 133-155. https://doi.org/10.1144/jm.10.2.133 ; Shahin et al., 1994Shahin, A.; Kora, M. & Semiet, A. (1994). Cenomanian ostracods from West Central Sinai, Egypt. Mansoura University Science Bulletin, 21: 33-102.). It has also been identified in the Turonian-Coniacian of the Tunisian Atlas (Salmouna et al., 2014Salmouna, D.J.; Chaabani, F.; Dhahri, F.; Mzoughi, M.; Salmouna, A. & Zijlstra, H.B. (2014). Lithostratigraphic analysis of the Turonien-Coniacian Bireno and Douleb carbonate Members in Jebels Berda and Chemsi, Gafsa basin, central-southern Atlas of Tunisia. Journal of African Earth Sciences, 100: 733-754. https://doi.org/10.1016/j.jafrearsci.2014.07.025 ) and in general, the Upper Cretaceous of Europe and America (Damotte & Freytet, 1974Damotte, R. & Freytet, P. (1974). Contribution à la connaissance du Cénomanien du Massif de Fontfroide (Aude, France): Etude des Ostracodes. Revista Española de Micropaleontología, 2: 201-207.).

Material: 11 specimens.

Dimensions: L: 0.88 mm; H: 0.55 mm; W: 0.44 mm.

Locality: El Kohol.

Description: Carapace of medium size, oval in lateral view. Anterior margin is rounded and slightly compressed in dorsal view. Posterior margin is strongly rounded and larger. Dorsal and ventral margins are curved. Maximum height at mid-length. Valve surface is smooth.

Age: Upper Cenomanian

Stratigraphic and geographic distribution: This species has been collected in the Cenomanian of Tunisia (Glintzboeckel & Magné, 1959Glintzboeckel, C. & Magné, J. (1959). Répartition des microfaunes à plancton et à Ostracodes dans le Crétacé supérieur de la Tunisie et de l’Est algérien. Revue de Micropaléontologie, 5: 53-59.; Grekoff, 1969Grekoff, M. (1969). Sur la valeur stratigraphique et les relations paléogéographiques des quelques ostracodes du Crétacé, du Paléocène et de l’Eocène inférieur d’Algérie orientale. Proceedings of the 3rd African Micropaleontological Coloquium, Cairo, 227-248.; Bismuth et al., 1981Bismuth, H.; Donze, P.; Lefevre, J. & Saint-Marc, P. (1981). Nouvelles espèces d’ostracodes dans le Crétacé Moyen et supérieur du Djebel Semmama (Tunisie du Centre-Nord). Cahiers de Micropaléontologie, 3: 51-69. https://doi.org/10.1016/0195-6671(82)90018-0 ), Tinrhert Basin of eastern Algeria (Tchenar et al., 2020Tchenar, S.; Ferré, B.; Adaci, M.; Zaoui, D.; Benyoucef, M.; Bensalah, M. & Kentri, T. (2020). Incidences de l’Évènement Anoxique Océanique II sur l’évolution des ostracodes des dépôts cénomano-turoniens du bassin du Tinrhert (SE Algérie). Carnets de Géologie, 20 (08): 145. https://doi.org/10.4267/2042/70792 ), Morocco (Andreu, 1989Andreu, B. (1989). Le Crétacé moyen de la transversale Agadir-Nador (Maroc): précisions stratigraphiques et sédimentologiques. Cretaceous Research, 10: 49-80. https://doi.org/10.1016/0195-6671(89)90029-3 ), Iran (Grosdidier, 1973Grosdidier, E. (1973). Association d’Ostracodes du Crétacé d’Iran. Revue Institute Français du Pétrole, 28 (2): 131-169.), Kuwait (Al-Abdul-Razzaq, 1979Al-Abdul Razzaq, S.K. (1979). Glenocythere, a new ostracode genus from the Hamadi Formation (Cretaceous) of Kuwait. Journal of Paleontology, 53: 920-930.) and Egypt (Hataba & Ammar, 1990Hataba, H. & Ammar, G. (1990). Comparative stratigraphic study on the Upper Cenomanian - Lower Senonian sediments between the Gulf of Suez and Western Desrt, Egypt. EGPC 10th Exploration-Production Conference, 1-16.; Shahin, 1991Shahin, A. (1991). Cenomanian-Turonian ostracods from Gebel Nezzazat, southwestern Sinai, Egypt, with observations on δ13C values and the Cenomanian/Turonian boundary. Journal of Micropalaeontology, 10: 133-155. https://doi.org/10.1144/jm.10.2.133 ; El-Nady, 2008El-Nady, H.; Abu-Zied, R. & Ayyad, S. (2008). Cenomanian Maastrichtian ostracods from Gabal Arif El-Naga anticline, Eastern Sinai, Egypt. Revue de Paléobiologie, 27: 533-573.). In Jordan, it has been collected from the upper Cenomanian (Babinot & Basha, 1985Babinot, J.F. & Basha, S.A. (1985). Ostracods from the Early Cenomanian of Jordan. A preliminary report. Geobios, 18: 257-262. https://doi.org/10.1016/S0016-6995(85)80019-X ) and the upper Albian-lower Cenomanian (Bergue et al., 2016Bergue, C.T.; Fauth, G.; Coimbra, J.C.; Ahmad, F.Y.; Smadi, A. & Farouk, S. (2016). The late Albian-early Cenomanian ostracodes from Naur formation, Jordan. Revista Brasileira de Paleontologia, 19: 195-210. https://doi.org/10.4072/rbp.2016.2.04 ).

