New insights on the latest Messinian-to-Piacenzian stratigraphic series from the Dahra Massif (Lower Chelif Basin, Algeria): Lago Mare, reflooding and bio-events

Geological investigations carried out on the Dahra Massif have revealed sedimentary changes and bioevents characterizing the post-gypsum detrital sediments (from Messinian to Piacenzian), which are followed by the Trubi equivalent Pliocene marls or white marly limestones. Structured into two superimposed steps, the late Messinian deposits yielded two successive ostracod assemblages. They indicate a brackish environment for the lower and a fairly open shallow brackish environment for the second. Based on their ostracod content, assemblage 1 (Cyprideis, Loxoconcha muelleri) corresponds to the Lago Mare biofacies 1 of the Apennine foredeep, which is correlated with the Lago Mare 1 episode dated between 5.64 and 5.60 Ma. Assemblage 2 (Loxocorniculina djafarovi) is referred to the Lago Mare biofacies 2 described in the same region. It is correlated with the Lago Mare 3 episode, dated between 5.46 and 5.33 Ma. Moreover, the stratigraphic succession is marked by a major discontinuity indicated by a hardground, separating step 1 from step 2 and corresponding to the ostracod assemblages 1 and 2, respectively. This discontinuity is considered here to be equivalent to the Messinian Erosional Surface, already evidenced in the region and widely known around the Mediterranean Basin. These late Messinian deposits and their ostracod assemblage 2, notably the detrital sedimentation with Ceratolithus acutus, Globorotalia margaritae, Reticulofenestra cisnerosii document a marine incursion into the Lower Chelif Basin, corresponding to the latest Messinian marine reflooding of the Mediterranean Basin, that happened before the earliest Zanclean R. cisnerosii occurrence. Finally, the bioevents evidenced in the Dahra Massif, reinforce the evidence of the late Messinian Lago Mare 3 episode, and support the ante-Zanclean age of the marine reflooding of the Mediterranean. The overlying deposits are marked by coral constructions (cf. Cladocora cf. caespitosa, Dendrophyllia sp) never described before and covering the entire early Zanclean, testifying the existence, at that time, of warm enough conditions, which may correspond to the marine isotopic stage TG5

Le Neogene de la bordure nord-occidentale du massif du Dahra (Algerie)

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Signification paléoécologique des assemblages de diatomées du Messinien du Dahra sud-occidental (bassin du Chélif, Algérie nord-occidentale)

Constituant l’une des composantes sédimentaires majeures du Messinien du bassin du Chélif au même titre que la formation gypseuse, les diatomites ont fait l’objet d’une étude détaillée reposant sur quatre coupes réparties sur le versant sud-occidental du massif du Dahra. Les coupes étudiées montrent d’importants changements verticaux et latéraux de faciès, permettant ainsi de distinguer deux unités sédimentaires (membre inférieur et membre supérieur). Le membre inférieur est caractérisé par un assemblage diatomique néritico-océanique et océanique (Coscinodiscus marginatus, C. oculus-iridis, C. radiatus, Nitzschia reinholdii, N. fossilis, Thalassiossira eccentrica, T. miocenica, Thalassiothrix longissima, etc. ) tandis que les formes planctoniques littorales (Actinoptychus senarius, Thalassionema nitzschioides, Actinocyclus octonarius, A. tenellus, Paralia sulcata, etc.) et accessoirement benthiques marquent surtout le membre supérieur, traduisant ainsi une évolution bathydécroissante du milieu de dépôt. Les variations horizontales de ces assemblages dans les quatre secteurs accusent d’ouest en est un approfondissement du milieu tout en évoluant en un milieu de sédimentation en contexte de bassin. L’abondance des diatomées « froides », Coscinodiscus marginatus dans le membre inférieur et Actinocyclus curvatulus dans le membre supérieur, semble conforter la subdivision lithologique et permet de considérer ce découpage comme source des repères stratigraphiques à l’échelle locale (bassin du Chélif) voire régionale (Bassin méditerranéen). Cette sédimentation diatomitique est caractérisée jusqu’aux derniers niveaux qui précèdent les dépôts de gypses, par des espèces marines à affinités néritico-océaniques et océaniques témoignant ainsi, avec les silicoflagellés et les radiolaires, d’un milieu marin franc, en connexion avec le domaine océanique. Par ailleurs l’abondance de Thalassionema nitzschioides, espèce constamment présente et souvent dominante associée à Thalassiothrix longissima, suggère un milieu à forte productivité caractéristique des zones à upwellings responsable du développement de la flore diatomique.As one of the main sedimentary Messinian components of the Chelif basin with the gypsum deposits, the diatomites were studied in detail along four sections from the southwestern border of the Dahra.The studied sections show significant vertical and lateral lithological changes, allowing to distinguish two units (the lower member and the upper member). The lower member is dominated by the neritic-oceanic and oceanic planktonic assemblage (Coscinodiscus marginatus, C. oculus-irridis, C. radiatus, Nitzschia reinholdii, N. fossilis, Thalassiosira eccentrica, T. miocenica, Thalassiothrix longissima, etc.). Whereas, the littoral planktonic species (Actinoptychus senarius, Thalassionema nitzschioides, Actinocyclus octonarius, A. tenellus, Paralia sulcata, etc.) and benthic forms characterized the upper member, indicating a general decrease in bathymetry over the Messinian diatoms. This assemblage is also dominated by cold water diatoms characteristic of boreal area (Coscinodiscus marginatus) in the lower member and Actinocyclus curvatulus in the upper member), which correspond to the defined lithological units. The paleoecological data from diatoms, silicoflagellates and radiolarians indicate that the diatomites were deposited in open marine environment submitted to the inputs of Atlantic cold water, until last levels before gypsum deposits. Moreover, the abundance of Thalassionema nitzschioides, constantly present from the base to the top of the section and often associated with Thalassiothrix longissima, is indicative of a high productivity, which can be characteristic of an upwelling regime, responsible of the development of the diatom microflora.</p