Material: More than 200 specimens.

Dimensions: L: 0.13-0.73 mm; H: 0.06-0.42 mm; W: 0.04-0.26 mm.

Locality: Rhoundjaïa, M’Daouer, Chellala Dahrania and El Kohol.

Description: Medium-size carapace, valves are elongated and subequal. The right valve is slightly larger than the left valve with an almost identical outline. Dorsal margin straight. Ventral margin becoming concave postero-dorsally. Posterior and anterior margins simmetrically rounded.

Age: Upper Cenomanian-lower Turonian.

Stratigraphic and geographic distribution: Middle to Upper Cretaceous of southeast Constantine, Algeria (Ruault-Djerrab, 2012Ruault-Djerrab, M.; Ferré, B.; Kechid-Benkherouf, F. & Djerrab, A. (2012). Etude micropaléontologique du Cénomano-Turonien dans la région de Tébessa (NE Algérie): implications paléoenvironnementales et recherche de l’empreinte de l’OAE2. Revue Paléobiologie, 31: 127-144.) and the upper Cenomanian-lower Turonian of Morocco (Andreu et al., 2013Andreu, B.; Lebedel, V.; Wallez, M.J.; Lézin, C. & Ettachfini, M. (2013). The upper Cenomanian lower Turonian carbonate platform of the Preafrican Trough, Morocco: Biostratigraphic, paleoecological and paleobiogeographical distribution of ostracods. Cretaceous Research, 45: 216-246. https://doi.org/10.1016/j.cretres.2013.04.005 ).

Material: More than 200 specimens.

Dimensions: L: 0.08-0.55 mm; H: 0.11-0.35 mm; W: 0.06-0.22 mm.

Description: Form potentially assigned to genus Cytherella. Oval in lateral view. Dorsal and ventral margins have very strong ray of curvature. Maximum height at mid-length. The right valve overlaps the left valve along the entire periphery. In dorsal or ventral view, the outline lozenge, subrombic is very characteristic, regular and rounded.

Locality: Rhoundjaïa and M’Daouer.

Age: Upper Cenomanian-lower Turonian.

Stratigraphic and geographic distribution: The Cenomanian-Coniacian of the South-East Constantine, Algeria (Ruault-Djerrab, 2012Ruault-Djerrab, M.; Ferré, B.; Kechid-Benkherouf, F. & Djerrab, A. (2012). Etude micropaléontologique du Cénomano-Turonien dans la région de Tébessa (NE Algérie): implications paléoenvironnementales et recherche de l’empreinte de l’OAE2. Revue Paléobiologie, 31: 127-144.) and the Maastrichtian of the El Koubbat syncline of the Middle Atlas of Morocco (Andreu & Tronchetti, 1996Andreu, B. & Tronchetti, G. (1996). Ostracodes et foraminifères du Crétacé supérieur du synclinal d’El Koubbat. Moyen Atlas. Maroc: biostratigraphie, paléoenvironnements, paléobiogéographie. Systématique des ostracodes. Geobios, 29: 45-71. https://doi.org/10.1016/S0016-6995(96)80071-4 ).

Material: Seven specimens.

Dimensions: L: 0.42-0.57 mm; H: 0.28 mm; W: 0.11-0.15 mm.

Locality: Rhoundjaïa, M’Daouer and El Kohol

Description: Subrectangular in lateral view, sculpted (nets ornamentation, muri and reticules). Anterior and posterior margins are well rounded. Dorsal and ventral margins concave at mid-length. Ribs are longitudinal, short and sinuous.

Age: Upper Cenomanian-lower Turonian.

Material: More than 200 specimens.

Dimensions: L: 0.33-0.68, H: 0.15-0.33 mm, W: 0.06-0.22 mm.

Locality: Rhoundjaïa, M’Daouer, Chellala Dahrania and El Kohol.

Description: This species is characterised by posterior margin very tapering and pointed. Anterior margin well rounded. Valve surface smooth and becoming strongly arched ventrally. Dorsal margin straight at mid-length.

Age: Upper Cenomanian-lower Turonian.

Stratigraphic and geographic distribution: This species has been described in the Aptian-Cenomanian of Egypt (Boukhary et al., 1977Boukhary, M.; Eissa, R. & Kerdany, M. (1977). Some ostracod species from the Galala Formation, western coast of the Gulf of Suez, Egypt. Proceedings Egyptian Academy Sciences Cairo, 30: 155-161.; Shahin et al., 1994Shahin, A.; Kora, M. & Semiet, A. (1994). Cenomanian ostracods from West Central Sinai, Egypt. Mansoura University Science Bulletin, 21: 33-102.; Ismail, 1999Ismail, A.A. (1999). Aptian-Turonian ostracods from Northern Sinai, Egypt. Egyptian Journal of Geology, 43: 293-315.; Morsi & Bauer, 2001Morsi, A.M. & Bauer, J. (2001). Cenomanian ostracods from Sinai Peninsula, Egypt. Revue de Paléobiologie, 20: 377-414.; Hewaidy & Morsi, 2001Hewaidy, A.A. & Morsi, A.M. (2001). Lower Cretaceous (Aptian-Albian) Foraminifera and Ostracoda from northern Sinai, Egypt. Egyptian Journal of Paleontology, 1: 229-252.; Bassiouni, 2002Bassiouni, M.A.A. (2002). Mid-Cretaceous (Aptian-Early Turonian) ostracoda from Sinai. Neue Paläontologische Abhandlungen, 5: 1-123.), middle and upper Cenomanian of Lebanon (Damotte & Saint-Marc, 1972Damotte, R. & Saint-Marc, P. (1972). Contribution a la connaissance des ostracodes Crétacé du Liban. Revista Española de Micropaleontología, 4: 273-296.) and Jordan (Morsi & Wendler, 2010Morsi, A.M. & Wendler, J.E. (2010). Biostratigraphy, palaeoecology and palaeogeography of the Middle Cenomanian-Early Turonian Levant Platform in Central Jordan based on ostracods. Geological Society Special Publication, 341: 187-201. https://doi.org/10.1144/SP341.9 ), Cenomanian-Turonian of Algeria (Vivière, 1985Vivière, J.L. (1985). Les ostracodes du Crétacé supérieur (Vraconien à Campanien basal) de la région de Tébessa (Algérie du Nord-Est. Stratigraphie, Paléoécologie, Systématique). Mémoire Science de la Terre, University Marie Curie, Paris 85, 261.; Majoran, 1989Majoran, S. (1989). Mid-Cretaceous Ostracoda of northeastern Algeria. Fossils Strata, 27: 1-67.; Slami et al., 2022Slami, R.; Ferré, B. & Benkherouf-Kechid, F. (2022). Cenomanian ostracods (Crustacea) of Djebel Sabaoune (Batna, Algeria): Specific assemblage and significance. Journal of African Earth Sciences, 193: 104604. https://doi.org/10.1016/j.jafrearsci.2022.104604 ), middle Cenomanian of Morocco (Andreu, 1991Andreu, B. (1991). Les ostracodes du Crétacé moyen (Barrémien à Turonien), le long d’une transversale Agadir-Nador (Maroc). PhD Thesis, Touluse 3, 756 p.), middle Cenomanian-lower Turonian of central Egypt (Boukhary et al., 2009Boukhary, M.; Morsi, A.M.; Eissa, R. & Kerdany, M. (2009). Late Cenomanian ostracode faunas from the area south of Ain Sukhna, werstern side of the Suez, Egypt. Geologica Croatica, 62: 19-30. https://doi.org/10.4154/GC.2009.02 ; Shahin & Elbaz, 2013aShahin, A. & Elbaz, S. (2013a). Cenomanian-Early Turonian of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie, 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 , bShahin, A. & Elbaz, S.M. (2013b). Cenomanian-Early Turonian Ostracoda of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 ), lower Turonian of South-East Constantine Algeria (Ruault-Djerrab, 2012Ruault-Djerrab, M.; Ferré, B.; Kechid-Benkherouf, F. & Djerrab, A. (2012). Etude micropaléontologique du Cénomano-Turonien dans la région de Tébessa (NE Algérie): implications paléoenvironnementales et recherche de l’empreinte de l’OAE2. Revue Paléobiologie, 31: 127-144.), Turonian of the Potiguar Basin, North-East Brazil (Poivesan et al., 2014Piovesan, E.K.; Cabral, M.C.; Colin, J.-P.; Fauth, G. & Bergue, C.T. (2014). Ostracodes from the Upper Cretaceous deposits of the Potiguar Basin, Northeastern Brazil: taxonomy, paleoecology and paleobiogeography, part 1: Turonian. Carnets de Géologie, 14: 211-252. https://doi.org/10.4267/2042/54003 ) and finally the Turonian-Coniacian of the Tunisian Atlas (Salmouna et al., 2014Salmouna, D.J.; Chaabani, F.; Dhahri, F.; Mzoughi, M.; Salmouna, A. & Zijlstra, H.B. (2014). Lithostratigraphic analysis of the Turonien-Coniacian Bireno and Douleb carbonate Members in Jebels Berda and Chemsi, Gafsa basin, central-southern Atlas of Tunisia. Journal of African Earth Sciences, 100: 733-754. https://doi.org/10.1016/j.jafrearsci.2014.07.025 ).