Signification paléoécologique des assemblages de diatomées du Messinien du Dahra sud-occidental (bassin du Chélif, Algérie nord-occidentale)

Mansour, Bouhameur, Bessedik, Mostefa, Martin, Jean-Paul Saint, Belkebir, Lahcene (2008): Signification paléoécologique des assemblages de diatomées du Messinien du Dahra sud-occidental (bassin du Chélif, Algérie nord-occidentale). Geodiversitas 30 (1): 117-139, DOI: 10.5281/zenodo.537326

Evolution de la diversité des bivalves messiniens de la bordure méridionale du bassin du Bas Chélif (Algérie nord occidentale)

International audienc

Biostratigraphie et lithologie des séries serravallo-tortoniennes du massif du Dahra et du bassin du Chélif (Algérie). Implications sur la position de la limite serravallo-tortonienne

Belkebir, Lahcene, Labdi, Amel, Mansour, Bouhameur, Bessedik, Mostefa, Martin, Jean-Paul Saint (2008): Biostratigraphie et lithologie des séries serravallo-tortoniennes du massif du Dahra et du bassin du Chélif (Algérie). Implications sur la position de la limite serravallo-tortonienne. Geodiversitas 30 (1): 9-19, DOI: http://doi.org/10.5281/zenodo.537316

Apports des foraminifères planctoniques à la biostratigraphie du Miocène supérieur et du Pliocène de Djebel Diss (bassin du Chélif, Algérie)

Belhadji, Ahmed, Belkebir, Lahcene, Martin, Jean-Paul Saint, Mansour, Bouhameur, Bessedik, Mostefa, Conesa, Gilles (2008): Apports des foraminifères planctoniques à la biostratigraphie du Miocène supérieur et du Pliocène de Djebel Diss (bassin du Chélif, Algérie). Geodiversitas 30 (1): 79-96, DOI: http://doi.org/10.5281/zenodo.537418

Contributions biostratigraphiques et paléoenvironnementales de l'étude des nannofossiles calcaires des dépôts tortonomessiniens du bassin du Chélif (Algérie)

Mansouri, Mohamed El Habib, Bessedik, Mostefa, Aubry, Marie-Pierre, Belkebir, Lahcene, Mansour, Bouhameur, Beaufort, Luc (2008): Contributions biostratigraphiques et paléoenvironnementales de l'étude des nannofossiles calcaires des dépôts tortonomessiniens du bassin du Chélif (Algérie). Geodiversitas 30 (1): 59-77, DOI: http://doi.org/10.5281/zenodo.537694

Biostratigraphic and paleoenvironmental contributions of calcareous nannofossil study from Tortonian-Messinian deposits of Chelif basin (NW Algeria)

Special Meeting of the APF on Biodiversity and Biodiversity Crisis in North Africa during Neogene, Paris, FRANCE, NOV 28-29, 2006International audienceFifty calcareous nannofossil species were listed in the upper Miocene deposits of the Northern Chelif Basin (Dahra, Ben Dourda section). The frequence of some of them (Discoaster loeblichii, D. quinqueramus, Amaurolithus primus and A. amplificus) suggests the presence of four subzones (NN 10a, NN 10b, NN 11b, NN 11 c) which are assigned to the Tortonian and Messinian stages. The NN 11 a subzone is absent (hiatus), testified by the (first) simultaneous occurrence (FO) of D. quinqueramus and A. primus. In the same samples, planktonic foraminifera analysis revealed a comparable succession of biozones (Neogloboquadrina acostaensis, N. humerosa-N. dutertrei and Globorotalia mediterranea) which make possible a good calibration between biostratigraphic scales (calcareous nannofossils, foraminifera). The Tortonian-Messinian boundary is pointed out at the sample 28 of the section and characterized by the first occurrence (FO) of A. delicatus and Reticulo/enestra rotaria on the one hand and G. mediterranea on the other hand. The assemblage analysis and relative abundance fluctuations of Coccolithus pelagicus and R. pseudo-umbilicus show evidence of seven successive phases which are characterized, alternately, by cold and hot water marine masses, light intensity variations and nutrient availability