Material: More than 200 specimens.

Dimensions: L: 0.17-0.8 mm; H: 0.06-0.33 mm; W: 0.04-0.22 mm.

Locality: Rhoundjaïa, M’Daouer and Chellala Dahrania

Description: Similar to Paracypris dubertreti, but it differs in its ventral margin which is not arched.

Age: Upper Cenomanian-lower Turonian.

Stratigraphic and geographic distribution: The species Paracypris mdaouerensis collected for the first time in the Monts des Ksour (Bassoullet & Damotte, 1969Bassoullet, J.P. & Damotte, R. (1969). Quelques ostracodes nouveaux du Cénomanien-Turonien de l’Atlas saharien occidental (Algérie). Revue de Micropaléontologie, 3: 130-144.) has been cited in the lower Cenomanian of Jordan (Babinot & Basha, 1985Babinot, J.F. & Basha, S.A. (1985). Ostracods from the Early Cenomanian of Jordan. A preliminary report. Geobios, 18: 257-262. https://doi.org/10.1016/S0016-6995(85)80019-X ), the Cenomanian of Gabon (Neufville, 1973Neufville, E.M.H. (1973). Ostracoda from the Ezu-Akshale (Turonian, Cretaceous), Nkalagu, Nigeria. Bulletin of the Geological Institution of the University of Uppsala, 4: 44-51.), the Albian-Cenomanian of the Brazilian Basin (Viviers et al., 2000Viviers, M.C.; Koutsoukos, E.A.M.; Da Silva-Telles, A.C. & Bengtson, P. (2000). Stratigraphy and biogeographic affinities of the late Aptian-Campanian ostracods of the Potiguar and Sergipe basins in northeastern Brazil. Cretaceous Research, 21: 407-455. https://doi.org/10.1006/cres.2000.0205 ), the Cenomanian to Coniacian-Santonian of the Eastern Saharan Atlas of Algeria (Ruault-Djerrab, 2012Ruault-Djerrab, M.; Ferré, B.; Kechid-Benkherouf, F. & Djerrab, A. (2012). Etude micropaléontologique du Cénomano-Turonien dans la région de Tébessa (NE Algérie): implications paléoenvironnementales et recherche de l’empreinte de l’OAE2. Revue Paléobiologie, 31: 127-144.; Mebarki et al., 2016Mebarki, K.; Sauvagnat, J.; Benyoucef, M.; Zaoui, D.; Benachour, H-B.; Mohammed, A.; Mahboubi, M. & Bensalah, M. (2016). Cenomanian-Turonian ostracodes fron the Western Saharan Atlas and the Guir Basin (SE Algeria): systematic, biostratigraphy and paleobiogeography. Revue de Paleobiologie, 35: 249-277.; Slami et al., 2022Slami, R.; Ferré, B. & Benkherouf-Kechid, F. (2022). Cenomanian ostracods (Crustacea) of Djebel Sabaoune (Batna, Algeria): Specific assemblage and significance. Journal of African Earth Sciences, 193: 104604. https://doi.org/10.1016/j.jafrearsci.2022.104604 ), and Tinrhert Basin of eastern Algeria (Tchenar et al., 2020Tchenar, S.; Ferré, B.; Adaci, M.; Zaoui, D.; Benyoucef, M.; Bensalah, M. & Kentri, T. (2020). Incidences de l’Évènement Anoxique Océanique II sur l’évolution des ostracodes des dépôts cénomano-turoniens du bassin du Tinrhert (SE Algérie). Carnets de Géologie, 20 (08): 145. https://doi.org/10.4267/2042/70792 ), the lower Cenomanian-Turonian of Egypt (El-Nady et al., 2008El-Nady, H.; Abu-Zied, R. & Ayyad, S. (2008). Cenomanian Maastrichtian ostracods from Gabal Arif El-Naga anticline, Eastern Sinai, Egypt. Revue de Paléobiologie, 27: 533-573.; Shahin & Elbaz, 2013aShahin, A. & Elbaz, S. (2013a). Cenomanian-Early Turonian of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie, 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 , bShahin, A. & Elbaz, S.M. (2013b). Cenomanian-Early Turonian Ostracoda of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 ) and Morocco (Andreu, 1989Andreu, B. (1989). Le Crétacé moyen de la transversale Agadir-Nador (Maroc): précisions stratigraphiques et sédimentologiques. Cretaceous Research, 10: 49-80. https://doi.org/10.1016/0195-6671(89)90029-3 ; Ettachfini et al., 2005Ettachfini, M.; Souhel, A.; Andreu, B. & Caron, M. (2005). La limite Cénomanien -Tutronien dans le Haut Atlas central, Maroc. Geobios, 38: 57-68. https://doi.org/10.1016/j.geobios.2003.07.003 ), in the Turonian-Coniacian of the Tunisian Atlas (Salmouna et al., 2014Salmouna, D.J.; Chaabani, F.; Dhahri, F.; Mzoughi, M.; Salmouna, A. & Zijlstra, H.B. (2014). Lithostratigraphic analysis of the Turonien-Coniacian Bireno and Douleb carbonate Members in Jebels Berda and Chemsi, Gafsa basin, central-southern Atlas of Tunisia. Journal of African Earth Sciences, 100: 733-754. https://doi.org/10.1016/j.jafrearsci.2014.07.025 ) and the Albian-Turonian of Morocco (Andreu, 1991Andreu, B. (1991). Les ostracodes du Crétacé moyen (Barrémien à Turonien), le long d’une transversale Agadir-Nador (Maroc). PhD Thesis, Touluse 3, 756 p.; Andreu & Tronchetti, 1996Andreu, B. & Tronchetti, G. (1996). Ostracodes et foraminifères du Crétacé supérieur du synclinal d’El Koubbat. Moyen Atlas. Maroc: biostratigraphie, paléoenvironnements, paléobiogéographie. Systématique des ostracodes. Geobios, 29: 45-71. https://doi.org/10.1016/S0016-6995(96)80071-4 ; Andreu et al., 2013Andreu, B.; Lebedel, V.; Wallez, M.J.; Lézin, C. & Ettachfini, M. (2013). The upper Cenomanian lower Turonian carbonate platform of the Preafrican Trough, Morocco: Biostratigraphic, paleoecological and paleobiogeographical distribution of ostracods. Cretaceous Research, 45: 216-246. https://doi.org/10.1016/j.cretres.2013.04.005 ).

Material: 50 specimens.

Dimensions: L: 0.26-0.77 mm; H: 0.28 mm; W: 0.06-0.15 mm.

Locality: Rhoundjaïa, M’Daouer, Chellala Dahrania and El Kohol.

Description: Carapace of medium size. Subrectangular to suboval in lateral view, tighten and convex in dorsal view. Maximum height at mid-length. The left valve overlaps the right valve along the entire periphery, except the dorsal view. Ventral margin straight. Valve surface smooth.

Age: Upper Cenomanian-lower Turonian.

Material: 20 specimens.

Dimensions: L: 0.48-0.73 mm; H: 0.40-0.42 mm; W: 0.11-0.22 mm.

Locality: Rhoundjaïa, M’Daouer, Chellala Dahrania and El Kohol.

Description: Studied carapace are usually deformed. Anterior margin truncated and extends downwards. The right valve overlaps the left valve along the entire periphery. Dorsal margin sinuous along anterior margin.

Age: Upper Cenomanian-lower Turonian.

Material: 50 specimens.

Dimensions: L: 0.80-1.11 mm; H: 0.46-0.73 mm; W: 0.31-0.37 mm.

Locality: Rhoundjaïa and El Kohol.

Description: Carapace of large size, smooth and finely porous. Anterior margin short, pointed and slightly turned up. Posterior margin tapered and rounded. Dorsal margin strongly convex with inflection well marked in the two extremity. Ventral margin convex to subrectlinear in mid-length. The left valve overlaps the right valve along the entire periphery.

Age: Upper Cenomanian.

Material: 22 specimens.

Dimensions: L: 0.84-1.11 mm; H: 0,53-0,64 mm; W: 0.31-0.48 mm.

Locality: Rhoundjaïa, M’Daouer and El Kohol.

Description: Carapace elongated and smooth. Dorsal margin convex with sharp inflection at extremity. Ventral margin convex. Anterior margin rounded. Posterior margin short and pointed. The left valve overlaps right valve along the entire periphery.

Age: Upper Cenomanian.

Material: More than 100 specimens.

Dimensions: L: 0.11-0.64 mm; H: 0.06-0.33 mm; W: 0.03-0.26 mm.

Locality: Rhoundjaïa, M’Daouer and Chellala Dahrania.

Description: Rectangular shape in lateral view, ornament with a network reticulations. Anterior margin rounded in a semicircle. Posterior margin pointed. We note the presence of three fine longitudinal ribs. Median ribs prolong to subcentral tubercle in continuity. Ventral ribs are located clearly above the ventral margin that it does not cover.

Age: Upper Cenomanian-lower Turonian.

Stratigraphic and geographic distribution: The upper Cenomanian-lower Turonian of the Western Saharan Atlas (Bassoullet & Damotte, 1969Bassoullet, J.P. & Damotte, R. (1969). Quelques ostracodes nouveaux du Cénomanien-Turonien de l’Atlas saharien occidental (Algérie). Revue de Micropaléontologie, 3: 130-144.; Bassoullet, 1973Bassoullet, J.P. (1973). Contribution à l’étude stratigraphique du Mésozoïque de l’Atlas saharien occidental (Algérie). PhD Thesis, Univ. Pierre et Marie Curie Paris, 477 p.) and the lower Turonian of Tunisia (Bismuth et al., 1981Bismuth, H.; Donze, P.; Lefevre, J. & Saint-Marc, P. (1981). Nouvelles espèces d’ostracodes dans le Crétacé Moyen et supérieur du Djebel Semmama (Tunisie du Centre-Nord). Cahiers de Micropaléontologie, 3: 51-69. https://doi.org/10.1016/0195-6671(82)90018-0 ).

Material: 20 specimens.

Dimensions: L: 0.46-0.66 mm; H: 0.28-0.31 mm; W: 0.26 mm.

Locality: Rhoundjaïa and M’Daouer.

Description: Subrectangular in lateral view, flattened laterally in dorsal view. Dorsal margin straight, very long, underlined by a denticulate ridge on its outer edge. Ventral margin short, slightly inclined and up towards the posterior margin. Anterior margin rounded almost in a semicircle. Posterior margin triangular, denticulate. Median ribs is non-existent. Low convexity forms the subcentral tubercle.

Age: Upper Cenomanian.

Stratigraphic and geographic distribution: Upper Cenomanian of the Western Saharan Atlas (Bassoullet & Damotte, 1969Bassoullet, J.P. & Damotte, R. (1969). Quelques ostracodes nouveaux du Cénomanien-Turonien de l’Atlas saharien occidental (Algérie). Revue de Micropaléontologie, 3: 130-144.).

Material: 11 specimens.

Dimensions: L: 0.69 mm; H: 0.38 mm; W: 0.22 mm.

Locality: Rhoundjaïa, El Kohol and Chellala Dahrania.

Description: The specimens differ from other individuals of Cythereis by the presence of cross-linking along the entire surface and the lateral costulation fading slightly in the mid-lenght of the valve.

Age: Upper Cenomanian.

Material: 5 specimens.

Dimensions: L: 0.65 mm; H: 0.35 mm; W: 0.23 mm.

Locality: Rhoundjaïa.

Description: Specimens shows deterioration of ornamentation which results in the appearance of irregular tubers at the posterior endings of ventral and dorsal ribs, as well as in the mid-length of the carapace.

Age: Upper Cenomanian.

Interpretation and comparison with other regions

The ostracod fauna of the upper Cenomanian-lower Turonian transition in the Ksour and Amour mountains has been previously studied and figured by Bassoullet & Damotte (1969)Bassoullet, J.P. & Damotte, R. (1969). Quelques ostracodes nouveaux du Cénomanien-Turonien de l’Atlas saharien occidental (Algérie). Revue de Micropaléontologie, 3: 130-144. and Benadla (2019)Benadla, M. (2019). Le passage Cénomanien-Turonien dans l’Atlas Saharien algérien: Sédimentologie, Biostratigraphie et Géochimie. PhD Thesis, University of Tlemcen, 184 p. in which several species determined for the first time, remain endemic. From a biostratigraphic point of view, two assemblages of ostracods could be found in the Cenomanian-Turonian transition (Figs 7-10).

The ostracod assemblages determined for the stratigraphic interval of the Cenomanian-Turonian transition indicate the presence of a biological event corresponding to the explosion of smooth ostracods called the Cytherellid Event, also described in Spain (Barroso-Barcenilla et al., 2011Barroso-Barcenilla, F.; Pascual, A.; Peyrot, D. & Rodríguez-Lazaro, J. (2011). Integrated biostratigraphy and chemostratigraphy of the upper Cenomanian and lower Turonian succession in Puentedey, Iberian Trough, Spain. Proceedings of Geologists’ Association, 122: 67-81. https://doi.org/10.1016/j.pgeola.2010.11.002 ), Egypt (Shahin & Elbaz, 2013aShahin, A. & Elbaz, S. (2013a). Cenomanian-Early Turonian of the shallow marine carbonate platform sequence at west central Sinai: Biostratigraphy, paleobathymetry and paleobiogeography. Revue de Micropaléontologie, 56: 103-126. https://doi.org/10.1016/j.revmic.2013.04.004 ) and Algeria (Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ). Cytherellids are relatively resistant to oxygen depleted conditions (Whatley, 1991Whatley, R.C. (1991). The platycopid signal: a means of detecting kenoxic events using Ostracoda. Journal of Micropalaeontology, 10: 181-183. https://doi.org/10.1144/jm.10.2.181 , 1995Whatley, R.C. (1995). Ostracoda and oceanic palaeoxygen levels. Mitteilungen aus dem Hamburgischen Zoologischen Museum und Institut, 92: 337-353.) and Cytherella has been interpreted as an ostracod indicative of warm waters adapted to survive during low oxygen episodes (Depêche, 1984Depêche, F. (1984). Les ostracodes d’une plate-forme continentale au Jurassique. Recherches sur le Bathonien du Bassin parisien. PhD Thesis, University Pierre et Marie Curie, Paris, 325 p.; Whatley, 1995Whatley, R.C. (1995). Ostracoda and oceanic palaeoxygen levels. Mitteilungen aus dem Hamburgischen Zoologischen Museum und Institut, 92: 337-353.; Bonnet et al., 1999Bonnet, L.; Andreu, B.; Rey, J.; Cubaynes, R.; Ruget, C.; N’Zaba-Makaya, O. & Brunel, F. (1999). Fluctuations of environmental factors as seen by means of statistical analyses in micropaleontological assemblages from a Liassic Series. Micropaleontology, 45: 399-417. https://doi.org/10.2307/1486122 ; N’Zaba-Makaya et al., 2003N’Zaba-Makaya, O.; Andreu, B.; Brunel, F.; Mouterde, R.; Rey, J. & Rocha, R.B. (2003). Biostratigraphie et paléoécologie des peuplements d’ostracodes dans le Domérien du Bassin Lusitanien, Portugal. Ciências da Terra, 15: 21-44.; Reolid, 2020Reolid, M. (2020). Microfossil assemblages and geochemistry for interpreting the incidence of the Jenkyns Event (early Toarcian) in the south-eastern Iberian palaeomargin (External Subbetic, SE Spain). Journal of Micropalaeontology, 39: 233-258. https://doi.org/10.5194/jm-39-233-2020 ; Reolid & Ainsworth, 2022Reolid, M. & Ainsworth, N.R. (2022). Changes in benthic microfossil assemblages before, during and after the eary Toarcian biotic crisis in the Portland-Wight Basin (Kerr McGee 97/12-1 well, offshore southern England). Palaeogeography, Palaeoclimatology, Palaeoecology, 599: 111044. https://doi.org/10.1016/j.palaeo.2022.111044 ). In the Rhoundjala section the Cytherellid Event coincides with the negative carbon isotopic excursion of the OAE2 (Benadla et al., 2018Benadla, M.; Reolid, M.; Marok, A. & El Kamali, N. (2018). The Cenomanian-Turonian transition in the carbonate platform facies of the Western Saharan Atlas (Rhoundjaïa Formation, Algeria). Journal of Iberian Geology, 44: 405-429. https://doi.org/10.1007/s41513-018-0070-6 ).

Intra-family comparisons with other regions

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This analysis compare the ostracod assemblages from Moroccan Basin (MB; Agadir Basin, Central High Atlas Basin, Middle Atlas Basin), Algerian Basin (AB; Ksour Sub-basin, Amour Sub-basin, Tébessa Sub-basin), Central Tunisian Basin (TB), Egyptian Basin (EB, East and Central Sinai Basin), Lebanese Basin (LB), Central Jordanian Basin (JB), and Western Oman Basin (OB).

The results of the processing of the generic matrix by the program PAST-Palaeontological STatistics, ver.1.89 (Hammer et al., 2009Hammer, Ø., Harper, D. A. T., & Ryan, P. D. (2001). PAST-palaeontological statistics, ver. 1.89. Palaeontologia Electronica, 4 (1): 1-9.; Table 1) are presented in the form of planar graphs (principal coordinate analysis, PCA) (Fig. 11A) and trees whose branch lengths are proportional to the distance between the taxonomic composition of the different regions (Fig. 11B). Thus, the intra-family generic diversity shows the following structure:

1. A first group made up of assemblages from basins belonging to four regions: Morocco (MB), Egypt (EB), Jordan (JB) and Oman (OB), which are more or less isolated on figures 11A, B.

2. A second group formed by the Algerian Saharan Atlas basins (AB) and Central Tunisian Basin (TB). It should be noted that the generic intra-family composition of the study region (Ksour and Amour mountains) is relatively close to Jordanian Basin.

3. Finally, the Central Lebanese Basin (LB) is isolated.

Figure 11.  A. Principal coordinates analysis (PCA) of the distance matrix of Bray-Curtis. B. Phenogram (tree of Neighbor-Joining) allowing the visualization of the proximity between basins as recorded in the distance matrix of Bray-Curtis.

These different basins on the northern edge of Gondwana show an abundance of smooth forms represented by families Cytherellidae, Cytherideidae, Cytheruridae and Paracyprididae, and usually ornamented individuals of Trachyleberidae. In the Saharan Atlas Basin Cytherellidae and Paracypridae dominated during the Cenomanian-Turonian transition.

Previous works by Khalil (2020)Khalil, M.M. (2020). Biostratigraphy and paleobiogeographic implications of the Cenomanian-Early Turonian ostracods of Egypt. Annales de Paléontologie, 106: 102408. https://doi.org/10.1016/j.annpal.2020.102408 and Shahin & Elbaz (2021)Shahin, A. & Elbaz, S. (2021). Early-Middle Cenomanian foraminifera and ostracods from BB-80-1 well, Gulf of Suez, Egypt: Biostratigraphy, palaeoecology, and palaeobiogeographic significance. Geological Journal, 56: 3745-3770. https://doi.org/10.1002/gj.4131 have stablished two different bioprovinces for Ostracoda: the North African Province (or South Tethysian Province; Shahin & Elbaz, 2021Shahin, A. & Elbaz, S. (2021). Early-Middle Cenomanian foraminifera and ostracods from BB-80-1 well, Gulf of Suez, Egypt: Biostratigraphy, palaeoecology, and palaeobiogeographic significance. Geological Journal, 56: 3745-3770. https://doi.org/10.1002/gj.4131 ) including Morocco, Algeria, Tunisia and Egypt, and the Middle East Province including Lebanon, Oman, Saudi Arabia, Kuwait and Iran. Mebarki et al. (2016)Mebarki, K.; Sauvagnat, J.; Benyoucef, M.; Zaoui, D.; Benachour, H-B.; Mohammed, A.; Mahboubi, M. & Bensalah, M. (2016). Cenomanian-Turonian ostracodes fron the Western Saharan Atlas and the Guir Basin (SE Algeria): systematic, biostratigraphy and paleobiogeography. Revue de Paleobiologie, 35: 249-277. found that ostracod species from Guir Basin (southwestern part of Saharan Atlas) are closer in affinity to those from Atlasic Basin of Morocco, and secondarily with assemblages fropm Tunisia and Egypt. Our results differ from these other proposals but have in common the dominance of smooth ostracods, mainly cytherellids, during the Cenomanian-Turonian transition.

Quantitative comparison of the taxonomic composition with other regions

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In this biogeographical quantification analysis, we dealt with 48 genera of which 33 (68%) are present in the Egyptian basins. The results given in the form of a phenogram (Fig. 12A) and a hierarchical association diagram (Fig. 12B), allowed us to reconstitute the following topology:

1. Proximity of the ostracod fauna of the Moroccan and Egyptian basins. These two regions share 12 genera (25%) (Bairdia, Brachycythere, Cythereis, Cytherella, Limburgina, Metacytheropteron, Nigeroloxoconcha, Ovocytheridea, Parakrithe, Paracypris, Reticulocosta, and Spinoleberis). To the Moroccan and Egyptian basins, the two basins belonging to the Middle East, Jordanian and Oman basins, are related, the Central Jordanian Basin with 4 genera in common (Brachycythere, Cythereis, Cytherella, and Parakrithe) and the Oman Basin with 4 genera in common (Brachycythere, Cythereis, Cytherella, and Metacytheropteron).

2. The ostracod fauna of the Algerian and Tunisian basins are very similar. This resemblance is reflected in the presence of 5 shared genera to both regions (Cythereis, Cytherella, Cytheropteron, Dolocytheridea, and Paracypris).

3. The remoteness of the ostracod fauna of Lebanese Basin compared to the regions analysed.

Figure 12.  A. Reconstituted phenogramm for Cenomanian-Turonian transition. B. Hierarchical association diagram between basins.

The similarity between the ostracod faunas from different basins shows the probable existence of communication routes during the Cenomanian-Turonian transition or the existence of equivalent palaeoenvironmental conditions.

Conclusions

The study of ostracods from the Cenomanian-Turonian transition (Whiteinella archaeocretacea Zone) through four sections surveyed in the Ksour Mountains (Western Saharan Atlas) and the Amour Mountains (Central Saharan Atlas) allowed the identification of fifteen species, seven genera and five families. The average ostracod assemblage is dominated by the Family Cytherellidae (mainly genus Cytherella), and secondarily by the families Paracyprididae (exclusively Paracypris) and Trachyleberididae (mainly Cythereis). Less common are components of families Bairdiidae, Bythocypridae and Macrocyprididae.

Two ostracod biozones have been identified within the Whiteinella archaeocretacea foraminiferal Zone, the Cythereis algeriana Zone of the upper Cenomanian, and the Cythereis mdaouerensis Zone of the lower Turonian.

From palaeoecological point of view, the studied assemblages highlight a global biological event corresponding to the explosion of smooth-shaped ostracods, represented by the Family Cytherellidae. The Cytherellid Event is related to the biotic crisis of the Cenomanian-Turonian transition (OAE2) and related to the increased temperature of sea water and oxygen depleted conditions in the bottom.

Furthermore, the calculation of ostracod similarity and distance indices by the BG-Index allowed the comparison of seven regions belonging to palaeobiogeographic provinces of North Africa-Middle East (Gondwana palaeomargin). The results thus obtained show a general topology in the Cenomanian-Turonian transition, marked by the binary similarity between the Moroccan and Egyptian basins on the one hand and the basins of the Saharan Atlas (Algeria, Tunisia) on the other. This palaeobiogeographical topology indicates the probable existence of communication routes between some basins and the isolation of the ostracod fauna of the Lebanese Basin.